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PUBLICATIONS

U.S. DEPART

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NATL INST OF STANDARDS & TECH R.I.C.

A1 11 02748507

/The effect of cigarette characteristics QC100 U5753 lfo.1841 1988 V198 C.1 NBS-P

NBS Technical Note 1241

The Effect of Cigarette Characteristics on the

Ignition of Soft Furnishings

Gann, Harris, Krasny, Levine, Mitler, and Ohlemiller

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, L

NBS Technical Note 1241

The Effect of Cigarette Characteristics on the

Ignition of Soft Furnishings

Richard G. Gann, Richard H. Harris, Jr., John F. Krasny, Robert S. Levine, Henri E. Mitler, Thomas J. Ohlemiller

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

This research was funded under the

Cigarette Safety Act of 1984.

January 1988

'•V

U.S. Department of Commerce

C. William Verity, Secretary

National Bureau of Standards

Ernest Ambler, Director
National Bureau of Standards U.S. Government Printing Office For sale by the Superintendent

Technical Note 1241 Washington: 1987 of Documents,

Natl. Bur. Stand. (U.S.), U.S. Government Printing Office,

Tech. Note 1241 Washington, DC 20402

215 pages (January 1988)

CODEN: NBTNAE
Contents

List of Figures and Tables v

Executive Summary 1

Section 1 : 5 Introduction 9

Project Background 9 Nature of This Project 10

References for Section 1 11

Section 2: Materials 13

Cigarettes 17

Description of Cigarettes 17

Series 1 Experimental Cigarettes 17

Series 2 Experimental Cigarettes 17

Patented, Low Ignition Propensity Cigarettes 17

Commercial Cigarettes 20

Quality Assurance of Cigarettes 20

Methods for the Determination of Cigarette

Characteristics 20

Results of Measurements of Physical and Chemical

Characteristics of Cigarettes 20

Series 1 Experimental Cigarettes 20

Series 2 Experimental Cigarettes 22

Substrates 29

Fabrics 29

Padding 29

Mockup Configurations 29

Chairs 31 References for Section 2 32

Appendix 2-A 33

Appendix 2-B 39

Appendix 2-C 43

Appendix 2-D 45

Appendix 2-E 49

Appendix 2-F 51 Appendix 2-G .' .... 53

Section 3: Performance Measurements 55

Introduction 59

Bench-Scale Evaluations 61 Methods 61

Ignition Propensity Measurements 61

Contamination of Fabrics with Alkali Metal Ions and

Natural Soil 61 Results and Discussion 62

Ignition Propensity Results 62

Primary Evaluation of Experimental Cigarettes for Ignition Propensity 62

Validation of Ignition Propensity Primary

Evaluation Results 65

Comparison of Full-Scale Furniture and

Bench-Scale Tests 71 Objective 71 Method 71

Cigarette Selection, Handling and Coding 71 Experimental Design 71 Test Procedure for Full-Scale Furniture Tests 72

General 72

Cigarette Location and Placement 72

Criteria for Ignition 73

Data from Full-Scale Tests 73

Difficulties with the Procedure 74

Conditioning of the Chairs 74

Drafts 74

Self-extinguishment of Cigarettes 74

Times to Ignition of Substrate 74

Crevice Shape 74

Influence of Substrate on Cigarette Burning 75

Results 75

Validation of Bench-Scale Tests by Full-Scale Tests .... 75

Validation Results Weighted by Numbers of Tests 80

Use of Kendall's Tau Correlation Coefficient

to Summarize the Agreement Between Full-Scale and

Bench-Scale Tests 80

Relative Ranking of Cigarettes in Full-Scale Tests and the Primary Evaluation 80

Average Per Puff Tar, Nicotine, and CO Yields

of Experimental Cigarettes 81 Summary of Characteristics of Experimental,

Low Ignition Propensity Cigarettes 85

Patented Cigarettes 87

Summary and Conclusions 89

References for Section 3 91 Appendix 3-A 93

Appendix 3-B 97

Section 4: Thermophysics of the

Ignition Process 99
Introduction 1 05

Experimental Methods 107

Experimental Methods for Heat Transfer

Measurement 1 07

Previous Work 107

Present Work 107

Experimental Methods for Measuring Oxygen

Depletion in the Substrate 111 Experimental Methods for Substrate

Temperature Probing 112

Results and Discussion 115

Substrate Effect on Cigarette 115

Heat Flux Scans on Various Substrates 120

Non-steadiness in the Coal Temperature 129

Oxygen Depletion in the Fabric 130

Substrate Temperatures 132

Summary and Conclusion 135

References for Section 4 1 37

Section 5: Modeling Ignition 139

Introduction 145

Background 1 47

Cigarette Dynamics 147

Previous Modeling Efforts 148

Modeling the Substrate 151

Thermal Physics 151

Ignition 152

Possible Improvements 152

Modeling the Free Cigarette 153

Semi-Empirical Model 153

Burning Rate as a Function of Various Parameters 1 53

The Surface Heat Flux 1 54

Correlation Between v and (c 155

Detailed Model 1 57

Partial Model 1 60

Equations 1 60

Numerics 161

Initial Conditions 162

Comments 1 62

Interactions Between Cigarette and Substrate 163

Conduction Flux to Substrate 163

Radiation Flux to the Substrate 165

Connection with the Semi-Empirical Model 165

Cigarette Energy Balance in the Presence

of a Substrate 1 67

Summary 1 69

Results from Using the Models 171 Substrate Program 171 Cigarette Program 1 77

Summary and Conclusions; Lessons Learned 181

References for Section 5 1 83

Appendix 5-A: A Description of the

Substrate Program 185

Appendix 5-B: The Cigarette Program CIG25 189

Appendix 5-C: Convective and Radiative

Losses from a Freely Burning Cigarette 199

Appendix 5-D. Derivation of the Transverse

Conductive Flux Distribution 203

Section 6: Evaluation of Test Methods

for Cigarette Ignition Propensity 207

Introduction 211

Methods Suggested in the Literature 213

Weight Loss of Polyurethane Foam 215

Procedure 215

Comparison of Weight Loss Results and

Number of Ignitions 215

Cigarettes Burning on an Alpha-Cellulose

Substrate 219

Cigarettes Smoldering on a Glass Plate .221 Methods 221

Results 221

Tentative Test Method Using Fabrics

and Padding Materials 223

General Considerations 223

Outline of Suggested Tentative Test Method 223

Summary 225

References for Section 6 227

Section 7: Conclusions 229

Section 8: Priority Further Research

Directions 233

Test Method Development and Baseline Data 237

Experimental Cigarette Testing 237

Baseline Performance Data .237

Broader Investigation of Ignition Physics 237

Ignition Model Predictions 238

Section 9: Acknowledgements 239

IV
List of Tables and Figures

Table ES-1. Ignition Propensities of Selected Test Cigarettes 2

Table ES-2. Ignition Propensity as a Function of Experimental

Cigarette Characteristics 2

Table ES-3. Average Per Puff Smoke

Component Yields from

Selected Cigarettes 3

Table ES-4. Ignition Propensities of Patented Cigarettes 3

Table ES-5. Comparison of Ignition

Propensities of Tested

Cigarettes at Full- and

Reduced-Scales 4

Table 2-1. Description of Series 1 Experimental Cigarettes 18

Table 2-2. Description of Series 2 Experimental Cigarettes 19

Table 2-3. Measured Physical and

Chemical Characteristics of Series 1 Experimental Cigarettes 21

Table 2-4. Measured Physical and

Chemical Characteristics of Series 2 Experimental Cigarettes 22

Table 2-5. Physical Characteristics and

Smoke Yields of Experimental

Cigarettes, Series 1, Data from Lorillard Laboratories 23

Table 2-6. Smoke Yields of Experimental

Cigarettes Series 2. Data

from Lorillard Laboratories 24

Table 2-7. FTC Values for Tar, Nicotine,

and Carbon Monoxide Yield and Puff Count of Series 1 Experimental Cigarettes 25

Table 2-8. FTC Values for Tar, Nicotine,

and Carbon Monoxide Yield and Puff Count of Series 2 Experimental Cigarette 26

Table 2-9. Upholstered Fabrics, Padding

and Sheeting Used in the Investigation 27

Table 2-10. Cation Content of Upholstery

Fabrics and Cotton Batting 28

Table 2-A-1. Cigarette Manufacturer's

Description of Series 1

,

21 mm Experimental Cigarettes 35

Table 2-A-2. Cigarette Manufacturer's

Description of Series 1

,

25 mm Experimental Cigarettes 35

Table 2-B-1. Cigarette Manufacturer's

Description of Series 2 Experimental Cigarettes 41

Table 2-D-1. Paper Permeability of Series 1 Experimental Cigarettes

Determined by Kimberly-Clark 46

Table 2-D-2. Paper Permeability of Series 2 Experimental

Cigarettes Determined by Kimberly-Clark .48

Table 2-G-1. Elemental Analysis of Upholstery Fabrics and Cotton

Batting Determined by U.S. CPSC 54

Table 3-1. Ignition Propensity of Series 1 Experimental Cigarettes 63

Table 3-2. Ignition Propensity of Series 2 Experimental Cigarettes 64
Table 3-3. Ignition Propensity as a

Function of Cigarette Parameters

Series 1 Experimental Cigarettes 65

Table 3-4. Ignition Propensity of Short

Cigarettes and Cigarettes

Without Filter 66

Table 3-5. Ignition Behavior of Cigarettes on Alkali Metal

Ion Treated Fabrics 67

Table 3-6. Ignition Behavior of Cigarettes on Soiled Fabrics 68

Table 3-7. Ignition Propensity of Selected Cigarettes on Low

Cigarette Ignition Resistance

Substrates 69

Table 3-8A. Summary of Full-Scale Furniture Test Results 76

Table 3-8B. Summary of Full-Scale Furniture Test Results 77

Table 3-8C. Summary of Full-Scale Furniture Test Results 78

Table 3-9. Numbers of Tests and

Results Full-Scale and

Bench-Scale, Various

Cigarettes and Substrates 79

Table 3-10. Per Puff Tar, Nicotine

and Carbon Monoxide Yields of Series 1 Experimental Cigarettes 82

Table 3-11. Per Puff Tar, Nicotine

and Carbon Monoxide Yields of Series 2 Experimental Cigarettes 83

Table 3-12. Per Puff Tar, Nicotine

and CO Yields as a Function

of Cigarette Parameters 83

Table 3-13. Summary of Characteristics

of Selected Cigarettes 85

Table 3-14. Ignition Propensity of Patented Cigarettes 86

Table 3-A-1. Significance Probabilities

(in Percent) of Design Factors

for Series #1 Cigarettes 93

Table 3-B-1. Use of Kendall's Tau

Correlation Coefficient to Summarize the Agreement Between

Full-Scale and Bench-Scale

Ignition Tests 98

Table 4-1. Upward Smolder Velocity,

Paper Only 119

Table 4-2. Lateral Scan at Burn Line 121

Table 4-3. Peak Heat Flux from FNHC-25

(#127) on Three Fabrics (over

Polyurethane Foam) 125

Table 4-4. Effect of Gap Between Flux Gage and Coal on Peak

Heat Flux Measured 125

Table 4-5. Effect of Fabric on

Total Incident Heat From FNHC-25 (#127) 127

Table 4-6. Summary of Oxygen

Measurements During Ignition 131

Table 4-7. Temperatures on Surface

of Calcium Silicate Board

Induced by Cigarettes 133

Table 5-1. First Choice of Initial Distributions

of Temperatures, Oxygen Mass Fraction,

and (Relative) Tobacco Density,

Assumed for the Calculation 162

VI
Table 5-2.

Table 5-B-1.

Table 6-1

Figure 2-1.

Figure 2-2.

Figure 3-1.

Figure 3-2.

Figure 3-3.

Figure 3-4.

Figure 3-5.

Figure 3-6.

Calculated and Experimental

Values of Temperatures

at TC#1 and TC#2

Figure 3-A-1,

Parameter Values Used for the Sample Run in the Text, Using

Program CIG25

173

191

Weight Loss of Polyurethane

Blocks Caused by Smoldering

Cigarettes, Five Blocks with 5 Cigarettes Each 217

Typical Mockup Configurations 30

Typical Chairs Used in the

Full-Scale Tests Arranged

in the Burn Room 31

Four Chairs as Viewed

Through the Window of the Burn Room 72

Gaseous Nitrogen Applicator

Used to Extinguish Ignited

Sites 72

Sites for Various Cigarette

Types Marked on a Damask

Cushion With Burn Scars

Near the Marks 73

Sites for Various "Crevice" Tests Marked on a

"California Velvet" Cushion 74

Cigarettes Placed on Top

of Welt Cord When Cushion

Shape Prevented Placement

Beside Welt Cord 74

Weight on (Cotton Batting)

Cushion Simulating Seated

Person Causes "Acute Angle"

Crevice Shape

Figure 3-A-2.

Figure 3-A-3.

Figure 3-A-4.

Figure 4-1,

Figure 4-2.

Figure 4-3.

Figure 4-4.

Figure 4-5.

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

CA/CB, Unc./Flat .94

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance of the Substrate

SPL/PU, Unc./Flat 94

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

SPL/PU* (One Half of Tobacco

Column Removed), Unc./Flat . . .95

75

Normal Probability Plot

of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

Denim/PU, Crev./Cov 95

Heat Flux Gage Used to Scan Flux Distribution Around Cigarette Coal 108

Arrangement for Measuring

Peripheral Temperature

with a Thermocouple 108

Temperature-time on

Periphery of Cigarette

Showing Perturbation Due

to Passage of Heat Flux Gage;

Commercial Cigarette #6

in Free Burn 109

Apparatus for Scanning Flux Gage Past Cigarette Coal 109

Flux Scan Configurations

Used in this Study 110

VII
Figure 4-6a.

Figure 4-6b.

Figure 4-7.

Figure 4-8.

Figure 4-9.

Six Individual Scans on Same

BEHC-21 Cigarette Sitting on Flat, Horizontal Substrate

(Calif. Fabric/2045 Foam) 111

Averaged Results for Same Cigarette Data 111

Apparatus for Sampling

Oxygen Level Between

Fabric and Foam 111

Burning Rate of Commercial

Cigarette No. 6 on Several

Inert, Flat, Horizontal Substrates

of Varied Thermal Responsivity .

Figure 4-1 3b. Coal Length on Horizontal

Flat Substrate (Calif. Fabric/2045

PU Foam) Versus Tobacco

Packing Density for Twenty-Eight

Experimental Cigarettes 118

Figure 4-1 3c.

Figure 4-14.

Burning Rate of Several

Experimental Cigarettes on

Inert, Flat, Horizontal Substrates

of Varied Thermal Responsivity .

115

116 Figure 4-15.

Figure 4-10. Smolder Velocity on Two

Substrate Configurations Versus Smolder Velocity

in Free Burn 117

Figure 4-1 1a. Effect of Configuration on Smolder Velocity of Six Cigarettes 1 1

Figure 4-1 1b. Effect of Configuration on

Coal Length for the Same

Six Cigarettes 117

Figure 4-12. Correlations of Oxygen

Control Parameter (Eq. 4-3) with Burn Configuration;

Same Cigarettes as Figure 4-1

Figure 4-16.

Figure 4-17.

Figure 4-1 3a. Coal Length in Free Burn

Versus Tobacco Packing Density

for Six Cigarettes (same as

Figure 4-11)

118

118

Figure 4-18.

Coal Length from Crevice Burn (Calif. Fabric/2045

PU Foam) Versus Tobacco

Packing Density for Six Cigarettes (same as Figure 4-11)

Three-Dimensional Flux

Distributions for Two

Cigarettes in Free Burn. BEHN-21(108) and FNHC25(127); Scans Along Horizontal

Plane Tangent to Bottom Edge of Cigarette

119

120

Axial Flux Scans of Cigarette

201 in Three Configurations;

Dashed Lines are ± Average

Deviation; Substrates are Calif. Fabric/2045 PU Foam 121

Axial Flux Scans of BELN21(106) in Three Configurations;

Dashed Lines are ± Average

Deviations; Substrates are Calif. Fabric/2045 PU Foam 123

Axial Flux Scans of Cigarette

FEHN-21(116) in Three

Configurations; Dashed Lines

are ± Average Deviations; Substrates are Calif. Fabric/2045

PU Foam 123

Axial Flux Scans of Cigarette FNHC-25(127) in Three Configurations; Dashed

Lines are ± Average

Deviations; Substrates are Calif. Fabric/2045 PU Foam 124

VIII
Figure 4-19.

Figure 4-20.

Figure 4-21 a.

Figure 4-21 b.

Figure 4-22.

Figure 4-23.

Total Number of Substrate

Ignitions (from Section 3) Versus Peak Heat Flux Measured with Each Cigarette on a Horizontal Flat Substrate

Made from Calif. Fabric/2045

PU Foam

Figure 4-24a.

Experimental Cigarettes and

Substrate Ignition Propensity

Found in the Bench-Scale

Tests of Section 3 128

Peak Coal Surface Temperature

Versus Peak Incident Flux on a

Substrate (Calif. Fabric/2045 Foam)

Measured Gap Between

Coal Surface and Substrate as a Function of Burn Time

on Substrate; Cigarette

FEHC-21(115). Substrate is Calif. Fabric/2045 PU

Foam. Individual Gap

Profiles for Three

Cigarettes

124

125

Figure 4-24b. Same Correlation as Above

but Restricted to Experimental

Cigarettes Containing Flue-cured

Tobacco Only; line is best fit second degree polynomial 128

Figure 4-25.

Figure 4-26. 126

Measured Gap Between

Coal Surface and Substrate as a Function of Burn Time

on Substrate; Cigarette

FNHC-25(127); Substrate is Calif. Fabric/2045 PU Foam;

Individual Gap Profiles

for Five Cigarettes 126

Total Number of Substrate

Ignitions Versus Total Heat

Input Along Cigarette Axis; Heat Input Calculated from

Flux Profiles on California Fabric/2045 PU Foam .... 127

Total Number of Substrate

Ignitions Versus Triangular

Estimate of Planar Projected

Coal Area; Cigarettes Burned on

Calif. Fabric/2045 PU Foam 128

Correlation Between Mass

Burning Rate of Batch One

Figure 4-27.

Figure 5-1.

Figure 5-2.

Figure 5-3.

Figure 5-4.

Correlation Between Mass

Burning Rate of Batch One

Experimental Cigarettes

and Coal Length (From

Cigarette Burning on Horizontal

Flat, California Fabric

Over 2045 Foam) 129

Oxygen Depletion (as a

function of time) Beneath

Fabric a) FNHC-25 on

Splendor Fabric/2045 PU

Foam; Igniting Case b) FNHC-25

on Calif. Fabric/2045 PU Foam;

Non-Igniting Case 130

Isotherm Contours on the Top

Surface of a Horizontal Flat Upholstery Mock-up (California

fabric/2045 foam) 1 32

Schematic of a Smoldering

Cigarette 147

Temperature Distributions (in °C) at and near the Hot Coal,

Shortly After a Draw 148

Gas Temperature (°C) and

Oxygen Concentration in the

Quietly Smoldering Cigarette 148

Measured Longitudinal

Surface Temperature Distribution

for Cigarette 105 155

IX
Figure 5-5.

Figure 5-6.

Figure 5-7.

Figure 5-8.

Figure 5-9.

Figure 5-10.

Figure 5-1 1a.

Figure 5-1 1b.

Peak Fluxes Measured by

a Thermocouple, for a

Representative Sample of Experimental Cigarettes

Smoldering on a California Fabric/Foam Substrate . . .

Figure 5-1 1c.

Plot of pCv vs l

c

, the Coal

Length, to Test Eq. (5-34) .

Average of Several

Measurements of the Flux Emitted by Cigarette

105 Toward the Substrate,

Along the Contact Line . . .

156

156

Figure 5-1 2a.

Figure 5-1 2b.

163

Peak Temperatures of the Calcium Silicate Substrate

Surface as a Function of Time, for the Flux Used for Cigarette 105, for Several

Values of o\

Figure 5-1 3a.

166

Reproduction of Figure F,6b

from Reference [5-12]. Theoretical streamlines for horizontal cylinder

Figure 5-1 3b.

168

Reproduction of Figure F.6a

from Reference [5-12]. Azimuth

function g(x) giving variation

of local heat transfer coefficient

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 2 sec

168

173

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 12 sec

Figure 5-1 4a.

Figure 5-1 4b.

Figure 5-1 4c.

Figure 5-1 4d.

Figure 5-1 4e.

Figure 5-1 5a.

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 84 sec

Flux Measured Under the Rod Heater Along the Substrate

174

174

Flux Measured Under the Rod

Heater in the Direction Orthogonal to that Traversed

in the Measurements Shown

in Figure 5-1 3a 174

Calculated and Predicted

Temperatures at Thermocouples

TC1 and TC2 When the Smolder

Wave from Cigarette 102 is Made to Pass Over Them 175

Calculated and Predicted

Temperatures at Thermocouples

TC1 and TC2 When the Smolder

Wave from Cigarette 102 is Made to Pass Over Them 175

173

Initial Temperature Distribution

(in °C) Chosen for Calculation,

to Simulate Effect of Lighting

Cigarette With a Match 175

Isotherms at t = 2 sec, after

Initiation as in Figure 5-1 6a 176

Isotherms at t = 4 sec 1 76

Isotherms at t = 6 sec 1 76

Isotherms at t = 7.86 sec 176

Isotherms for Second Set of Starting Conditions. These

were Taken from Figure 5-2 177
Figure 5-1 5b. Isotherms Corresponding to Smolder Wave at t = 6 sec 1 77

Figure 5-1 5c. Isotherms in the Model

Cigarette at t = 1 2 sec 1 77

Figure 5-1 5d. Isotherms at t= 18 sec 177

Figure 5-1 6a. Contours of Constant Oxygen

Mass Fraction Corresponding

to Figure 5-17a (t = 0) 178

Figure 5-1 6b. Oxygen Mass Fractions at

t = 6 sec from the Same

Calculation That Yielded

Figure 5-1 7b 178

Figure 5-1 6c. Oxygen Mass Fractions at t= 12 sec 178

Figure 5-1 6d. Oxygen Mass Fractions at

t = 1 8 sec 1 78

Figure 5-17. Calculated Velocities of the Upper and Lower Intersections

of the 700°C Isotherm with the Axis, as a Function of Time 179

Figure 5-1 8a. Contours of Constant Radial

Gas Velocity at t = 6 sec from

the Calculation That Yielded

Figures 5-1 7b-d and 5-1 8b-d 1 79

Figure 5-1 8b. Contours of Constant Radial

Gas Velocity at t= 1 2 sec 1 79

Figure 5-1 8c. Contours of Constant Radial

Gas Velocity at t= 18 sec 180

Figure 5-19. Cross Section of Buried

Cable, with Various Distances

and Temperatures Indicated 203

Figure 5-20. Cross Section of Cigarette on

Substrate 205

Figure 6-1. Relationship of Polyurethane/

Cigarette System Weight Loss and Number of Ignitions

Obtained in Primary Evaluation 216

XI
Photograph showing achievable differences in cigarette ignition potential.

The mockup on the left has ignited; the one on the right is barely discolored.

XII
.xecutive Summary

Introduction

Cigarette ignition of furniture is by far the leading cause of

fire deaths and injuries in the United States. While more

ignition-resistant furnishings are being manufactured, fire casualties could be more rapidly reduced if cigarettes were

manufactured to cause fewer ignitions. To provide both the fundamental understanding of the cigarette/furniture ignition

process and practical application of that knowledge, the Center for Fire Research of the National Bureau of Stan- dards pursued the following fundamental and applied

research tasks under the Cigarette Safety Act of 1984.

• Identify the characteristics of cigarettes that could lead to a reduction in ignition propensity (using experimental

cigarettes of well-characterized composition and construction supplied by the cigarette industry);

• Obtain and analyze data to verify the composition of and

statistical variation in the experimental cigarettes in order

to provide a reliability analysis of laboratory findings using

those cigarettes;

• Measure the ignition propensities of patented, non- commercial cigarettes, as supplied by their inventors;

• Validate the cigarette ignition propensity data from the bench-scale testing by comparison with test results, using

real furniture items (supplied by the furniture industry)

indicative of the most common or high risk types;

• Elucidate the thermal conditions associated with lit cigarettes, their energy transfer to various substrates, and

the ensuing ignition process;

• Create a computer model of the ignition process to enable prediction of the direction and approximate magnitude of effects of variations in the characteristics of a cigarette on its ignition propensity;

• Quantify the effect of smolder-promoting alkali metal ion concentration in fabrics and paddings on their susceptibility to smoldering ignition by cigarettes to account for the effect of ignitability variations within or between lots of commercially-produced upholstery materials; and

• Develop a laboratory method for measuring the ignition

propensity of cigarettes.

Approach

This research project comprised several concurrent, interactive studies. These ranged from computational to experimental, fundamental to empirical.

1. Materials

A common set of materials was used in the various laboratory experiments. Forty-one types of experimental cigarettes were specially prepared for this study by the cigarette

industry. They varied in tobacco type and density, paper

permeability and citrate content, and circumference. The

wrappers and fillers were selected for systematic and broad

property variation, not necessarily indicative of current commercial cigarettes. Laboratories expert in the appropriate

measurements were commissioned to characterize the composition of and variance in these cigarettes. Five

embodiments of cigarette patents were received from their inventors. Several commercial cigarettes, remaining from a

prior project under the Act, were used here as well. Selected

fabrics and padding materials were acquired in large quantities to allow for the numerous bench-scale and full-scale

tests.

2. Performance Measurements

Ignition performance measurements of the cigarettes were

carried out on substrates having a range of ignition resis- tance, including some which simulated the most easilyignited furniture. At least five replicate tests were performed

for each cigarette/substrate combination. The data were

statistically analyzed for correlations between numbers of ignitions and the individual cigarette characteristics. Similar

testing was performed on chairs manufactured of some of the same materials, and the data analyzed to determine the

extent to which the results were predicted by the small-scale

tests.
3. Thermophysics of the Ignition Process 5. Effects of Materials Treatment

The ignition process was assumed to depend on the energy

transfer from cigarettes to furniture items. This was studied

using fine thermocouples and a heat flux gauge to follow the temperature and energy flux histories while cigarettes smoldered on different substrates. Two- dimensional infrared imaging radiometry was used to map the thermal response

of the substrate. Graphical correlations were explored

between measured properties of the burning cigarettes and

the measured ignition propensities.

4. Modeling Ignition

Both fundamental and semi-empirical mathematical

modeling of the lit cigarette and ignition of the substrate were pursued. Each borrowed heavily from prior efforts else- where. A comprehensive list of the involved materials properties and physical processes was compiled. Substantial

simplifications were made in representing these. The predictions from the resulting FORTRAN programs were tested, to a limited extent, against the trends observed in the laboratory tests.

Fabrics were treated with known concentrations of alkali metal chlorides and tested for changes in cigarette ignition resistance. Similar comparative tests were performed on

clean fabrics, to which was added soil extracted from used

fabrics.

6. Test Method Development

Finally, the experience and knowledge gained from the above research were applied to the task of developing a

convenient, accurate test method for cigarette ignition

propensity. Several previously-suggested and new

approaches were analyzed and tested in the laboratory, but

the development of a viable test method has not yet been

completed.

Table ES-2. Ignition Propensity as a

Function of Experimental Cigarette

Characteristics

Table ES-1. Ignition Propensities of

Selected Test Cigarettes

No. Ignitions

Designation 20 Tests %

Experimental

Cigarettes

201

106 1 5 202 2 10

130 4 20

114 4 20

105 6 30

113 6 30

108 7 35

122 7 35

129 10 50

Least Ignition-Prone

Commercial Cigarettes

1 16 80

2 12 60

Typical Ignition

Propensity Commercial

Cigarettes

3 18 90

6 20 100

Cigarette Parameters

Number of

Ignitions/Tests %

Tobacco Packing Density

High

Low

282/320

1 53/320

88

48

Cigarette Circumference (mm)

25

21 243/320192/320

76

60

Paper Permeability

High

Low

256/320

1 79/320

80

56

Paper Citrate Cone. (%)

0.8 231/320

204/320

72

64

Paper Citrate (%)

(Low Ignition Propensity

Cigarettes) 0.8

0.0

47/100

23/100

47

23

Tobacco Type

Flue-cured

Burley

222/320

213/320

69

66
Conclusions

Substantial progress has been made in understanding how

to study cigarette ignition, the nature of the cigarette ignition process, and the effects of cigarette characteristics on both

the thermal physics and the observed ignition of furniture. The principal findings of this research are as follows.

• In furniture mock-up tests involving a wide range of fabrics and paddings, the best of the experimental

cigarettes tested had considerably lower ignition propensities than commercial cigarettes.

• Three cigarette characteristics were found to reduce igni- tion propensity significantly: low tobacco density, reduced

circumference, and low paper permeability. Considerably

larger reductions were achieved with combinations of these. The tobacco column length, the presence of a filter

tip, and citrate content of the paper had effects in limited cases. The tobacco blend had minimal impact on ignition

propensity.

• Non-ignitions were often achieved without the cigarettes

self-extinguishing during the test; i.e., many cigarettes

burned their full length without igniting the substrate.

• Some of the best-performing experimental cigarettes had

average per puff tar, nicotine, and CO yields comparable

to or only slightly greater than typical commercial

cigarettes.

• Each of five patented cigarette modifications also showed

reduced ignition propensity over cigarettes that were identical except for the patented feature. These included variaTable ES-3. Average Per Puff Smoke

Component Yields from

Selected Cigarettes

Table ES-4. Ignition Propensities of

Patented Cigarettes

HHHHHHHPHH

Experimental

Cigarettes Tar (mg) Nicotine (mg) CO (mg)

105 1.6 0.09 1.9 106 1.8 0.10 2.0 108 1.3 0.09 1.1 113 2.4 0.19 2.2 114 2.6 0.21 2.1 122 2.4 0.15 2.4 130 2.5 0.20 2.2 201 2.5 0.18 2.5 202 2.0 0.16 2.4

Average for 6

Most Popular

Commercial

Cigarettes 2.0 0.13 1.7

No. Ignitions

Designation No. Tests Percent

301 -Control 25/25 100

301 29/50 58

302-Control 24/25 96

302 10/50 20

303-Control 24/25 100

303 32/60 53

304-Control 25/25 100

304 33/50 66

305-Control 25/25 100

305 13/60 22

Possible differences in the composition or toxicology of the smoke delivered by these cigarettes have not been

investigated.

tions in the paper, an additive to one location of the tobacco column, an additive throughout the tobacco

column, and an additive to the exterior of the paper.

Ignition results from the bench-scale testing correlated very well with corresponding data from experiments with chairs made with the same fabrics and padding materials. The physics of the ignition process is a function of both

the cigarette and the substrate. Therefore, an accurate

ignition propensity measurement apparatus must involve the two components.

Intrusive probes of the ignition process (e.g., ther- mocouples, heat flux gauges) perturb the delicately

balanced system. The induced errors can be estimated if the probes are small and well-selected. With care, (nonintrusive) infrared imaging can be used to study the thermal profiles on non-igniting or igniting substrates. An approximate correlation exists between the cigarette coal area and ignition propensity. Peak coal surface

temperatures (and thus peak heat fluxes) did not vary

sufficiently to demonstrate a correlation with ignition

tendency for the cigarettes tested. Oxygen depletion in the vicinity of the ignition site is important during the ignition process, but is sufficiently similar for all cigarettes examined so as not to account for their relative ignition propensities.

It is possible to construct a complex computer model of the smoldering combustion of a cigarette and the response of an idealized substrate. With all its simplifications, this preliminary model is sufficiently realistic to (1) manifest the most important and most sensitive physical features of the ignition process and (2) reproduce some of the cigarette characteristics that do and do not affect igni- tion propensity. Thus, the model could potentially be used

to screen possible combinations of (included) charac-
Table ES-5. Comparison of Ignition

Propensities of Tested Cigarettes at

Full- and Reduced-Scales

Cigarette

Percent Ignitions

Number Bench-Scale Full-Scale

6 74 73

129 13 23

106 3 6

114 6 14 201 6

teristics that offer increased fire safety. At present,

however, the code for this preliminary model is very slow

and not user-friendly

The current, mini-mockup methods are valid for research

measurements of the ignition propensity of cigarettes.

However, their use in a standard test method of cigarette

performance is compromised by the variability in the commercial fabrics and paddings used in the mockup.

Several alternative candidate test methods for measuring

the cigarette ignition propensity of soft furnishings were

evaluated; none was usable in its current state of develop- ment. Two promising approaches to cigarette testing are proposed. The first modifies the existing mockup proce- dure using specially-prepared, well-controlled fabrics and

paddings. The second uses a non-reactive substrate at variable temperature to determine the minimum needed

cigarette heat-loss rate for extinguishment. All need further development before promulgation.

Priority Further Research Directions

In any closed-end research effort such as this one, there are many ideas that cannot be pursued and others that evolve

during the project. The following is a tabulation of those

studies whose results are important to a sound understanding of the cigarette/furniture ignition phenomenon and

to realization of the research into practical usage.

• Both cigarette manufacturers and the public need a test to determine how less ignition-prone cigarettes perform.

The test should be relatable to the real-world situation and

should be simple enough to be used as part of a quality

assurance program. Three promising approaches for distinguishing between high, moderate, and low ignition

propensity cigarettes are: — Testing with non-smoldering (inert) substrates, e.g., extinguishment of cigarettes on a glass plate or a porous

frit, heated to adjusted, controlled temperatures. — Testing with alternative reactive (smoldering) substrates,

such as with controlled addition of selected amounts of smolder-enhancing ions to multiple layers of a-cellulose paper. — Testing with controlled reactive fabric/padding

substrates; mockup testing using "standardized" substrates created by the addition of selected amounts of smolderenhancing ions. The current research has indicated positive directions for reducing cigarette ignition propensity. Research is needed

on more combinations of these factors, especially lower

tobacco content and modified paper permeability and

thickness. Variations selected with the computer model

should also be studied. Performance data for current market cigarettes should be

generated by use of a new test method. These data could

then be compared to future year cigarette performance.

For a wider range of cigarettes and substrates, extensive

research is needed to better measure and define the

effect of the substrate on cigarette ignition propensity, the

ignition kinetics, and the components of heat transfer

(radiation, convection, conduction).

More measurements are needed of the cigarette ignition

physics in crevice configurations.

The preliminary computer model of the smoldering cigarette, while operational, would benefit from key upgrades:

multi-step tobacco pyrolysis and combustion, including

changes resulting from paper modification; inclusion of free and combustion-generated water; more realistic movement of air and combustion gases within the cigarette; and detailed paper behavior (changes in permeability and combustibility) as a function of temperature.

Similarly, the substrate model should be amended to include: two-layer (fabric plus padding) construction, heat- induced reactivity, and crevice geometry capability.

The computer models should be made more time-efficient

for efficient parametric variation of cigarette and substrate

variables.
The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 1

Introduction

Contents for Section 1

Project Background 9

Nature of This Project 10

References for Section 1 11

Introduction

Project Background

Cigarette ignition 1 of furniture is by far the leading cause of

fire deaths and injuries in the United States [1-1]. Although

the actual probability of a dropped, lit cigarette igniting soft furnishings and leading to a death or injury is small (49,000

fires [1-1] from 600 billion cigarettes purchased [1-2] in 1984), there were a sufficient number of such occurrences that an

estimated 1530 deaths and 3950 injuries occurred [1-1]. These most often happen in residences when a lit cigarette

is dropped onto bedding or a piece of upholstered furniture. The fabric and/or padding smolder slowly and for a long

time, and then often burst into flames. The victims succumb

to burns and/or to inhaled toxic smoke.

For over a decade, intense efforts have been devoted to reducing the susceptibility to cigarette ignition of both upholstered furniture and mattresses (soft furnishings). The

implementation of a mandatory standard for mattresses [1-3] and voluntary standards for upholstered furniture [1-4,5] has

resulted in the manufacture of soft furnishings with improved

resistance to cigarette ignition. The newer furnishings show a

reduction in total fire losses, but an increase in the risk of death or injury per fire [1-6]. Moreover, these commodities

have average useful lifetimes of fifteen to twenty years [1-7]. Thus, the full impact of the improved furnishings on fire safety will not be realized for decades to come. By contrast, cigarettes are consumed with a few months of their production [1-8], leading to the possibility that fire deaths and inju- ries could be reduced more rapidly if the cigarette were also

suitably modified.

In response to this, Public Law 98-567, the "Cigarette

Safety Act of 1984," was passed by the 98th Congress and

signed into law on October 30, 1984. It established an Inter- agency Committee to direct, oversee, and review the work of a Technical Study Group on Cigarette and Little Cigar Fire Safety (TSG). The TSG was directed to:

"undertake such studies and other activities as it considers

necessary and appropriate to determine the technical and

ignition is defined as sustained, expanding smoldering of the material on which the burning cigarette rests. This may or may not lead to flaming ignition.

commercial feasibility, economic impact, and other conse- quences of developing cigarettes and little cigars that will have a minimum propensity to ignite upholstered furniture or mattresses. Such activities include identification of the

different physical characteristics of cigarettes and little cigars

which have an impact on the ignition of upholstered furniture and mattresses, an analysis of the feasibility of altering any

pertinent characteristics to reduce ignition propensity, and

an analysis of the possible costs and benefits, both to the industry and the public, associated with any such product

modification."

The TSG constructed its initial work plan in February, 1985

and refined it through October, 1986. As part of this plan,

the Center for Fire Research (CFR) of the National Bureau of Standards (NBS) was sponsored to perform the following research:

Commercial Cigarette Testing

Determine the extent to which commercially available cigarette packings2 vary in their propensity to ignite soft furnishings substrates. 3

Ignitability Measurement

• Review and summarize the prior state-of-the-art in understanding cigarette ignition of soft furnishings;

• Identify the characteristics of cigarettes that could lead to a reduction in ignition propensity;

• Measure the ignition propensities of selected patented,

non-commercial cigarettes, as supplied by their inventors;

• Elucidate the thermal conditions associated with lit

2A cigarette packing is defined as a commercial cigarette, described by

its name, its diameter, its length, whether menthol or non-menthol, whether filter or non-filter, and by its package type (e.g., soft pack).

3 The term "substrate" is used to describe one combination of a specific

fabric and padding, in either the flat or the crevice (juncture of vertical and horizontal cushions) configuration, with or without a sheet covering

the cigarette. An example is the flat area of a piece of polyurethane foam covered with a specific fabric, with the cigarette covered by a piece of sheeting. The crevice made from the same materials is a

different substrate.
cigarettes, their energy transfer to various substrates, and

the ensuing ignition process (using experimental cigarettes

of controlled and well-characterized composition and

construction supplied by the cigarette industry); Create a computer model of the ignition process to enable prediction of the direction and approximate magnitude of effects of variations in a cigarette's characteristics on its ignition propensity; and

Develop a laboratory method for measuring the ignition

propensity of cigarettes.

impact of the changes in cigarettes and more realistic input

for the benefit/cost model.

Separate reports have already been issued on two of the

topics: "Relative Propensity of Selected Commercial

Cigarettes to Ignite Soft Furnishings Mockups," by John F. Krasny and Richard G. Gann, [1-9] and "Cigarette Ignition of Soft Furnishings - A Literature Review With Commentary," by

John F. Krasny [1-10]. The present report is a unified presentation of the approach, procedures, results and conclusions

from the remainder of the CFR study.

Quality Assurance of Experimental Cigarettes

Obtain and analyze data to verify the composition of and

statistical variation in the experimental cigarettes obtained

from the cigarette industry in order to provide a reliability analysis of laboratory findings using those cigarettes.

Alkali Metal Ion Effects

Quantify the effect of alkali metal ion concentration in fabrics and paddings on their susceptibility to smoldering ignition

by cigarettes. Since alkali metal ions are known smolder

promoters, this is pivotal to reducing or accounting for the

effect of ignitability variations within or between samples of commercially-produced upholstery materials. A similar, exploratory study was to be performed on the effect of in- use soiling on smoldering ignition.

Full-Scale Furniture Testing

Validate the cigarette ignition data from the bench-scale

testing by comparison with test results using real furniture items. This project used selected furniture items, supplied by

the furniture industry and made of fabrics and paddings

covering a wide range of ease of cigarette ignition. (Some

represented pre-UFAC and BIFMA standards of constructipn.) This allowed a more accurate assessment of the

Nature of This Project

The work reported here ranges from basic research into the physics of the ignition process to highly empirical studies of the manifest cigarette features affecting ignition. Substantial progress has been made in understanding

how to study cigarette ignitions, the very nature of that process, and the effects of cigarette construction on both the thermal physics and the observed ignition of soft furnishings.

Nonetheless, the research is incomplete. It was not possible, nor was it the intent, to resolve fully all the technical issues

involved in cigarette-initiated fires. The authors have therefore been attentive to documenting the experimental rationale, the procedures developed, and the logic utilized in interpreting the results. These will enable future researchers to evaluate

this work and use the appropriate portions to further advance the field. The report begins with a description of the materials used

in the various parts of the project. It then proceeds to the

cigarette performance experiments, both at bench and full scales. Next is a presentation of the research into the physics that controls the ignition process, followed by an

accounting of the transfer of that knowledge into a computer

model. The report continues with the rationale for and initial efforts to develop a new test method for measuring cigarette

ignition propensity. Last are conclusions and a listing of unresolved issues worthy of further research.

10
references for Section 1

[1-1] Hoebel, J.F., "1984 National Fire Loss Estimates,"

Consumer Product Safety Commission, July 22, 1986.

[1-2] Maxwell, Jr., J.C., "The Maxwell Report: Revised 1985

Year-End Sales Estimates for the Cigarette Industry,"

Furman Selz Mager Dietz & Birney, Inc., 1985.

[1-3] "Standard for the Flammability of Mattresses and

Mattress Pads," 16 Code of Federal Regulations, Part 1632, 1973.

[1-4] "Cigarette Ignition Resistance of Components of Upholstered Furniture," NFPA 260A-1983, National Fire Codes, National Fire Protection Association, Qumcy,

MA, published annually.

[1-5] "Resistance of Mock-up Upholstered Furniture Material Assemblies to Ignition by Smoldering Cigarettes,"

NFPA 260B-1983, National Fire Codes, National Fire Protection Association, Quincy, MA, published

annually.

[1-6] Harwood, B., "Trends in Cigarette-Ignited Fires," Consumer Product Safety Commission, March 1, 1985.

[1-7] Ray, Q, Consumer Product Safety Commission,

private communication.

[1-8] Spears, A., Lonllard, private communication.

[1-9] Krasny, J.F and Gann, R.G., "Relative Propensity of Selected Commercial Cigarettes to Ignite Soft Furnishings Mockups," NBSIR 86-3421, U.S. National

Bureau of Standards, Gaithersburg, MD, 1986.

[1-10] Krasny, J.F, "Cigarette Ignition of Soft Furnishings—

A

Literature Review With Commentary," NBSIR 87-3509,

U.S. National Bureau of Standards, Gaithersburg, MD,

1987

11

The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 2

Materials

13

Contents for Section 2 List of Tables

Cigarettes 17 Table 2-1 . Description of Cigarettes 17

Series 1 Experimental Cigarettes 17

Series 2 Experimental Cigarettes 17 Table 2-2. Patented, Low Ignition Propensity Cigarettes 17

Commercial Cigarettes 20

Quality Assurance of Cigarettes 20 Table 2-3. Methods for the Determination of Cigarette

Characteristics 20

Results of Measurements of Physical and Chemical

Characteristics of Cigarettes 20 Table 2-4. Series 1 Experimental Cigarettes 20

Series 2 Experimental Cigarettes 22

Substrates 29

Fabrics 29 Table 2-5. Padding 29

Mockup Configurations 29

Chairs 31 References for Section 2 32

Appendix 2-A 33 Table 2-6. Appendix 2-B 39

Appendix 2-C 43

Appendix 2-D 45

Appendix 2-E 49 Table 2-7. Appendix 2-F 51 Appendix 2-G 53

Description of Series 1 Experimental Cigarettes 18

Description of Series 2 Experimental Cigarettes 19

Measured Physical and

Chemical Characteristics of Series 1 Experimental Cigarettes 21

Measured Physical and

Chemical Characteristics of Series 2 Experimental Cigarettes 22

Physical Characteristics and

Smoke Yields of Experimental

Cigarettes, Series 1. Data from Lorillard Laboratories 23

Smoke Yields of Experimental

Cigarettes Series 2. Data

from Lorillard Laboratories . . 24

FTC Values for Tar, Nicotine,

and Carbon Monoxide Yield and Puff Count of Series 1 Experimental Cigarettes .... 25

Table 2-8. FTC Values for Tar, Nicotine,

and Carbon Monoxide Yield and Puff Count of Series 2 Experimental Cigarette 26

Table 2-9. Upholstered Fabrics, Padding

and Sheeting Used in the Investigation 27

Table 2-10. Cation Content of Upholstery

Fabrics and Cotton Batting 28

15
List of Figures

Figure 2-1. Typical Mockup Configurations

Figure 2-2. Typical Chairs Used in the

Full-Scale Tests Arranged

in the Burn Room

.30

31

List of Appendices

Appendix 2-A 33

Table 2-A-1. Cigarette Manufacturer's

Description of Series 1, 21 mm

Experimental Cigarettes 35

Table 2-A-2. Cigarette Manufacturer's

Description of Series 1 , 25 mm

Experimental Cigarettes 35

Appendix 2-B 39

Table 2-B-1. Cigarette Manufacturer's

Description of Series 2 Experimental

Cigarettes 41

Appendix 2-C 43

Appendix 2-D 45

Table 2-D-1. Paper Permeability of Series 1 Experimental Cigarettes Determined by

Kimberly-Clark 46

Table 2-D-2. Paper Permeability of Series 2 Experimental Cigarettes Determined by

Kimberly-Clark 48

Appendix 2-E 49

Appendix 2-F 51

Appendix 2-G 53

Table 2-G-1. Elemental Analysis of Upholstery

Fabrics and Cotton Batting

Determined by U.S. CPSC 54

16
igarettes

Series 2 Experimental Cigarettes

In this study, forty-one experimental cigarettes, five patented

cigarettes, and three previously tested commercial cigarettes were used. The following is a documentation of their composition.

Description of Cigarettes

Series 1 Experimental Cigarettes

Thirty-two cigarettes varying systematically in five parameters

at two levels were manufactured by the cigarette industry

with current hardware at slower speeds. The parameters

studied were 1) tobacco blend (Burley 1 or flue-cured2

), (2) expansion3 (non-expanded, 60 cuts/inch or expanded, 30

cuts/inch), (3) cigarette circumference (nominally 21 or 25

mm), (4) cigarette paper permeability (nominally 10 or 75

CORESTA4

), and (5) cigarette paper treatment (untreated

and treated with approximately 0.8% sodium potassium

citrate). Table 2-1 gives the experimental cigarette designations with respect to the five parameters; the acronym, which

is a mnemonic for the cigarette construction, and an

experimental number will be used interchangeably

throughout this report. Additionally, Appendix 2-A gives infor- mation concerning individuals in the cigarette industry who

arranged for manufacturing the cigarettes, specifics on the designations of tobacco cut, cigarette paper, tipping paper,

filter rod, the Burley and flue-cured blends, and cigarette

manufacturing specifications.

Mn air-cured tobacco grown primarily in Kentucky and Tennessee. It is light brown to reddish brown in color and has a somewhat greater

filling power than flue-cured tobacco.

2 Commonly called Bright or Virginia tobacco. It is lemon or orangeyellow in color and possesses a sweet aroma and slightly acidic taste.

It is high in sugar content and low to average in nitrogenous materials,

acids, and nicotine. ^Expansion refers to a process which increases the volume of individual tobacco shreds. ^Corresponds to cmVmin cm2 measured at 1 cbar.

A second series consisted of nine cigarettes varying in paper parameters. These were produced by the cigarette

industry with research hardware. The expanded, flue-cured tobacco blend was the same as used in Series 1 cigarettes.

The papers contained no additives. The variables were (1) single vs. double paper wrapping of the cigarettes (the inner, second wrapping was a thin tissue paper with a permeability

of 7000 CORESTA), (2) paper permeability (a base paper of 4-6 CORESTA units, with certain cigarettes covered with paper electrostatically perforated to 60 CORESTA units), and

(3) embossed (raised dot pattern) vs. normal texture paper. One cigarette had nominally a 21 mm circumference, the others 25 mm. Table 2-2 gives a detailed description of the

cigarette variables and the experimental designations that

will be used throughout this report. Appendix 2-B gives

information on the manufacturing specifications.

Patented, Low Ignition Propensity Cigarettes

A group of non-commercial, patented cigarettes were also included in this study. The cigarettes were supplied in accor- dance with the Federal Register notices, vol. 51, no. 115, June 16, 1986 and vol. 51, no. 148, August 1, 1986

(Appendix 2-C). The conditions for acceptance of such

cigarettes for evaluation were that the person submitting:

1. "select the single embodiment of his or her patent(s)

believed to be most effective for consideration,

2. submit documents which show that a patent has been

issued or that the application for a patent has been filed,

3. supply information as to the specific nature of the partic- ular modification or additive employed in the cigarette invention in quantitative terms,

4. provide evidence of significantly reduced propensity of the cigarette invention to ignite substrates found in mattresses and upholstered furniture,

5. provide free of charge 300 invention cigarettes and 300

control cigarettes that are identical to the invention cigarettes except for the feature that comprises the effective ignition repression, and

6. supply uniformity data (mean value plus standard deviation) for both the patented and control cigarettes with regard to the following properties: cigarette mass, ciga17
Table 2-1. Description of Series 1 Experimental Cigarettes

Packing Des>cription

Experimental Tobacco Paper

Designation Blend Expanded Porosity Additive Circumference (mm)

101 BNLC-21 Burley Non-Expanded Low Citrate 21 102 BNLN-21 Burley Non-Expanded Low No Additive 21 103 BNHC-21 Burley Non-Expanded High Citrate 21 104 BNHN-21 Burley Non-Expanded High No Additive 21 105 BELC-21 Burley Expanded Low Citrate 21 106 BELN-21 Burley Expanded Low No Additive 21 107 BEHC-21 Burley Expanded High Citrate 21 108 BEHN-21 Burley Expanded High No Additive 21 109 FNLC-21 Flue-Ci red Non-Expanded Low Citrate 21 110 FNLN-21 Flue-Ci red Non-Expanded Low No Additive 21 111 FNHC-21 Flue-Ci red Non-Expanded High Citrate 21 112 FNHN-21 Flue-Ci red Non-Expanded High No Additive 21 113 FELC-21 Flue-Ci red Expanded Low Citrate 21 114 FELN-21 Flue-Ci red Expanded Low No Additive 21 115 FEHC-21 Flue-Cured Expanded High Citrate 21 116 FEHN-21 Flue-Cured Expanded High No Additive 21 117 BNLC-25 Burley Non-Expanded Low Citrate 25

118 BNLN-25 Burley Non-Expanded Low No Additive 25

119 BNHC-25 Burley Non-Expanded High Citrate 25

120 BNHN-25 Burley Non-Expanded High No Additive 25

121 BELC-25 Burley Expanded Low Citrate 25

122 BELN-25 Burley Expanded Low No Additive 25

123 BEHC-25 Burley Expanded High Citrate 25

124 BEHN-25 Burley Expanded High No Additive 25

125 FNLC-25 Flue-Cured Non-Expanded Low Citrate 25

126 FNLN-25 Flue-Cu red Non-Expanded Low No Additive 25

127 FNHC-25 Flue-Ci red Non-Expanded High Citrate 25

128 FNHN-25 Flue-Ci red Non-Expanded High No Additive 25

129 FELC-25 Flue-Ci red Expanded Low Citrate 25

130 FELN-25 Flue-Ci red Expanded Low No Additive 25

131 FEHC-25 Flue-Ci red Expanded High Citrate 25

, 132 FEHN-25 Flue-Ci red Expanded High No Additive 25

rette length and diameter, mass burning rate [in air], and

magnitude of modification."

In publishing the results, the identities of the individual patented cigarettes were to be kept confidential; each one of the inventors would be informed only of the test results on

his cigarette(s). Five patented cigarette embodiments were submitted,

each in accordance with the Federal Register notices. The

embodiments, which the suppliers claim make them less

ignition-prone, are listed below. No verification of the invention disclosures was made by NBS.

• "The cigarette wrapper was made to a very tight natural porosity (3 cm/min [CORESTA]) and at a higher-thannormal basis weight of 32 g/m2

. The paper was subsequently treated with 11% potassium citrate and electrically

perforated to 70 cm/min (CORESTA)." U.S. patent application no. 06/627,710. Introduction of a proven and safe inorganic fire retardant

(0.02 ml of sodium silicate [viscosity of 60 CP, 26% Si02 ]) onto 5 mm in the center of the 85 mm tobacco rod. U.S. patent application no. 06/734,118. "Small bands of diffusionally tight paper (containing only

cellulose derived from wood pulp) were attached at fixed

intervals to the inside surface of otherwise conventional

cigarette wrapper.[sic] The latter has a permeability of 30

cm/min (CORESTA) and contains sodium potassium citrate

[sic] at a level of 0.8% (expressed as anhydrous citric acid). The dimensions of each band are 6.5 mm by 27 mm. These were spaced, two per cigarette, so that the

first band is 15 mm from the lighting end and the second

18
Table 2-2. Description of Series 2 Experimental Cigarettes

Experimental

Designation Blend Circumference (mm) Paper (Outer) Paper (Inner)3 Construction

201 Flue-cured

Expanded

21 4-6 CORESTA Units/

23.5 mm

None Single Wrap

202 Flue-cured

Expanded

25 4-6 CORESTA Units/

27.5 mm

None Single Wrap

203 Flue-cured

Expanded

25 4-6 CORESTA Unit Base

Electrostatically

Perforated to 60

CORESTA Units/27.5 mm

None Single Wrap

204 Flue-cured

Expanded

25 4-6 CORESTA Units

Embossed/27.5 mm

None Single Wrap

205 Flue-cured

Expanded

25 4-6 CORESTA Units

Electrostatically

Perforated to 60

CORESTA Units/Embossed/

27.5 mm

None Single Wrap

206 Flue-cured 25 4-6 CORESTA Units/ 7000 CORESTA Double Wrap

Expanded 27.5 mm Microporous

Structure/25 mm

207 Flue-cured 25 4-6 CORESTA Unit Base 7000 CORESTA Double Wrap

Expanded Electrostatically

Perforated to 60

CORESTA Units/27.5 mm

Microporous

Structure/25 mm

208 Flue-cured 25 4-6 CORESTA Units 7000 CORESTA Double Wrap

Expanded Embossed/27.5 mm Microporous

Structure/25 mm

209 Flue-cured 25 4-6 CORESTA Units 7000 CORESTA Double Wrap

Expanded Electrostatically

Perforated to 60

CORESTA Units/Embossed/

27.5 mm

Microporous

Structure/25 mm

(a) Same width as cigarette circumference, i.e., no overlap; also extends under the overwrap to the tilter

is 30 mm from the lighting end. Each band has a mass of approximately 2.5 mg." (U.S. patent applied for.)

".

. .the brush application to the exterior surface of the

Commercial Cigarette of a water suspension containing

(8.9%) percent by weight of Non-fat Dry Milk and (0.1%)

percent by weight of Mono-ammonium Phosphate. . ." U.S. Patent 4453,553.

Addition to the tobacco column of Expantrol VTM (a moisture stable, intumescent silicate fire retardant material) at a

tobacco to additive ratio of 4:1. U.S. patent application no. 06/877,803.

The cigarettes were coded 301 through 305, in random

order. The controls were correspondingly labeled with a "C"

19
Commercial Cigarettes

In a prior study [2-1], 12 commercial cigarettes were studied

to determine their relative ignition propensities. Four of these

cigarettes (1-3 and 6) were selected to compare with the experimental and patented cigarette performance in this study: two having the lowest ignition propensity of the twelve

commercial cigarettes (1 and 2) and two with a high ignition

propensity typical of eight of the commercial cigarettes (3 and 6).

Quality Assurance of Cigarettes

Methods for the Determination of

Cigarette Characteristics

The experimental cigarettes were characterized with respect

to total weight, tobacco weight, filter weight, paper weight,

and circumference in the following manner:

Cigarettes which had been placed in sealed containers

and placed in freezers held at -15°C upon arrival at CFR

were transferred to bins in a conditioned room (55 + 10%

RH, 22 ± 3°C). The cigarettes were conditioned for at least 48 hours before measurements were taken. Weights were

determined on an analytical balance with 0.0001 g resolution. Cigarette dimensions were determined on a ruler with

0.5 mm resolution. Four randomly-selected replicates of each

of the Series 1 cigarettes and five randomly-selected repli- cates of each of the Series 2 and patented cigarettes were

measured. First, the cigarettes were weighed. Then a scalpel was used to cut the cigarette at the wrapper and over-wrap seam to remove the filter. The wrapper was then cut lengthwise to allow removal of the tobacco. The tobacco remaining

under the over-wrap paper was removed and combined with the main tobacco column. The filter with the over-wrap

paper, the tobacco, and the paper were individually

weighed. The paper was flattened on a dark background

and the width (circumference) and length were measured to the nearest 0.5 mm. It would have been difficult to determine

the dimensions more accurately because measurements

would have had to be made under a microscope.

Means and standard deviations for the values were calculated. Additionally, the packing density of each cigarette was

determined based on the measured values of tobacco

weight, circumference, and tobacco column length. These

data are presented in Tables 2-3 and 2-4 for Series 1 and

Series 2, respectively.

Values of the total cigarette weights, tar, nicotine and CO

yields, and puff counts were supplied by the laboratory of

Lorillard, Inc., a division of Loews Theatres, Inc., Greensboro,

North Carolina. Additionally, linear and mass burn rates and

tar deliveries for Series 1 cigarettes and pressure drops for Series 1 and 2 cigarettes were furnished by Lorillard. These

data are presented in Tables 2-5 and 2-6. The experimental cigarettes were also analyzed for tar, nicotine, and CO deliveries and puff count by the Tobacco

Research Laboratory of The Federal Trade Commission,

Washington, DC. Approximately fifty of each of the cigarettes were removed from the freezer and sealed in zip-lock bags.

The cigarettes were delivered to FTC and analyzed by established methods [2-2,3], The results are shown in Tables 2-7 and 2-8. Determination of the experimental cigarette tobacco blend

from measurements of the total alkaloids and reducing

sugars using a method given in [2-4] was performed by the Department of Crop Science, North Carolina State University,

Raleigh, North Carolina. The determination for the Series 1 experimental cigarettes was made from six individuallywrapped tobacco columns of each cigarette. Three tests were performed on each of the thirty-two cigarettes using

approximately one-gram samples. These data are presented

in Table 2-3. Since the Series 2 cigarettes were prepared

from one tobacco batch, the tobacco columns from twenty

each of the nine experimental cigarettes were blended and

analyzed. These data appear in Table 2-4. The permeability of the wrapping paper on the experimental cigarettes was determined by the KimberlyClark Corporation, Roswell, Georgia. Approximately twentyfive of each of the two series of experimental cigarettes were

supplied. The method used for the determination is briefly

described in Appendix 2-D and the data appear in Tables 2- 3 (Series 1) and 2-4 (Series 2). Citrate analysis of six selected Series 1 experimental

cigarettes was done by the Health Sciences Laboratory, U.S. Consumer Product Safety Commission, Washington, DC.

Fifteen wrappers of each cigarette (three with no reported

citrate and three with reported citrate treatment) were removed from cigarettes stored in the freezer. The wrapper seam was removed from all samples to avoid possible

contamination from the adhesive. The results are shown in Table 2-3 in parentheses. The method for determining the

citrate content is described in Appendix 2-E.

Results of Measurements of Physical and

Chemical Characteristics of Cigarettes

Tables 2-3 and 2-4 show the measured physical and chemical properties of the Series 1 and Series 2 experimental

cigarettes. The measured values generally indicate reasonable adherence to the design specifications of, these

cigarettes. No measurements are presented for the physical

and chemical characteristics of the patented cigarettes. The

details of the experimental cigarettes are discussed below.

Series 1 Experimental Cigarettes

Half of the 32 cigarettes in this series had nominally 21 mm,

the other 25 mm circumference. The actual measurements— performed with a millimeter scale on papers

cut off the cigarettes — confirmed these values within the accuracy of the measurement. Similarly, all tobacco

columns, measured from the cigarette tip to the overwrap

paper, were found to be of about the same length, about 72 mm.

The determination of the Burley or flue-cured tobacco

blend was based on the amounts of reducing sugars and

total alkaloid content (Tables 2-3 and 2-4). The analysts's

20
Table 2-3. Measured Physical and Chemical Characteristics of Series 1

Experimental Cigarettes

Measured Physical

Experimental

Tobacco Analysis3

Packing Paper Tobacco Total

Cigarette Characteristics

Total Tobacco Filter Paper

Cigarette alkaloid Sugar density Perm." citrate Circum. column cigarette weight weight weight

Designation (0/0) (%) (mg/mm3

) (CORESTA) (cone.)d (mm) length (mm weight (mg) (mg) (mg) (mg)

101(BNLC-21) 1.99 ±0.02 2.66 ±0.28 0.24 8.9 ± 0.5 0.8 21.0±0 72.5 ±0.5 831 ±14 619+15 174 + 2 39 ±0.6

102(BNLN-21) 2.00 ±0.1

9

2.48 ±0.1

9

0.25 7.8 ± 0.5 0.0 21.0 + 72 ±0.5 840 ± 6 627 ± 3 173 + 4 42 ±0.9

103(BNHC-21) 2.04 ±0.04 2.48 ±0.27 0.25 75 ± 10 0.8 21.0 + 72.5±0 835 ±36 626 ±34 171 +2 39 ±0.5

104(BNHN-21) 2.00 ±0.11 2.52 ±0.22 0.24 66 ± 7 0.0 21.0+0 72.5 ±5 829 ±14 618 + 13 172 + 2 41 ±1.1

105(BELC-21) 1.82 ±0.07 2.07 ±0.34 0.16 9.4 ± 0.7 0.8 21.0+0 72 ±0.5 606 ±13 401 ±12 169 + 2 38 ±0.6

106(BELN-21) 1.83 ±0.06 2.02 ±0.24 0.17 8.2 + 0.5 (0.0) 21.0 + 73 ±0 640 ± 9 428 ± 7 172±4 41 ±0.5

107(BEHC-21) 1.85 ±0.05 2.16 + 0.18 0.17 70 ± 10 (0.74) 20.0 ±0 72 ±0.5 599 + 1

6

387 + 17 170±4 40±1.0

108(BEHN-21) 1.85 ±0.06 1.89 ±0.23 0.14 69 ± 10 0.0 21.0±0 72.5 ±0.5 565 ±40 356 ±39 171 ±2.5 39 ±0.9

109(FNLC-21) 1.95 ±0.05 12.69 ±0.88 0.31 8.9 ± 0.6 0.8 21.0±0.5 73 ±0 985 ±25 768 ±25 174±2 44 ±0.6

110(FNLN-21) 1.96 ±0.06 12.72 ±0.56 0.31 8.5 ± 0.6 0.0 21.0 + 72.5±0 994 ±17 777 ±22 174±5 43 ±0.4

111(FNHC-21) 1.90 ±0.04 12.37±0.72 0.32 67 ± 7 0.8 21.0 + 72.5 ±0 1018 + 10 802 ± 6 176 + 4 42 ±0.3

112(FNHN-21) 1.94 ±0.06 1278±0.97 0.31 67 ± 6 0.0 21.0±0.5 72.5±0.5 992 ± 7 778 ± 6 173±2 41 ±0.7

113(FELC-21) 1.74 ±0.03 10.37 ±0.69 0.15 9.2 ± 16 0.8 20.5 ±0 72.5±0.0 588 + 1

8

372±16 175±3 42 + 1.4 114(FELN-21) 1.69 ±0.06 10.49 ±0.72 0.15 8.6 ± 17 0.0 21.0 + 72.5 ±0.5 601 ±17 385 + 1

6

176 + 1 42 ±0.7

115(FEHC-21) 1.71 ±0.06 10.13 + 0.55 0.17 68 ± 5 (0.57) 20.0 ±0 72.5 ±0.5 607 ±10 387±10 174±5 43 ±0.8

116(FEHN-21) 1.66 ±0.05 10.35 ±0.70 0.15 68 ± 6 0.0 21.0+0 73 ±0.5 592 ±14 376 ± 5 176 + 5 41 ±0.6

117(BNLC-25) 2.01 ±0.13 2.52±0.14 0.24 9.4 ± 0.8 0.8 25.0±0 72.5 ±0 1 126 + 31 848 ±29 232 ±5 48 ±0.5

118(BNLN-25) 2.12±0.06 2.54±0.19 0.24 8.6 ± 0.5 (0.0) 24.5±0 72.5 ±0 1112+ 8 834 ± 3 233 ±4 47 ±0.9

119(BNHC-25) 2.1 2 ±0.06 2.61 ±0.17 0.23 69 ± 8 0.8 25.0 ±0 72.5 ±0.5 1111± 2 832 ± 2 233 ±3 47±0.6

120(BNHN-25) 2.13±0.08 2.68 + 0.17 0.23 76 ± 8 0.0 24.5 ±0 72.5 ±0.5 1090 ±42 810±43 232 ±4 45 + 1.2

121(BELC-25) 1.93 ±0.05 2.29 ±0.1

7

0.14 9.2 ± 0.5 0.8 24.5 ±0 72 ±0.5 765 ±19 488 + 1

6

232 ±5 48 ±0.3

122(BELN-25) 1.89 ±0.06 2.27 ±0.21 0.13 9.2 ± 0.4 0.0 25.0 ±0 72.5±0 748 ±18 470 ±20 230 ±4 46±0.3

123(BEHC-25) 1.91 ±0.10 227±0.19 0.14 69 ± 9 0.8 24.5 ±0 72.5±0.5 749 ±21 472 ±23 232 ±5 46 ±0.3

124(BEHN-25) 1.89 ±0.04 2.21 ±0.21 0.14 78 ± 7 0.0 25.0 ±0 72.5±0 772 ± 9 495 ± 9 232 ±2 45 ±0.3

125(FNLC-25) 1.91 ±0.07 11.76 + 1.40 0.28 9.9 ± 0.9 (0.61) 25.0 ±0 71.5+0.5 1 268 + 1

8

993 + 1

8

229 ±2 48 ±0.5

126(FNLN-25) 1.92 ±0.08 1 1 .86 ± 1 .06 0.28 9.4 ± 0.5 0.0 25.0 ±0 71.5±0.5 1281 ±44 1007 ±43 229 ±2 46 ±0.8

127(FNHC-25) 1.91 ±0.05 11. 85 ±0.55 0.28 68 ± 11 0.8 25.0 ±0 71 ±0.5 1 269 + 1

7

989 ±20 233 ±4 47 ±0.7

128(FNHN-25) 1.95 ±0.04 12.13±0.66 0.29 68 ± 6 0.0 25.0 ±0 71.5 + 0.5 1299 ±21 1018 + 26 230 ±5 47 ±0.5

129(FELC-25) 1.80 ±0.06 10.19 + 1.26 0.16 9.2 ± 0.7 0.8 25.0±0 71.5 + 0.5 836 ±47 560 ±47 232 ±6 47 ±0.6

130(FELN-25) 1.82 ±0.06 9.97 ±0.81 0.16 9.4 ± 0.8 (0.0) 24.5 ±0 72 ±0.5 841 ± 7 563 ± 9 230 ±2 45 ±0.5

131(FEHC-25) 1.85 ±0.03 10.17 + 0.36 0.21 70 ± 8 0.8 24.1 ±0.5 71 ±0 959 ±22 679 ±22 230 ±3 47 ±0.7

132(FEHN-25) 1.86 ±0.04 9.89 ±0.58 0.16 75 ± 8 0.0 25.0 ±0 71.5+0 840 ±13 563 + 1

1

230 ±2 45 ±0.2

(a) Measured at North Carolina State University, Department of Crop Science

(b) Measured at Kimberly-Clark Corporation

(c) CORESTA corresponds to cm3/min-cm2 measured at 1 cbar.

(d) Nominal, except for those in parentheses which were determined by U.S.CPSC

21
Table 2-4. Measured Physical and Chemical Characteristics of Series 2

Experimental Cigarettes

Circum. (mm)

Tobacco column

length (mm)

Total cigarette weight (mg)

583 ±24

828 ±14

784 ± 29

798+19

819+ 6 848 ±32

829 ± 1

1

836 ±16

819± 13

Tobacco Analysis3 Paper variables

Tobacco

weight

(mg)

366 ±24

566 ± 1

4

519 + 25

531 ±17.6

549 ± 7.7 5^0 ±20

530 ± 1

1

531 ±18

514+ 9

Filter weight (mg)

171 ±2

216 + 3 216 + 6

218 + 3 216±1

213 + 3

214 + 3 219 + 5 218 + 2

Paper

(rr Inner

weight

ig)Outer

43+0.6

45 ±0.9 48±0.4

47 ±0.5

47 ±0.6

46 ±1.2

47 + 1.3 46 ±0.6

48 ±1.9

Experimental

Cigarette Designation

201 202

203

204

205

206

207

208

209

Total alkaloid (%)

1 88

1.97

1.95

1.95

1.90

1.88

1.92

1.97

1.90

Sugar

(%)

12.0

12.5 12.6

12.5

12.4

11.1

12.1 12.5

12.1

Packing

density (mg/mm3

)

0.14

0.16 015

0.16 019

0.16

0.16

0.16

0.16

Permeability13 CORESTAc Embossed8

YES

YES

YES YES

Outer Inner

7300 ± 700

7700 ±700

6800 ±400

7200 ±600

5.2± 0.6 6.4+ 0.8

58. + 5.3d

87. ±59

160. ±49. d

6.2 ± 1.2

59. + 12.

d

84. ±47.

140. ±33. d

21 ±0.5

25 ±0.5

25 +0.5

24 ±0.5

25 ±0.5

25 ±0.5

24.5 ±0.5

25.5 ±0

25 ±0.5

73 ±0

72 ±0

72 ±0.5

71.5 + 0.5 71.5 + 0.5 72 ±0.5

72 ±0.5 71.5±0

71.5 +

35±0.7

35 ± 1 .1 35 ±0.7

35 ±0.9

(a) Measured at North Carolina State University, Department of Crop Science

(b) Measured at Kimberly-Clark Corporation

(c) expressed in cm 3 /min-cm2 -cbar

(d) 4-6 CORESTA, electrostatically perforated to 60 CORESTA units

(e) Outer paper embossed

report is shown in Appendix 2-F. According to this report, the Burley tobacco was clearly as labelled. Some uncertainty arose about the contents of the cigarettes containing nominally 100 percent flue-cured tobacco. The analyst's guess was that they contained a 90/10 blend of flue-cured and

Burley tobacco. (We have been told that tobacco analysis

from cigarette specimens is a rather imprecise art [2-5].) The cigarette and tobacco weights were affected by the Burley or flue-cured tobacco blend, tobacco packing

density and cigarette diameter. The non-expanded, flue- cured cigarettes were on average about 160 mg heavier

than the cigarettes made from the Burley tobacco blend. However, the expansion process reduced this difference, in that, the expanded Burley cigarettes weighed about 30

percent less, and the expanded flue-cured cigarettes about

40 percent less than their non-expanded counterparts,

indicating that flue-cured tobacco can be expanded more

effectively than Burley. The 25 mm circumference cigarettes

weighed about 30 percent more than the 21 mm circumfer- ence cigarettes.

In general, the weight values obtained by the Lorillard Laboratories (Tables 2-5 and 2-6) were often but not always

higher than those obtained at NBS. The slightly higher

weights might reflect a higher relative humidity in the

Lorillard laboratories. The packing densities of cigarettes containing expanded

tobacco were about 1/2 to 2/3 of those containing non- expanded tobacco. They were higher for the non-expanded,

flue-cured cigarettes than the comparable Burley cigarettes,

but rather similar after expansion. The packing densities of 21 and 25 mm cigarettes were similar. With respect to the data for the paper wrapping, the important information is in the treatment and permeability.

The three measured citrate content results appear to be

somewhat lower than specified. The permeability of the nominally 10 CORESTA (low porosity) papers and that of the nominally 75 CORESTA (high porosity) papers appear to be

reasonably close to the specified values. There appears to be no significant difference between the values for tar, nicotine, and carbon monoxide deliveries and

puff counts supplied by the Lorillard Laboratories and the Federal Trade Commission.

Series 2 Experimental Cigarettes

These nine cigarettes were all made from the same flue- cured expanded tobacco as the cigarettes in Series 1. They

were covered with a paper, as described in Table 2-2, with lower permeability than the paper used in the Series 1 cigarettes. All but one cigarette were nominally 25 mm

circumference; one was nominally 21 mm circumference.

Some of the cigarettes had paper which had been made

more permeable by electrostatic perforation and/or

embossed paper, and some had a light, highly permeable

inner wrapping between the cigarette paper and the tobacco column.

Table 2-4 shows that the cigarette, tobacco, and paper

weights, as well as packing densities were quite similar, as

expected. The exception was, of course, cigarette number

22
Table 2-5. Physical Characteristics and Smoke Yields of Experimental Cigarettes,

Series 1. Data from Lorillard Laboratories

CIGT^IGT LBR LBR MBR MBR/LBR C WT C WT PD P0 NIC NIC TAR TAR CO CO PC PC TAR

NO DESC SO SD SD SD SD SD SD RE

l BNLC-21 5.79 0.34 54.9 9.48 0.873 0.0049 261.8 15.3 1.65 0.09 18.4 0.66 20.1 0.98 8.0 0.10 35.7

2 RNLN-21 4.80 0.18 45.6 9.50 0.866 0.008Z 245.8 9.8 1.93 0.02 21.6 0.96 19.4 0.13 8.0 0.22 33.4

3 BNHC-21 7.42 0.36 71.5 9.64 0.882 0.0102 226.5 14.1 1.30 0.08 12.7 0.60 13.4 0.07 7.8 0.16 33.3

4 BNHN-Z1 6.82 0.32 64.4 9.44 0.860 0.0073 221.7 19.2 1.47 0.04 15.1 0.62 11.7 0.62 7.9 0.15 31.9

5 BELC-21 7.77 0.67 47.2 6.07 0.612 0.0050 * 500.0 0.0 0.46 0.04 7.9 0.68 9.0 0.00 6.2 0.33 32.1

6 BELN-21 6.58 0.60 39.8 6.05 0.613 0.0051 * 500.0 0.0 0.61 0.04 10.1 0.71 10.7 0.00 6.5 0.33 35.2

7 BEHC-21 9.99 1.16 59.6 5.97 0.605 0.0016 344.3 40.5 0.36 0.03 5.6 0.87 6.3 0.76 5.7 0.18 42.5

8 BEHN-21 8.89 0.70 53.3 6.00 0.612 0.0054 382.8 46.9 0.40 0.02 6.5 0.57 6.0 0.43 6.3 0.24 40.0

9 FNLC-21 4.46 0.28 49.4 11.08 0.984 0.0126 217.8 22.9 2.26 0.06 26.7 0.77 20.9 1.31 11.4 0.26 33.9

10 FNLN-21 3.40 0.17 40.3 11.85 1.038 0.0012 254.9 20.5 2.54 0.35 28.3 1.38 18.7 0.35 12.7 0.37 39.0

11 FNHC-21 5.30 0.38 62.3 11.75 1.037 0.0007 215.0 11.3 1.86 0.07 20.0 0.61 12.4 0.28 11.1 0.23 36.3

12 FNHN-21 4.96 0.34 57.9 11.67 1.027 0.0068 202.7 8.6 1.84 0.12 19.0 1.52 15.8 0.28 10.7 0.33 36.6

13 FELC-21 7.34 0.60 42.4 5.78 0.593 0.0063 252.7 32.5 1.03 0.06 13.4 0.61 12.4 0.57 6.1 0.27 35.0 H FELN-21 5.52 0.46 33.8 6.12 0.621 0.0041 288.0 22.7 1.40 0.05 18.0 0.62 14.1 0.48 6.9 0.17 37.2

15 FEHC-21 8.99 0.70 55.2 6.14 0.617 0.0073 222.3 18.6 0.75 0.04 8.9 0.65 7.8 0.95 6.0 0.25 43.6

16 FEHN-21 7.58 0.60 45.6 6.'02 0.612 0.0032 219.0 19.0 0.96 0.02 11.4 0.42 7.6 0.51 6.5 0.17 41.3

17 BNLC-25 5.84 0.34 72.5 12.41 1.140 0.0054 151.7 7.4 1.99 0.01 20.9 0.63 27.4 0.00 8.4 0.08 37.2

18 BNLN-25 4.78 0.J8 58.9 12.32 1.130 0.0059 155.7 5.0 2.19 0.15 25.3 0.37 26.6 0.00 8.8 0.08 34.5

19 BNHC-25 7.60 0.41 93.1 12.25 1.127 0.0045 136.3 5.4 1.65 0.04 15.9 0.66 18.9 0.91 7.9 0.15 34.9

20 BNHN-25 6.72 0.28 83.2 12.38 1.131 0.0055 135.6 6.3 1.83 0.09 17.4 0.38 15.1 1.17 8.1 0.24 35.6

21 BELC-25 8.11 0.45 61.2 7.55 0.774 0.0023 259.4 29.3 0.73 0.03 12.1 0.49 16.0 0.40 5.8 0.14 44.2

22 BELN-25 6.38 0.28 46.8 7.34 0.770 0.0041 254.9 27.2 1.D0 0.03 15.5 0.36 16.0 0.52 6.3 0.14 40.8

23 BEHC-25 10.63 0.78 78.2 7.36 0.759 0.0001 196.0 22.2 0.57 0.05 8.6 0.43 11.2 0.83 5.6 0.27 43.6

24 BEHN-25 9.12 0.45 67.6 7.41 0.769 0.0061 186.8 12.4 0.72 0.03 10.2 0.78 9.6 0.74 6.2 0.00 37.9

25 FNLC-25 4.05 0.15 61.7 15.23 1.341 0.0025 139.9 6.0 2.79 0.10 30.7 1.29 24.2 1.51 13.3 0.34 37.9

26 FNLN-25 3.46 0.14 51.1 14.77 1.317 0.0024 134.0 7.4 3.06 0.11 35.0 0.60 22.8 0.52 13.6 0.49 33.9

27 FNHC-25 5.08 0.18 75.5 14.86 1.314 0.0053 119.4 6.2 2.52 0.14 25.0 0.86 19.3 1.22 11.5 0.13 30.0

28 FNHN-25 4.58 0.17 69.1 15.09 1.335 0.0010 116.5 4.8 2.75 0.11 27.2 2.13 16.9 1.10 12.1 0.22 36.7

29 FELC-25 5.17 0.35 44.2 8.55 0.846 0.0053 178.9 39.5 1.62 0.01 18.9 0.81 16.8 0.81 7.8 0.08 44.2

30 FELN-25 3.88 0.41 33.6 8.66 0.862 0.0039 192.6 22.5 2.06 0.09 24.0 0.81 19.4 1.42 9.1 0.13 40.2

31 FEHC-25 6.43 0.85 61.9 9.63 0.936 0.0011 247.4 80.2 0.94 0.07 11.2 1.19 9.7 0.59 8.8 0.41 38.7

32 FEHN-25 5.27 0.34 45.1 8.56 0.857 0.0049 161.4 13.9 1.45 0.07 16.3 0.56 11.0 0.60 8.3 0.30 39.4 LBR - linear burr rate, nmi/tnin. PC - pu 11 count

HBR - mass burn rate, mg/min. TAR RE - tar resi due

C WT - cigarette weight, g nlc, tai•, and tar RE. in mg PD - pressure drop , mm H >° 1 - correspc nd to 101-132, res pectively

Nlc - nico :ine

201 which was thinner and lighter. The electrostatic perforation increased the CORESTA permeability value to about 58, the embossing to about 85, and the combination of electrostatic perforation and embossing to 140 to 160. Visual inspection of the embossed paper indicated that the embossing caused small holes in the paper, and was rather uneven. The standard deviation of the permeability resultsfor the embossed papers was much higher than that of the base and perforated-only papers, indicating poor control. The inner wrappers were very light and permeable.

There appeared to be no significant differences between

the values for tar, nicotine, and carbon monoxide deliveries and puff counts supplied by the Lorillard Laboratories and

the Federal Trade Commission.

23
Table 2-6. Smoke Yields of Experimental Cigarettes, Series 2. Data from Loriiiard

Laboratories

CODE

! WEIGHT2 WEIGHT

S.D.

PRESSURE

DROP mm-H20

PRESSURE

DROP

S.D. TAR

3 TAR

S.D. NICOTINE 3 NICOTINE

S.D. CO 3 CO

S.D. PUFF COUNT

PUFF COUNT

S.O.

1.2 0.613 0.0024 278 22.99 18.2 1.31 1.55 0.095 15.6 0.97 7.0 0.21

2.Z 0.891 0.0011 260 28.36 20.0 0.74 1.80 0.074 18.4 0.72 10.3 0.47

3.2 0.858 0.0040 205 15.44 18.4 0.84 1.66 0.054 15.3 0.54 10.5 0.29

4.2 0.853 0.0041 191 23.31 14.2 0.36 1.26 0.050 9.8 1.03 11.8 0.26

5.2 0.856 0.0077 155 10.80 13.9 1.02 1.35 0.087 10.2 0.94 11.0 0.34

6.2 0.886 0.0020 259 35.14 22.5 0.75 1.88 0.053 22.2 0.26 9.7 0.33

7.2 0.867 0.0035 212 17.87 18.6 0.35 1.66 0.037 17.9 0.54 10.1 0.1-1

8.2 0.859 0.0064 207 19.61 17.2 0.50 1.45 0.010 15.1 0.86 10.1 0.29

9.2 0.861 0.0060 176 12.05 15.3 0.92 1.36 0.112 12.1 0.70 11.1 0.35

S.D. STANDARD DEVIATION

123

CORRESPOND TO 201-209, RESPECTIVELY

EXPRESSED IN CRAMS EXPRESSED IN MILLIGRAMS

24
Table 2-7. FTC Values for Tar, Nicotine, and Carbon Monoxide Yields and Puff

Count of Series 1 Experimental Cigarettes

HHKSHBflH

Experimental

cigarette

"far Nicotine CC1 designation

101 (BNLC-21)

(mg)

19 ± 0.8

( mg) (mg)

21 ± 0.7

Puff Count

1.4 + 0.07 7.7 ± 0.20

102 (BNLN-21) 22 + 0.3 1.6 + 0.06 21 + 0.2 8.0 ± 0.12

103 (BNHC-21) 13 + 0.7 1.2 ± 0.05 14 ± 0.6 7.4 ± 0.24

104 (BNHN-21) 15 + 0.6 1.3 ± 0.02 13 + 0.5 7.4 ± 0.22

105 (BELC-21) 9 ± 0.6 0.5 ± 0.06 11 ± 0.5 5.8 ± 0.12

106 (BELN-21) 11 ± 0.7 0.6 ± 0.01 12 ± 0.3 6.0 ± 0.40

107 (BEHC-21) 6 + 0.7 0.4 + 0.03 6 + 0.7 5.8 ± 0.28

108 (BEHN-21) 7 ± 0.5 0.5 + 0.04 5 + 0.4 5.6 ± 0.16

109 (FNLC-21) 28 + 1.1 2.3 ± 0.05 22 + 1.9 11.2 ± 0.26

110 (FNLN-21) 28 ± 0.9 2.4 ± 0.12 20 + 1.0 12.8 ± 0.44

111 (FNHC-21) 20 + 0.9 1.9 ± 0.12 15 ± 1.9 10.4 ± 0.14

112 (FNHN-21) 21 + 1.4 1.9 ± 0.13 14 ± 0.5 11.4 ± 0.32

113 (FELC-21) 14 ± 0.6 1.1 + 0.06 13 + 1.0 5.8 ± 0.32

114 (FELN-21) 17 ± 0.5 1.4 + 0.02 14 + 0.9 6.6 ± 0.10

115 (FEHC-21) 10 ± 0.4 0.8 + 0.05 9 ± 0.1 5.8 ± 0.10

116 (FEHN-21) 12 ± 0.7 1.0 ± 0.04 8 + 0.6 6.4 ± 0.20

117 (BNLC-25) 22 + 0.8 1.7 ± 0.04 27 ± 0.9 8.4 ± 0.22

118 (BNLN-25) 25 ± 0.7 1.9 + 0.03 25 + 0.6 8.8 ± 0.16

119 (BNHC-25) 16 ± 0.3 1.4 ± 0.04 18 ± 1.3 7.7 ± 0.16

120 (BNHN-25) 18 + 1.0 1.6 ± 0.03 15 ± 1.5 8.4 ± 0.20

121 (BELC-25) 12 ± 0.4 0.7 ± 0.01 15 ± 1.0 5.6 ± 0.16

122 (BELN-25) 15 ± 0.8 0.9 ± 0.02 15 ± 1.5 6.2 ± 0.22

123 (BEHC-25) 8 + 0.9 0.5 ± 0.03 10 ± 0.9 5.4 ± 0.22

124 (BEHN-25) 9 + 0.7 0.6 ± 0.03 8 ± 0.9 5.8 ± 0.20

125 (FNLC-25) 32 + 1.0 2.7 ± 0.07 25 + 1.3 13.0 ±0.18

126 (FNLN-25) 34 ± 1.2 2.8 ± 0.11 24 ± 1.0 13.8 ± 0.26

127 (FNHC-25) 25 ± 0.9 2.3 ± 0.10 20 ± 0.6 11.2 + 0.30

128 (FNHN-25) 27 ± 0.9 2.4 ± 0.06 17 ± 1.2 11.2 ± 0.28

129 (FELC-25) 19 ± 0.4 1.5 ± 0.04 17 + 0.4 8.4 ± 0.28

130 (FELN-25) 22 ± 0.6 1.8 ± 0.09 19 ± 0.4 8.8 ± 0.36

131 (FEHC-25) 10 ± 1.1 0.8 ± 0.06 9 + 0.6 10.4 ± 0.52

132 (FEHN-25) 16 ± 0.7 1.4 ± 0.06 11 ± 0.9 8.4 ± 0.20

25
Table 2-8. FTC Values for Tar, Nicotine, and Carbon Monoxide Yields and Puff

Count of Series 2 Experimental Cigarettes

Experimental

cigarette Tar Nicotine CO

designation

201

(mg) (mg) (mg)

19 ± 1.3

Puff Count

19 ± 0.6 1.4 ± 0.10 7.6 202 20 ± 0.07 1.6 ± 0.07 24 ± 1.5 10.0

203 18 ± 0.7 1.5 ± 0.09 19 + 0.7 10.4

204 15 ± 1.1 1.2 ± 0.10 14 ± 1.5 11.4 205 13 ± 0.9 1.2 ± 0.08 14 ± 1.5 11.2

206 22 ± 0.2 1.6 ± 0.09 29 ± 1.1 9.0

207 19 ± 0.5 1.5 ± 0.11 23 ± 1.0 10.2 208 17 ± 0.6 1.4 ± 0.07 18 + 1.1 10.6

209 15 ± 0.7 1.3 ± 0.07 16 ± 0.7 11.0

26
Table 2-9. Upholstered Fabrics., Padding and Sheeting Used in the Investigation

Material Designation Number and Description Abbrev.

Bolt Width

(m)

Yarn Density Thread Count

#/2.54 cm Yarn Ply Fiber Content Areal Density warp weft

(g/m2

) a Tex

b N

p

c

Tex

b N

p

c warp weft warp weft warp weft pile

A. Materials Used in Bench-Scale Tests Only

1. California Standard CA

beige cotton velvet, 2x2

basket weave, warp pile

1.4 340 31 19 38 15 80 80 2 2 cot cot cot

e

2. Denim

blue warp, gray weft,

reverse twill weave, sized

DEN 1.5 480 101 6 98 6 66 40 1 1 cot cot

3. "Splendor"

beige, plain weave, back- coated

SPL 1.4 560 145 4 696 0.8 10 11 2 1 cot cot

4. "Haitian Cotton"

natural cotton plain weave,

variable thickness of weft

yarns, backcoated

HA 1.4 660 183 3 1159 0.5 14 10 2 1 cot cot

5. Duck

natural, plain weave

DU 1.3 360 118 5 96 6 50 35 2 2 cot cot

6. Sheeting - 2.4 130 18 34 18 34 104 88 1 1 cot cot

B. Materials Used in Full-Scale and Comparative Bench-Scale Tests

7 California Standard (see above specifications)

8. Velvet

plain weave, cotton warp

pile, backcoated

VEL 1.4 525 68 9 68 9 44 36 >60 >60 polye

1 polye cot9

9. "Splendor" (see above specifications)

10. Damask 1

pink, plain weave with float yarns to create small

patterns, backcoated

DA1 1.4 200 36 16 125 5 136 51 2 2 cot cot

11. Damask

red, plain weave with float yarns to create geometric

pattern, backcoated

DA2 1.4 250 42 14 75 8 144 88 2 2 cot cot

12. Olefin

black, plain weave, back- coated

OL 1.4 180 272 2 272 2 20 20 >30 >30 ole

h ole

C. Paddings Used in Bench-Scale Tests Only

Cotton batting No. 300 quality untreated

CB - 40"

Polyurethane foam HD2045

PU - 32"

D. Padding Used in Full-Scale and Comparative Bench-Scale Tests

Cotton batting same as above

CB - 40"

Polyurethane foam same as above

PU - 32"

Welt cord - - 5700

27
Table 2-9. (Continued)

Material Number

1.

Supplier

Van Waters & Rogers

Address

16300 Shoemaker Avenue, Cerntos, CA 90701

2. local supplier

3. Douglas, Inc. P.O. 701, Egg Harbor, NJ 08215

4. local supplier

5. Test Fabrics, Inc. RO. Drawer O, 200 Blackford Avenue, Middlesex, NJ 08846

6. local supplier

7 same as # 1

8. supplied by UFAC

9. same as # 3

10. supplied by UFAC

11. supplied by UFAC

12. supplied by UFAC

CB B.C.F. Supply Company 2335 W. Franklin Street, Baltimore, MD 21223

PU Leggett & Piatt RO. Box 2024, High Point, NC 27261

welt cord supplied by UFAC

(a) to convert SI to pounds per square yard, multiply by 0.00184

(b) Tex = grams per 1000 meters

(c) Ne = hanks per one pound, where one hank equals 840 yards

(d) cot = cotton

(e) pile weight to material weight ratio is 0.38

(f) polye = polyester

(g) pile weight to material weight ratio is 0.57

(h) ole = olefin

(i) bulk density, kilograms per cubic meter

(j) to convert SI to pounds per cubic foot, multiply by 0.063

Table 2-10. Cation Content of Upholstery Fabrics and Cotton Batting

Material

Elemental Analysis (PPM)a Na+ K

+ Ca+2 Mg +2

California Standard 662 ± 25 <100 285 ±13 94 ±5

Denim 1033 ±92 402 ± 42 61 7 ±84 422 ±41

"Splendor" 589 ± 1 00 4890 ±351 755 ±5 549 ± 1

"Haitian Cotton" 814±32 61 36 ±520 28969 ±1620 2876 ±181

Duck 135 ±25 < 100 494 ± 52 146 ±22

Cotton Batting 226 ±21 5069 ± 260 919±45 51 2 ±55

(a) Values are the average of the replicate values reported in Appendix 2-G, i.e., the six values for the cotton batting and the three values for the remaining fabrics. The standard deviations were calculated from the replicates, since these values are a measure of the differences in the fabric

bolt or cotton batting bundle. The standard deviations reported in Appendix 2-G are a measure of the technique's variability.

28
Substrates

The upholstery fabrics and paddings were chosen by the Upholstered Furniture Action Council (UFAC) and NBS to represent a range of substrates which ignite with commercial

cigarettes. They could thus be used to illustrate possible

lower ignition propensities of the experimental and patented

cigarettes.

Fabrics

The upholstery fabrics and sheeting used in this study are described in Table 2-9. Fabrics of the same name in parts

(A) and (B) of Table 2-9 are nominally the same, but come

from different batches and thus may differ somewhat. The

first three upholstery fabrics were used to test all of the

cigarettes.

Upholstery fabric 4 was used to evaluate low ignition

propensity cigarettes. Upholstery fabrics 1, 3 and 7 to 11 were used in the comparison of cigarette ignition propensities from bench-scale and full-size (chair) tests. Fabric 6 was

used as a covering for cigarettes tested in the covered

configuration. This is prescribed in many standard methods

[e.g., 2-6, 7] and makes the test somewhat more severe and

reproducible [2-8]. It also simulates a situation in which

cigarettes are covered by loose clothing, sheets, etc. Fabric 5 was used for experiments in which alkali metal ions or soil were added.

Upholstery fabrics 1-3, which were used in the benchscale study of all cigarettes and also for the work reported in Section 4, and fabrics 4 and 5 were analyzed for Na +

, K

+

, Mg + 2

, and Ca + 2 content by the Health Sciences Laboratory, U.S. Consumer Product Safety Commission. A summary

of the data is shown in Table 2-10. The analytical procedure

and raw data are included in Appendix 2-G.

Padding

Two padding materials together with the above fabrics, were used in all evaluations. The paddings were non-fire retardant-treated (a) cotton batting and (b) HD 2045, Leggett

and Piatt polyurethane foam5

, both purchased at BCF

Supply Co., 2335 W. Franklin St., Baltimore, MD. The cotton

batting was analyzed in the same manner as the fabrics for Na +

, K

+

, Mg + 2

, and Ca + 2 content. The results are shown

in Table 2-10. Previous results on the ion content of the polyurethane foam [2-1] showed such a small ion content that the analysis was not repeated for this study. Additional infor- mation on the padding is also presented in Table 2.9.

Mockup Configurations

The mockup configurations used in this investigation were

flat, crevice, or crevice with welt cord. In some cases the

smoldering cigarette was covered with a piece of 100%

cotton sheeting (fabric 6). The configurations are shown in Figure 2-1.

^Certain commercial equipment, instruments, and materials are identi- fied in this report to adequately specify the experimental procedure.

Such identification does not imply recommendation or endorsement by

the National Bureau of Standards, nor does it imply that the materials

or equipment are necessarily the best available for the purpose.

29
Figure 2-1. Mockup Configurations

Location of covering sheet

for covered

tests

Padding

Upholstery fabric

(a) Flat All dimensions

In millimeters

Location of covering

sheet for covered tests

pholstery fabric

152

Padding 2ig ^Plywood support

(b) Crevice (same size substrates as flat)

Straight pin

Welf cord

Upholstery fabric

All dimensions In millimeters

(c) Crevice w/ welt cord (same size substrates as flat)

30
'hairs

The chairs used in the full-scale investigation of the ignition

propensity of the experimental cigarettes were made under

the supervision of UFAC by a commercial manufacturer. The

width, depth, and height of the chairs were 750, 838 and

813 mm (29.5, 33 and 32 in.), respectively. They were

constructed from the same wooden framing, webbing, and

decking materials. The skirt was omitted. The sides were

straight and the back was slightly inclined. Each chair was

provided with two seat cushions. The chairs were

constructed with the upholstery fabrics and paddings

mentioned in Table 2-9 B and D. The 10 California Standard

chairs were padded entirely with cotton batting; the 10

"Splendor" chairs were padded entirely with polyurethane

padding. The eight each of the damask, heavy velvet, and

olefin chairs contained polyurethane padding in the seat cushions and back and cotton batting in the arms. Four of each chair were provided without a welt cord and four were

provided with a welt cord, with the exception of those

prepared with California Standard fabric and "Splendor"; in these cases two additional chairs without welt cord were

supplied for preparatory experiments. The damask chairs were supplied with two different fabrics varying slightly in weight.

Figure 2-2 shows four of the chairs arranged in the burn room prior to testing.

Figure 2-2. Typical Chairs Used in the

Full-Scale Tests Arranged in the Burn

Room

31
references for Section 2

[2-1]

[2-2]

[2-3]

[2-4]

Krasny, J. F. and Gann, R. G., "Relative Propensity of Selected Commercial Cigarettes to Ignite Soft Furnishings Mockups," NBSIR 86-3421, U.S. National

Bureau of Standards, Gaithersburg, MD, 1986.

Pillsbury, H. C, Bright, C C, O'Connor, K. J., and

Irish, F W., "Tar and Nicotine in Cigarette Smoke,"

Journal of the AOAC, 52, 3 (1969). Federal Register, 45, no. 134, July 10, 1980. Harvey, W. R., Stahr, H. M., Smith, W. C, "Automated

Determination of Reducing Sugars and Nicotine

Alkaloids on the Same Extract of Tobacco Leaf," Tobacco Science, 13, 13 (1969).

[2-5]

[2-6]

[2-7]

[2-8]

Samfield, M., Personal Communication, April, 1986. Important Information from UFAC (Test Methods),

Upholstered Furniture Action Council, High Point, NC

(1985). The Business and Institutional Furniture Manufacturer's

Association First Generation Voluntary Upholstered

Furniture Standard for Business and Institutional Markets, BIFMA, Grand Rapids, Ml (1980).

Loftus, J.L., Back-Up Report for the Proposed Stan- dard for the Flammability (Cigarette Ignition Resis- tance) of Upholstered Furniture, PFF 6-76, Appendix

G1, NBSIR 78-1438, [U.S.] Nat. Bur. Stand., (1978).

32
Appendix 2-A

November 6, 1985

DR. GIL ESTERLE

DR. ALLEN KASSMAN

DR. PRESTON LEAKE

MR. BILL OWEN

DR. ALAN RODGHAN

DR. FRED SCHULTZ

Gentlemen

I believe that we have everything in place for the manufacture of the National Bureau of Standards samples.

However, there have been a few small changes in specifications

since my prior memos, and I think it worthwhile to repeat everything in this memo so that all the information is set forth in one place.

I am also including in this memo sample designations that

I ask the manufacturers and the suppliers to follow. In addition, each of the materials that you ship should contain

the 'following label on the shipping container: Technical

Study Group Materials - Cigarette Safety Act. In this way, materials will not be confused with any other sample materials that may be arriving at the same receiving point.

Reynolds has agreed to manufacture the filter rods for all 21 mm circumference cigarettes and will supply Philip

Morris with about 40,000 108 mm rods. American has agreed

to manufacture the filter rods for the 25 mm circumference

cigarettes and will supply Brown & Williamson with about

40,000 108 mm filter rods. Individual tows, plug wraps,

and plasticizer levels are to be selected by the manufacturer.

Ecusta will supply the cigarette papers in partial

bobbin lengths of 4,000 m. One bobbin each of the following cigarette paper designations, as shown on the attached table, will be shipped to both American and Brown & Williamson:

LN27, LC27, HN27, and HC27. One bobbin each of the following

cigarette paper designations, LN23, LC23, HN23, and HC23, will be shipped to both Philip Morris and Reynolds.

Lorillard has made some filling value measurements on the tobacco and will calculate a cigarette tobacco weight.

Bear in mind that there are some errors in making this estimate, and this will not necessarily be the exact weight

that you will need to manufacture acceptable cigarettes in the commercial firmness range. It should, however, be a good starting point. we now have individual names and shipping addresses for the materials. They are as follows:

Mr. Leonard Ti lley Manager, Reidsville Branch American Tobacco Company

301 North Scales Street

Reidsville, NC 27320

Mr. B. A. Bandy/Esterle

Brown & Williamson Tobacco Corporation

Development Center

Gate 21, Dock 10F McCloskey South of Lee Louisville, KY 4 0210 Cigarette paper and tipping paper only should be sent to:

Mr. James Crichton/Kassman

Philip Morris Operations Center

Building Al-E

2001 Walmsley Blvd. Richmond, VA 23234 Lorillard will supply the tobacco and will ship 600 pounds each of tobacco designations BN and BE, per the attached table, to both American and Philip Morris.

Six hundred (600) pounds each of tobacco designations

FN and FE will be shipped to both Brown & Williamson and Reynolds. Lorillard will supply the tipping paper with no bobbin designation as shown in the attached table. Each manufacturer will receive one bobbin of 64 mm x 2700 m.

The shipping point for tobacco and filter rods to Philip Morris will be designated a little later.

Mr. Ronald Pegram

R. J. Reynolds Tobacco Company

Bowman Gray Technical Center Building 61112 Reynolds Boulevard

Winston-Salem, NC 27102

For those manufacturers that choose to package

cigarettes in individual packs of 20, the numerical

pack designation shown in the attached table should be used to identify the sample. Cases, trays, or similar packaging materials should show the box designation shown

in the attached tables for purposes of sample identification. Cigarette tobacco is being shipping at a moisture content

that is suitable for the direct manufacture of cigarettes.

Z5Z5 East m^h Siimi

The National Bureau of Standards also desires 1-2 pound samples of each of the cut tobaccos. These will

be shipped by Lorillard directly to NBS.

All tobacco samples will be shipped this week. I also understand that all paper samples will be shipped this week.

It, therefore, seems that all materials should be received

no later than the first part of next week. Sincerely

Xc: Dr. Richard Gann Attachments

AWS/hs

j

33
CUT TOBACCO DESIGNATIONS

Burley Non-Expanded, 60 cuts/inch

Burley Expanded, 30 cuts/inch

Flue-cured Non-Expanded, 60 cuts/inch

Flue-cured Expanded, 30 cuts/inch

Box Designation

BNBEFN

FE

CIGARETTE PAPER DESIGNATIONS

23 mm Bobbin Designation

Low Porosity, No Additive (10 CORESTA Units) LN-23

Low Porosity, Citrate (10 CORESTA Units, LC-23

0.8% Citrate)

High Porosity, No Additive (75 CORESTA Units) HN-23

High Porosity, Citrate (75 CORESTA Units, HC-23

0.8% Citrate)

27 mm

Low Porosity, No Additive (10 CORESTA Units) LN-27

Low Porosity, Citrate (10 CORESTA Units, LC-27

0.8% Citrate)

High Porosity, No Additive (75 CORESTA Units) HN-27

High Porosity, Citrate (75 CORESTA Units, HC-27

0.8% Citrate)

TIPPING PAPER DESIGNATION

64 mm, White, 36.5 gm/m

Bobbin Designation

None

FILTER ROD DESIGNATION

20.8 mm x 108 mm, PD 270 mm

24.7 mm x 108 mm, PD 270 mm

Box Designation

FR-21

FR-2 5

34
Table 2-A-l. Cigarette Manufacturer's Description of Series 1, 21 mm Experimental Cigarettes

CIGARETTE DESIGNATIONS

21 mm Circumference

Box Designation Pack Designation

Burley-Non-Expanded-Low Porosity Citrate

Burley-Non-Expanded-Low Porosity-No Additive

Burley-Non-Expanded-High Porosity-Citrate

Burley-Non-Expanded-High Porosity-No Additive

Bur ley-Expanded- Low Porosity-Citrate

Burley-Expanded-Low Porosity-No Additive

Burley-Expanded-High Porosity-Citrate

Burley-Expanded-High Porosity-No Additive

Flue-Cured-Non- Expanded- Low Porosity-Citrate

Flue-Cured-Non-Expanded-Low Porosity-No Additive

Flue- Cur ed-Non- Expanded-High Porosity-Citrate

Flue-Cured-Non-Expanded-High Porosity-No Additive

Flue- Cured- Expanded- Low Porosity-Citrate

Flue-Cured-Expanded-Low Porosity-No Additive

Flue -Cured- Expanded- High Porosity-Citrate

Flue-Cured-Expanded-High Porosity-No Additive

BNLC-21 1 BNLN-21 2 BNHC-21 3 BNHN-21 4 BELC-21 5 BELN-21 6 BEHC-21 7 BEHN-21 8 FNLC-21 9 FNLN-21 10 FNHC-21 11 FNHN-21 12 FELC-21 13 FELN-21 14 FEHC-21 15

FEHN-21 16

Table 2-A-2;. Cigarette Manufacturer's Description of Series 1, 25 mm Experimental Cigarettes

CIGARETTE DESIGNATIONS

25 mm Circumference

Burley-Non-Expanded-Low Porosity-Citrate

Burley-Non-Expanded-Low Porosity-No Additive

Burley-Non-Expanded-High Porosity- Citrate

Burley-Non-Expanded-High Porosity-No Additive

Burley-Expanded-Low Porosity-Citrate

BurLey-Expanded-Low Porosity-No Additive

Burley-Expanded-High Porosity-Citrate

Burley-Expanded-High Porosity-No Additive

Flue-Cured-Non-Expanded-Low Porosity-Citrate

Flue-Cured-Non-Expanded-Low Porosity-No Additive

Flue-Cured-Non-Expanded-High Porosity-Citrate

Flue-Cured-Non Expanded-High Porosity-No Additive

Flue-Cured-Expanded-Low Porosity-Citrate

Flue-Cured-Expanded-Low Porosity-No Additive

Flue-Cured-Expanded-High Porosity-Citrate

Flue-Cured-Expanded-High Porosity-No Additive

Box Designation Pack Designation

BNLC-2 5 17 BNLN-25 18 BNHC-2 5 19 BNHN-25 20

BELC-25 21 BELN-25 22 BEHC-2 5

4 23 BEHN-25 24 FNLC-2 5 25

F*NLN-25 26 FNHC-25 27 FNHN-25 28 FELC-25 29 FELN-25 30

FEHC-25 31

FEHN-2 5 32

35
Burley Blend

Flyings 19.7%

Lugs 17.3%

Leaf 47.5%

Tips 7.4%

Invert Sugar 5.3%

Glycerine 2.8%

Total 100.0%

Flue-Cured Blend

Primings 13 8% Lugs & Cutters 24 3%

Smoking 10 6%

Leaf 43 2%

Invert Sugar 5 3%

Glycerine 2 8%

Total 100.0%

All cigarettes will be manufactured to the following

specifications

:

Quantity:

Length

Type:

Filter Length:

Tipping Paper Length:

Circumference

:

Cut Width:

Firmness:

Moisture:

Weight:

Filter Tip Pressure

Drop (Encapsulated)

:

Filter Tow

Characteristics:

Plasticizer Level

Plasticizer

:

Packaging

:

10,000

100 mm

Filter

27 mm

32 mm

+ 0.1 mm of specification

As specified

Within commercial limits of

acceptance

Commercial standards

+ 1.5% of mean

67.5 mm

A commercial standard

Commercial range

Commercial product

Suitable to avoid moisture loss and

damage in shipment.

Shipping: Mr. John Krasny

National Bureau of Standards

Building 224, Room A363

Quince Orchard Road

Gaithersburg, Maryland 20899

36
PROBLEMS WITH MATERIALS

Cigarette Papers: Bill Owen (704-877-2311) or (Ecusta) Wayne McCarty (704-877-2211)

Tipping Paper: Fred Schultz (919-373-6602)

(Lorillard)

Tobacco: Fred Schultz (919-373-6602)

(Lorillard)

Filter Rods: Preston Leake (804-748-4561)

of American Tobacco

orAlan Rodgman (919-773-4269)

of Reynolds

Miscellaneous: Alex Spears (919-373-6776)

(Lorillard)

37

Appendix 2-B

D* * w srtARt October 23, 1986

Dr. Jim Charles

Dr. Preston Leake

Dr. Alan Rodgman

Dr. Fred Schultz

Gentlemen:

I believe th»t I now have everything in place for the manufacture of the second series of cigarettes for the National Bureau of Standards in relation to the Technical

Study Group activities.

Reynolds has agreed to manufacture one cigarette of 21 mm circumference, designated as Sample 1.2 in the accompanying material, which is a replicate of Cigarette #16

as described in my memo of November 4, 1965 except for the cigarette paper. Lorillard will manufacture eight

cigarettes, and I have procured two from the National Cancer

Institute. The samples will be supplied in quantities of 2,000 each and Ehipped no later than November 14 to the attention of:

Mr. John Krasny

National Bureau of Standards

Building 224, Room A363

Quince Orchard Road Gaithersburg, MD 20899

Mr. Ronald Pegram will be responsible for the manufacture of the Reynolds sample, and Dr. Fred Schultz

will be responsible for the manufacture of the Lorillard

samples. Lorillard will Ehip 300 lbs. of cut tobacco to RJR

for manufacture of Sample 1.2. The procured samples were obtained from the National

Cancer Institute archives and were prepared under tbe NCI Smoking and Bealth Program, the Second Set of Experimental

Cigarettes. Code 146 was made from a synthetic 6moking

material filler known as NSK consisting of heat treated cellulose and sodium carboxymethyl cellulose. Code #43 was

made from a synthetic filler from Celanese Corporation

consisting of inorganic materials and sodium carboxymethyl

cellulose. Both filler materials contain an added 2.8% glycerine and 5.3* invert sugar. Cigarette specifications

were 85 mm length, 25 mm circumference, 26 CORTSTA Dnits

paper porosity, and an 0.85 citrate level in the cigarette

paper

.

?Wi East u»<if. Sv«-

G'etnsrxxc N=rth Cxowna 27401

39
Sample S pecifications

Expanded Flue-Cured Blend (FE)

Primings 13.8%

Lugs t Cutters 24.3%

Smoking 10.6%

Leaf 43.2%

Invert Sugar 5.3%

Glycerine 2.8%

Total 100.0%

Quantity

Length

Type

Filter Length

Tipping Paper

Circumference

Cut Width

Firmness

Moisture

Weight

Filter Tip Pressure

Drop/Encapsulated

Filter Rod

Filter Tow

Characteristics

Plast icizer

Cigarette Paper

Packaging

Markings

2,000 cigarettes

100 mm

Filter

27 mm - 64 mm, white, 36.5 gm/m

+ 0.1 mm of specification

30 cuts/inch

Within commercial limits

Commercial standard

+ 1.5% of mean

67.5 mm

As specified - 24.7 mm x 108 mm, PD 27 mm

or20.8 mm x 108 mm, PD 270 mm

Commercial Standard

Commercial product/commercial range

No burn additives

Porosity: as specified

Dimensions: as specified

Suitable to avoid moisture loss and

damage during shipment.

Each packaging unit to be clearly

marked with sample number

Xc: Dr. Pichard Gann

Mr. Ron Pegram

AWS/hsj

Sincerely,

A. W. Spears

40
3-1. Cigarette Manufacturer's Description of Series 2 Experimental Cigarettes

Blend Circumference Paper (Outer) Paper.. (I nner) Construction

1.2 FE 21 4-6 CORESTA Units/

2 3.5 mm

None Single Wrap

2.2 FE 25 4-6 CORESTA Units/

27.5 mm None Single Wrap

3.2 FE 25 4-6 CORESTA Unit Base None Single Wrap

4.2

5.2

6.2

7.2

8.2

9.2

FE

FE

FE

FE

FE

FE

25

25

25

25

25

25

Electrostatically

Perforated to 60

CORESTA Units/27. 5 mm

4-6 CORESTA Units

Embossed/27 .5 mm

4-6 CORESTA Units

Electrostatically

Perforated to 60

CORESTA Units/Embossed/

27.5 mm

4-6 CORESTA Units/

27.5 mm

4-6 CORESTA Unit Base

Electrostatically

Performated to 60

CORESTA Units/27.5 mm

4-6 CORESTA Units

Embossed/27.5 mm

4-6 CORESTA Units

Electrostatically

Perforated to 60

CORESTA Units/Embossed/

27.5 mm

None

None

7000 CORESTA

Microporous

Structure/

25 mm

7000 CORESTA

Microporous

Structure/

25 mm

7000 CORESTA

Microporous

Structure/

25 mm

7000 CORESTA

Microporous

Structure/

25 mm

Single Wrap

Single Wrap

Double Wrap

Double Wrap

Double Wrap

Double Wrap

41

Appendix 2-C

21790 Federal Register / Vol. 51. No. 115 / Monday. June 1ft. 1986 / Notices

CONSUMER PRODUCT SAFETY COMMISSION

lnter»gency Committee on Cigarette and Uttle CJo*r Fare Safety, Request

for Samples of Patented, Non- commercial Cigarettes for Ignrtton Propensity Testing agency: Interagency Committee on

Cigarette and Utile Cigar Fire Safety. action: Notice. summary: The Technical Study Croup

on Cigarette and Little Cigar Fire Safely

invites inventors of cigar? (lev which are not produced commercially but which

are claimed to have reduced propensity

to ignite upholstered furniture and

mattresses, to submit samples of such

cigarettes for Ignition propensity testing. A description of the tasting program and how inventors may participate follows. date Inventors who desire to

participate in this testing program

should submit samples of cigarette Inventions and the information specified

in this notice not later than September 30.198a ADDRESS: Samples and Information concerning cigarette inventions should be sent to: Dr. Richard C. Genu. Center,

for Fire Research. National Bureau of Standards, Geilhersburg. Maryland

20899. FOR FURTHER INFORMATION CONTACT.

Mrs. Tawanna Segears. Office of Program Management Consumer

Product Safety Commission,

Washington. DC 20207; telephone (301) 492-65M. SUPPLEMENTARY INFORMATION: The

Cigarette Safety Act of 1984 (Pub. L. 95-

567. 98 Stat. 2925, October 30. 1984) created the Technical Study Group on

Cigarette end Little Cigar Fire Safety (TSG) to investigate the technical and

commercial feasibility of developing

cigarettes and little cigars with minimum

propensity to ignite upholstered

furniture and mattresses. The TSG has developed an ignition propensity test and has tested some commercial

cigarettes. The TSG also has decided to

test the ignition propensity of some

cigarettes which ere not commercially

available but which are claimed by their inventors to have less propensity than commercially available cigarettes to

ignite upholstered furniture and

mattresses. A limited cigarette ignition propensity testing program will be conducted by the Center for Fire Research at the National Bureau of Standards (NBSJ at no charge by NBS to inventors whose inventions ere selected

for testing Testing will be blind to the extent possble. Cigarette inventions which are patented or for which a patent has been filed will be candidates

for testing Cigarette inventions for which a potent hos not been issued or

for which o patent application has not been filed os of the date of this Federal

Register Notice, will not be tested.

If an inventor desires to have his or ber cigarette invention considered for testing on this program, the inventor must:

1. Select the single embodiment of his or her patent(s) believed to be most

effective lor consideration

2 Submit documents which show that a patent has been issued or that the

application for a patent has been filed.

3. Supply information as to the

specific nature of the particular modification or additive employed In the

cigarette invention in quantitative

terms.

4. Provide evidence of significantly reduced propensity of the cigarette invention to ignite substrates found in mattresses and upholstered furniture.

5. Provide free of charge 300 Invention

cigarettes and 300 control cigarettes that are identical to the invention cigarettes except for the feature that comprises the

effective ignition repression. The

patented cigarettes and the control

cigarettes should be clearly

differentiated on their packages. The

cigarettes should be packed so as to safeguard against damage during

transport and should identify a person

to contact if the shipment has been

damaged.

6. Supply uniformity data (mean value

plus standard deviation) for both the patented and control cigarettes with

regard to the following properties:

cigarette mass

cigarette length and diameter mass burning rate (in air) magnitude of modification (e.g., concentration of additive)

Additionally, the TSG requests

inventors submitting cigarettes for testing to provide information showing

the absence of any obvious toxicity problems associated with the invention. and an analysis of the tar. nicotine, and

carbon monoxide content of the smoke

produced by the cigarette mvention. However, the failure to provide this information will not preclude

consideration of the cigarette invention

for testing. Samples of the cigarette invention,

control cigarettes, and the information

described above must be received by Dr. Richard C. Gann, Center for Fire Research, National Bureau of Standards.

Caithersburg. Maryland 20899. not later than September 30. 1986. Materials received ofter September 30. 1936. will not be accepted. Inventors who submit their cigarettes

for consideration as candidates for

testing are advised that there will be

absolutely no payment or reimbursement for the samples of

cigarettes provided for testing. These

samples will not be returned. Further, submission of lest sample cigarettes which meet the criteria above does not

necessarily mean that the sample

cigarettes will be selected for testing. Selection of cigarette inventions for

43
Federal Register / Vol. 51, No 115 / Monday. June 16, 1986 / Notices 21791

testing will be made by the TSG. whose

decision will be final. While the TSG

desires lo test all cigarette inventions meeting the criteria set forth above, lack

of funds, time constraints and other

factors may limit the amount of testing which can be done. The results of this testing program will be included in the TSG's final report to Congress. The TSG will not report

results of testing individual cigarette inventions to patent holders. The TSG

intends to report results of this testing program in a format which will not

disclose results obtained from any

individual cigarette invention. Selection

of any cigarette invention for testing in

this program does not constitute any

form of endorsement or approval of the invention by the government of the United States. Dated: June 3. 1986. Cotin B. Church,

Federal Employee Designated by the Interagency Committee on Cigarette and

Little Cigor Fire Safety. [FR Dot 86-13483 Filed 6-1S-86; 8:45 am] MLLMO COCt UM-Ot-H

Federal Register / Vol. 51, No. 148 / Friday. August 1, 1986/ Notices 27577

CONSUMER PRODUCT SAFETY COMMISSION

Interagency Committee on Cigarette and Uttle Cigar Fire Safety; IgnrUon

Propensity Testing of Patented, Noncommercial Cigarettes AGENCY: Interagency Committee on

Cigarette and Little Cigar Fire Safety, CPSC.

ACTION: Notice.

summary-. In the Federal Register of June 16, 1988 (51 FR 21790), the Technical Study Group on Cigarette and

Little Cigar Fire Safety (TSG) invited inventor* of cigarette* which are not

produced commercially butwhich are

claimed to ha-v* reduced propensity to ignite upholstered fumlrare and

mattresses to submit samples of such

cigarettes for Ignition propensity testing. That notice described the tea' ting program'and requirements for consideration of cigarette inventions as

candidates' lor Resting in this program. That notice specified that only cigarette

inventions for which a patent had been

issued or for which a patent application had been filed by June 16, 1986, would

be eligible for consideration as

candidates for testing in this program. The TSG has revised its criteria for selection of candidate inventions to include any cigarette invention for which a patent has been issued or for which a patent application has been

filed by September 30. 198a

FOB FURTHER INFORMATION CONTACT:

Colin B. Church, Office of Program Management Consumer Product Safety Commission. Washington, D.C. 20207;

telephone: (301) 492-6554.

Daled: July IB.1966. CotiD B. Church.

Federal Employee Designated by the Interagency Committee on Cigarette and

Little Cigar Fire Safety. [FR Doc 86-17348 Filed 7-31 -aa 8:45 am)

SIUJNO CODE 09S-«1-a

44
Appendix 2-D

Kimberfy-CJark Specialty Products

2 September 1986

Dr. Richard G. Gann Chairman, Technical Study Group National Bureau of Standards Gaithersburg. Maryland 20899

Dear Dick:

We received from you the samples of the thirty-two experimental cigarettes

for which we were contracted to determine the permeability of the paper. The work waa performed under your Department of Commerce Reference Number: 41 USC 252 C03 and your Order Number: A3NANB61726A. The analyses

have been completed and the data are summarized on the attached sheet.

m A word of explanation about the data. We removed the paper from five cigarettes chosen at random from each of the thirty-two packets. The permeability of each swatch was determined using CORESTA Recommended Method No. 3 [Determination of the air permeability of cigarette paper , CORESTA Information Bulletin. 1975 (3, A)] and reported aa the velocity of air (in centimeters per minute) drawn through the paper at a pressure differential of one centibar (ten centimeters of water). In most cases,

we made ten measurements, two on each swatch. For some of them we added an extra determination or so to beef up the statistics. In the table are listed the identification number of each item, the permeability of the wrapper, the standard deviation, and the number of measurements made.

You will receive our invoice mailed under separate cover.

Beet regards

Sincerely,

Charles F. Mattina

Mr. John Kraany

National Bureau of Standards Room A363, Building 22A

Route 270 and Quince Orchard Road Gaithersburg, Maryland 20899

CFM: 86-200

45
Table 2-D-l. Paper Permeability of Series 1 Experimental

Cigarettes Determined by Kimberly-Clark

1 1 em No . Permeability (cm/min)

1 8.9

2 7.8

3 75.

4 66.

5 9.4

6 8.2

7 70.

8 69.

9 8.9

10 8.5

11 67. 12 67.

13 9.2

14 8.6

15 68.

16 68.

17 9.4

18 8.6

19 69. 20 76.

21 9.2

22 9.2

23 69. 24 78.

25 9.9

26 9.4

27 68. 28 68.

29 9.2

30 9.4

31 70. 32 75.

Standard deviation (cm/min) N

0.5 10 0.5 10

10. 10

7. 13 0.7 10 0.5 10

10. 15

10. 15 0.6 10 0.5 10

7. 11

6. 13 0.6 10 0.7 10

5. 10

6. 11 0.8 10 0.5 10

8. 14

8. 12 0.5 10 0.4 10

9. 11

7. 16 0.9 10 0.5 10

11. 13

6. 10 0.7 10 0.8 10

8. 11

8. 13

46
Kimberly-Clark Specialty Product*

21 January 1987

Mr. John Krasny

Rational Bureau of Standards

Room A363. Building 224

Route 270 and Quince Orchard Road Caitberaburg

Maryland 20899

Dear Jobn:

About a month ago, ve received from you samples of nine experimental cigarettes vhich vere manufactured aa part of the the Second Series in tbe Technical Study Croup'a effort to examine tbe role played by the different components of cigarettes in affecting their ignition of (oft furnishings.

Kimberly-Clark was contracted to determine the permeability of the different relies of papers which wrap these cigarettes. This work was performed under your Department of Commerce Reference Number: 41 DSC 252 C03 and your Order Number: 43NANB705681 . We have completed tbe analyses and the data are presented in the table attached to this letter.

Aa with the work for which we were contracted last Fall, we measured the permeability of tbe papers using CORESTA Recommended Method No. 3 i Det erroin- ation of tbe air permeability of cigarette paper . CORESTA Information Bulletin, 1975 (3, A)]. The data are reported as tbe velocity of air (in centimeters per minute) drawn through tbe paper at a pressure differential

of one centibar (ten centimeters of water).

The sampling scheme used was as follows: five cigarettes were selected at random from each set and the wrapper(s) were, removed. When an inner wrapper was present (Items 6-2, 7-2, 8-2 and 9-2), its permeability was determined at two different locations on each swatch for a total of ten readings. For tbe outer wrappers, five different positions were selected per swatch for a total of twenty-five measurements; in one case, Item 5-2,

ten positions were measured per swatch for a total of fifty measurements.

The reason for tbe additional testing was that tbe embossed samples gave

such scattered readings, we wanted tbe mean to be as well-specified as possible.

Some other comments on tbe data are appropriate. For tbe four samples which

were embossed--Itema 4-2, 5-2, 8-2, anad 9-2 —it is clear from an examination of tbe means and standard deviations (tbe latter range from twentyfive to aeventy percent of tbe former) that the permeability of those papers have been increased non-reproduc ibly through the embossing process. This finding is merely a measured confirmation of wbat is readily apparent when one looks closely at those cigarettes. Tbe embossing does not impinge

on tbe measured permeability of tbe inner wrappers, wbere present, since

those papers are so open tbat the embossing adds little or nothing to the

net flow of air through them.

Item 1-2 was smaller in circumference (twenty-one millimeters y_j_. twentyfive millimeters) than were tbe other eight items. Items 3-2, 5-2, 7-2 and 9-2 were wrapped with a cigarette paper that bas been electrically

perforated.

Our invoice bas been mailed to you under separate cover.

Beat regards.

Sincerely,

Charles F. Mattina

cc: Dr. Richard C. Cann Chairman, Technical Study Croup

National Bureau of Standards Caitheraburg , Maryland 20899 CFM:87008

47
Table 2-D-2. Paper Permeability of Series 2 Experimental Cigarettes

Determined by Kimberly-Clark

OUTER WRAPPER INNER WRAPPER

Item No. Pfi nneab il itY (cm/min)

stand ard Dev N

1-2 5.2 0.6 25

2-2 6.4 0.8 25

3-2 58 5.3 25

4-2 87 59 25

5-2 160 49 50

6-2 6.2 1.2 25

7-2 59 12 25

8-2 84 47 25

9-2 140 33 25

Permeability Standard Deviation N Emt?g9Pg^

U«/«li,a) (cm/min)

7300

7700

6800

7200

"" __ no — — DO — — yes — — yes

700 10 no

700 10 no

400 10 yes

600 10 yes

48
Appendix 2-E

MEMO RECORD AVOID ERRORS HI IT IK WRfTINC

DATEMarch 23, 1987

TO: K.C. Gupta, DVM, Ph.D., HSHL

Prom: Saura Sahu , HSHL sJiifc

subject: Citrate analysis in cigarette paper

SUMMARY

Introduction

The following 6 batches of cigarette papers were received for citrate

analysis: Series 1-6, 1-7, 1-15, 1-18, 1-25 and 1-30.

Experimental Methods

The papers to be analized were weighed, cut into smaller pieces and

extracted with distilled water. The paper extracts were centrifuged at 300 x g

for 10 min to remove debris. The clear supernatante were analized for citrate.

The spectrophotometic method of Surles (Microchemical Jcurnal 19_, 153,

1974) was used for citrate analysis. A standard curve with known concentrations

of sodium citrate was made to calculate the citrate concentration in the paper

extracts. Briefly, the paper extract was taken in a 10 ml volumetric flask followed by 1 ml of ferric annioniur: sulfate (2.5 g/1) . The flasks were made up with

distilled water and the absorbance of the resulting solution was »easured

at 375 nm. The absorbance of the solution before the addition of the Fe+-' was

subtracted from the absorbance of the solution after the addition of Fe+3 to

calculate the absorbance due to citrate.

Results

The weight of the paper extracted for analysis is given in Table 1.

The standard curve of sodium citrate is given in Table 2 and Pig. 1. Table 3

and Pig. 2 give the absorbance of paper extracts without Fe+3. Table 4 and Fig3

give absorbance of paper extract with Fe+ 3. Table 5 gives absorbance due to

citrate alone in the paper extract and the citrate concentration in the extract.

SIGNATURE DOCUMENT Nj«tt

CPSC Form 247 14,761

49
MEMO RECORD A \ OID ERRORS

PIT IT IN WRITISG

SUBJECT

Table b gives the citrate concentration in the 10 ml of total extract and

its concentration in the cigarette paper by weight per cent.

Sur=ary of Results

The citrate concentration, as determined spectrophotometrically with

sodium citrate as the standard, was found in the cigarette paper in

the following concentration!:

Paper serie s

1-6

1-7

1-15

1-18

1-25

1-30

Citrate concentration (2 by weight)

0.74

0.57

0.61

u

SlCMiTuCt DOCUMENT NJVbLD

CPSC Fo-m i«7 (4/761

50
Appendix 2-F

June 17, 1986

Richard G. Gann, Chief

Fire Measurement & Research Division

Center for Fire Research

United States Dept. of Commerce

National Bureau of Standards

Calthersburg, Maryland 20899

Dear Richard:

Enclosed are the data for the cigarettes you sent for us to analyze. Groups 1 through 8 and 17 through 2 1* are beyond a doubt burley cigarettes. This determination was made because of the low reducing sugar. I think there were some casing added prior to cigarette manufacturing; normally that Is more closely related to sucrose but the extraction process Is made with acid; therefore, seme inversion to reducing sugars occurred. The remaining samples appear

to be a blend of tobaccos. The reducing sugars are much too low for pure bright tobacco. Flue^cured cigarettes would be at least 1 51 or more reducing sugar. My guess; they are a blend 90:10 flue-cured burley. One could determine nitrates quantitatively and total N and possibly positively confirm the composition. I discussed the analyses

with a couple other experienced tobacco people and they confirm this hypothesis

I hope this is some help. The data are included.

Sincerely,

\j!)uj0^^

Wes Weeks

/ds

Enclosure

51

Appendix 2-G

LIMITED STATES GOVERNMENT

Memorandum

US CONSUMER PRODUCT

SAFETY COMMISSION

TO: John F. Krasny, Ph.D., Center for Fire Research

National MOIIUHUI Bureau u i c u u ofu I Standards JlUHUUl uj -—. Through: Andrew G. Ulsamer, Ph.D., AED, HS Y\&Ls> r>

FROM:

Warren K. Porter, Director, HSHL

Kailash C. Gupta, D.V.M., Ph.D. wm.-^H^

SUBJECT: Analysis for Na, K, Ca , and Mg Content in Fabrics and Cotton-Batting Specimens Provided by Dr. Krasny

The smoldering, property of the cellulosic materials has been reported to be affected by the presence of inorganic free radical ions. The factors influencing the smoldering property of cellulosics are of interest to the Commission because of their impact on the fires resulting from cigarettes. • Samples of five fabrics and three cotton

battings provided by Dr. Krasny, of the National Bureau of Standards, were analyzed for Na, K, Ca , and Kg content. The results are provided

in the attached table. Analysis of this data, along with data from

other studies, will be conducted by Dr. Krasny.

The analytical procedures used were as follows:

Reference standard solutions (1000 ppm) for Na, K, Ca, and Mg, and the concentrated nitric acid were obtained from Fisher Scientific Company. Plastic laboratory wares were used as much as possible. The glassware, when used, was washed with a 35% nitric

acid wash. The samples were shredded into small pieces and each subsample was analyzed in replicate. About a gram of material was digested with 50 ml of concentrated nitric acid by heating for 4 to

6 hours until it was completely digested and the solution was

clear. Upon cooling, the digested solution was diluted with

deionized distilled water to the appropriate dilutions. The standard solutions for each element and the reagent blanks were

treated the same as the samples and run with each batch of samples.

The elements were analyzed with a Leeman's Plasma Spec. I, ICP Spectrometer. A standard curve for each element was prepared for each batch of analysis. The elemental content of the materials was calculated using the standard curves, dilution factors, and the weight of material used. Reagent blanks were used for zero correction for sample analyte determination.

Attachment

53
Table 2-G-l. Elemental Analysis of Upholstery Fabrics and Cotton Batting Determined by U.S. CPSC

Cotton Batting and Fabric

Elemental Analysis (PPM)*

Material Sub Na K Ca Mg

Cotton Batting 1A 216 4 71 4650 + 759 950 + 26 423 4 90

593-0180 IB 210 4 61 5082 4" 794 941 4 63 493 4 75 593-0181 2A 229 + 74 5073 4 807 907 »" 42 507 4"95

2B 214 4 52 5418 4 786 932 4 45 579 4 45

593-0182 3A 268 82 5236 4 655 950 4 22 560 4 64

3B 221 + 73 4952 4 917 832 4 76 507 4 34

Fabric A 681 * 104 <100 284 4 36 89 4 11 593-0175 B 633 * 78 <100 273 4 60 98 4 3

C 671 +93 <100 298 4 36 95 ;t 2

Fabric A 599 + 60 4796 4 739 750 4 67 541 4 41 593-0176 B 484 + 33 4596 4 751 757 4 95 568 4 28

C 683 + 40 5279 4 1147 759 4 96 537 4 33

Fabric A B02 97 5573 4 688 30574 4 4084 2938 4 144 593-0177 B 790 4 165 6599 4 1285 27334 4 1958 2672 4 185

C 851 4 146 6236 4 863 28998 4 2080 3018 4 245

Fabric A 969 4 55 391 4 103 593 4 70 411 4 42

593-0178 B 1136 + 113 449 4 94 710 4 73 468 4 54

C 992 4 45 367 4 82 547 4 80 388 4 76

Fabric A 163 4 36 <100 554 4 57 171 4 21 593-0179 B 115 4 34 <100 466 4 35 135 4 10

C 126 4 42 <100 463 4 42 132 4 10

Results from five replicate analysis.

54
The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 3

Performance

Measurements

55

Contents for Section 3

Introduction 59

Bench-Scale Evaluations 61 Methods 61

Ignition Propensity Measurements 61 Contamination of Fabrics with Alkali Metal Ions and

Natural Soil 61 Results and Discussion 62

Ignition Propensity Results 62

Primary Evaluation ot Experimental Cigarettes for Ignition Propensity 62

Validation of Ignition Propensity Primary

Evaluation Results 65

Comparison of Full-Scale Furniture and

Bench-Scale Tests 71 Objective 71 Method 71 Cigarette Selection, Handling and Coding 71 Experimental Design 71 Test Procedure for Full-Scale Furniture Tests 72

General 72

Cigarette Location and Placement 72

Criteria for Ignition 73

Data from Full-Scale Tests 73

Difficulties with the Procedure 74

Conditioning of the Chairs 74

Drafts 74

Self-extinguishment of Cigarettes 74

Times to Ignition of Substrate 74

Crevice Shape 74

Influence of Substrate on Cigarette Burning 75

Results 75

Validation of Bench-Scale Tests by Full-Scale Tests .... 75

Validation Results Weighted by Numbers of Tests 80

Use of Kendall's Tau Correlation Coefficient

to Summarize the Agreement Between Full-Scale and

Bench-Scale Tests 80

Relative Ranking of Cigarettes in Full-Scale Tests and the Primary Evaluation 80

Average Per Puff Tar, Nicotine, and CO Yields

of Experimental Cigarettes 81

Summary of Characteristics of Experimental,

Low Ignition Propensity Cigarettes 85

Patented Cigarettes 87

Summary and Conclusions 89

References for Section 3 91

List of Tables

Table 3-1. Ignition Propensity of Series 1 Experimental Cigarettes 63

Table 3-2. Ignition Propensity of Series 2 Experimental Cigarettes 64

Table 3-3. Ignition Propensity as a

Function of Cigarette Parameters

Series 1 Experimental Cigarettes 65

Table 3-4. Ignition Propensity of Short

Cigarettes and Cigarettes

Without Filter 66

Table 3-5. Ignition Behavior of Cigarettes on Alkali Metal

Ion Treated Fabrics 67

Table 3-6. Ignition Behavior of Cigarettes on Soiled Fabrics 68

Table 3-7. Ignition Propensity of Selected Cigarettes on Low

Cigarette Ignition Resistance

Substrates 69

Table 3-8A. Summary of Full-Scale Furniture Test Results 76

Table 3-8B. Summary of Full-Scale Furniture Test Results 77

57
Table 3-8C.

Table 3-9.

Table 3-10.

Table 3-11.

Table 3-12.

Table 3-13.

Table 3-14.

Summary of Full-Scale Furniture Test Results .78

Numbers of Tests and

Results Full-Scale and

Bench-Scale, Various

Cigarettes and Substrates 79

Per Puff Tar, Nicotine

and Carbon Monoxide Yields of Series 1 Experimental Cigarettes 82

Per Puff Tar, Nicotine

and Carbon Monoxide Yields of Series 2 Experimental Cigarettes 83

Per Puff Tar, Nicotine

and CO Yields as a Function

of Cigarette Parameters 83

Summary of Characteristics

of Selected Cigarettes 85

Ignition Propensity of Patented Cigarettes 86

List of Figures

Figure 3-1

Figure 3-2.

Figure 3-3.

Four Chairs as Viewed

Through the Window of the Burn Room 72

Gaseous Nitrogen Applicator

Used to Extinguish Ignited

Sites 72

Sites for Various Cigarette

Types Marked on a Damask

Cushion With Burn Scars Near the Marks

Appendices

Appendix 3-A 93

Table 3-A-1.

Figure 3-A-1.

Figure 3-A-2.

Figure 3-A-3.

Figure 3-A-4.

Significance Probabilities

(in Percent) of Design Factors

for Series #1 Cigarettes

Appendix 3-B

.93

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

CA/CB, Unc./Flat .94

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance of the Substrate

SPL/PU, Unc./Flat .94

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

SPL/PU* (One Half of Tobacco

Column Removed), Unc./Flat . . .95

Normal Probability Plot of Estimated Factorial Effects from a 2

5 Factorial Analysis

of Variance for the Substrate

Denim/PU, Crev./Cov .95

97

Table 3-B-1. Use of Kendall's Tau

Correlation Coefficient to Summarize the Agreement Between

Full-Scale and Bench-Scale

Ignition Tests 98

73

Figure 3-4. Sites for Various "Crevice" Tests Marked on a

"California Velvet" Cushion 74

58
I ntroduction

This section covers the evaluation of the ignition propensities

of the previously described 41 experimental and five patented cigarettes under a variety of experimental

conditions. 1 The results were compared with those obtained on current commercial cigarettes to determine performance

relative to today's market. The procedure was to give all cigarettes a "primary evaluation," and then to confirm the

results on selected cigarettes by exposing them to a wider

variety of conditions simulating those which could occur when cigarettes are dropped inadvertently on upholstered

furniture. The primary evaluation consisted of placing each of the

cigarettes on three mini-mockup substrates varying in cigarette ignition resistance. On one of these substrates, full- length as well as half-length cigarettes (to simulate cigarettes

after they have been smoked foi some time) were tested. The main objective of the validation phase of this work was to assure that the relative ignition propensity rankings

established in the primary evaluation hold true under the full range of substrate conditions under which cigarettes are dropped on upholstered furniture. Several low ignition

propensity cigarettes were chosen for this purpose (since the emphasis in this work is on low ignition propensity) as well as intermediate propensity cigarettes and commercial

controls. A variety of test conditions was used for this work, as follows: To cover an as complete range of substrate cigarette

ignition resistance as possible, experiments were carried out

1 (a) Ignition is defined as sustained, expanding smoldering of the

material on which the burning cigarette rests. This may or may not

lead to flaming ignition.

(b) The term "substrate" is used to describe one combination of a

specific fabric and padding, in either the flat or the crevice

(juncture of vertical and horizontal cushions) configuration, with or without a sheet covering the cigarette. An example is the flat area

of a piece of polyurethane foam covered with a specific fabric, with the cigarette covered by a piece of sheeting. The crevice made

from the same materials is a different substrate.

(c) In this report, the term "cigarette ignition resistance" will be used to characterize substrates, with low cigarette ignition resistance used

to describe substrates which ignite easily.

(d) Similarly, the term "ignition propensity" will be used to characterize

cigarettes, with low ignition propensity cigarettes denoting those which are unlikely to ignite most substrates.

on over 20 substrates. These included a very low cigarette

ignition resistant substrate, a heavy, raw cotton fabric and

cotton batting or polyurethane foam padding.

To establish the effects of filters and of short tobacco

columns, selected experimental cigarettes were evaluated

with the filter and/or one half of the tobacco column

removed.

The effect of cover fabric contamination on the relative ignition propensity of cigarettes was investigated. One of the

contaminants used was alkali metal ions (known smolderpromoters) [3-1,2]. They were applied to a cotton duck fabric which, without treatment, did not ignite from any cigarette.

Since furniture becomes soiled with use, tests were also conducted with soiled fabric from discarded furniture, and

with the same fabrics after cleaning. Soil was also extracted from discarded furniture fabric covers and applied to the

cotton duck fabric.

All the above work, as well as the primary evaluation, was

carried out with mockup bench-scale tests. To evaluate the relevance of these bench-scale ignition propensity results, results obtained on 44 full-scale chairs (representing four flat and 19 crevice substrates) were compared with results on mockups containing the same materials in the same

configurations.

It must be emphasized that these various modes of validation can only produce a ranking of the cigarettes

which can be compared with the results of the primary

evaluation. The actual number of ignitions in each of those

modes depends on the cigarette ignition resistance of the

substrate; one should thus not expect the same number of ignitions in the primary evaluation as in the validation tests. The bench-scale evaluations will be described first, followed by a section on the comparison of the full-scale and

bench-scale results and a short discussion of the smoke

yields of the experimental cigarettes. Finally, the evaluation of patented cigarettes will be discussed.

59

ench-Scale Evaluations

Methods

Ignition Propensity Measurements

In both the primary evaluation and the validation measurements, the determination ot the ignition propensity

of the experimental and patented cigarettes was done in the same manner and using the same mockups and associated

equipment as reported in Appendix B of [3-3], Four minor

changes were made for this study. The first change was the use of five (5) replicates per cigarette (unless otherwise

indicated) for increased statistical precision. The second

change was to use the same size vertical pad as horizontal pad (203 x 127 x 51 mm, 8x5x2 in.) in the crevice

configuration, to save material and effort. The third change

was to record as a smoldering ignition a weight loss of greater than 3.5 g (instead of 5.5 g) for polyurethane

mockups in the flat configuration because the substrates had obviously ignited at this weight loss, and carrying the

tests further would result in contamination of the ambient air. The fourth change was equilibrating the cigarettes (stored in freezers at -15°C) as well as the substrates, in a conditioned room at 55 ± 10% RH and 22 ± 3°C for a minimum of 24

hours. They were exposed to the less controlled conditions

(20-60% RH, 23-26°C) in the test room for a maximum of 20

minutes before the last of the five tests were begun.

Contamination of Fabrics with Alkali Metal Ions

and Natural Soil

This work was part of the effort to confirm results of the primary evaluation under different test conditions as well as

to investigate the effect of fabric contamination in a

systematic manner. Only preliminary work was performed.

Specifically, the objective was to determine whether

cigarettes which had been found to have low ignition

propensity in the preliminary evaluation would still maintain

their low ignition propensity under conditions in which the

fabric ignition resistance was changed by contamination.

Two types of contamination were considered: (1) by alkali metal ions, which occurs in real life both on raw cotton and

as a residue of a variety of fabric finishing agents and which

are known smolder-promoters [3-1,2]; and (2) by soil recovered from discarded furniture cover fabrics. The procedure for determining the effect of alkali metal ion concentration on the cigarette ignition resistance of fabrics in a systematic manner was as follows. It was established that a mockup of a 100% cotton duck fabric and polyurethane

foam in the flat configuration was not ignited by a commercial cigarette, No. 6; this cigarette had been found to have an ignition propensity similar to that of several other commercial cigarettes in earlier work, with an ignition

propensity typical of present production. [3-3] Various

concentrations of Na +

, K

+

, and Na + plus K

+ were then

applied to the fabric until a concentration at which the

ignition-prone cigarette would ignite the substrate was found.

Then somewhat higher concentrations would be applied.

Selected experimental cigarettes were then tested on these

substrates, to establish whether their ignition propensities

would still rank them as they had ranked in the primary

evaluation. For the treatment, the cotton duck fabric samples were immersed in solutions containing various concentrations of NaCI, KCI, or NaCI plus KCI and a wetting agent, then

padded (immersion in the solution and extraction on "pad"

rolls) and air dried in the horizontal attitude to prevent

migration of the solutions over the fabric. (The work was

conducted at the College of Human Ecology, The University

of Maryland, College Park, Maryland). The approximate ion concentration on the fabric specimens was calculated from

the wet pick-up of the specimens after padding them

through the bath of known salt concentration; e.g., a specimen with a 60 percent wet pickup and a bath

concentration of 8000 ppm would contain approximately

4800 ppm ions. Weighing the conditioned specimens before and after treatment would not provide accurate ion concentration results because the hygroscopicity of the specimens is undoubtedly changed by the added ions, and

because the expected weight changes due to treatment are so small (add-ons in the range of 5 percent) that this uncertainty would matter. Also, yarns from the edges of specimens are often lost during treatment, and this further

61
adds to the uncertainty of dry add-on determinations.

After the concentration for each ion and ion combination

had been established, ten (10) 420 x 205 mm swatches of fabric containing the various ions and a control containing

only the wetting agent were prepared. The test fabrics were

evaluated over polyurethane foam or cotton batting in the

flat configuration using the low ignition prone (BELN-21, No

106) and a moderately ignition prone (FELC-25, N 0.129)

cigarette of the Series 1 experimental cigarettes and the above commercial cigarette, No. 6. Fourteen different soiled, discarded upholstery cover

fabrics were collected from reupholstery establishments.

Swatches of each fabric were retained. The remainder of the

fabric was sent to The International Fabricare Institute, Silver Spring, Maryland. The soil was extracted by immersion in tetrachloroethylene and subsequently in water (without a

wetting agent) and collected. The fabrics were returned to CFR for evaluation of cigarette ignition resistance and the

soil was given to the Department of Human Ecology,

University of Maryland, for application to the cotton duck.

The soil extract which was still suspended in the solvent was

not padded on but the duck specimens were immersed in the solutions, then air-dried horizontally. In one case the specimens were immersed first in the water, in the other

case, first in the tetrachloroethylene. The specimens were

dried and then immersed in the other solution. The solids add-on was about 3 percent in both cases. Time did not permit refining the method of application of the actual soil or choosing various concentration levels, nor analyzing the soil. Specimens of the 14 soiled and extracted fabrics, of the purposely soiled cotton duck and a control which had been

immersed in the two solvents were tested with three

replicates each of the low ignition propensity experimental

cigarette BELN-21, No. 106, and the commercial cigarette, No. 6.

Results and Discussion

Ignition Propensity Results

In this section, the results of the ignition propensity

evaluations are described. In summary, in the primary

evaluation, five of the 41 experimental cigarettes produced

only to 4 ignitions while typical commercial cigarettes

produced 18 to 20 ignitions. (20 is the maximum possible

number.) Thirteen of the experimental cigarettes produced 10

or fewer ignitions. The cigarettes which produced the low

number of ignitions combined low packing density (attained

by use of expanded, relatively large particle size tobacco),

low paper permeability and paper citrate content, and small

cigarette circumference. They contained Burley or flue-cured tobacco. During the validation process, the low ignition

propensities of several cigarettes were further confirmed on

additional substrates and under a variety of experimental

conditions, in bench-scale tests as well as on full-scale chairs. It thus appears that some cigarettes which have

significantly lower ignition propensity than current

commercial cigarettes could be produced on commercial

equipment without major hardware changes, albeit at reduced speed.

Primary Evaluation of Experimental Cigarettes for Ignition Propensity

The number of ignitions of both series of experimental

cigarettes are shown in Tables 3-1 (Series 1) and 3-2 (Series

2). Table 3-2 also shows comparable values for commercial

cigarettes. Three substrates each representing a different

level of cigarette ignition resistance of residential furniture were used; on one of these, both full length and half length

cigarettes were exposed. These substrates ignited with all five replicates of the commercial cigarette, No. 6 [3-3]. All five replicates of another commercial, No. 3, ignited in three

of the test modes; on one relatively high cigarette ignition

resistance substrate, this cigarette caused ignition in 3 of 5 cases. The first substrate listed in the tables, the standard

California velvet over cotton batting in the flat configuration,

had been previously used for the screening of commercial

cigarettes [3-3]. The next substrate, a relatively heavy cotton

fabric ("Splendor") over polyurethane foam, had a similar, low

cigarette ignition resistance. Again, only cigarettes with low

ignition propensity produced fewer than five ignitions. Finally, lower numbers of ignitions were obtained in the crevice

configuration formed by a denim fabric over polyurethane

foam, with the cigarette covered with a piece of sheeting.

(The use of sheeting as a cover is prescribed in many

procedures for testing the cigarette ignition resistance of upholstered furniture and mattresses [e.g., 3-4,5].) Evaluation

of the results could then proceed by the total number of ignitions in the four test modes, e.g., 20 ignitions will be

called high ignition propensity; this occurred with five of the

41 tested cigarettes. Four or fewer ignitions will be called low

ignition propensity ogareites; this occurred with five of the

cigarettes.

The shortened cigarettes of Series 1 produced significantly

lower number of ignitions (at the 0.2 percent significance

level for the Series 1 cigarettes).

This was not observed for the cigarettes of the second

series. The analysis of variance methods used are described

in [3-6,7]. Additional results with shortened cigarettes on a

different substrate are discussed below. The average effects of the various cigarette design

parameters of the Series 1 experimental cigarettes are shown in Table 3-3. (It should be noted that these are averages for 16 cigarettes with one parameter held constant and four other parameters systematically varied.) The data were analyzed by analysis of variance for a 2

5 factorial design for each of the four ignition modes. The response

variable was obtained by applying the Freeman-Tukey

modification of the angular transformation to the raw count

data shown in Table 3-3 [3-6,7,8], Only overall effects are discussed here; more detailed statistical discussions are given in Appendix 3-A. The findings can be summarized as

follows:

• Low packing density, achieved by use of expanded, large

particle size tobacco (30 cut width) was the most

62
Table 3-1. Ignition Propensity of Series 1 Experimental Cigarettes

HHH89HHI

Cigarette

Number of Ignitions

CA/CB SPL/PU SPL/PUa Denim/PU

No Design. unc./flat unc./flat unc./flat crev./cov. Total

101 BNLC-21 3 5 5 13

102 BNLN-21 2 5 5 12

103 BNHC-21 5 5 5 2 17

104 BNHN-21 5 5 5 4 19

105 BELC-21 3 3 6

106 BELN-21 1 1 107 BEHC-21 4 5 2 11 108 BEHN-21 3 4 7

109 FNLC-21 5 5 5 15

110 FNLN-21 5 5 5 1 16

111 FNHC-21 5 5 5 4 19

112 FNHN-21 5 5 5 5 20

113 FELC-21 5 1 6

114 FELN-21 1 3 4 115 FEHC-21 4 5 5 14

116 FEHN-21 4 5 3 12

117 BNLC-25 5 5 5 3 18

118 BNLN-25 5 5 5 3 18

119 BNHC-25 5 5 5 5 20

120 BNHN-25 5 5 5 5 20

121 BELC-25 5 5 4 14

122 BELN-25 3 2 2 7 123 BEHC-25 5 5 5 15

124 BEHN-25 5 5 5 15

125 FNLC-25 5 5 5 3 18

126 FNLN-25 5 5 5 2 17

127 FNHC-25 5 5 5 5 20

128 FNHN-25 5 5 5 5 20

129 FELC-25 5 3 2 10

130 FELN-25 3 1 4

131 FEHC-25 5 5 5 15

132 FEHN-25 5 5 2 12

127 142 119 47 435

Maximum number of ignitions per cigarette is 20, per substrate 160. CA/CB California test fabric/cotton batting SPL/PU 100% cotton Splendor fabric/polyurethane 2045

Denim/PU 100% cotton Denim fabric/polyurethane 2045

Unc/flat Uncovered cigarette on a flat mockup

Crev/cov Covered cigarette in mockup crevice

a Cigarette with filter with one half of the tobacco column removed before lighting.

63
important factor in reducing ignition propensity. This effect was statistically significant at or below the 0.1 percent level

for all test modes. This was apparently due to the reduction in the available fuel per unit length by 30 to 40

percent. Commercial cigarettes generally are a blend of non-expanded and expanded tobacco, with the latter component ranging between 10 and 65 percent [3-9]. The

packing density of a popular, commercial, low tar-nicotine

yield cigarette was found to be 0.18 mg/mm3

, within manufacturing scatter of the packing density of one of the experimental cigarettes with the lowest ignition propensity,

0.17 mg/mm3. Second in importance was low paper permeability. This

effect was significant at or below the 0.7 percent level for

all test modes. The low permeability paper used in these

experimental cigarettes, nominally 10 CORESTA, would

probably rarely be used in commercial cigarettes,

primarily because it could result in relatively high yields of

tar, nicotine and CO. Papers with 20 to 70 CORESTA

permeability, with a median range of 35 to 40, are used in commercial cigarettes [3-9]. However, other means are

available to reduce these yields, such as improved filter design and use of the ventilation principle- holes near the

filter which permit air to enter during the draw and dilute the smoke- are available [3-10]. Such ventilation reduces

smoke yields as measured by the FTC method. However,

the FTC does not measure the "side stream" smoke, the smoke which emanates from the cigarette between puffs. Cigarettes with 21 mm circumference were, as a group,

less ignition prone than those with 25 mm circumference.

This difference was significant at the 0.01 to 0.03 percent

level for the California standard fabric/cotton batting and

denim/polyurethane foam substrates, at the 3 percent level

for the shortened cigarettes on the Splendor fabric/ polyurethane substrate, and was not significant for the full length cigarettes on this substrate. (These results again

indicate the dependency of ignition propensity results on

the substrate.) Cigarettes with 21 mm circumference are

Table 3-2. Ignition Propensity of Series 2 Experimental Cigarettes

Cigarette

number

201

202

203

204

205

206

207

208

209

Paper variables

Permeability'

CORESTA'1

Outer Inner

5.2 6.4 58

87

160

6.2 59

84

140

Embossed

7300

7700

6800

7200

yes

yes

yes

yes

Circum.

(mm)

2125

25

25

25

25

25

25

25

CA/CB

Unc./flat

2

4

4

52

15

3

TOTALS 26

Commercial cigarettes

1 i lowest ignition propensity of 12 commercial cigarette 2

2

j packings 2

3 [ ignition propensity typical of commercial cigarettes 5 6 5

Mockup Test Conditions

Number of Ignitions

SPL/PU

Unc./flat

13

3

2

3

5

5

22

SPL/PIC

Unc./flat

2

4

3

4

3

4

5

25

Denim/PU

crev./cov.

Total

ignitions

2

7

11

118

7 14

13

73

16

12

18

20

(a) Measured at Kimberly Clark

(b) CORESTA corresponds to cm3 /min-cm 2 at /cbar

(c) Cigarette with filter with one half of the tobacco column removed

CA/CB California test fabric/cotton batting SPL/PU 100% cotton Splendor fabric/polyurethane 2045

Denim/PU 100% cotton Denim fabric/polyurethane 2045

Unc/flat Uncovered cigarette on a flat mockup

Crev/cov Covered cigarette in mockup crevice

B Burley F Flue-cured N 1 00% non-expanded tobacco

E 100% expanded tobacco

64
currently an article of commerce, and even cigarettes with about 17 mm circumference have been recently

introduced. The lower ignition propensity of the 21 mm

circumference cigarettes is probably due to both less available tobacco and paper per unit length and to reduced contact area with the substrate.

• Citrates are added to the cigarette paper to regulate the paper burn rate and to obtain ash of the desired

coherence and appearance [3-11]. Overall, this had a

highly variable effect on ignition propensity. The

significance levels of this effect were 0.7 percent for shortened cigarettes on the Splendor fabric/polyurethane

foam substrate, and 2 to 25 percent in the other modes.

Overall statistical significance aside, it is noteworthy that the paper of the three lowest ignition propensity cigarettes

in this series contained no citrate.

• The choice of Burley or flue-cured tobacco had no

significant effect on the ignition propensity. Most

commercial cigarettes contain a blend of these and other tobaccos. The data imply that this practice may not affect

ignition propensity.

The experimental cigarettes of Series 2 were designed to probe the effect of paper permeability, paper embossing

(hopefully providing less contact with the substrate), and the use of double layers of cigarette paper (Table 3-2). Paper

permeability can be regulated by two methods: "inherent paper porosity" is adjusted by varying the amount of calcium

carbonate in the slurry; further adjustments can be made by

perforation of the paper by electrostatic, laser, or mechanical means [3-12], It seemed of interest to establish whether the two methods to achieve a given level of permeability would

have the same effect on ignition propensity; higher innate

porosity has been reported to increase burn rate, while

perforating the paper did not [3-13]. Consequently, a very

low permeability (4-6 CORESTA) paper was chosen, and

parts of this paper were electrostatically perforated and/or

embossed.

The results shown in Table 3-2. indicate that the cigarettes 201 and 202, with the low permeability base paper, had

very low ignition propensities. For the single layer paper

cigarettes, ignition propensity increased at the higher

permeabilities, whether due to perforating or embossing.

The electrostatic perforation resulted in an increase to about

60 CORESTA, and a modest increase in ignitions.

Embossing further increased the permeability and number of ignitions because holes were formed during the process. Adding a second layer of thin, highly permeable paper had

no consistent effect. The results again indicate that low paper permeability is one important route to reducing ignition propensity, as had

been predicted by industry experts [3-14]. The embossing

experiment was flawed because the permeability was

inadvertently increased in this process. Use of a light weight,

permeable inner wrapper does not seem to be promising.

Validation of Ignition Propensity Primary

Evaluation Results

In this section, results of ignition propensity tests performed

under a much broader range of test conditions than in the primary evaluations are reported. The relative ignition

Table 3-3. Ignition Propensity as a

Function of Cigarette Parameters

Series 1 Experimental Cigarettes

Cigarette Parameters Number of lgnitionsa

°/o Tobacco Packing Density

High

Low

282

153

88

48

Paper Permeability

High

Low

256

179

80

56

Cigarette Circumference (mm)

25

21 243192

76

60

Paper Citrate Cone. (%)

0.8 231

204

72

64

Tobacco Blend

Flue-cured

Burley

222

213

69

67

(a) Maximum possible number is 320 (16 packings x 4 substrates x 5

replicates)

propensity rankings obtained in the primary evaluation were

confirmed, as described in detail below.

Ignition Propensity of Short Cigarettes and of

Cigarettes with the Filter Removed. It appears more likely that partially smoked cigarettes rather than full length

cigarettes are dropped on upholstered furniture. The

question arises whether evaluation of ignition propensity

performed with full length cigarettes is valid for short

cigarettes. Furthermore, it seemed of interest to determine

whether the filter had an effect on cigarette ignition

propensity.

In the primary evaluation, full length cigarettes and

cigarettes with half of the tobacco column removed were

tested on a substrate consisting of the Splendor fabric and

polyurethane padding. Some of the shorter cigarettes had a somewhat lower ignition propensity so that, at least for this substrate, testing full length cigarettes provides a certain

safety factor. However, similar experiments carried out on a second substrate, California fabric over cotton batting (Table

3-4), showed no difference between short and long cigarette

ignition propensities. This held for normal cigarettes and

cigarettes with the filter removed. The statistical methods

used are discussed in [3-6,7]. (Similarly, there was no

consistent effect of length among the patented cigarettes

which will be discussed later.) The results indicate that length

65
matters only on certain substrates, primarily those which take a long time to ignite. On this substrate, removal of the filter significantly (at the

0.01 percent level) increased the ignition propensity, of full length cigarettes as well as of cigarettes with half of the tobacco column removed. This should not be interpreted to mean that all commercial non-filter cigarettes have higher

ignition propensity since commercial filter and non-filter cigarettes generally also differ in other design factors. However, several investigators found a greater propensity to ignite of commercial non-filter cigarettes as compared to (not necessarily strictly comparable) filter cigarettes [3-15,16] while

others have found no such difference, e.g., [3-3]. A possible

explanation is that the removal of the filter increases the

overall oxygen supply to the smolder front. This is particularly noticeable at the very end of the cigarette, where

increased glowing can be observed. In such cases, the increased burning may cause ignition of borderline substrates which resist ignition along the main part of the

cigarette.

It should be mentioned that Canadian investigators found

the opposite, an ignition propensity increase when one half and one third length cigarettes were placed into the depressions near the tufts of mattresses [3-17], This can be

ascribed to the fact that on very curved surfaces (near the

tuft) the weight of the filter and the adjoining parts of the

cigarettes may cause the burning end to be lifted from the

surface, while it remains in contact with the surface when

the cigarettes were short.

Effect of Fabric Contamination on Ignition Propensity.

As described in more detail below, and based on a limited amount of experimental work, it appears that the cigarette

rankings obtained in the primary evaluation were maintained on contaminated fabrics. Of the two contaminants

investigated, alkali metal ions decreased substrate cigarette

ignition resistance while soil collected on used furniture did

not appear to have an effect. Time did not permit us to find the alkali metal concentrations which would show the

differences between cigarettes in a quantitative manner, by

number of ignitions and non-ignitions. However, the lower

ignition propensity cigarettes produced considerably less char on these substrates than the high ignition propensity

cigarettes. A methodology for systematic contamination of fabrics has been developed which, while in need of further development, may be useful in future studies. The investigation of the effect of alkali metal ions was

prompted by the finding that such ions decrease the

cigarette ignition resistance of fabrics. This has been clearly

demonstrated by work described in the literature [3-1,2], In spite of the clear evidence of the importance of this factor, neither UFAC, the fabric finishers, nor the upholstered

furniture manufacturers seem to have taken steps to reduce

alkali metal ion concentration and thus to increase cigarette

ignition resistance. Alkali metal ions are naturally found in raw cotton, such as unscoured fabrics and cotton batting.

In fabric finishing, they can be deposited in the fabrics by

rinsing in hard water, by residual detergents, dye auxiliaries, softeners, or other finishing agents which contain such ions. They can be removed by scouring in soft water. The primary evaluation work had been carried out on new

fabrics containing only the incidental smolder-promoting

contaminations found in raw cotton or those originating from

the final fabric finishing steps. Two approaches were used in the present work which were intended to establish whether

cigarette rankings obtained on new fabric would still be

found on contaminated substrates. One was to apply alkali metal ions which are known smolder promoters to a

scoured, undyed 100 percent cotton duck fabric which, in the untreated state, does not ignite. In addition, soil from 14

dirty fabrics which had been removed from furniture being

prepared for re-upholstering was collected by extraction in

Table 3-4. Ignition Propensity of Short Cigarettes and Cigarettes Without Filter

Substrate: CA standard fabric, cotton batting, flat, uncovered

Cigarette

number

Number of Ignitions

Cigarette

with filter

1/2 tobacco

Cigarette

w/o filter

1/2 tobacco

column

with filter

1/2 tobacco

column

w/o filter

103 BNHC-21

105 BELC-21

106 BELN-21

113 FELC-21

114 FELN-21

119 BNHC-25

120 BNHN-25

5

15

5

5

55

4

3

55

3

5

4

5

5

5

5

5

5 _5

16 32 12 35

66
Table 3-5. Ignition Behavior of Cigarettes on Alkali Metal Ion Treated Fabrics

Cigarette

number

129 (FELC-25)

6 (COM)

Ign

modea

106 (BELN-21) SE

Nl

SE

Nl

I

SE

Nl

Substrate: Cotton duck/polyurethane foam/flat

NaCI KCI

Water

control

(ppm)

14

5280

(ppm)

2

3

14

4

1

5530

(ppm)

2

3

5

3

2

4920

(ppm)

4

1

3

2

5

5170

(ppm)

2

3

14

2

3

NaCI/KCI

Ratio 1:1 5020

(ppm)

3

2

4

1

5

Ratio 1:1.2 5460

(ppm)

3

2

5

5

(a) SE - Cigarette self-extinguished

Nl - Cigarette burned whole length, substrate did not ignite

I • Substrate ignited

water and solvent and applied to the same fabric. Such

fabric soil could, of course, contain smolder-promoting ions (such as sodium from perspiration, etc.). However, their effect could be diluted if the soil contained possible smolder

inhibitors; mineral dust comes to mind. In a smaller, less controlled effort, high and low ignition propensity cigarettes were placed on substrates made up from the 14 soiled

fabrics and cotton batting, and compared with the results

after the fabrics were cleaned.

A study comparing new chairs with the same chairs after considerable use was undertaken at Cornell University [3-18]. A small decrease in cigarette ignition resistance due to use was reported. However, the criterion used, measurement of surface char length five or ten minutes after exposure of the

cigarettes, would not be appropriate in light of more recent experience that surface smoldering rate is not a proper

evaluation procedure for ignition propensity. This is because

smoldering can proceed into the substrate without expansion

on the surface so that one must rely on signs of obvious

ignition such as considerable smoke and heat evolution

[e.g., 3-19], However, we have found that char damage

caused by cigarettes after they burn their entire length but do not ignite the substrates is related to their ignition

propensity as established on other substrates.

Effect of Alkali Metal Ions. Table 3-5 shows the behavior of

five replicates each of three cigarettes placed on fabrics treated with two concentrations each of NaCI, KCI, and

NaCI/KCI combined. The two concentrations were chosen on

the basis of a limited amount of screening of specimens with a wider range of concentrations. They did not produce

quantitative ignition/non-ignition results as had been hoped

but provided qualitative information based on the char

damage on non-igniting substrates. The cigarettes chosen

were BELN-21, No. 106 representing low ignition propensity,

FELC-25, N o.1 29, representing intermediate ignition

propensity and the commercial cigarette No. 6. The results are shown in terms of cigarettes which self-extinguished, of those which burned their entire length but did not ignite the

substrates, and those which ignited the substrate. The commercial cigarette ignited the substrates in only

three of 35 tests. However, it burned its entire length without

igniting the substrate in 30 tests, and self-extinguished

before burning its entire length in only 2 tests. On the other hand, cigarettes Nos. 106 and 129 did not cause any ignitions. More than half of the cigarette No. 106

replicates self-extinguished before burning their entire length, as did about a third of the cigarette No. 129 replicates.

Again, the remaining cigarettes burned their entire length.

Thus, the size of the char ranked the cigarettes in the same

manner as the ignition/non-ignition results of the primary

evaluation which had been performed on substrates with lower cigarette ignition resistance. Similarly, the

substrate/cigarette system weight losses of non-igniting substrates were largest for the commercial cigarette No. 6. intermediate for No. 129, and lowest for No. 106. As

discussed in the first report on cigarette ignition propensity,

these weight losses occasionally vary considerably between

67
replicates [3-3], and were therefore not treated statistically. But they showed, understandably, similar trends to the

visually observed char pattern sizes on the fabrics. These

char patterns, as on many borderline ignition/non-ignition

substrates, showed Rohrschach-like forms.

Unfortunately, nothing quantitative can be said about the

effect of various levels of alkali metal ion concentrations. The

concentration levels shown in Table 3-5 are only

approximate, as discussed earlier, and can be considered

duplicate treatments. (The differences between the two levels shown was smaller than intended, but such are the vagaries

of experimental treatments with no time for repeats.)

However, with both the concentration and the cigarette

behavior very similar, it appears that two similar treatments

with three salts gave very similar ignition propensity results. This is of importance because fabrics treated to various

levels of alkali metal concentrations may be candidates for standard materials for both upholstered furniture cigarette

ignition resistance and cigarette ignition propensity testing.

Soiled Fabrics . In limited experiments, soiling during use of fabrics did not seem to have an effect on cigarette ignition

resistance, nor did it have an effect on the relative ignition

propensity ranking of cigarettes. The details follow. The 14 soiled fabrics removed from used furniture and

their cleaned and conditioned counterparts were found to have the same cigarette ignition resistance. More specifically, the commercial cigarette No. 6 ignited seven of the soiled

fabrics and six of the same fabrics after extraction (only one

replicate cigarette used). No ignition with either soiled or extracted fabric occurred with cigarettes Nos. 106 or 129. Table 3-6 shows the results obtained on cotton duck

fabrics treated with the combined soil extracted from other

parts of the above 14 soiled fabrics. The white cotton duck

appeared very discolored after these treatments; the concentration of the soil of about 3 percent can only be

approximately stated, since soil was first deposited from one

extraction bath — trichloroethylene or water — then from the

other. (This order was reversed in a second treatment

series.) Some soil deposited in the first treatment may have

been removed by the second treatment. The results show

that even at this apparently high soiling level, the cigarette

ignition resistance of this substrate was not increased over

that of the unsoiled fabric. The cigarette with the lowest

ignition propensity, BELN-21, No. 106, self-extinguished more

frequently before burning its entire length that the other two

cigarettes. Again, the difference can be only stated

qualitatively on the basis of frequency of self-extinguishment

and non-ignition since no ignitions occurred.

Validation of Low Ignition Propensity on Additional

Substrates. Table 3-7 shows that the relative ignition

propensities of commercial and low ignition propensity,

experimental cigarettes were maintained when they were

tested on three additional substrates. "Haitian cotton" fabric was chosen because a large number of studies

Table 3-6. Ignition Behavior of Cigarettes on Soiled Fabrics

Substrate: Cotton duck/polyurethane/flat

Cigarette

number

106 BELN-21

ign.

Mode3 Water/Perc.Control

Soiled Specimens

Perc./waterb Water/Perc.c 3500 ppmd 3.48 ppmd

1 1 2 2 SE

Nl

I

2

1

129 FELC-25 SE

Nl

I 3

1 3 2

6 COM SE

Nl

I 3 3 3

(a) SE - Cigarette self-extinguished Nl - Cigarette burned whole length, substrate did not ignite

I - Substrate ignited

(b) Specimen first treated with perchloroethylene soil extract, then water extract

(c) Specimen first treated with water extract, then perchloroethylene extract

(d) Concentrations shown are maximum possible values; some of deposit from first treatment may have been removed by second treatment.

68
Table 3-7. Ignition Propensity of Selected Cigarettes on Low Cigarette Ignition

Resistance Substrates

Number of Ignitions

Haitian Cotton

Cigarette

106 (BELN-21)

114 (FELN-21)

130 (FELN-25)

201

202

Com

1 mercial Cigarettes

26

Polyurethane

Flat ~

1

12

b

Flat

1 b

1 b

Cotton batting

Crevice

(a) Untested

(b) Some replicates self-extinguished on the substrate

(summarized in [3-20]) have shown that heavy cotton fabrics which contain high concentrations of alkali metal ions (see Table 2-9 and Appendix 2-7, Fabric 593-0177) have very low

cigarette ignition resistance. (A chair made with a similar Haitian cotton/cotton batting combination and ignited with a commercial cigarette placed into the crevice smoldered so

vigorously that it burst into flames in 22 minutes, the shortest such transition time on record [3-20,21].) It seemed of interest to test cigarettes which had shown low ignition

propensity on other substrates (including those used in the

full-scale tests discussed below) on such an approximately

worst case fabric. (Cotton batting without fabric cover or covered by very light weight fabrics— which are not generally

used in upholstered furniture or mattresses — may have an

even lower cigarette ignition resistance than the Haitian

cotton fabric covered substrates.) This fabric was used over

cotton batting as well as polyurethane foam, the former in both the flat and crevice configurations. There were zero or only one ignition with the low ignition propensity cigarettes

BELN-21, No. 106, FELN-21, No. 114, and Nos. 201 and

202. A cigarette with intermediate ignition propensity, FELN25, No. 130, produced three ignitions.

Three commercial cigarettes were used for comparison.

No. 6 had been found to have an ignition propensity which was typical of that of eight other commercial cigarettes; Nos.

1 and 2 had been found to have somewhat lower ignition

propensity [3-3]. The full-scale and comparative bench-scale experiments

described below further validated the ignition propensity

rankings obtained in the primary evaluation.

69

Comparison of Full-Scale

Furniture and Bench-Scale

Tests

Objective

The objective of these full-scale tests is to assess the validity

of the ignition data from the mini-mockup tests and thus

determine whether the apparent low ignition propensities of some of the experimental cigarettes are true.

Method

The furniture fabrics, padding, and welt cord were chosen

by UFAC and the chairs were manufactured under their supervision. Some of the chosen materials would not meet

UFAC standards. They represent various levels of cigarette

ignition resistance. The substrates included cotton batting

and polyurethane foam as padding, and four cotton fabrics and one olefin fabric (see Section 2). Four or six identical upholstered chairs were delivered at a time, and because of the short time for execution of the testing, were usually

completely tested before the next delivery. A chosen set of cigarettes was used on the cushion, and in the crevices of the chair.

Cigarette Selection, Handling and Coding

The test plan for this portion of the program was based on

the use of five cigarette types, spanning the range of possible fire safety modifications of cigarette design. The

types included a representative commercial design that was

expected to ignite most of the fabric-padding combinations

to be tested, three experimental cigarettes that probably

would not ignite these combinations, and one "in-between"

experimental cigarette. This selection was designed to provide a sensitive indicator of any differences in measuring

ignition propensity between these full-scale tests and the bench-scale test method.

The cigarettes were stored in a conditioning room at 55 ± 10% relative humidity and 22 ± 3°C. Enough cigarettes for one series of tests (5 to 10 of each kind) were removed from

the conditioning room, marked "A," "B," . . . "E" as

appropriate on the paper seam near the butt, and taken to the burn room (relative humidity about 30%). They were used over the times required for that day's tests. The

(arbitrary) cigarette designations used in the data book, in the data tables, and to mark sites were:

A. Commercial No. 6

B. Series 2, C. Series 1, D. Series 1, E. Series 1,

No. 201

No. 129 (FELC-25)

No 114 (FELN-21)

No. 106 (BELN-21)

All cigarettes had filters except Commercial No. 6.

Experimental Design

A rigorous experimental design was prepared for these tests, but proved to be impractical.

The original design involved randomizing the order of the

chairs and the placement of the different kinds of cigarettes, with several different cigarettes used simultaneously in each

test. The reasons this design was impractical are:

(a) Some cigarettes, if they were going to ignite the chair, would do so long before the other cigarettes had burned

to completion. Since we could not extinguish a single

smolder zone without affecting the other cigarette tests, the first smolder zone would grow massively. There was

always danger the massive zone would erupt into flaming, and in any event its smoke created a problem

and the large smoldering zone was difficult to extinguish.

(b) The chairs were generally delivered in groups of 4

(identical) chairs, several days apart. Each group of 4 was usually completely tested before the next groups

were available for test.

So each set of 4 chairs was fully tested as received, and

with all the cigarettes the same in a given test of a given

chair. Chairs were tested with cigarettes on the cushions and, (in separate tests) in the crevices as discussed under "Test Procedure."

71
Test Procedure for Full-Scale Furniture

Tests

Some difficulties or differences encountered during the

tests are described in a following section of this report.

General

As many as 4 chairs could be under test at any one time,

each with multiple (up to 5) cigarettes on it. All 4 chairs could be viewed through the window in the burn room door, as shown in Figure 3-1, and any resulting smoldering could

be extinguished by gaseous nitrogen injected into the smolder zone by a tube with small holes in the discharge

end (Figure 3-2). A thin aluminum foil disk with a central hole for the nitrogen tube was used to "seal off" the smolder zone to prevent air being entrained into the zone. Since it was possible that nitrogen would flow through the padding

to zones near other cigarettes, it was assumed that the use

of nitrogen might have an effect on possible ignition by the

other cigarettes on that chair. However, multiple identical cigarettes could be used on a single chair by delaying

extinction until all had yielded test data. As previously mentioned, the chairs in each group of four were identical. However, in most chairs the padding on the sides of the chair was different (cotton batting) from the padding on the back (polyurethane foam). In these cases

the side crevice was considered a different test than the back crevice.

Figure 3-1. Four Chairs as Viewed

Through the Window of the Burn Room.

Note that a Second Set of Cushions is in

Place Permitting Additional Cigarette Tests

in a Second Set of Crevices

•

Cigarette Location and Placement

The planned cigarette locations were randomized and

marked on the cushions as shown in Figure 3-3 and Figure

3-4. Cigarettes were ignited, allowed to burn in air for 1 minute (this reduced the tendency for the cigarettes to self- extinguish on the chair) and placed near, not on, the mark.

Crevices caused a special problem in cigarette placement.

Sometimes the cushions, as made, did not contact the sides

or backs closely to form a "right angle" joint. We always

adjusted the position and shape of the cushion, to the degree that was possible, to achieve a good joint, but sometimes an "acute angle" (wedge-shaped gap) was the

best possible fit. When placing cigarettes in crevices next to welt cords, the cigarettes were located on the chair side of the welt cord (against the arm or back of the chair). This was done as a precaution since some of the welt cord was

found to be smolder-resistant. A cigarette on the cushion

side of the welt cord might ignite the cushion, but this would

not constitute a crevice test. If the crevice was shaped so

that the cigarette could only be placed on top of the welt cord (Figure 3-5), of course this was done. Also, in the case

of an "acute angle" crevice, the cigarette might lie below the upper surface level of the cushion.

Extra cushions were requested and were provided so that an adequate number of crevice tests could be performed.

Figure 3-2. Gaseous Nitrogen Applicator Used to Estinguish Ignited Sites

72
After crevices next to the original cushion had been tested

(leaving scorch marks), the extra cushion was placed on top

of the original cushion, providing a second set of crevices

against the arms and back of the chair, not near the previous scorch marks.

As previously mentioned, each cigarette was marked on

the paper seam, near the butt, with its code letter. This

insured that the right cigarette was used, and that contact

with the fabric was not on the paper seam. The several ignited cigarettes were placed on the chairs at 10 second intervals. This facilitated measuring the time to

ignition, if ignition took place.

Criteria for Ignition

The three criteria selected for an ignition were:

(a) Size of smolder zone — at least 1 inch from the side or end of the cigarette scorch mark on the upholstery. The

padding must be involved. We experienced no self- extinguishments after the padding had been involved to

this degree. The scorch mark at C7 in Figure 3-3, for instance, was not deemed an ignition because the foam

padding was not involved. Instead, only the fabric smoldered, and then went out by itself.

(b) Amount of smoke - must be substantially more than

that from the cigarette alone. For an example, see Figure

3-4, location A5. Figure 3-3. Sites for Various Cigarette

Types Marked on a Damask Cushion,

With Burn Scars Near the Marks. There

were no Ignitions in these Tests

I

\

(c) Color of smoke — yellowish if the polyurethane foam is involved. In most of the crevice tests the padding was

cotton batting, so in those tests there was no yellow

smoke.

Tests could be viewed through the window in the door to the burn room, or by a technician in the burn room who wore a mask attached to a cylinder of breathing air (smoke from the polyurethane foam is irritating). The room had an air- handling system which included a separate supply and

exhaust, so no smoke leaked into the rest of the building.

If the cigarette self-extinguished before it fully burned, it was removed, and replaced by a new ignited cigarette of the same type near the same site. The summary tables of data are based primarily on results that would have been

obtained if the cigarette had not been replaced, but the

additional data are useful as a guide to the propensity of that cigarette design to ignite the fabric-padding

configuration.

Data from Full-Scale Tests

Locations of cigarettes, whether or not they ignited the

substrate, and if they did, the time to obvious ignition were

all recorded in the project data book, and into the attached

Figure 3-4. Sites for Various "Crevice"

Tests Marked on a "California Velvet"

Cushion. Site A5 is an Ignition - Note

Smoke. Site Al was Ignited, then

Extinguished in an Earlier Test

73
Figure 3-5. Cigarettes on Top of Welt

Cord When Cushion Shape Prevented

Placement Beside Welt Cord

summary tables (Tables 3-8A,B,C). In general there is one

table for each chair type. Chairs with welt cords are considered a different type than similar chairs without welt cords, and are recorded in separate tables.

Difficulties with the Procedure

Several contingencies are noted here that could potentially

affect the accuracy of the results.

Conditioning of the Chairs

The first chair tested was run within 2 hours after it had

been delivered by truck from the manufacturer. Probably it had been exposed to higher relative humidities than the

laboratory environment (about 30%). At any rate, it seemed

to ignite slightly less readily than sister chairs stored in the

laboratory one or more days. Subsequently all chairs were

stored in the laboratory at 30% relative humidity for one or more days before testing.

Drafts

In an early test (California velvet over cotton batting

padding -see Figure 3-4) where considerable smoke was

evolved, the door to the burn room was propped open

about 6 inches. The resulting draft could be seen to blow

the smoke around in a turbulent fashion. In the next test (a

crevice test with the same substrate) all the cigarettes ignited the crevice, whereas in an earlier crevice test on this kind of

chair, only the A cigarette had caused ignition. These latter data were discarded.

Later we measured the air velocities on the cushion under

these conditions. They were: Normal ventilation -20-25 ft/minute (7-8 m/min.)— few

gusts

Door propped open-40-60 ft./minute, (13-20 m/min.)

gusts to 80 ft./minute (26 m/min.)

Bench-scale tests— average 14 ft./minute (5 m/min. )— few

gusts

Note: a 1 mph breeze is 88 ft./minute (29 m/min.)

Subsequent tests on later chairs (all with polyurethane

padding) failed to show any effect of the drafts that occurred

with the door propped open. From time to time one of the test personnel would open

the door briefly, pass through it, and close it while a test was proceeding. This did not cause drafts since the automatic control system, designed to keep the burn room

at a slightly lower pressure than ambient, had a 15 second

delay. It would not cause a large air flow through the door

unless the door were held open for that length of timeSelf-extinguishment of Cigarettes

Cigarettes that self-extinguished were replaced with new

ignited cigarettes of the same type near the same site at least once to complete the test, but not before waiting about

10 minutes, to make sure that incipient smoldering had not occurred. In 63 of these cases, the second identical cigarette either ignited the substrate (25 cases) or burned

without igniting the substrate (38 cases). In 553 cases the second cigarette also self-extinguished.

Usually self-extinguishment occurred soon after the

cigarette was placed on the substrate, leaving only a minor

scorch mark on it; but in some cases the cigarette burned

longer before self-extinguishing. Therefore, we deemed it a

"self-extinction" if the scorch mark was less than 1 inch long,

and a "non-ignition" if longer than 1 inch.

Times to Ignition of Substrate

The times-to-ignition that were recorded are unavoidably

inexact. There is some subjectivity to deciding when ignition of the substrate is certain. One would expect, therefore, that the times-to-ignition would be greater than those determined

from weight loss traces in the bench-scale tests. This

comparison of full-scale and bench-scale tests was not made

because of the strong correlation of the ignition data. Further comparisons were considered redundant.

Crevice Shape

Difficulties with obtaining a proper crevice shape have been

described under "Cigarette Location and Placement." A few

74
tests were carried out with weights on the cotton batting

filled cushions (Figure 3-6) to cause "acute angle" crevices

similar to those that would be caused by an occupant sitting

in the chair. Foam cushions were so firm that this application

of weights did not change the shape of the crevice.

Figure 3-6. Weight on (Cotton Batting)

Cushion Simulating Seated Person

Causes "Acute Angle" Crevice Shape

Results

Validation of Bench-Scale Tests by Full-Scale Tests

Tables 3-8A, B and C list the percentage of ignitions for each cigarette type for each kind of chair construction and

each location on the chair (cushion, crevice with welt and

crevice without welt cord). These data are compared in the same tables with results of the bench-scale tests. It is concluded that the bench-scale tests are validated in 64 out

of the maximum possible 75 cases. The criterion for comparison is as follows:

The full-scale results are based on 10 or more cigarettes, and the bench-scale on 5

cigarettes. The results are considered in agreement if the percentage ignition would

be the same if one of the five bench-scale

single cigarette tests had come out

differently.

A further look at the results show that deviations from

bench-scale to full-scale agreement were distributed as

follows among the cigarette types:

lliiti?

Influence of Substrate on Cigarette Burning

With heavy cotton velvet, two of the commercial cigarettes, No. 6, caused smoldering ignition of a welt cord crevice after the cigarettes smoldered for times of 58:45 and 61:00

minutes. The other identical cigarettes either did not ignite or self-extinguished before burning completely. Usually, if ignition were to happen it would occur in 20 minutes or less. Without the welt cord this unfiltered cigarette caused crevice

ignition in 30-36 minutes. We have no explanations, only

conjectures, for the long cigarette burn times. As for substrate ignition at the end of cigarette burning, it has been

observed by others [3-16] that an unfiltered cigarette can

ignite a substrate at the end of burning because the

cigarette coal at that time gets ventilation from both sides,

and can burn hotter.

Type of CigaretteNo. of Agreement

No. of Non- agreement Comments

A (6)

B (201) C (129) D (114) E (106)

14

14

111213

1

14

3_2

a commercial cig. No. 6 [3-3] low ign. propensity an "in between" cig. low ign. propensity low ign. propensity Tota 64 11

Thus those cigarettes with low ignition propensity (B, D, and

E) and those with normal ignition propensity (A) gave results such that the full-scale tests and the bench-scale tests agreed in 53 out of 60 cases. The conclusion is that the bench-scale tests can be used

with a high degree of confidence to predict full-scale performance. This is in agreement with findings by the Consumer Product Safety Commission laboratories which

tested full-scale, commercial chairs and then mockups made

from the remaining materials [3-22]. The agreement between

the tests was good in those cases when the same fabrics were used in both tests.

75
Table 3-8A. Summary of Full-Scale Furniture Test Results

(First cigarette per test only)

Hjbra_^_

Material Location Cig. Type Ignitions Tests %

Bench-scale Comparisons

Ignitions No. of Tests % Ignition

Calif Cushion A 12 12 100 5 5 100

velvet B 9 12 75 5 over C 12 13 92 5 5 100

cotton D 10 12 83 2 5 40

batting E 5 12 42 1 5 20

Calif Crevice A 14 14 100 5 5 100

velvet (no welt B 4 24 17 5 over cord) C 12 14 86 5

cotton D 8 19 42 1 5 20

batting E 3 19 16 5

Calif Crevice A 10 10 100 5 5 100

velvet (with welt B 10 5 over cord) C 7 15 47 1 5 20

cotton D 2 17 12 1 5 20

batting E 14 1 5 20

"Splendor" Cushion

(cotton) A 10 10 100 5 5 100

over P.U. B 16 5 Foam C 10 10 100 2 5 40

D 8 11 73 1 5 20

E 3 10 30 5

"Splendor" Crevice

(cotton) (no welt A 10 10 100 5 5 100

over P.U. cord) B 20 5 Foam C 1 19 5 5 D 20 5 E 20 5

"Splendor" Crevice

(cotton) (with A 10 10 100 5 5 100

over P.U. welt B 20 5 Foam cord) C 20 5 D 20 5 E 20 5

F

a 4 4 100

(a) Commercial Series 3

76
Table 3-8B. Summary of Full-Scale Furniture Test Results

(First cigarette per test only)

Material Location Cicj. Type Ignitions Tests °/o

Bench-scale Compa risons

Ignitions No. of Tests °/o Ignition

Damask Cushion A 10 6

over B 12 6

Foam C 11 6

D 11 6

E 10 6

Damask Crevice A 10 10 100 6 6 100

over B 3 20 15 6

cotton C 6 15 40 1 6 17

batting D 2 18 11 6 E 1 19 5 6

Damask Crevice A 10 10 100 6 6 100

over with welt B 20 6

cotton cord) C 2 19 11 6

batting D 1 20 5 6

E 1 20 5 6

Heavy Cushion A 10 5

velvet B 16 5 over C 13 5 Foam D 13 5 E 11 5

Heavy Crevice A 8 11 73 4 5 80

velvet B 20 5

over C 20 5

cotton D 20 5

batting E 20 5

Heavy Crevice A 2 12 17 4 5 80

velvet (with B 20 5

over welt C 20 5

cotton cord) D 20 5

batting E 20 5

77
Table 3-8C. Summary of Full-Scale Furniture Test Results

(First cigarette per test only)

HHHHJfflHMnnHHgffi HMMunn

HUffilHi

Material Location Cig. Type Ignitions Tests %

Bench-scale Comparisons

Ignitions No. of Tests % Ignition

Olefin Cushion A 2 10 20 5 over B 10 5 Foam C 10 5 D 10 5

E 10 5

Crevice A 6 10 60 3 5 60

(against B 19 5

side- C 1 16 6 1 5 20

cotton D 13 5

batting) E 16 5

Crevice A 10 10 100 5 5 100

welt cord B 20 5

(side-with C 18 5

cotton D 19 5

batting E 20 5 padding)

Crevice A 1 4 25

(Back-P.U. B 4 Foam) C

D

E

4

4

4

Crevice A 4 4 100

with welt B 4 cord back C

D

E

4

4

4

78
Table 3-9. Numbers of Tests and Results Full-Scale and Bench-Scale, Various

Cigarettes and Substrates

HBMWMHHMHMMHnMHHnMnagMHMHHnOM MM|MMU|HHn

A C E D B

Cig. Type

Substrates

C-6 #129 #106 #114 #201

Ign

12

Tof SE

12

Ign

12

Tot

a

1

SE

13

Ign

5

Tof SE

12

Ign

10

Tot

a SE

12

ign

9

Tot

a SE

CA.fl FS 12 BS 5 5 5 5 \ 5 2 5 5 CA,Cr FS 14 14 12 2 14 3 7 19 8 7 19 4 18 24 BS 5 5 5 5 5 5 1 4 5 5 5

CA,Cr,wlt FS 10 10 7 8 5 14 18 2 12 17 18 19 BS 5 5 1 4 5 1 4 5 1 3 5 5 5 CA,Cr

a FSBS

FS

5 5 5 1 6 3 1 6 4 5 9 2 5 8

Sp1,f1 10 10 10 10 3 10 8 1 11 8 16 BS 5 5 2 3 5 2 5 1 3 5 5 5 Sp1,Cr FS 10 10 1 18 19 20 20 20 20 20 20 BS 5 5 5 5 5 5 5 5 4 5 Sp1.Cr.wlt FS 10 10 20 20 20 20 20 20 20 20 BS 5 5 5 5 5 5 4 5 5 5

Vel.fl FS 10 3 13 1 11 5 13 9 16 BS 5 3 5 3 5 5 5 5 5

Vel.Cr FS 8 1 11 20 20 20 20 20 20 20 20 BS 4 5 5 5 5 5 5 5 5 5

Vel.Cr.wlt FS 2 1 12 3 20 20 20 20 20 20 20 20 BS 4 5 5 5 5 5 5 5 5 5

Da.fl FS 10 1 11 10 2 11 3 12 BS 6 2 6 1 6 3 6 4 6 Da.Cr FS 10 10 6 9 15 1 18 19 2 16 18 3 17 20 BS 6 6 1 5 6 6 6 6 6 5 6

Da,Cr,wlt FS 10 10 2 17 19 1 19 20 1 19 20 20 20 BS 6 6 6 6 6 6 5 6 5 6

Ole.fl FS 2 10 10 10 10 10 17 BS 5 5 1 5 5 2 5

Ole.Cr FS 6 10 1 8 16 10 16 6 13 19 16 BS 3 5 1 1 5 1 5 5 2 5

Ole.Cr.wIt FS 10 10 17 18 19 20 9 19 20 20 BS 5 5 4 5 4 5 5 5 5 5 177 4 242 66 198 317 18 222 329 40 215 330 18 286 361 % 73 2 21 62 5 67 12 65 5 79 % Ignitions Full-scale 73 23 6 14 6 Bench-scale 74 13 3 6

Legend: Ign - means number of ignitions Da - damask

SE - means number of self- extinguisshments Ole — olefin fabric Tot - means total number of tests fl - flat (on a cushion)

CA - California velve cr - crevice

Spl - Splendor fabric wit - welt cord

Vel - heavy cotton velvet

a Total tests run for a given cigarette type on a given substrate. This includes three possible results: ignition, self-extinguishment, or a cigarette burning

its entire length without causing substrate ignition.

bcrevice formed by weights on cushion

79
Validation Results Weighted by Numbers of Tests

Table 3-9 presents actual results of both bench-scale and

full-scale tests, arranged with substrate types as rows and

cigarette types as columns. The "%" rows near the bottom of the table show first the weighted (by number of tries) percentages of ignition, then self-extinguishments, and these

are compared with the weighted percentages for the full- scale tests and the bench-scale tests. Several conclusions are obvious:

1. The percentage ignitions of the experimental cigarettes

(range 7-35%) are a different population than that of the commercial No. 6 cigarette (73%). In fact, the "in- between" cigarette, #129, at 35% ignitions, is different than the three low ignition propensity cigarettes (7-11%).

Recall, these data are with a variety of substrates.

2. There are no differences in conclusion no. 1 if it had

been arrived at by considering bench-scale tests alone or

full-scale tests alone.

3. The literature concludes that commercial cigarettes are more likely to ignite the substrate if they are located in crevices. This is also true for the commercial No. 6

cigarette in this project. But the experimental cigarettes are not more likely to ignite substrates in crevices than on

flat surfaces.

4. The overall percentages of "self-extinctions" range from

0.4% for the commercial cigarette (only two of the many

cigarettes and only on one substrate) to 51-69% for the experimental cigarettes. It is tempting to conclude that a

major reason for the success of the experimental

cigarettes is that they self-extinguished when on the

substrate. However, examination of the data in Table 3-9 and the note on the table, show that there are many tests where the experimental cigarette did not self-extinguish, but still did not ignite the substrate.

5. Self-extinctions are also very much affected by the

substrate and the location (flat surface, crevice, or crevice

with welt cord). If the location, cigarette, and substrate are

all kept constant, many cigarette types either did all self- extinguish or not self-extinguish, whether full-scale or bench-scale. With another substrate or location on the same substrate, the results could be totally different.

Use of Kendall's Tau Correlation Coefficient to Summarize the Agreement Between Full-Scale and

Bench-Scale Tests

In Appendix 3-B is a memo from Dr. Keith R. Eberhardt of the Statistical Engineering Division of NBS giving a statistical analysis of the data. Most statistical methods are difficult to apply to these data, but Dr. Eberhardt was able to test the hypothesis that there is "no relation between the full-scale data and the bench-scale data." The hypothesis was rejected

at a significance level of 0.01%.

Relative Ranking of Cigarettes in Full-Scale Tests and

the Primary Evaluation

Table 3-8 summarizes the ignition results obtained in the full- scale tests. The cigarettes had been chosen on the basis of the primary evaluation to represent a high ignition propensity

cigarette — commercial, No. 6, an intermediate cigarette, 129,

and three low ignition propensity cigarettes, 106, 114, and

201. These rankings were fully confirmed by the full-scale

results, as well as the corresponding bench-scale (mockup)

results. Table 3-9 lists the number of self-extinguishments. There were essentially none for No. 6. For the other cigarettes the

results were substrate dependent, with no major differences between the four experimental cigarettes.

This seems to indicate that a common mechanism for self- extinguishment prevailed in those cigarettes, in spite of their differences in burn rates in air and other physical

characteristics.

80
Average Per Puff Tar,

Nicotine, and CO Yields

of Experimental Cigarettes

The Federal Trade Commission and Lorillard Laboratories

results for per cigarette tar, nicotine, and CO yields are discussed in Section 2. Tar, nicotine and CO yields are

generally used to compare commercial cigarettes. These

measurements do not tell the whole story about toxic effects

of other smoke constituents which could differ for the experimental cigarette and commercial cigarettes. This

section deals with per puff yields of the experimental

cigarettes. This is important because the number of puffs of the experimental cigarettes varied widely but could be

adjusted to the commercial norm, 7 to 9 [3-9], if the

cigarettes were produced commercially. It was found that one of the low ignition propensity cigarettes, BELN-21,

No.106, had per puff yields comparable to the average yield

of 25 per cent of U.S. commercial cigarettes. Other low

ignition propensity cigarettes had higher per puff yields. The

details are given below. The per puff yields are given in Tables 3.10 and 3.11. For comparison, the average yields per puff of the six most

popular cigarette packings which represent about 25

percent of the market were the following: tar, 2.0 mg;

nicotine, 0.13 mg, and CO, 1.7 mg [3-22, 23]. (The puff counts for these packings were obtained from the FTC

[3-25].) The puff count can be adjusted to the norm by increasing

or decreasing the cigarette length. Thus the low ignition

propensity cigarette BELN-21, No. 106, with a low puff

count, could be made longer, and the high puff count

cigarette No.201, shorter. It should, however, be noted that the per puff yields increase as the cigarettes become shorter

[3-25], so that shortening would not reduce the yields in direct proportion to the length. Nevertheless, the per puff

yields results would still provide guidance for attempts to design cigarettes with both acceptable yields and low

ignition propensity.

Table 3-12 shows the effects of the Series 1 cigarette

design variables on per puff yields. No statistical analysis of the results is indicated in view of the above mentioned

uncertainties. In general, the trends shown correspond to what would be expected from the results of research in this area [e.g., 3-26].

The design factors which reduced available tobacco, i.e., use of expanded, large particle size tobacco and smaller circumference, also reduced per puff yields as well as

ignition propensity.

On the other hand, low paper permeability, which was

second in importance in reducing ignition propensity,

resulted in substantial increases in the per puff yields.

However, it should be kept in mind that the high permeability

paper in these experimental cigarettes was purposely

chosen to be higher than that commonly used in most

commercial cigarettes, accentuating the differences due to paper permeability in this series. Also, as mentioned before, other means for reducing yields are available. The cigarettes containing flue-cured tobacco had higher per puff yields than the Burley cigarettes. However, the tobacco type had no significant effect on ignition propensity.

The effect of the presence of citrate in the cigarette paper

appears minor for per puff yields; however, the paper of the low ignition propensity cigarettes did not contain citrate. The tar, nicotine, and CO yields per cigarette and per puff

yields of the Series 2 cigarettes (Table 3-11) decreased, in the first approximation, with increasing paper permeability,

regardless of whether the increase was caused by

perforation, embossing, or both. The ignition propensity

increased with increasing permeability. Addition of the highly

permeable, thin second paper layer had only little effect on

yields or ignition propensity.

81
Table 3-10. Per Puff Tar, Nicotine and Carbon Monoxide Yields of Series 1

Experimental Cigarettes

Cigarette Packing

Per Puff Yield Burn Rateb

Tar Nic. CO linear mass Number Ignitions density mga mga mga mm/min mg/min

101 13 0.24 2.47 0.18 2.73 5.79 54.9

102 12 0.25 2.75 0.20 2.63 4.80 45.6

103 17 0.25 1.76 0.16 1.89 7.42 71.5

104 19 0.24 2.03 0.18 1.76 6.82 64.4

105 6 0.16 1.55 0.09 1.90 7.77 47.2

106 1 0.17 1.83 0.10 2.00 6.58 39.8

107 11 0.17 1.03 0.07 1.03 9.99 59.6

108 7 0.14 1.25 0.09 1.07 8.89 53.3

109 15 0.31 2.50 0.21 1.96 4.46 49.4

110 16 0.31 2.19 0.19 1.56 3.40 40.3

111 19 0.32 1.92 0.18 1.44 5.30 62.3

112 20 0.31 1.84 0.17 1.23 4.96 57.9

113 6 0.15 2.41 0.19 2.24 7.34 42.4

114 4 0.15 2.58 0.21 2.12 5.52 33.8

115 14 0.17 1.72 0.14 1.55 8.99 55.2

116 12 0.15 1.88 0.16 1.25 7.58 45.6

117 18 0.24 2.62 0.20 3.21 5.84 72.5

118 18 0.24 2.84 0.22 2.84 4.78 58.9

119 20 0.23 2.08 0.18 2.34 7.60 93.1 120 20 0.23 2.14 0.19 1.79 6.72 83.2

121 14 0.14 2.14 0.13 2.68 8.11 61.2

122 7 0.13 2.42 0.15 2.42 6.38 46.8

123 15 0.14 1.48 0.09 1.85 10.63 78.2

124 15 0.14 1.55 0.10 1.38 9.12 67.6

125 18 0.28 2.46 0.21 1.92 4.05 61.7

126 17 0.28 2.46 0.20 1.74 3.46 51.1 127 20 0.28 2.23 0.21 1.79 5.08 75.5 ! 128 20 0.29 2.41 0.21 1.52 4.58 69.1

129 10 0.16 2.26 0.18 2.02 5.17 44.2

130 4 0.16 2.50 0.20 2.16 3.88 33.6

131 15 0.21 0.96 0.08 0.87 6.43 61.9

132 12 0.16 1.90 0.17 1.31 5.27 45.1

(a) Based on FTC data.

(b) Data from the Lorillard Laboratories (see Table 2-5)

82
Table 3-11. Per Puff Tar, Nicotine and Carbon Monoxide Yields of Series 2

Experimental Cigarettes

Cigarette

Number Ignitions

Packing

density

mg/mm3 Per puff yields, mga Tar Nic. CO

201 0.14 2.5 0.18 2.5 202 2 0.16 2.0 0.16 2.4 203 7 0.15 1.7 0.14 1.8 204 11 0.16 1.3 0.11 1.2 205 11 0.16 1.2 0.11 1.0 206 8 0.16 2.4 0.18 3.2 207 7

' 0.16 1.9 0.15 2.3 208 14 0.16 1.6 0.13 1.7 209 13 0.16 1.4 0.12 1.5

(a) Based on FTC data

' Burn rates not available

Table 3-12. Per Puff Tar, Nicotine and CO Yields

as a Function of Cigarette Parameters

MHH^n

Experimental Cigarette Series 1

Cigarette parameters

Per Puff Yields (mg)

e Number of Tar Nicotine Monoxid Ignitions

Tobacco Packing Density

High 2.29 0.19 2.02 282

Low 1.84 0.13 1.74 153

Paper Permeability

High 1.76 0.15 1.50 256

Low 2.37 0.18 2.26 179

Cigarette Circumference (mm)

25 2.15 0.17 1.99 243

21 1.98 0.16 1.77 192

Paper Citrate Cone. (%)

0.8 1.97 0.16 1.96 231

0.0 2.16 0.17 1.80 204

Tobacco Type

Flue-cured 2.14 0.18 1.67 222

Burley 2.00 0.15 2.10 213

83

Summary of Characteristics

of Experimental, Low Ignition

Propensity Cigarettes

Table 3-13 compares ignition propensities and certain other

characteristics of selected experimental cigarettes from

Series 1 and Series 2. For comparison, the results are included for three commercial cigarette packings; one, No.

6, had been found to have typical (for current production)

ignition propensity and No.2, slightly lower than typical

ignition propensity in the previous investigation [3-3]. Not all cigarettes were tested on all substrates; cigarettes for this work were selected over a period of many months during

which time the interest in various cigarette design variables was subject to change as various findings were made. The

following can be deduced from the data:

• The selected low ignition propensity experimental

cigarettes had considerably lower ignition propensity when

tested on a wide variety of substrates, including some

with very low cigarette ignition resistance, than even the

relatively low ignition propensity commercial cigarette

packing.

• The ignition propensity rankings of the cigarettes were

approximately the same on all substrates.

• The low ignition propensity experimental cigarettes

covered a wide range of linear burn rates in air. It had

generally been assumed that only cigarettes with low burn

rates — causing self-extinguishment in air— could have a

Table 3-13. Summary of Characteristics of Selected Cigarettes

82&tiiiff±##9 ——Number of Ignitions (%) Burn Rates' Per Puff Smoke Yieldsf

Primary HA Full- Comparable Linear Mass Tar Nicotine CO

Cigarette No. Eval. a CB/PUb Scale' Mockupsd mm/min mg/min (mg) (mg) (mg)

106 BELN-21 5 10 10 3 6.58 39.8 1.83 0.10 2.00

114 FELN-21 20 10 7 6 5.52 33.8 2.58 0.21 2.12

129 FELC-25 50 — 35 13 5.12 44.2 2.26 0.18 2.02

130 FELN-25 20 30g — — 3.88 33.6 2.50 0.20 2.16

201 10s 11 — — 2.5 0.18 2.5 Commercial

1 80h — — — — — — - -

2 60h 100 — — — - - - -

3 901 — — — — — - - -

6 1001 100 74 74 — — — — —

(a) 20 tests

(b) 1 tests

(c) Variable numbers tests

(d) 105 tests

(e) Data from the Lorillard Laboratories

(f) Based on FTC data

(g) Many of these cigarettes self-extinguished on these substrates

(h) Found to have relatively low ignition propensity in [3-3]

(i) Found to have normal ignition propensity in [3-3]

85
low ignition propensity [3-14]. The experimental low

ignition propensity cigarette with the lowest burn rate, FELN-25, No. 130, often self-extinguished on some of the

substrates while other replicates burned their whole

length, in most cases without causing smoldering

ignitions. Cigarette 202 also tended to self-extinguish in

air. However, the low ignition propensity cigarette BELN21, No. 106, had a high linear burn rate, and did not self- extinguish in air. One of the low ignition propensity cigarettes, BELN-21,

No. 106, had considerably lower per puff tar, nicotine, and

CO yields than the other low ignition propensity cigarettes.

As discussed in detail in Section 4, it appears that

lessened heat transfer to a substrate can be caused by

reduction in heat output of cigarettes due to partial

blocking of oxygen influx by the substrate, as well as by

the substrate heat sink effect. If the heat output rate is low

because of low tobacco content per unit length, or if the oxygen supply (which is already partially blocked by the

substrate) is further restricted by low permeability paper,

or by a combination of both factors, low ignition

propensity can be achieved, even though the cigarette

does not self-extinguish in air. Other factors, such as

generation of smoldering inhibiting gases including water vapor and carbon dioxide may also play a role [3-27].

Table 3-14. Ignition Propensity of Patented Cigarettes MHgMHjl^i , .^___

Total

Cigarette

Burns

in air

weight

(g)

Substrates Ign. HA/CB HA/PU SPL/PU CA/CB CA/CB (0/0) a

301 -C yes 1.06 5/5 5/5 5/5 5/5 5/5 100

301 yes 1.10 8/10 1/10 5/10 7/10 8/10 58

302-C yes 0.93 5/5 5/5 5/5 5/5 4/5 96

302 no 0.94 3/10 2/10 2/10 1/10 2/10 20

303-C yes 0.99 5/5 5/5 5/5 5/5 5/5 100

303 yes 0.98 6/10 0/10 2/10 18/20 6/10 53

304-C yes 1.14 5/5 5/5 5/5 5/5 5/5 100

304 yes 1.18 9/10 8/10 10/10 4/10 2/10 66

305-C yes 0.99 5/5 5/5 5/5 5/5 5/5 100

305 no 1.00 3/20 4/10 3/10 1/10 2/10 22

All tests on flat substrate; some cigarettes with firestops self-extinguished on mockups.

Fabrics: HA - Haitian cotton SPL - Splendor

CA - California standard Padding: CB - Cotton batting PU — Polyurethane foam

Cigarettes: C - Controls submitted with patented cigarettes

(a) a half of tobacco column removed

86
Patented Cigarettes

The ignition propensities of five embodiments of patented

cigarettes and of the controls submitted with each of them

were evaluated. In short, it was found that all the embodiments showed improvement over those designated

as controls. The details are discussed below. The patented cigarette embodiments and the controls submitted with them were tested in three of the modes used

in the primary evaluation. Instead of evaluating them on the

relatively high ignition resistance denim substrate which had

been used in the primary evaluation, they were tested on the

very low cigarette ignition resistance Haitian cotton

substrates. Table 3-14 shows the ignition results. When the patented

cigarettes showed poor reproducibility, the number of cigarettes tested was increased. The number of ignitions is presented as a percentage of total possible ignitions.

All of the cigarettes submitted as controls caused

essentially 100 percent ignitions.

The patented cigarettes caused ignition in 20 to 66

percent of the cases. The overall differences between the patented cigarettes and the controls were significant at the

0.01 percent level. (A method suggested by Cochran for combining information in 2 x 2 tables was used in this analysis [3-28].) The information submitted by the inventors indicates that only limited development work had been

performed prior to submission of the cigarettes in most

cases; further improvements may be possible.

Two patented cigarettes used the firestop concept by

placing obstacles in the path of the smolder front. These

cigarettes self-extinguished at their firestops when burning in

air, and, in our experiments, also on the substrates. Unless

puffed at such firestops, the cigarette will go out. If the number of firestops is too small, the cigarette may ignite the

substrates; smoldering ignition of substrates can occur in as

little as 2 minutes [3-29].

87

Summary and Conclusions

The propensities to ignite soft furnishings substrates of 41 systematically varied experimental cigarettes and five patented cigarettes were compared to those of commercial

cigarettes. Some experimental and patented cigarettes

performed distinctly better. A combination of low tobacco content per unit length (low

packing density and low circumference of the cigarettes)

and low paper permeability and paper citrate content produced cigarettes which did not ignite most substrates used in our experiments. These substrates included some

which, on the basis of a large number of investigations

[summarized in [3-20], would be expected to have very low

cigarette ignition resistance and which were readily ignited

by commercial cigarettes, even one which had previously

been found to have relatively low ignition propensity. One

could expect the proportion of upholstered furniture which

would be ignited by the low ignition propensity experimental

cigarettes to be small. The low ignition propensity of these cigarettes was

demonstrated under a wide variety of conditions which

could occur in real life. These included full-scale chair tests, as well as a large number of bench-scale tests on substrates

in the lower cigarette ignition resistance range; on flat surfaces and in crevices of various configurations; and on

full length cigarettes and on short cigarettes, simulating

partially smoked cigarettes. Similarly, low ignition propensity

of the same cigarette was demonstrated, albeit less clearly,

in limited experiments on new fabric and on fabrics which

had been intentionally contaminated with smolder-promoting

agents, as well as on fabrics badly soiled in use. However, no claim can be made that the present experimental

cigarettes would prevent all cigarette initiated fires. Based on

the fact that they did not readily ignite substrates which have

very low ignition resistance, one could expect that the number of soft furnishings in use which would be ignited by

them would be small. High ambient air velocity may

increase ignition propensity. However, the number of such

cigarette-caused ignitions would clearly be reduced.

Another important finding is that low ignition propensity

does not necessarily lead to unacceptably high tar, nicotine and CO yields as had been proposed [e.g., 3-14]. The five patented cigarettes which were submitted by their inventors exhibited various levels of ignition propensity, all significantly lower than the controls submitted with them.

From the present results, it is not possible to state which of the invention concepts would give the best results.

89

references for Section 3

[3-1] McCarter, R.J., Smoldering Combustion of Cotton and Rayon, J. Consumer Product Flammability, 4, 346-358 (1977).

[3-2] Shafizadeh, F., Bradbury, A.G.W., deGroot, W.F. and

Aanerud, T.W., Role of Inorganic Additives in the Smoldering Combustion of Cotton Cellulose, Industrial and Engineering Chemistry, Product Research and

Development 21, 97-101 (1982).

[3-3] Krasny, J.F., and Gann, R.G., Relative Propensity of Selected Commercial Cigarettes to Ignite Soft Furnishings Mockups, NBSIR 86-3421, [U.S.] Nat. Bur. Stand. (1986).

[3-4] Important Information from UFAC (Test Methods),

Upholstered Furniture Action Council, High Point, NC

(1985).

[3-5] The Business and Institutional Furniture Manufacturer's Association First Generation Voluntary

Upholstered Furniture Standard for Business and

Institutional Markets, BIFMA, Grand Rapids, Ml

(1980).

[3-6] Freeman, M.F., and Tukey, J.W., Transformations

Related to the Angular and the Square Root, Anal, of Mathematical Statistics, 21, 607-611 (1950).

[3-7] Box, G.E.P., Hunter, W.G., and Hunter, J.S., Statistics for Experimenters, New York: John Wiley

and Sons (1978).

[3-8] Dixon, W.J., and Massey, F.J., Introduction to

Statistical Analysis, 3rd ed., pp 335 ft, New York: McGraw Hill Book Co. (1969).

[3-9] Samfield, M., personal communication (April 1986).

[3-10] Keith, C.H., Physical Methods for the Modification of Tobacco Smoke, Banbury Report, G. Gori and F.G. Bock editors, Cold Spring Harbor Laboratory (1980).

[3-11] Owens, W.F., Jr., Effect of Cigarette Paper on Smoke

Yield and Composition, Recent Advances in Tobacco

Science, 4, 3-24 (1978).

[3-12] Selke, W., personal communication (June 1986).

[3-13] Schur, M.O. and Rickards, J.C., The Design of Low

Yield Cigarettes, Tobacco Science 4, 69-77 (1960).

[3-14] Spears, A.W., A Technical Analysis of the Problems

Relating to Upholstered Furniture and Mattress Fires Relative to Proposed Cigarette Legislation Including a Review of Relevant Patents, Testimony,

[3-15]

[3-16]

[3-17]

[3-18]

[3-19]

[3-20]

[3-21]

[3-22]

[3-23]

[3-24]

[3-25]

Subcommittee on Health and the Environment,

Committee on Energy and Commerce, U.S. House of Representatives (March 21, 1983).

Klancnik, A., Sealy, Inc., Presentation to the Technical Study Group of the Cigarette Safety Act of 1984 (1985).

Loftus, J.L., Back-Up Report for the Proposed

Standard for the Flammability (Cigarette Ignition

Resistance) of Upholstered Furniture, PFF 6-76,

Appendix G1, NBSIR 78-1438, [U.S.] Nat. Bur. Stand., (1978).

Viau, R. and Kasem, M.A., Some Aspects of Fire Safety of Upholstered Furniture and Mattresses,

Presented at the Ninth International Conference on

Fire Safety, San Francisco, CA (Jan. 1984).

Harabin, D., Ostrander, E.R., and Stout, E.E., Properties of Textile Upholstery Fabrics and Their

Importance to Consumer Satisfaction, (Bulletin 1032).

Cornell University Agricultural Experiment Station,

Ithaca, NY (May 1973).

Shaw, A. and Gill, J.T., The Smoldering Behavior of Selected 100 Percent Cotton Fabrics in Combination

with Three Different Batting Materials, AATCC

International Conference, Chicago, IL (1984).

Babrauskas, V., Krasny, J., Fire Behavior of Upholstered Furniture, Monograph 173, [U.S.] Nat. Bur. Stand. (1985).

Braun, E., Krasny J., Peacock, R.D., Paabo, M., Smith, G.F, and Stolte, A., Cigarette Ignition of Upholstered Chairs, J. Consumer Product

Flammability, 9, 162-183 (1982).

Upholstered Furniture Flammability Briefing Package:

Reference 14: Fairall, P. and Madison, R., Analysis of Upholstered Furniture Test Program; Reference 15: Pressler, C. and Oakley, M., Upholstered Furniture Test Methods and Data Summary; Reference 41:

Fairall, P., Relationship of Small-Scale Testing to Full- Scale Furniture Performance, U.S. Consumer Product

Safety Commission (1981).

"Tar", Nicotine, and Carbon Monoxide of the Smoke

of 207 Varieties of Domestic Cigarettes, Federal

Trade Commission, Washington, DC (1985).

The Maxwell Report, New York, NY (1986).

Pillsbury, H.C., Federal Trade Commission, personal

communication (1987).

91
[3-26] DeBardeleben, M.Z., Claflin, W.E. and Gannon, W.F., [3-29] Krasny, J.F., Allen, P., Maldonado, A., Juarez, N., Role of Cigarette Physical Characteristics on Smoke Development of a Candidate Test Method for the Composition, Recent Adv. Tob. Sci. 4, 85-111 (1978). Measurement of the Propensity of Cigarettes to [3-27] Norman, V., Some Considerations Concerning the Cause Smoldering Ignition of Upholstered Furniture Heat Output of Cigarettes, presentation to Technical and Mattresses (NBSIR 81-2363) [U.S.] Nat. Bur. Study Group (March 1985). Stand. (1981).

[3-28] Cochran, W.G., Some Methods for Strengthening the Common x

2 Tests, Biometrics, 10, 417-451 (1954).

;

92
Appendix 3-A

Statistical Analysis of Ignition

Propensity Data for Series #1

Experimental Cigarettes

Prepared by Keith R. Eberhardt

Analysis of Variance for Table 3.1

The data in Table 3.1 constitute a complete 25 factorial design for each of the four substrates. To adjust for the fact that the basic data in Table 3.1 are count data, and thus not normally distributed, the response

variable used in the analysis was obtained by using the Freeman-Tukey modification of the commonly used angular

transformation [3-6], The formula is Y = 0.5*| ARCSIN( SQRT(IGNS/6) ) + ARCSIN( SQRT((IGNS+1)/6) ) | where IGNS denotes the number of ignitions (out of 5 trials). After transformation, the data were analyzed by standard

Analysis of Variance (ANOVA) methods [3-7]. The results of the ANOVA are presented graphically in Figures 3-A-1 through 3-A-4, and are summarized numerically in the table. Figures 3-A-1 through 3-A-4 and the table show that two

factors, namely, Packing Density and Permeability, were

Table 3-A-1. Significance Probabilities (in Percent) of Design Factors for Series

#1 Cigarettes

(Experimental error was estimated from 4- and 5-way interactions.)

Substrate

SPL/PU

CA/CB SPL/PU unc./flat Denim/PU

unc./flat unc./flat (

1/2 cig.) crev./cov.

Factors D (Packing Density) 0.05 0.10 0.01 0.01 P (Permeability) 0.08 0.23 0.69 0.01 R (Circumference) 0.03 85 2.7 0.01 C (Citrate Cone.) 25 2.0 0.69 7.6 T (Tobacco Type) 8.9 52 56 7.6

Interactions

D*P 1.55 0.23 0.69 0.01 D*R 0.45 85 2.7 0.01 D*C 43 2.0 0.69 7.6 D*T 45 52 56 7.6 P*R 0.93 52 39 5.5 P*C 45 6.6 85 21 P*T 17 85 7.4 21 R*C 29 85 62 2.2 R*T 8.9 3.8 2.8 2.2

C*T 45 52 62 81

93
Figure 3-A-1. Normal probability plot of

estimated factorial effects from a 25 factorial analysis of variance for the

substrate CA/CB, unc/flat. if none of the

factorial effects were significant, the data would cluster

about a single straight line on the plot. The factors are coded as: 1 = Citrate, 2 = Paper permeability, 3 =

Packing density, 4 = Tobacco type (Burley or flue- cured), 5 = Circumference (21 mm vs. 25 mm). The

indicated 95% and 99% limits on the plot are computed using the 4- 5-way interaction terms to esti- mate experimental error. These limits correspond,

respectively, to 5% and 1% tests of the hyopthesis that

the factorial effects are zero.

Figure 3-A-2. Normal probability plot of

estimated factorial effects from a 25 factorial analysis of variance for the

substrate SPL/PU, unc/flat. if none of the

factorial effects were significant, the data would cluster

about a single straight line on the plot. The factors are coded as: 1 = Citrate, 2 = Paper permeability, 3 =

Packing density, 4 = Tobacco type (Burley or flue- cured), 5 = Circumference (21 mm vs. 25 mm). The

indicated 95% and 99% limits on the plot are computed using the 4- and 5-way interaction terms to estimate experimental error. These limits correspond,

respectively, to 5% and 1% tests of the hypothesis that

the factorial effects are zero.

J- ff

0.3 - % f

i>- /

0.2 - * 'If /

0.1 - 'UJ--

0.1 - **/

2 - 7

0.3 -

0.« -

J J

99*

95*

9S*

99*

95*

- *>*

^p,

? J VJ-A*

J' 1

" 1 1 1 1 r

NORMAL PROBABILITY PLOT NORMAL PROBABILITY PLOT

highly significant consistently across all four substrates. Two

additional factors, Circumference and Citrate Concentration,

showed clear significance in two of the four substrates. The

factor for Tobacco Type (i.e. burley vs. flue-cured) did not show a significant effect on number of ignitions on any of the four substrates. The interactions among these factors were frequently

significant whenever the factors were. Generally, the pres- ence of a significant interaction indicates that the magnitude

of the effect on ignition propensity for an given factor is not constant across the levels of the interacting factor. For example, on the CA/CB substrate, the significant interaction between Packing Density and Circumference indicates that the effect of Packing Density on ignition propensity is different in magnitude for the smaller circumference

cigarettes than for the larger circumference cigarettes in the experiment. Detailed study of the data suggests that many of the significant interactions can be explained by the single

fact that the maximum number of ignitions per test condition

could not exceed five in this experiment, thus limiting the

possible magnitudes of the estimated effects.

Effect of Shortened Cigarettes

The two substrates on SPL/PU differ only in that the

cigarettes used had half of the tobacco column removed in one case. This provides information on the effect of length of the tobacco column. The data were analyzed in two ways to

test for a significant effect of the "Length" factor.

Sign Test. Of the 32 cigarette packings studied, 22 had the same number of ignitions on SPL/PU for the whole and

shortened cigarettes. The remaining 10 had fewer ignitions

for the shortened cigarettes. Using a sign test [3-8] to evaluate the statistical significance of this result yields a (2- sided) p-value of 0.2%. This reflects strong evidence that shortened cigarettes have a lower ignition propensity on this substrate.

ANOVA. The subtable obtained from Table 3.1 by

considering only the two SPL/PU substrates has 2

6 factorial structure. However, since all of the cigarettes in the subtable

with high packing density had 5 out of 5 ignitions, there is

t

94
Figure 3-A-3. Normal probability plot of

estimated factorial effects from a 25 factorial analysis of variance from the

substrate SPL/PU* (one half of tobacco

column removed, unc./flat. if none of the

factorial effects were significant, the data would cluster

about a single straight line on the plot. The factors are coded as: 1 = Citrate, 2 = Paper permeability, 3 =

Packing density, 4 = Tobacco type (Burley or flue- cured), 5 = Circumference (21 mm vs. 25 mm). The

indicated 95% and 99% limits on the plot are computed using the 4- and 5-way interaction terms to estimate experimental error. These limits correspond,

respectively, to 5% and 1% tests of the hypothesis that

the factorial effects are zero.

Figure 3-A-4. Normal probability plot of

estimated factorial effects from a 25 factorial analysis of variance from the

substrate Denim/PU, crev./cov. if none of

the factorial effects were significant, the data would

cluster about a single straight line on the plot. The

factors are coded as: 1 = Citrate, 2 = Paper permeability, 3 = Packing density, 4 = Tobacco type (Burley or flue-cured), 5 = Circumference (21 mm vs. 25 mm).

The indicated 95% and 99% limits on the plot are computed using the 4- and 5-way interaction terms to estimate experimental error. These limits correspond,

respectively, to 5% and 1% tests of the hypothesis that

the factorial effects are zero.

*f**

*s,ji. ^&

-m -. __ ____-Vp£-_

1 1

1 1

99%

95*

95*

99*

NORMAL PROBABILITY PLOT NORMAL PROBABILITY PLOT

no information about the effect of shortened cigarettes in that portion of the data. Thus, the relevant subtable extracted from Table 3.1 includes only cigarettes with low packing

density. The remaining factors, Permeability, Circumference,

Citrate Concentration, Tobacco Type, and Length (whole vs.

half), form a complete 2

5 factorial experiment. An ANOVA

similar to the main analysis described in Section 3-A.1 was

performed. This analysis showed that the three factors, Permeability, Citrate Concentration, and Length, were all significant with p-values less than 1.0%. For evaluating the

significance of the Length factor, this result is agrees with the

(simpler) sign test described above.

95

Appendix 3-B

AI'HKNDIX 3-B

UtMITED STATES (DEPARTMENT OF COMMERCE

National Bureau of Standards

Gb.l lic'rstxjrg Maryland SDB99

August 26, 1987

MEMORANDUM FOR John Krasny

Center for Fire Re

From: Keith R. Eberhardt KW<££l*i—^

Statistical Engineering Division

Subject: Use of Kendall's Tau Correlation Coefficient to Summarize the Agreement Between Full-Scale and Bench-Scale Ignition Tests

This is to comment on how to summarize the agreement between the full-scale

(FS) and bench-scale (BS) ignition tests listed in the attached table. The

table contains comparisons between FS and BS results for five cigarettes and

15 substrates. (The 16th substr bench-scale data.) The basic qu what extent, the FS and BS data

6 lis tionCA Std./d

these da

to agree.

has no

is whether, and to

In seeking inspiration for what to do with these data, 1 had the benefit of

some veiy useful discussions with Stefan Leigh, Carroll Croarkin and Jim

Filliben.

Vhen I put the data on the computer, I first re-cal

your table from the raw data you supplied. There w between the summary table and my calculations. The

attached copy, and the "

;ed the percentages in

.everal differences

. „je marked on the —

ted values were what I used subsequently.

To summarize the agreement between FS and BS ignition percentages, I have used

the Kendall's Tau Correlation Coefficient. This choice was made partly

because the data are not normally distributed. Kendall's Tau correlation

coefficient is sensitive to the agreement (between the FS and BS methods) of

the relative rankings of the ignition percentages for various test conditions.

In the rightmost column of the attached table, I have written-in the values of Kendall's Tau for each substrate. At the bottom is the value for all data

combined. In this instance, I think the best overall summary of the correlation is the combined value, which is r = 0.73.

Kendall's Tau can be used to carry out a statistical significance test of the hypothesis that the FS and BS values are unrelated. For these data, with

t = 0.73, the hypothesis of no relationship is rejected at a significance

level of 0.01%. This indicates that the data provide strong evidence against

the hypothesis of zero correlation. As you know, strong evidence of nonzero

correlation is not the same as evidence of strong correlation, so this result

must be interpreted carefully. In addition, while r is like the ordinary

(Pearson) correlation coefficient in that its value Is always between -1 and

+1, it has other characteristics that are quite different fron the Pearson

correlation.

In the present context, a careful statement of the null hypothesis of "no relationship" between FS and BS results Is the following. (I am using the term "test conditions" to denote all the 5 x 15 = 75 experimental conditions

as defined by substrate and cigarette type that are summarized in the table.)

Rank the test conditions from lowest to highest according to the percentage of ignitions recorded for the FS tests. Then the null hypothesis states that all possible rankings of those same test conditions by the respective BS results are equally likely. The calculated p-value of O.Oll indicates that. If this null hypothesis were

correct, there would be a very small chance that the ranks of the BS results would be as consistent with the ranks of the FS results as they were in these data. (The roles of FS and BS test results can be reversed

In this statement without changing Its mathematical Implications.)

A reference for Kendall's Tau is: Maurice C. Kendall, Rank Correlation

Methods . 2nd edition, London: Charles Griffin & Co.. 1955. pp. 4-8. 34-35. 49-53.

97
Table 3-B-1. Use of Kendall's Tau Correlation Coefficient to Summarize the

Agreement Between Full-Scale and Bench-Scale Ignition Tests

Ignitions (percent) Materials

Configuration Test Mode

Cigarette Designation

Fabric Cushions Side or Back Welt Cord C86 (A) 129 (C) 106 (E) 114 (D) 201 (B) Kendall's x

CA Standard CB - no flat FSBS

100

100

92

100

42 83 75 20 40 0.74 CA Standard CB CB no crevice FSBS

100

100

86 16 42 17 20 0.60 CA Standard CB CB yes crevice FSBS

100

100

472012 20 20 0.76 CA Standard CB CB no crevice3 FSBS

100 100 60 80 40 -

Splendor PU - no flat FSBS

100

100

1004030 7320 0.89 Splendor PU PU no crevice FSBS

100

100

5

0.76 Splendor PU PU yes crevice FSBS

100

100 1.00

Heavy Velvet PU - no flat FSBS

Heavy Velvet PU CB no crevice FSBS7380 0

1.00 Heavy Velvet PU CB yes crevice FSBS

1780 1.00

Damask PU - no flat FSBS

Damask PU CB no crevice FSBS100

100

40

17

5 11 15

0.84 Damask PU CB yes crevice FSBS

100

100

11 5 5

0.67

Olefin PU - no flat FSBS

20

Olefin PU CB no crevice FSBS

60

60

620 1.00

Olefin PU CB yes crevice FSBS

100

100 1.00

(a) Deep Crevice CB - Cotton Batting FS - Full-Scale PU - LAP 2045 Polyurethane Foam

BS - Bench-Scale

combined:

t = 0.73

(p-value =

0.01%)

98
The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 4

Thermophysics of

the Ignition Process

99

Contents for Section 4

Introduction 1 05

Experimental Methods 107

Experimental Methods for Heat Transfer

Measurement 1 07

Previous Work 1 07

Present Work 1 07

Experimental Methods for Measuring Oxygen

Depletion in the Substrate 111 Experimental Methods for Substrate

Temperature Probing 112

Results and Discussion 115

Substrate Effect on Cigarette 115

Heat Flux Scans on Various Substrates 1 20

Non-steadiness in the Coal Temperature 129

Oxygen Depletion in the Fabric 130

Substrate Temperatures 132

Summary and Conclusion 135

References for Section 4 1 37

List of Tables

Table 4-1. Upward Smolder Velocity,

Paper Only 119

Table 4-2. Lateral Scan at Burn Line 121

Table 4-3. Peak Heat Flux from FNHC-25

(#127) on Three Fabrics (over

Polyurethane Foam) 125

Table 4-4. Effect of Gap Between Flux Gage and Coal on Peak

Heat Flux Measured 125

Table 4-5. Effect of Fabric on

Total Incident Heat

From FNHC-25 (#127) 127

Table 4-6. Summary of Oxygen

Measurements During Ignition 131

Table 4-7. Temperatures on Surface

of Calcium Silicate Board

Induced by Cigarettes 133

101
List of Figures

Figure 4-1. Heat Flux Gage Used to Scan Flux Distribution Around Cigarette Coal 1 08

Figure 4-2. Arrangement for Measuring

Peripheral Temperature

with a Thermocouple 108

Figure 4-3. Temperature-time on

Periphery of Cigarette

Showing Perturbation Due

to Passage of Heat Flux Gage;

Commercial Cigarette #6

in Free Burn 109

Figure 4-4. Apparatus for Scanning Flux Gage Past Cigarette Coal 109

Figure 4-5. Flux Scan Configurations

Used in this Study 110

Figure 4-6a. Six Individual Scans on Same

BEHC-21 Cigarette Sitting on Flat, Horizontal Substrate

(Calif. Fabric/2045 Foam) 111

Figure 4-6b. Averaged Results for Same Cigarette Data 111

Figure 4-7. Apparatus for Sampling

Oxygen Level Between

Fabric and Foam 111

Figure 4-8. Burning Rate of Commercial

Cigarette No. 6 on Several

Inert, Flat, Horizontal Substrates

of Varied Thermal Responsivity 115

Figure 4-9. Burning Rate of Several

Experimental Cigarettes on

Inert, Flat, Horizontal Substrates

of Varied Thermal Responsivity 116

Figure 4-10. Smolder Velocity on Two

Substrate Configurations Versus Smolder Velocity

in Free Burn 117

Figure 4-1 1a. Effect of Configuration on Smolder Velocity of Six Cigarettes 117

Figure 4-1 1b. Effect of Configuration on

Coal Length for the Same

Six Cigarettes 117

Figure 4-12. Correlations of Oxygen

Control Parameter (Eq. 4-3) with Burn Configuration;

Same Cigarettes as Figure 4-11 118

Figure 4-1 3a. Coal Length in Free Burn

Versus Tobacco Packing Density

for Six Cigarettes (same as

Figure 4-11) 118

Figure 4-1 3b. Coal Length on Horizontal

Flat Substrate (Calif. Fabric/2045

PU Foam) Versus Tobacco

Packing Density for Twenty-Eight

Experimental Cigarettes 118

Figure 4-1 3c. Coal Length from Crevice Burn (Calif. Fabric/2045

PU Foam) Versus Tobacco

Packing Density for Six Cigarettes (same as Figure 4-11) 119

102
Figure 4-14.

Figure 4-15.

Figure 4-16.

Figure 4-17.

Figure 4-18.

Figure 4-19.

Figure 4-20.

Three-Dimensional Flux

Distributions for Two

Cigarettes in Free Burn. BEHN-21(108) and FNHC25(127); Scans Along Horizontal

Plane Tangent to Bottom

Edge of Cigarette

Figure 4-21 a.

120

Axial Flux Scans of Cigarette

201 in Three Configurations;

Dashed Lines are ± Average

Deviation; Substrates are Calif. Fabric/2045 PU Foam

Figure 4-21 b.

121

Axial Flux Scans of BELN21(106) in Three Configurations;

Dashed Lines are ± Average

Deviations; Substrates are Calif. Fabric/2045 PU Foam 123

Axial Flux Scans of Cigarette

FEHN-21(116) in Three

Configurations; Dashed Lines are ± Average Deviations; Substrates are Calif. Fabric/2045

PU Foam

Figure 4-22.

123

Axial Flux Scans of Cigarette FNHC-25(127) in Three Configurations; Dashed

Lines are ± Average

Deviations; Substrates are Calif. Fabric/2045 PU Foam

Figure 4-23.

124 Figure 4-24a.

Total Number of Substrate

Ignitions (from Section 3) Versus Peak Heat Flux Measured with Each Cigarette on a Horizontal Flat Substrate

Made from Calif. Fabric/2045

PU Foam

Peak Coal Surface Temperature

Versus Peak Incident Flux on a

Substrate (Calif. Fabric/2045 Foam)

124

125

Figure 4-24b.

Measured Gap Between

Coal Surface and Substrate as a Function of Burn Time

on Substrate; Cigarette

FEHC-21(115). Substrate is Calif. Fabric/2045 PU

Foam. Individual Gap

Profiles for Three

Cigarettes 126

Measured Gap Between

Coal Surface and Substrate as a Function of Burn Time

on Substrate; Cigarette

FNHC-25(127); Substrate is Calif. Fabric/2045 PU Foam;

Individual Gap Profiles

for Five Cigarettes 126

Total Number of Substrate

Ignitions Versus Total Heat

Input Along Cigarette Axis; Heat Input Calculated from

Flux Profiles on California Fabric/2045 PU Foam 127

Total Number of Substrate

Ignitions Versus Triangular

Estimate of Planar Projected

Coal Area; Cigarettes Burned on

Calif. Fabric/2045 PU Foam 128

Correlation Between Mass

Burning Rate of Batch One

Experimental Cigarettes and

Substrate Ignition Propensity

Found in the Bench-Scale

Tests of Section 3 128

Same Correlation as Above

but Restricted to Experimental

Cigarettes Containing Flue-cured

Tobacco Only; line is best fit second degree polynomial 128

103
Figure 4-25. Correlation Between Mass

Burning Rate of Batch One

Experimental Cigarettes

and Coal Length (From

Cigarette Burning on Horizontal

Flat, California Fabric

Over 2045 Foam) 129

Figure 4-26. Oxygen Depletion (as a

function of time) Beneath

Fabric a) FNHC-25 on

Splendor Fabric/2045 PU

Foam; Igniting Case b) FNHC-25

on Calif. Fabric/2045 PU Foam;

Non-Igniting Case 130

Figure 4-27. Isotherm Contours on the Top

Surface of a Horizontal Flat Upholstery Mock-up (California

fabric/2045 foam) 132

104
I introduction

In this section the emphasis is on the interaction between

the cigarette and an upholstery substrate which may ulti- mately lead to smoldering combustion of the substrate or one of its components. The problem will be broken into two

parts. First, the focus will be on the cigarette as a heat source for any object in contact with it; this contact will be

seen to alter the cigarette coal and thus the heat flux pattern

it imposes on any substrate. Second, the focus is more

briefly directed to the impact of cigarette contact on an

upholstery substrate and how this may lead to smolder initia- tion. The overall objectives in examining these two aspects

of the cigarette ignition problem are: (1) To gain insight into the factors that cause the varying ignition propensities of cigarettes seen in the previous section; this may aid in the

future development of cigarettes with further lessened igni- tion propensity. (2) To help clarify the important physics in the ignition process so as to guide the modeling results described in the next section. The splitting of the problem into two parts, as noted

above, implies that the role of interactions between the two

elements (cigarette and substrate) is assumed not to be very

strong. As Salig has shown, the interaction ultimately

becomes considerable once the cigarette and fabric are smoldering together; they are competing for the same

oxygen supply and the cigarette coal 1 is, as a result, substantially altered [4-1]. To avoid this complication, the emphasis here is on the time up to the initiation of smolder

in the fabric char. 2 In many (but not all) cases, this initiation event implies that the substrate (or at least the fabric) will thereafter be consumed by self-sustained smoldering (even if the cigarette is removed after it initiates fabric smolder); cases where initiation of self-sustaining substrate (or fabric)

smolder requires the extensive interaction of a cigarette coal and the fabric char beneath it are thus not considered here. By the same token, substrates which consist of a non- smoldering fabric over a smolder-prone filling material (e.g., a thermoplastic fabric over cotton batting) are not considered here. The sequence of events that is considered here can be

briefly described as follows. A cigarette initially in a steadystate, free burn condition is brought abruptly into contact

with an upholstery substrate (usually a cellulosic fabric on a polyurethane foam for the tests in this section). The surface

of the cigarette coal sees a radially non-symmetrical altera- tion in its heat exchange with the surroundings and in its oxygen influx. Initially the adjacent substrate surface is cold

and so draws heat from the closest portion of the coal; at the same time the oxidation process in the coal, being a

sink for gaseous oxygen, draws oxygen out of the pores in the substrate. As the substrate heats it may eventually

become a relative insu'ator to the contacted portion of the

coal, permitting less heat loss locally from the cigarette coal than would exist in free burn. The oxygen depletion in the

substrate tends toward a constant level. Substrate heating

continues in response to the hot coal which is slowly

propagating in the direction of the cigarette axis. Heat trans- port in the substrate (in all directions away from the hottest

point) occurs at a rate which is comparable to the coal propagation velocity (smolder velocity) and so there is a tendency for heat to accumulate more rapidly in the direction of coal movement. The substrate beneath the moving

coal thus becomes hot enough to begin to react chemically. For a cellulosic fabric the first stage of reaction degrades the

cellulose to a char; the polyurethane foam beneath the

fabric degrades similarly but it also tends to shrink locally in the process. The foam used in this study never reached a condition of active smoldering during the time that the cigarette continued to burn; this apparently required a longer

exposure to a large area of smoldering fabric. The char from

at least some of the fabrics used here was capable of initia- tion to a state of active, self-propagating smolder based on

the heat released from char oxidation; as noted above,

achievement of this state signalled the end of the interval examined here. The present examination of the heat flux pattern imposed

on a substrate by a given cigarette is based on the premise

that the characteristics of this pattern (e.g., peak flux, width

of the flux pattern, rate of flux pattern movement) largely

1 The word coal as used in this chapter refers to the hot, ash-covered

region beyond the paper burn line. The principal concern here is with the peripheral surface of this coal since it is the immediate heat source

for the heat flux seen by the substrate. Of course, this heat originates

within the bulk volume of the coal so that events within the coal interior dictate the heat available at the surface. Section 5 examines this rela- tionship in much greater detail.

2 Unless otherwise stated, "ignition" in this section refers to this more

restricted event of the initiation of rapid oxidation in the fabric char.

105
determine whether self-sustaining smolder (when possible) is initiated in the fabric char. Of course, the fabric characteristics count as well since, as will be seen, they can have some influence on the cigarette coal, but the flux pattern is presumed to respond primarily to the design parameters of the cigarette.

In probing this interval up to fabric ignition, the cigarette is to be examined separately as a heat source. The above

discussion indicates that, even prior to the initiation of smoldering in the fabric char, the presence of the substrate has

had some impact on the cigarette coal; this must be taken

into account. Similarly, in probing the response of a

substrate to a cigarette coal, the cigarette must be allowed

to adapt to the presence of the substrate. There are several objectives in examining the interval prior to fabric char ignition. The first is to obtain a quantitative measure, to the extent possible, of the heat flux transmitted

from the cigarette coal and incident on a substrate. The

second is to measure the variability of this flux with cigarette

parameters. The third is to ascertain the extent to which

these measurements explain the observed variability in igni- tion tendency as seen in substrate ignition tests with the experimental cigarettes. In general, these objectives have

been successfully achieved, although there are a number of complications and limitations that have been encountered in their pursuit, as will be explained below.

In pursuing these objectives, we have been led to examine

other aspects of the cigarette/substrate interaction. These

include the length of the coal and its variation with both

cigarette design and the configuration of an adjacent

substrate, the spacing or gap between the coal and the

substrate surface, and the depletion of oxygen beneath the

fabric surface induced by a smoldering cigarette coal on top

of it. All of these factors have some impact on the cigarette

ignition problem; the most important, because it is coupled

to the flux distribution from the coal, is the coal length.

106
Experimental Methods

Experimental Methods for Heat Transfer

Measurement

All available methods for measuring the heat flux from an

object are intrusive, i.e., they make contact with the object

and thereby extract some heat from it during the measure- ment process. Since a burning cigarette is evolving heat at a

low rate, it is readily disturbed by this heat extraction which

in turn alters the measured heat flux. The situation is worse

than might be inferred from the total heat evolution rate of the coal; what counts most is the heat content and heat

evolution rate in the small portion of the coal which is in 'contact with the flux measuring device, together with the rate

of heat transport in the coal itself. These complexities make

it impossible to calculate the degree of disturbance but they

certainly imply that the flux-measuring device must be as

small as possible. The need for small size also follows from

'the desire to obtain good spatial resolution of the distribution

of heat flux from a cigarette coal. Generally, small size brings other complications, however, such as decreased

sensitivity of the measuring device. There are other considerations as well; it is highly desirable to be able to scan the

spatial distribution of heat flux rapidly to facilitate acquisition

of enough data to assess the variability of a given type of cigarette.

Previous Work

There have been at least two previous efforts to characterize

the heat flux from cigarettes. Behnke [4-2] examined the peak heat flux from 16 commercial cigarettes. He used a

thin sheet of copper with a thermocouple on the back as an

integrator of the incoming flux; the rate of temperature rise in such a device is a measure of the heat flux it is receiving.

Since the lateral dimension of the sheet was not given, the

spatial resolution is not known. The flux was measured just as the cigarette, initially adapted to free burn conditions, was

placed on a horizontal surface supporting the gage. The

average result was 4.2 W/cm2 with a standard deviation of 0.8 W/cm2

; the variation among commercial cigarettes was

judged to be not significant.

Damant [4-3] also reported measurements of maximum

and "average" heat fluxes for 4 commercial cigarettes. Unfortunately the technique of measurement was not described.

The results for maximum flux were all quite low, about 0.9 W/cm2

. This is much lower than any value seen in this study;

the reason for this is not known.

The total heat output (watts) of 4 experimental cigarettes was reported by Ihrig et al. [4-4], using a technique devel- oped by Norman [4-5]. This technique, which provides a somewhat restricted free burn condition, essentially captures

and measures a known fraction of the total heat output of a

cigarette coal. The values obtained ranged from about 4 to 6 watts. Comparable numbers were obtained by Muramatsu

[4-6] using measurements of the evolved CO, CO2 and H2Q

A heat flux cannot be measured by these methods but one

can estimate the approximate magnitude of the flux using

the approximate coal area. The result (a few W/cm2

) is close

to that of Behnke and to those of this study.

Present Work

A miniaturized version of the technique used by Behnke was

considered for this study. It was estimated that metal flakes 1 mm wide by 2 mm long having a 0.0025 cm thermocouple on the back would form about the smallest practical calorimeter; an array of such calorimeter flakes would be needed to obtain a flux distribution along one direction. There are

several practical problems in the utilization of such calorimeter flakes that ultimately led to the rejection of their use in this work. Probably the most serious is the necessity of bringing the cigarette and flakes into very rapid contact in order to get a flux measurement. The cigarette must adapt

to a substrate surface then quickly be moved to sit atop the

flux gage array; any such move would destroy the adaptation of the cigarette coal to the substrate, since the coal surface responds rapidly to the local oxygen supply

conditions. A compromise between speed of measurement and

spatial resolution led to the choice of a Medtherm Model

20321 Schmidt-Boelter flux gage (see Figure 4-1). This is a modified thermopile whose hot junctions form the 1.6 mm

diameter sensor face and whose cold junctions are water- cooled. The front sensor surface is blackened to absorb

radiation; of course, it also responds to any incoming

conductive or convective heat flux, as well as any heat of

107
Figure 4-1. Heat Flux Gage Used to

Scan Flux Distribution Around

Cigarette Coal

,1.6mm dia. tip, blackened

Water cooling extends to sensor tip 15mm

Wate

(0.26 I

,rin /min) I t Water out

condensation of volatiles, such as water (this last factor should be a rather minor contributor to the heat flux). The

gage response time is about 100 milliseconds. This gage

can thus be scanned past the surface of the cigarette coal and provide a measure of the total flux profile along the

direction of the scan. The spatial resolution is limited by the gage diameter. On the basis of Baker's temperature profiles

[4-7], this does not appear to be a source of serious distor- tion of the flux profile; the tendency is to flatten the flux profile slightly and the peak flux is thus underestimated

somewhat. 3 The maximum speed of scanning is limited by

the gage response time. The scan speed was always the same at 2.7 mm/s. This means that it took 3 to 4 seconds to scan the central 10 mm portion of a flux distribution; this is 30 to 40 time constants so there should be minimal distor- tion of the distribution due to this cause. There are two other aspects of the flux measurements,

obtained in the above manner, which must be noted. First, it must be realized that the flux gage measures a "cold wall heat flux," i.e., during the process of measurement, the gage

3 This flattening is a function of the coal dimensions; it is greatest for cigarettes with the shortest coals and thus it introduces some

systematic distortion into comparisons of peak fluxes among cigarettes. However, even for the cigarettes with the shortest coal lengths, the gage diameter is about one quarter of the width of the distribution at

its half-peak height and the error (flux underestimate) appears to be of the order of 5% for this case.

surface remains much cooler than the cigarette coal surface.

In this regard it is the same as a substrate which has just come into contact with the coal. The low substrate or gage

surface temperature enhances the conductive contribution to the heat flux and suppresses surface re-radiation. Because

the gage is water cooled, its surface remains cool even if it stays in contact with the coal. The substrate surface, on the

other hand, immediately begins to heat up as a conse- quence of contact with the coal. This causes the net rate of heat transfer to the substrate to decrease; conduction

(across the gap between the coal surface and the substrate

surface) decreases as the temperature difference decreases

and re-radiation lessens the net radiative flux to the

substrate. This decay of the net heat transfer flux is virtually

impossible to calculate or to measure precisely; it is a very complex, three-dimensional, time-dependent problem. The

inability to precisely determine this flux decay behavior

presents a significant problem when one attempts to model

the ignition process in the substrate given the initial incoming flux distribution from the coal; this issue is dealt

with extensively in Section 5. It is less of a problem in comparative measurements of incident flux on the same

substrate, as is the concern here, but it should be borne in mind.

The second limitation on the flux measurements described

here has to do with inevitable disturbances to the cigarette coal due to the proximity of the flux gage. This was alluded

to above. Some measure of the disturbance can be obtained

by placing a fine thermocouple just inside the periphery of the cigarette on the side past which the flux gage is scanned. Figure 4-2 shows the method of imbedding the thermocouple; this same technique was used throughout this work whenever peripheral temperatures were needed. Such

Figure 4-2. Arrangement for Measuring

Peripheral Temperature with a

Thermocouple

Commercial 0.0050cm wire thermocouple, Type K or R; sewn in with needle to keep

junction just under cigarette paper

Sealed with

methylcellulose

108
igure 4-3. Temperature-time on

Periphery of Cigarette Showing

Perturbation Due to Passage of Heat

lux Gage; Commercial Cigarette #6 in

ree Burn

700

Second passage

First passage

J I I

|

I I 40 80 120 TIME (s)

160 200

fine thermocouples (0.0050 cm) have been shown to provide accurate temperature measurements in a cigarette coal [4-

18]. Figure 4-3 shows a typical result of temperature versus

time obtained as the coal burns past the thermocouple. The

two sudden dips in temperature near the top of the profile are due to two successive passages of the flux gage. Twelve

repeats of this experiment on the same commercial cigarette

(with two thermocouples per cigarette and two scans per thermocouple) gave an average temperature dip of 70°C. If the heat flux from the coal were totally conductive, this average temperature dip would imply that the peak gage

reading is about 10% less than the value to be obtained

from an undisturbed coal; if the heat flux were totally radiative, this dip would imply that the peak gage reading is about 27% low. The actual underestimate of the peak flux due to cooling by the flux gage is somewhere inbetween,

probably near 15-20%. It is possible that this source of error varies somewhat with cigarette properties, but this has not been explored. It is worth noting that a metal flake used as

a calorimeter, as discussed above, would extract heat from a

cigarette coal at the same rate per unit area as does the flux gage used here and so does not provide a means for avoiding this source of error. The apparatus for scanning the flux gage past the cigarette coal is illustrated in Figure 4-4. The gage is mounted

on a vertical positioning stage that permits fine control of the

position of the sensor surface relative to the bottom surface

of the cigarette. This vertical stage is in turn mounted on top

of a motor-driven slide which permits 3.5 cm of horizontal motion along one direction. The average scan speed, as

noted above, is 2.7 mm/s. This varies slightly with position

so, instead of using the average scan velocity and elapsed

time to compute gage position during a scan, a position

transducer is used. This is a linear resistor with a constant imposed voltage; a separate calibration is made to relate

voltage and gage position. Flux scans were made in three different configurations

illustrated in Figure 4-5 In all configurations the flux gage

was positioned so that the sensor surface was in contact

with the lower surface of the unburned cigarette over the

length to be scanned. Coal shrinkage during burning typically caused a gap between the sensor surface and the

hottest portion of the coal surface during the actual flux scans; this same gap exists between the coal surface and a

substrate (see below).

Note that when a substrate was present it was necessary

to insert the flux gage into it in order to get a measure of the flux from the coal at the interface between the cigarette

and the substrate. This required a slit through the upper 1.27 cm of polyurethane foam and the fabric which was 1.6 mm

wide (the width of the sensor face) and 6 cm long. The

presence of the slit disturbs the interaction between the cigarette and the substrate. A series of thermocouple measure- ments of the temperature profile at the cigarette/fabric interface (thermocouple just inside the cigarette periphery

with the junction on the bottom) gave a peak temperature

there of 682 ± 18°C (average deviation) when there was no

slit present; when a slit was present the result was

649 ± 14°C. These results were obtained with one cigarette

type (FNLN-21, #110) on one non-igniting substrate

(California fabric on polyurethane foam; fabric washed to prevent ignition; see below); the cigarette was allowed to adapt to smolder on the substrate surface for several

Figure 4-4. Apparatus for Scanning

Flux Gate Past Cigarette Coal

-£&

-Gage position indicator \/-lux gage

Substrate

109
c Figure 4-5. Flux Scan Configurations

Used in this Study

(a) Free Burn

Gage

Axial scan Lateral scan

(b) Horizontal Flat

Fabric \ Cigarette ^Coai^ %j /

.Fabric

r^1—^ PU ft'tuii /\ Gage V

Axial scan Lateral scan

(c) Crevice

Fabric Scan along cigarette longitudinal axis only

Fabric

minutes before the coal reached the thermocouple. The

temperature decrease due to the slit means that the peak

flux obtained in this manner is 5% to 13% lower than it would be if the slit was not present. This error range once

again corresponds to either purely conductive or purely radi- ative heat transfer from the cigarette to the substrate and the most probable value is midway or about 9%. The fact that the temperature at the interface is lower in the presence of the slit suggests that the insulating effect of the substrate is more important than oxygen blockage in determining the

local coal surface temperature, at least for this cigarette.

There is a further possible complication to incident flux measurements in which the flux gage is within the substrate: the hot substrate itself could contribute a significant portion

of the flux seen by the gage. This factor was checked by a

slight modification to the normal procedure with a flat horizontal substrate. A cigarette was placed on the substrate and given its first two sets of flux scans as usual; immediately after the last pass of the second set the cigarette was

removed from the substrate and a final set of two scans was

conducted within a few seconds. Any flux seen by the gage

during this last set of scans must have come from the heated substrate; it was never more than 0.25 W/cm2

. This

amounts to about 5% of the typical peak flux on a flat substrate; it is the first factor noted which increases, rather

than decreases, the apparent heat flux.

In summary, an algebraic summation of the above error estimates for the heat flux measurements puts the net error (underestimate of the actual peak flux) at about 25 to 30%

with the biggest contribution coming from the tendency for the flux gage to cool the periphery of the cigarette. This

latter contribution is present for all configurations, as is that due to the finite diameter of the flux gage; when the flux gage is placed within the substrate, there are two further sources of error whose net contribution to the tendency of the gage to underestimate the peak flux is about 5%. The

total net error of 25 to 30% should be largely independent

of cigarette design and thus should not interfere with relative comparisons among the experimental cigarettes.

The axial scan for the various configurations in Figure 4-5 was easily implemented. The lateral scanning needed to build up a complete picture of the three-dimensional flux distribution was more problematical. The only natural position reference for these lateral scans is the paper burn line on the cigarette; this is a rather diffuse and erratically

moving reference. What is needed is to make several lateral scans at known distances from the paper burn line as the

coal burns past the gage scan line. Because of the behavior

of the paper burn line, this cannot really be done reproducibly for successive cigarettes of the same or different type.

Difficulties such as this, coupled with the fact that real differ- ences in lateral flux distribution were difficult to demonstrate

(see below), led to principal reliance on the axial scans for comparisons among cigarette types.

Each cigarette to be scanned was ignited by hand with a

small flame (no suction) and allowed to burn freely in air for at least two minutes to yield a fully-developed coal. If the scans were to be done on a substrate, the cigarette was

placed there after two minutes and given another two

minutes (for a few fast burning cigarettes this was closer to one minute) to adapt to the new conditions of oxygen supply

and heat loss before the first scan. Since, as explained

above, the emphasis here is on behavior prior to any

substrate ignition, a non-ignitable substrate was chosen to

indefinitely extend the "pre-ignition" period in most tests. California fabric on 2045 polyurethane foam is not a very

ignitable substrate in any event but fabric non-ignition was

further assured by two successive soakings in distilled water

(to remove catalytic alkali metals) after which it was air dried

and ironed flat. Axial flux scans were typically made at preset positions

along the length of the burning cigarette. In most cases a

set of scans was made as the paper burn line reached each

of the following distances from the initial position of the lit end: 3.3, 4.2 and 5.1 cm. A set of scans means one scan

with the flux gage moving in the same direction as the coal propagation and one scan in the opposite direction; thus a

total of six scans was typically made on each cigarette. The

coal is propagating during any given scan, of course, but

this movement is typically less than 0.5 mm during a scan

so it does not cause appreciable distortion of the flux distri- bution and the two scans in a set are not of significantly different width in spite of the difference in relative movement

of gage and coal. Figure 4-6(a) shows a typical set of six scans from a cigarette with a moderate ignition tendency

110
igure 4-6a. Six Individual Scans on

ame BEHC-21 Cigarette Sitting on

lat, Horizontal Substrate (Calif.

Fabric/2045 Foam)

20 30 40 50

AXIAL DISTANCE (mm)

j Figure 4-6b. Averaged Results for

Same Cigarette Data

70

CVJE

o

x3

<

HIX

-10 10

AXIAL DISTANCE (mm)

30

(BEHC-21, #107)4

. These plots are produced by the

computer which has simultaneously recorded the flux gage

signal and the position transducer signal and converts them

both via their respective calibrations. Note that, because of the limited scan distance available, the edges of the first and

third scan sets are truncated. Occasionally individual cigarettes would show a consistent upward or downward

"In constructing Figure 4-6(a), account was taken of the fact that the

flux distribution is potentially asymmetric about the peak value and all of the scan data were plotted such that the ash side of the paper burn

line is on the right.

trend in peak flux measured along the length of a cigarette.

Since no cigarette type consistently showed such a trend,

the six scans for each cigarette were superposed at their peak values and averaged. Figure 4-6(b) shows the average

axial flux distribution thus obtained for one BEHC-21 cigarette. The dashed lines show the average deviation from the

local average flux. It is curves such as that in Figure 4-6(b)

which will be mainly used to compare cigarette types in the discussion below. To reiterate, the 1.6 mm diameter flux gage used here

gives a reasonably quantitative measure of the heat flux coming from a cigarette coal; the errors that exist in the measurements tend to yield peak flux values that are too low

by about 25-30%. The measured flux is a "cold wall" value

which is the same as is transferred to a substrate at the first instant of contact with a cigarette coal; this should not inter- fere with an inter-comparison of flux distributions among the experimental cigarettes nor with attempts to correlate these

distributions with ignition propensity. Axial scans showed the

greatest variation among cigarettes and will be used below

in their inter-comparison.

Experimental Methods for Measuring

Oxygen Depletion in the Substrate

The cigarette is an oxygen sink and so it imposes some

oxygen depletion on its surroundings. This depletion is of particular interest in the hottest region of the substrate since

this is where smolder initiation is likely to occur. If the oxygen level there is greatly reduced, it will tend to retard smolder initiation, making the requisite temperature for fabric

ignition higher. If the reduction varies substantially among

the experimental cigarettes, it will influence their relative igni- tion propensity.

A series of experiments was performed to determine the approximate oxygen level at the fabric/foam interface just

below a burning cigarette coal. Figure 4-7 illustrates the sampling system used. The sampling probe is a 1.06 mm

OD by 0.8 mm ID stainless steel tube inserted between the

fabric and the polyurethane foam; a smaller diameter probe was tried but it was readily plugged by condensate. Care was taken to assure that the probe did not introduce an

Figure 4-7. Apparatus for Sampling

Oxygen Level Between Fabric and

Foam

Needle valve

Rotameter

Polarographlc 0-60

oxygen aentor cc/mln

Cigarette Fabric _Q_ -o fL

3 _ To diaphragm pump

Bullar voiur Bubbl. 500 cc malar

10 cc

Manometer

0-10' H 2

111
external gas flow path along its own length that would pull in air from other than the coal region. The probe attaches to a

short length of 0.16 mm OD tubing and then to a small volume (3.5 mm3

) chamber glued on the end of the sensor

from a Beckman model 778 polarographic oxygen analyzer.

The goal is to minimize the volume between the sampling

point and the analyzer so as to minimize the system

response time in spite of very low flow rates. The flow was

varied in a series of preliminary tests with one cigarette/substrate combination from 30 cm3 /min. to 3 cm3 /min.; the results were independent of flow rate from 8 down to 3

cm3 /min, implying that disturbance to the coal by the sampling process was probably eliminated. A flow rate of 3

cm3/min. was used in all subsequent tests to minimize distur- bance of the concentration field being measured. The

system response time was about 12 seconds, determined

largely by the analyzer response time, but lowering the sampling rate still further would have extended it undesirably.

The remainder of the flow system shown in Figure 4-7 provides for flow control and measurement.

When a test was to be performed the flow system was

stabilized and adjusted to the desired flow rate after the sampling probe was inserted under the fabric. A cigarette was lit with a small flame and allowed to smolder freely in air for 3 minutes. It was then placed on the horizontal surface of the substrate directly on top of the probe inlet position

(previously marked on the fabric with a small ink dot). The

coal was typically positioned such that the paper burn line was about 2 mm to the ash side of the probe position, i.e., the hottest part of the coal surface was placed directly over

the probe position. In two tests this positioning was varied

by a few millimeters but this did not appear to make a

significant difference in the minimum oxygen level observed.

Tests such as this were performed using three different cigarette types and three different fabrics, always on the same

polyurethane foam type; these covered, in a limited manner,

the range of cigarette and fabric characteristics seen in this study. A few tests were also done in which the cigarette was

replaced by an electrically heated rod to determine the

extent to which the observed oxygen depletion was due to causes other than the proximity of the cigarette coal. The

rod heater was oriented vertically so that only its hot end

(9.5 mm diameter) approached the substrate. The rod end was heated to a dull red glow and it was positioned about 2 mm above the horizontal fabric surface so that the size of the ignited region and its ignition delay time were about the same as in the case where a cigarette was the heat source.

In all tests the oxygen level was recorded for about 4 minutes after heat source placement to ascertain its time

evolution; the results are described below.

Experimental Methods for Substrate

Temperature Probing

In response to the imposition of a slowly moving, three- dimensional heat flux distribution (from the cigarette coal), the substrate heats up. The transient temperature field development is made quite complex by several factors- the nature of the thermal interaction with the cigarette, the twolayer structure of the substrate and the complex chemistry of the substrate materials. Attempts to predict this temperature

field are discussed in Section 5. Here the emphasis is on

efforts to measure some aspects of this field experimentally.

The overall objective (Section 4 and 5) is to learn to what

extent we understand the quantitative development of this

field by comparing the measurements with the predictions.

A one-dimensional temperature distribution is easily measured; multi-dimensional fields are a much bigger challenge

due to the need for a great deal more measurement points.

Thermocouples are easy to use and would be the trans- ducer of choice here were it not for the large number that would be required. The temperature field on the top surface

of the substrate is potentially quite informative, especially

since it is fabric ignition that initiates the substrate smolder

process. The ready optical access to this surface opens the

possibility of utilizing its emitted radiation as the measure of local temperature. This requires a sensor that can detect

radiation in the middle to far infrared portion of the spectrum. An Inframetrics Model 525 scanning infrared radiometer was available and has been employed here for this purpose. This can be thought of as an infrared television which sees emitted infrared light rather than the usual

reflected visible light. Radiation in the 8-12p. region is imaged onto an infrared detector that is cooled by liquid

nitrogen. By means of a pair of oscillating mirrors, the partic- ular small spot that the detector is looking at is swept at 30

frames per second in a rectangular raster scan pattern to form the field of view. The net result is that the IR camera

gathers and displays information about objects in its field of view much like a television picture except that the number of horizontal lines is smaller (200 instead of 256). The instan- taneous radiation intensity falling on the detector is proportional to the amount of radiation coming from the instantaneous object point in the field of view; the instan- taneous detector output and the amplified signal from it that

is displayed on a TV monitor are thus indicators of the brightness of the object point. If there is no significant 8-12n

radiation reflection from that object point (coming from other

radiation sources) and if the object point is a blackbody

emitter in this wavelength range, the intensity of the image of that point on the TV monitor is a measure of the temperature

of the point. Both of these two conditions pose difficulties in the present application, which required special procedures, as discussed below.

Ideally one would be able to use this infrared camera to measure the temperature distribution on top of the substrate as a burning cigarette produces it. However, the cigarette is then the hottest object in the field of view. The cigarette coal emits intensely in the wavelength region of interest, more

intensely than the substrate surface since it is hotter. Some

of this coal radiation is reflected from the substrate surface

since it is not perfectly black (though it may be close). The

IR camera cannot distinguish between emitted and reflected radiation so it is unable to yield a correct temperature as

long as the reflected radiation is present. Attempts to momentarily block this radiation by interposing a shield between the coal and the substrate surface (off to one side

of the coal) were unsuccessful primarily because the

inherent roughness of the fabric surface always allowed

112
significant coal radiation leakage beneath the shield. An

alternative technique was developed which called for rapid

removal of the cigarette at the moment when a temperature

measurement was to be made. Thus only one measurement

could be made per cigarette/substrate burn test and that measurement was made after the cigarette had been

allowed to heat the substrate for some pre-determined time

such as two minutes; determination of the temperature distri- bution at some different time required another burn test with the same type of cigarette and substrate. This technique entails further complications. As soon as

the cigarette is removed from the substrate, the substrate begins to cool. The rate of cooling is variable, being generally higher where the local temperature is higher. Unfortunately it is quite high in an absolute sense everywhere of

interest; the rates were in the range from 150 to 250°C/s.

Because of video noise on each video frame, it is not practical to simply utilize just the frame at the instant of cigarette '

removal; instead one must average several frames to improve the signal-to-noise ratio. This requires an image

processor5 and the use of a video recorder to store the IR camera output prior to processing. At the same time one

must compensate for the substrate cooling that is occurring

over the frame averaging interval. Here averaging was done

over two successive sets of four frames each, starting at the

time of cigarette removal. An average temperature field was

i thus obtained for Vs s and Va s intervals after cigarette removal. At selected spatial points in these fields, a simple

exponential decay function was fitted through the two known

temperatures at that point and used to back extrapolate to time zero. In this manner the temperature field at time zero was estimated.

Surface emissivity in the 8-12|i region is less than unity for any real material. Thus it is necessary to measure it for the

fabrics of interest and their chars which are formed due to heating. The technique chosen for this utilizes the IR camera. A sample of the material of interest is coated on one part of its surface with a known-em issivity material (e.g., carbon black or 3M Nextel Velvet Black paint); the remainder is uncoated. The material is then heated uniformly

to some desired temperature in the range from to 400°C.

The IR camera then provides a means of quantitative

comparison between the brightness of the uncoated surface

and the coated surface; the brightness ratio allows calcula-

:

; tion of the unknown surface emissivity at the given temperature. The values do tend to be rather high, between 0.9 and

1.0. Uniform heating of the fabric materials is difficult to achieve in some cases and this limits the accuracy of the

emissivity determination.

There are other factors which limit the accuracy of the temperature obtained from the IR camera in the manner

described above. There appears to be some error added to the signal in going through the video recorder in spite of

\ 5An IVS Model 210 image processing system was used for this

j| purpose. It permits averaging up to 8 frames and provides for auto- matic conversion of pixel intensity to local temperature (given information on surface emissivity and possible reflected radiation as well as an

instrument calibration).

automatic compensation for its gain control circuitry. The

camera has a limited dynamic brightness range over which

it can make quantitative measurements on images; it was

necessary to use the least sensitive temperature range

(500°C) in order to compress the very wide inherent bright- ness of the scene of interest into the dynamic range of the camera. Furthermore, there is something of a problem with the calibration between image brightness as seen by the IR camera and the actual source temperature apart from the

emissivity issue. The camera operates by difference in its determination of an unknown temperature; it infers the temperature of the unknown by measuring the brightness

difference between it and a source of known temperature

and emissivity. This determination is more accurate if the known source (a black body in the work here) is close in temperature to the unknown. This same tendency affects the accuracy of the instrument calibration curves. The factorysupplied calibration curves are all obtained with a low refer- ence source temperature (30°C). As a result, considerable

effort was put into developing calibration curves for several higher reference source temperatures. However, the software

program in the image processor would not accept these

calibration curves due to limitations in its formulation. There was not sufficient time to rectify this problem and so the

factory-supplied calibration was used. To compensate for this loss of accuracy, a fine thermocouple (0.0050 cm dia. chromel/alumel wire) was sewn into the fabric surface to provide an independent measure of temperature history at one point along the cigarette axis. The thermocouple junction location was marked for the IR camera by means of the heads of straight pins forming a 1 cm box pattern around it (away from the coal). A final area of uncertainty with some of the fabrics of interest is the diffuseness of their surface. Particularly with a

velvet fabric, the IR camera is likely to see radiation originating over some finite depth in the upper half millimeter or so; this is somewhat lessened by the fact that the camera

views the surface at an angle of about 60° from the vertical. This would be unimportant if there were no temperature

gradients over this depth but the insulating nature of velvet

pile makes it probable that some gradient exists which is very difficult to assess. However, it is unlikely that this is a

major source of error since the optical depth is rather small.

In summary, the IR camera is a very useful device for discerning the sizes and shapes of the isotherms on the top

surface of substrates heated by cigarettes; in this sense it is quite capable of revealing the relative differences in isotherm

pattern induced by cigarettes of differing characteristics. However, in this application its quantitative accuracy is limited by the need to remove the cigarette before getting a

reading. It is possible that the actual temperatures differ from

those indicated by the camera by ± 25 to 40°C.

It should be apparent from all of the preceding discussion

of experimental methods that there are substantial barriers to obtaining highly quantitative values for heat flux, temperature

or oxygen concentration in this fragile, readily-disturbed

system consisting of a cigarette interacting with a substrate.

In all cases, however, it is possible to make reasonable esti- mates of the accuracy of the results. More importantly, it is clear that the results are sufficiently quantitative to permit

113
valid intercompansons of measurements for the differing

experimental cigarettes thus permitting the identification of those cigarette characteristics which influence ignition

propensity.

114
lesults and Discussion

The first area of focus is the response of a cigarette to the

proximity of a substrate and the way in which this affects the

heat transfer from the various experimental cigarettes. As

noted above, measurements were made in three configurations: on freely burning cigarettes in air, atop a flat substrate

(usually California fabric on polyurethane foam) and in a 90°

crevice formed by the same California fabric and foam. In seeking to understand how these flux measurements relate

to ignition propensity, we have also examined cigarette coal dimensions, the gap between the cigarette coal and the

substrate surface, and the depletion of oxygen in the fabric caused by the cigarette coal. In this same vein, a limited examination was made of the degree of unsteadiness in the

coal surface temperature.

Substrate Effect on Cigarette

Before the incident flux data are examined, it is of interest to look at what a substrate does to the cigarette coal. The

presence of a substrate in contact with a burning cigarette could: (1) alter the heat losses from the coal and (2) alter the

rate of oxygen supply relative to the free burn case. Either or both of these effects could thereby alter the incident flux that a substrate sees. The conventional view of a steadily smoldering material is that it is burning at a rate dictated by the rate of oxygen

supply [4-8]. Thus the principal effect one might expect on a

cigarette sitting on a non-smoldering substrate is that it burns somewhat more slowly than in open air; the altered heat exchange with the surroundings would not be expected

to have any appreciable effect, at least on the burning rate. Palmer [4-9] found such an insensitivity of burning rate to heat losses for dust layers smoldering on flat horizontal surfaces of asbestos and iron. This was tested here by

placing a commercial cigarette (#C-6) on flat horizontal substrates of varied thermal "responsivity" or thermal "inertia". This parameter (the product of thermal conductivity, heat

capacity and density) is the appropriate measure of transient thermal insulative capacity; the square root of thermal

responsivity is a measure of the amount of heat an inert

Figure 4-8. Burning Rate of

Commercial Cigarette No. 6 on Several

Inert Flat Horizontal Substrates of

Varied Thermal Responsivity

oo_J

LU>

UJQ

_lO

CO

14

12

10

8

6

4

2 -

Avg. Smolder Velocity In Air

Ceramic fiber Board, 0.28 g/cc Ceramic tlber board, 0.79 g/cc

10"5 10~4 10" 3 THERMAL RESPONSIVITY (W 2 • s/cm 4

10" °C2)

insulator absorbs per unit time. 6 The lower it is, the less is the rate of heat removal from the smoldering cigarette coal as it burns in contact with the substrate surface. Figure 4-8 shows the results for four inert materials that vary in thermal

responsivity by a factor of about 580 (or about a factor of 24

in heat absorption ability). For comparison, the thermal

responsivity of the polyurethane foam, while it is still cool enough to be chemically inert, would fall near the fiberglass

in Figure 4-8; that of the fabric, while it remains inert, would

fall near the lower density ceramic fiber board. It is apparent

that, for this cigarette, the effect of increasing the heat loss

rate to the substrate is only a very gradual decrease in smolder velocity and yet the smolder velocity on all of these

e The heat content of a thermal wave in a material is proportional to the product of the average temperature in that wave, the density, the heat

capacity and the wave thickness. This last variable is proportional to the square root of the product of thermal diffusivity and the time. One

thus finds that the material properties measuring the heat content of the wave combine to yield the square root of the thermal responsivity.

115
substrates is about 20% below that in air. This is consistent

with the idea that oxygen blockage, not heat loss effects, dominates this 20% decrease in burn rate. Ultimately, of course, the heat losses, if sufficient relative to the rate of heat generation, will be overwhelming and their effect will be

profound; the cigarette coal was severely distorted on the

firebrick (the lower portion of the paper did not burn) and

one in eight of the tests with this cigarette on this substrate yielded extinction. Figure 4-9 illustrates the effect of heat losses on six of the experimental cigarettes used in this study. Three of these

cigarettes have a rather weak propensity to ignite upholstery

substrates as seen in the results of Section 3; these are BELN-21 (#106), FELN-21 (#114) and #201. One (BEHC-21,

#107) has an intermediate ignition tendency and two (BNHC25, #119 and FNHC-25, #127) have a strong ignition

tendency. There are varying degrees of response to contact

with the inert substrates which appear to correlate approximately with the ignition tendency; the cigarettes with the

lowest ignition tendency are most susceptible to extinction due to substrate heat losses and conversely. One does not expect a perfect correlation here since extinction is probably

dictated by an imbalance between rate of heat generation

and rate of heat loss. The tendency to ignite upholstery is not solely dictated by the rate of heat generation in a cigarette, but for the cigarettes in this study, they may be closely

enough tied together to produce a potentially useful correlation. Some exploration of a test method based on heat loss extinction is reported in Section 6. Four of the cigarettes

(BEHC-21, #107; FELN-21, #114; #201; FNHC-25, #127) show

a significant decrement in smolder velocity in going from the

Figure 4-9. Burning Rate of Several

Experimental Cigarettes on Inert, Flat,

Horizontal Substrates of Varied

Thermal Responsivity

EFFECT OF THERMAL RESPONSIVITY (inert substrate)

ON SMOLDER VELOCITY

O

O

_i

LU>

<ruiQ

_lO

2

co

I FreeI Burn Smolder Velocity X 10 3 (cm/s> 14 o BELN-2K106)

FELN-2K114) BEHC-2N107)

10.1 8.9

14.2 12

•O

BNHC-25M19)

FNHC-251127)

201

11.8 8.4

8.9 10

8

«

Flberg ass 13 ol 6 .063 cc extlng'd) 6 T\ t

1 Ceramic liber \ i board. 0.2E g/cc Ceramic fiber Fire brick 4 2.0 g/cc -

V board, 0.79 g/cc

v I 1 2

n I V i nn 1CT 5 NT4 10 -3 THERMAL RESPONSIVITY (W 2 • s/cm 4 • °C 2 )

fiberglass to the low density ceramic fiber board. Further- more, their smolder velocity on the fiberglass is not less than

in air as was the case in Figure 4-8 (in fact none of the

cigarettes in Figure 4-9 is significantly slower on fiberglass

than in free burn). Evidently any oxygen supply rate inhibi- tion due to the fiberglass is made up for by what is probably

a smaller heat loss in the presence of fiberglass. Some of the cigarettes (especially BEHC-21, #107)show an apparent

sensitivity to heat losses over a wide range of substrate properties that does not seem to go along with the idea that oxygen supply rate is chiefly responsible for dictating

smolder velocity. The smolder model of Moussa et al. [4-10], which includes predictions of extinction, implies that this kind

of sensitivity to heat loss rate is possible over only a narrow range of temperatures and hence heat loss rates. It seems

probable that what is happening here that is not included in such models is an interaction between heat losses and rate

of oxygen supply. The heat losses may influence the area of the cigarette coal that is available for oxygen consumption

and thus in turn affect smolder velocity; such an effect is quite apparent at least in the extreme cases where a cigarette is subject to a high heat loss rate, as when it was

placed on a brick substrate. A similar point will arise later in relation to the role of the cigarette paper. The point is of interest because, as noted above, fabrics have thermal

responsivities near the lower density ceramic fiber board.

Evidently, in this range, some of the experimental cigarettes are vulnerable to both heat effects and oxygen blockage

effects. The issue of what a fabric/foam substrate does to a cigarette in contact with it is complicated by the fact that, above

about 250-300°C, these substrate materials are not inert like those in Figures 4-8 and 4-9. The effect of a realistic substrate (after it is hot enough to begin to decompose)

might not be to remove heat; its effect might be to add heat. Thermal analysis (DSC) of the California fabric in 9.3%

oxygen (roughly the level present in the fabric when a cigarette is atop it; see below) yields an exothermicity of 950

cal/g of fabric for the pyrolysis step (preceding char oxidation). One can show that, from this degree of exothermicity

and an estimate of the amount of fabric pyrolyzed by the

cigarette coal, the cigarette heat release rate ought to be

significantly supplemented (10-15%). However, this exothermicity result is for a heating rate of 5°C/min.; the heating

rate that a fabric sees when it is placed in contact with a

cigarette coal is closer to 200°C/min. The effect of this differ- ence in heating rate on the net heat release from the fabric

is indeterminate due to instrumentation limitations but it is likely to decrease the exothermicity somewhat since there is less time available for oxygen attack; such a decrease at lower heating rates has been seen for polyurethane foams

which are also exothermic in their decomposition at very low

heating rates [4-11]. In short, the net thermicity of the

substrate's response to contact with a cigarette coal prior to fabric ignition cannot currently be determined directly. There

are indirect indications from oxygen depletion measurements

(below) that the pyrolysis heat release from the fabric prior to

its ignition is probably minimal.

If the oxygen blockage effect by a substrate is the predominant influence on a cigarette coal, one expects that

116
Figure 4-10. Smolder Velocity on Two

Substrate Configurations Versus

Smolder Velocity in Free Burn

15

13

CO

- 9

Substrates are Calif, fabric/2045 PU foam

Horizontal flat- (slope=0.83)

Crevice

5 7 9 11 13 15 17 SMOLDER VELOCITY IN AIR x 10+3 (cm/s)

all cigarettes will respond about equally to the same

substrate, assuming the stoichiometry of char oxidation is about the same for all cigarettes. Figure 4-10 shows the

decrease in smolder velocity on two different substrate

configurations for several of the experimental cigarettes. The

average decrease for cigarettes on the flat substrate (-

17%) is approximately the same as was seen above for the commercial cigarette on the inert substrates; the data for the

crevice configuration are few, but they imply a decrease in smolder velocity about twice the fractional amount seen on

the flat configuration. The scatter for both configurations is substantial and raises the question whether all the relevant

factors are accounted for. As the discussion of Figure 4-9 implied, the above argu- ment about oxygen supply blockage is overly simple; it neglects the fact that the area for oxygen attack can change

if the size of the coal changes with substrate contact. Six of the experimental cigarettes were examined in detail for this type of effect; coal lengths were measured about midway

along the cigarette after extinction in a water bath. The

results shown in Figure 4-11 are based on the average of three or more cigarettes; the average deviation was typically

5-10%. It is apparent that: (1) for any particular configuration

there is a factor of two or more variation in the length of the

coal; (2) the length of the coal generally increases as the

cigarette comes in contact with configurations that increasingly block its oxygen supply (and perhaps significantly alter the local rate of heat loss). Both of these facts are pertinent

to the substrate ignition tendency of these cigarettes; coal

length directly affects the axial length of the incident flux distribution at the substrate surface. A more detailed consideration of the issue of oxygen

supply rate control on the cigarette burning rate leads to the

following. Assume that the mass burning rate of tobacco is

Figure 4-1 1a. Effect of Configuration

on Smolder Velocity of Six Cigarettes:

BELN-21(106), FEHN-21(116), FHNC25(127), FEHC 25(131), 201,

BNLN-21(102)

COo

X

InE

o

>-H

O

o

_J

LU>

LUQ_l

o

CO

15

10

5 -

(a]

j_

Free

Burn

Horiz. Flat Crevice

Figure 4-1 1b. Effect of Configuration

on Coal Length for the Same Six

Cigarettes

15 - E

E

<

OO 10

LLo

X

h-o

-z. LU 5

FNHC-25

(b)

FEHC-25

Free

Burn

Horiz. Flat Crevice

117
related to the rate of oxygen supply through a fixed stoichio- metric coefficient: m-roB = PtbVsAcs = (1/n T)kAC0AL Yoxa (4-1) where mToB is the mass burning rate of the tobacco (g/sec),

Ptb is the bulk density of the tobacco in the cigarette, vs is the smolder velocity of the cigarette (cm/sec), Acs is the cross sectional area of the cigarette, n T is the effective stoichiometric coefficient of the cigarette burning process, k

is the mass transfer coefficient for oxygen transport across

the boundary layer around the coal (and through the ash),

Acoal is the area of the coal where oxygen is being

consumed by char oxidation and Yoxa is the mass fraction

of oxygen in the ambient atmosphere. Assuming further that the coal oxidation area can be approximated as a cone and

substituting also for the cross sectional area in terms of diameter, one obtains:

PTBVS (7t/4)dc

2 = (1/noT)k(n/2)dcSCYoxA (4-2) Here dc is the cigarette diameter and sc is the length of the slanted side of the coal (sc = (fc

2 +(dc/2) 2

)

1/a

; k is the

length of the coal). For a given configuration, the mass

transfer coefficient, k, is essentially independent of cigarette

diameter, having only a weak dependence that is masked by

the small diameter range employed here. Assume also that n T is constant for the two types of tobacco used here. Then, gathering constants on one side of the equation gives:

(piBVsdc/sc) = (2/n0T)kY xA =

constant for a given configuration (4-3)

This last relation provides a test of the assertion that oxygen supply rate dominates the behavior of the cigarettes

in the configurations examined above. Figure 4-12 shows the

result of replotting the data in Figure 4-11 in accord with the above relation; the average deviation in the points shown in Figure 4-12 is 10% or less. Clearly most of the cigarettes in

most of the configurations conform to this relation. The

decline in the value of the constant from left to right in Figure 4-12 is a measure of the change in the overall mass

transfer coefficient with configuration. One cigarette, BELN21 (#106), fails to conform when it is in contact with a

substrate and the failure does not appear to be due to data

scatter. BELN-21 is exceptional in that it has one of the

lowest ignition tendencies among the experimental

cigarettes; however, so does cigarette #201. The reason for the exceptional behavior of BELN-21 in Figure 4-12 is not apparent at present; perhaps it does not adjust to heat

losses or oxygen supply restriction by altering its coal length

in the same manner as the other cigarettes. The direction of

its departure from the correlation is such that, on a

Figure 4-1 3a. Coal Length in Free Burn

Versus Tobacco Packing Density for

Six Cigarettes (same as Fig. 4-11)

15

5 10 Iz

111

<o

o

5 -

I I I I

FEHC-2si

FNHC-25I ^S*-^"^Best fit y-3. 188+23. 10x -

Correl. Coef. 0.73

FEHN-21$

^^ 1bNLN-21 ^^JBELN -21 ^^^201$

I I I I 0.1 0.2 0.3 0.4 TOBACCO PACKING DENSITY (g/cm3)

0.5

Figure 4-12. Correlations of Oxygen

Control Parameter (Eq. 4-3) with Burn

Configuration; Same Cigarettes as Fig.

4-11

no

x

"w

(1W

o

o

~o

V) —

.

oo

in >m

Figure 4-1 3b. Coal Length on

Horizontal Flat Substrate (Calif.

Fabric/2045 PU Foam) Versus Tobacco

Packing Density for Twenty-Eight

Experimental Cigarettes

15

10

COAL LENGTH VS. TOBACCO DENSITY

BEHC-21

FEHC-21 \ BEHC-25. \\fEHC-2J

BEHN-25. I BNLN-M*

BEHN-21.1.FEHN-21

'"

N-25.^ffI Y

B ""

20,| | /•FELN-25

FEUJ-21

Best Fit y-4. 640+20. 30x

Correl. Coef. 0.57

|fnu*-21

Horizontal Flat Coal length corrected

tor cigarette diameter

Free Burn Horlz. Flat Crevice

0.1 0.2 0.3 0.4 TOBACCO PACKING DENSITY (g/cm 3 )

0.5

118
Figure 4- 13c. Coal Length from Crevice

Burn (Calif. Fabric/2045 PU Foam)

Versus Tobacco Packing Density for

Six Cigarettes (Same as Fig. 4-11)

Table 4-1. Upward Smolder Velocity,

Paper onlya

Best fit y-59.4x-0.659

Correl. Coef. 0.92

0.1 0.2 0.3 0.4 TOBACCO PACKING DENSITY (g/cm 3 )0.5

substrate, either its smolder velocity is exceptionally high or

its coal dimensions are exceptionally short. Conformance to the above relation, while confirming that the interplay of coal dimensions and smolder velocity of most cigarettes is dominated by oxygen supply rate considerations, does not seem to fully explain how they

show the considerable variability in coal length seen in Figure 4-11 (b). The variation with configuration is explained as due to the need for increased coal area to compensate

for the decrease in average rate of oxygen attack per unit area of coal (because of the partial blockage). However, this leaves the question as to what causes the coal length variability seen in Figure 4-11(b) among cigarettes in the same

configuration. Variation in the packing density of the tobacco

is the most obvious answer; one expects the coal to be

longer if there is more tobacco per unit length to be

consumed by the incoming oxygen flux. Figure 4-13 shows

the correlation between coal length and tobacco packing

density for the same three configurations discussed above.

In all cases the coal length measured for a 21 mm circumference cigarette has been corrected upward by the ratio of diameters of the two sizes of cigarette; this was necessary to eliminate this source of bias and it assumes that the coal is conical in shape. Examination of Figure 4-13 leads to the conclusion that packing density is only one of the factors

affecting coal length. All of the data in Figure 4-13 appear to be consistent with the idea that paper permeability is also a determinant of coal length; note the distinct tendency for cigarettes with high permeability paper to have a longer coal

length. A possible tendency for citrate content also to increase coal length is more obscure.

The physical mechanism whereby paper characteristics

affect coal length is not clear. It is well known that they affect the cigarette smolder velocity; higher citrate content and

higher permeability both increase the static burning rate

[4-12]. As will be seen, a longer coal does indeed go along

Paper Typeb

LC

LN

HC

HN

Smolder Velocity

(cm/s)

0.21 ± 0.01 0.20 ± 0.01 0.29 ± 0.01 0.22 ± 0.02

Downward Smolder Velocity,

Paper Typeb

LC

HC

paper only

Smolder Velocity

(cm/s)

0.14 ± 0.01 0.18 ± 0.01

(a) Non-citrate papers self-extinguish; therefore, smolder velocity is from

distance they did burn, others are from 4 cm length

(b) L indicates low permeability, 10 CORESTA; H is high permeability, 75 CORESTA; C indicates a citrate content of 0.8%; N indicates a

lack of citrate

with a higher mass burning rate. It could be argued that the higher permeability paper, in facilitating a greater oxygen

supply rate to the coal region, enhances the mass burning

rate in accord with Eq. 4-1. This glosses over what part of the coal receives this enhanced oxygen supply (apparently

the pyrolysis zone) and it also offers no clue as to what the

citrate in the paper does to enhance burn rate or coal

length.

Paper HC (high permeability with citrate) does smolder

faster by itself than the other three papers when burning

upward and downward in air; see Table 4-1. 7 On the other hand, paper HN (high permeability without citrates) tends to self-extinguish in air. One can speculate that a faster paper

might tend to advance more quickly along the cigarette,

exposing a greater length of oxidizing char behind it, but

this assigns the paper the role of a pilot in the cigarette

smolder process. Such a role is dubious since the noncitrate papers want to self-extinguish and yet cigarettes

7 Wore that the velocities in Table 4-1 are much faster than the smolder

velocity of a cigarette. This does not mean that the papers could

potentially smolder much faster than the tobacco when on a cigarette.

It appears to reflect only the much better rate of oxygen supply that the paper receives when it is smoldering as a single flat sheet; placing

several flat sheets together or forming a cylinder from a single sheet

slows down the rate of paper smolder since either configuration reduces the rate of oxygen supply per unit area per unit mass of fuel.

119
made with them smolder normally. Furthermore, inspection

of extinguished and sectioned cigarettes suggests that the paper is relatively passive, pyrolyzing as the tobacco heats

it; this may be only part of the story since low permeability,

non-citrate papers appear to lag behind the tobacco char

front. A paper that merely pyrolyzes at a lower temperature

would lengthen the coal somewhat, but Baker's temperature

profiles [4-7] imply that a paper would have to pyrolyze at 70°C less than normal in order to lengthen the coal by 1 mm. Thermal analyses of the papers used here (5°C/min.,

air) show practically no differences (3-5°C) between the

pyrolysis peak temperatures for the high and low permeability papers and 25-30°C lowering of the pyrolysis peaks in the presence of citrates. These effects could be greater or lesser at the much higher heating rate seen by the paper

during cigarette smolder (300-500°C/min.); this cannot be

judged from the present information. Ohlemiller [4-13] has

found indirect evidence that the leading edge of a two- dimensional smolder wave is sensitive to the oxidation

kinetics of the material in this region and has argued that these kinetics affect the length of the exposed char oxidation zone. These conclusions were based on studies of a thick

layer (10-11 cm) of a homogeneous material (wood fibers) but they should be pertinent here as well. Thermal analytical

results on the cigarette papers used here are not definitive with regard to the question of whether the paper oxidation

kinetics differ in the proper manner here to explain such

effects. Differences exist as seen in the thermal analysis

results for paper oxidation at 1 to 5°C/min. but their effect on

cigarette behavior is not clear in the absence of a model

that incorporates the paper as an active and distinct element

of the smoldering cigarette. It is worth noting that low paper

permeability alone can cause a cigarette to self-extinguish

[4-14]; the mechanism for this is also unknown but it suggests that model studies of the role of the paper could prove very interesting.

In summary, it is apparent from the behavior of the experimental cigarettes on inert substrates that the substrate can cause both oxygen blockage and heat loss effects on

the cigarette; the extent of the effect on the smolder velocity

appears to correlate in some approximate way with ignition

propensity On upholstery substrates, the alterations to the smolder velocity and coal length for most cigarettes are

consistent with the assertion that the overall mass burning

rate is dictated by the overall oxygen supply rate. This can be consistent with the idea that heat effects also count, if they act by altering the coal area available for oxygen attack. The cigarette design factors which have the largest impact on the coal length (which is a measure of the area available

for oxygen attack) are diameter, packing density (determined

by tobacco expansion and the cut width of the shreds) and

paper permeability. The mode of action of the last is not immediately apparent.

Heat Flux Scans on Various Substrates

One result of the preceding discussion is that one expects

the incident flux distribution seen on a substrate, even prior to substrate ignition, to be different from that from a cigarette

in free burn. This is in fact the case as will be seen below

for axial flux scans. It was also noted that there are substantial variations in coal length that should be reflected in the

axial flux scans.

Recall that both axial and lateral flux scans are possible. If a complete set of both types of scan is taken on a given

cigarette coal, the result is a picture of the three-dimensional

flux distribution in the horizontal plane tangent to the bottom

surface of the cigarette; Figure 4-14 shows two examples of

this. In this figure the maximum of the axial scans has been

placed at zero axial distance; the maximum is more likely at about +1 mm but it was not measured for these runs. Since

the axial and lateral scans must be done on two different cigarettes, data scatter yields disagreement between them at several of their intersection points.

The two cigarettes in Figure 4-14 differ substantially in their smolder initiation tendency as measured by the total number

of substrate ignitions reported in Section 3 (primary evaluation). BEHN-21 (#108) gave 7 out of a possible 20 ignitions;

FNHC-25 (#127) gave 20 ignitions. One expects to see such

differences reflected in the incident flux distributions. It is apparent that it is difficult to make quantitative comparisons

between flux distributions with plots of this type, though it is

Figure 4-14. Three-Dimensional Flux

Distributions for Two Cigarettes in

Free Burn. BEHN-21 (108) and FNHC-25

(127); Scans Along Horizontal Plane

Tangent to Bottom Edge of Cigarette

BEHN-21

-i 10 *i

<mm) LINE

FNHC-25

-10 °ISTANC FRZ^»

120
Table 4-2. Lateral Scan at Burn Line

Cigarette Configuration

Average Peak

Flux at Burn Line

(W/cm2

)

Peak Width

at Half of Maximum

(mm)

BEHN-21

BELC-21

FNHC-25

FNLN-25

BELC-21

BELC-25

BELN-21

BELN-25

AIR

AIR AIR

AIR FABRIC/FOAM

FABRIC/FOAM

FABRIC/FOAM

FABRIC/FOAM

5.8

6.1 6.0

7.1 5.5

5.0

5.3

5.2

1.0 0.9

0.2

0.5

0.2 0.5

0.4 0.2

5.5

5.5

6.3 5.9

5.9

7.0

6.1 7.2

0.4 0.6

0.3

0.6

0.6

0.4

0.4

0.4

The ± values are the average deviations

evident that they differ. Plots of this type are also not readily

integrated numerically to obtain the total "volume" under the

flux distribution surface though this is of interest, as will be

seen below.

Lateral scans were made on several cigarettes, four in free burn and four on a flat substrate8

; these were chosen to cover the range of ignition propensity. The paper burn line was the area examined most closely. Table 4-2 shows the

results for the peak flux and the width of the flux distribution

at the point where it has dropped to half of the maximum

value; these values are averages for five to six cigarettes of each type with two scans past the burn line region per cigarette. The results for the first four cigarettes suggest that the peak width varies with cigarette diameter by about the same

absolute amount as the diameter itself varies. There is some

indication (perhaps not statistically significant) that peak

width is somewhat wider on a substrate than in free burn

(see BELC-21, #105); schlieren photos of the thermal

boundary layer around the cigarette show that the presence

of the substrate thickens it and this could broaden the flux distribution. The differences are rather small in both cases and do not justify the considerably increased effort required

to obtain lateral scan profiles for all of the cigarettes examined in this study. In view of this discussion, the principal

basis for comparing differing cigarette types here will be

their axial flux scans.

Axial flux scans in three different configurations (free burn,

flat horizontal surface and crevice) were made on four cigarettes9 that span the spectrum of ignition propensity (as

^Recall that the substrates have been rendered non-ignitable by

washing any alkali metal ions out of the fabric; thus all results on

substrates apply to pre-ignition conditions.

9Axial heat flux scans were made on a substantial number of other

cigarettes in the experimental series, in both free burn and on a

horizontal flat substrate (California fabric/2045 polyurethane foam). Copies of these are available for review at the National Bureau of Standards.

Figure 4-15. Axial Flux Scans of

Cigarette 201 in Three Configurations;

Dashed Lines are + Average

Deviation; Substrates are Calif.

Fabric/2045 PU Foam

10

CMEo

X

3

<

IDI

CMEo

X3

LUX

—

I

1 1 1

i) CIG. 201; FREE BURN

PEAK FLUX: 5.82 W/cm 2 PEAK WIDTH: 5.7 mm

8 -

7 -

=tr -30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

30

109

8 -

7 -

6

54 I- 32

1 -

1

1 1 1

b) CIG. 201; HORIZ. FLAT

PEAK FLUX: 5.60 W/cm 2 PEAK WIDTH: 7.4 mm

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

30

•20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

121
reported in Section 3) ; the averaged results are shown in Figures 4-15, 4-16, 4-17 and 4-18. The cigarettes in the first two figures (4-15, 4-16) have a minimal ignition propensity;

that in Figure 4-17 has a moderate ignition propensity and

that in Figure 4-18 has a strong ignition propensity. Two

trends are evident with all four cigarettes as a function of configuration: (1) the flux distribution gets broader as one

goes from free burn to the crevice configuration; (2) the peak flux gets lower or stays constant with the same change

in configuration. These trends are qualitatively consistent

with the cigarette temperature measurements of Salig, who

subjected his cigarettes to more extreme oxygen blockage

[4-1]. The first trend follows from the coal length data in Figure 441(b); recall that the coal gets longer because the

substrate partially inhibits the inflow of oxygen and this slows

the rate of char oxidation per unit length of coal. This same

effect also slows the rate of heat generation per unit of char

length and this is a prime determinant of the local surface

temperature on the coal; it is the coal surface temperature

which drives the heat flux incident from the coal on the

substrate. However, the second major factor in determining

the local temperature is the net rate of heat loss from the

coal surface which is not so readily assessed. Recall that the overall thermicity of the substrate prior to fabric ignition

is not known. Obtaining sufficient surface thermocouple data on the various cigarettes to provide a definitive comparison

of the temperature profiles (at the side toward the interface) as a function of configuration has proven to be quite difficult; surface thermocouples are very prone to move and thus

disrupt the measurement when thev reach the coal region.

The limited data available on BElN-21 (#106) and FNHC-25

(#127) suggest that any change in peak surface temperature

with configuration is not large

Inspection of Figures 4-15 to 4-18 allows one to compare

the flux scans in any of three configurations for cigarettes

that vary substantially in their ignition propensity. The most

striking thing one sees is the lack of great differences; BELN-21 (#106, Figure 4-16) caused one substrate ignition in the tests reported in Section 3 whereas FEHN-21 (#116, Figure 4-17) caused twelve ignitions. Only FNHC-25 (#127, Figure 4-18) looks very obviously different from the other

three; it caused twenty ignitions. The first implication that this comparison suggests is that peak flux does not clearly

emerge as a controlling factor in the differing ignition

tendencies of these cigarettes. One would expect peak flux to be a clearly dominant factor if the fabric ignition process

took place in a time that is short compared to the coal movement time and compared to the time scale for lateral spread of heat in the substrate; in fact, all of these times are comparable here.

If peak incident heat flux did clearly dominate, the number

of smolder ignitions for a given type of substrate and config- uration would, ideally, go abruptly from zero to maximum as

the critical flux needed to achieve the ignition temperature10

of the fabric was reached; various substrates or configurations would then produce a series of steps in the total number of ignitions achieved in all tests. Figure 4-19 shows a

plot of the number of substrate ignitions (from Section 3, primary evaluation) versus the peak heat flux from nineteen

of the experimental cigarettes. The experimental situation

represented in this figure is not optimal. The ignition tests of Section 3 were performed on three different substrate material combinations. On the other hand, the flux measurements

here were all made on a single type of substrate —

California fabric on polyurethane foam; horizontal flat config- uration (Figure 4-5(b)) - because it was not feasible to test

all of the cigarettes on all of the substrates. To help assess

the effects of these differences, cigarette FNHC-25 (#127) was examined on three different fabrics (each on top of 2045 polyurethane foam in a horizontal flat configuration).

Table 4-3 shows the results which are somewhat ambiguous

as to whether different fabrics induce statistically significantly different peak incident heat fluxes from a cigarette (as a

result of fabric/cigarette interactions); there could be a 20%

difference between the California fabric and the other two

fabrics. 11 Such a difference, even if real, is comparable to the data scatter in Figure 4-19. The correlation with peak flux does not look any better if only the ignition data for the one

substrate covered in the California fabric is included in a plot

like that of Figure 4-19. Thus the experimental data are unable to reveal a clear correlation between peak heat flux

^Measurements of fabric ignition temperature were made using a large area electric heater as a radiation source; the flux was such as to provide a 1 to 1 Vz mm. ignition delay, comparable to a cigarette. The

fabric was placed on top of the polyurethane foam used throughout

this work. The heater was about 1 cm above the fabric so that the appearance of glowing in the fabric char could be noted. A fine chromel/alumel thermocouple (usually 0.0051 cm dia. but 0.0076 dia. was used for some tests) was sewn into the fabric, making sure that the junction was within a thread or yarn and that the lead wires were

in good contact also. Defining the ignition temperature in this type of experiment is problematical; ideally one wants the fabric surface temperature at which the ignition process becomes irreversible, such

that, if the external heat flux were suddenly removed, the fabric would

just be able to continue to smolder. Determining this ideal ignition temperature is an order of magnitude more difficult that what was done here. Here if the thermocouple record showed a rather abrupt

increase in its rate of signal rise, indicating that the fabric temperature was rapidly rising due to the char oxidation exotherm, the temperature

at which the rate of rise reached 21°C/sec. was arbitrarily taken to be

the ignition temperature; for one fabric, halving this rate criterion would have lowered the inferred ignition temperature by 12°C and doubling it would have raised the temperature by 30°C. Visible appearance of char glowing as an alternative ignition criterion proved to be

substantially less reproducible, although it was the only useful criterion with Splendor fabric which did not exhibit an abrupt increase in its thermocouple signal. For other fabrics this glowing char criterion tended to give ignition temperatures that were 40 to 85°C higher than

the rate of rise criterion. With these caveats in mind, the results were

as follows: Splendor fabric (glow criterion) - 536 ± 15°C; the remainder used the rate of rise criterion: blue denim fabric -456 ±

13°C; unwashed California fabric - 454 ± 15°C; washed California fabric - 430 ± 5°C; second batch of washed California fabric - 424 ± 6°C The California fabrics never smoldered beyond the area heated by the igniter. Note that these ignition temperatures apply to a

situation where the heated area was several square centimeters; for a smaller heated area, comparable to that heated by a cigarette coal, the effective ignition temperature could be somewhat higher. Small

area ignition temperature measurements were attempted but they gave much worse data scatter. "If the 20% variation in peak flux is real, this says only that the

different fabrics vary somewhat in their oxygen blockage and heat

sink effects on the coal of a cigarette. This does not imply that the

fabric characteristics play an equal roll to the cigarette characteristics

in determining the heat flux pattern produced by a given cigarette on

a given substrate.

122
Figure 4-16. Axial Flux Scans of BELN21(106) in Three Configurations;

Dashed Lines are + Average

Deviations; Substrates are Calif.

Fabric/2045 PU Foam

10 i

1

i

1 r

i) CIG. BELN-21; FREE BURN

PEAK FLUX: 5.37 W/cm 2

E -, PEAK WIDTH: 5.5 mm

o

X

<

til X

-20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

10

CMEo

X3

<

IDX

1 1 1 1

b) CIG. BELN-21; HORIZ. FLAT

PEAK FLUX: 5.45 W/cm 2

PEAK WIDTH: 6.7 mm

T

10

9

C\J 8

Eo I £ fi *—

X <s 3

LL 4 S 3

UJX 2

1

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

1 1 1 r~

c) CIG. BELN-21; CREVICE

PEAK FLUX: 5.15 W/cm2

PEAK WIDTH: 9.3 mm

T

=1= -30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

30

30

Figure 4-17. Axial Flux Scans of

Cigarette FEHN-21(116) in Three

Configurations; Dashed Lines are ±

Average Deviations; Substrates are

Calif. Fabric/2045 PU Foam

10

CMEo

x3

<

UJX

CMEo

9

-

87

6

5

-

4 -

3 -

2

-

1 -

10

CMEo

X

3

<

UJX

8 -

7 -

6

-

5

-

4

-

3

2 -

1 -

10

9

87

6

54

3

2

1

1

1 1 1 r

a) CIG. FEHN-21; FREE BURN

PEAK FLUX: 5.86 W/cm 2

PEAK WIDTH: 6.9 mm

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm) —

i

1 1 1 r

i) CIG. FEHN-21; HORIZ. FLAT

PEAK FLUX: 5.21 W/cm2

PEAK WIDTH: 9.4 mm

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

i 1 1

1

c) CIG. FEHN-21; CREVICE

PEAK FLUX: 4.55 W/cm 2

PEAK WIDTH: 11.4 mm

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

30

30

123
Figure 4-18. Axial Flux Scans of

Cigarette FNHC-25(127) in Three

Configurations; Dashed Lines are ±

Average Deviations; Substrates are

Calif. Fabric/2045 PU Foam

q

_. —r. T ....

a) CIG. FNHC-25;

-1FREE —

i

r- BURN

PEAK FLUX: 7.08 w/ cm2

C\J 8 PEAK WIDTH:

- Eo 7 12.4 mm i \ m

-^. 5 6

J'\\ j\\ - X 5

n \ » _ 3 L * -J \ » LL 4 T •\'l - < 3

-

if -

LU '/< \\l I 2 - '/•

* V -

1n

-

1 ^

It,

l

1 %^l

-

<

LUX

CME

o

<

LUI

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

109

c\T 8 ' Eo

x

-30

10

9 r 8

7 h 6

5

43

2

1

30

1 1 1 1 r

b) CIG. FNHC-25; HORIZ. FLAT

PEAK FLUX: 5.57 W/cm 2

PEAK WIDTH: 16.6 mm

•20 -10 10 20

POSITION WITH RESPECT TO

• MAXIMUM FLUX (mm)

30

T T

c) CIG. FNHC-25; CREVICE

PEAK FLUX: 4.65 W/cm 2

PEAK WIDTH: 19.1 mm

-30 -20 -10 10 20

POSITION WITH RESPECT TO

MAXIMUM FLUX (mm)

30

Figure 4-19. Total Number of Substrate

Ignitions (from Section 3) Versus Peak

Heat Flux Measured with Each

Cigarette on a Horizontal Flat

Substrate Made from Calif. Fabric/2045

PU Foam

coz

LU

co

COZ>

CO

O

z

o

20 -

15

10

Heat flux measured

on substrate

_ (Calif. fabric/PU foam)

5

-

FNHN-25 FNHC-25

FNLC-25

FNLN-25 FEHC-25

BNHC-25 -H •

FEHN-21

I 1 •-

-H-»-

-+*-

3 4 5 6

PEAK HEAT FLUX (W/cm 2 )

and the ignition propensity of the experimental cigarettes. 12

It can be argued that Figure 4-19 contains some real trends; thus the average peak flux for cigarettes containing

expanded and non-expanded tobacco is different as is the average peak flux for the two types of tobacco. Unfortunately the data scatter, coupled with the limited number of tests, makes it very risky to extract such trends. The peak flux in all cases in Figure 4-19 is more than high

enough, if it alone were limiting, to assure fabric ignition

to smoldering. Such fluxes, if applied steadily over a suffi- cient area (significantly larger than the area of a cigarette

coal), will quickly bring the fabric char to nearly the same

temperature as the cigarette coal surface which will surely

ignite it. Other factors must be preventing this in the case of some cigarettes; the speed of coal movement and the

limited size of the coal are the most likely candidates.

12 77?e results in Section 5 indicate the peak flux should be the most

important characteristic of the incident flux distribution in determining

the maximum temperature achieved on a substrate, though it is not

the only characteristic which affects this temperature. The results in Figure 4-19 do not clearly support such a principal role for peak flux because of the data scatter. In fact, there would seem to be some

conflict with this idea in the results for low ignition propensity

cigarettes such as BELN-21 (#106). This particular cigarette caused

only one ignition in the primary evaluation of Section 3. Its average

deviation in peak flux (Figure 4-19), coupled with the idea of peak flux dominance, would lead one to expect several ignitions, not just one. On the other hand, this cigarette has one of the shortest coal lengths

(Figure 4-13(b)) and the raw heat flux data show a tendency for an

inverse relation between peak flux and the axial width of the flux distribution; such a relation, particularly for a small coal length, would

tend to allow radial heat conducting effects in the substrate to suppress ignition. Thus, resolving the results of Figure 4-19 with the

results of Section 5 requires one to invoke a mix of flux distribution characteristics as being the determinants of ignition.

124
Table 4-3. Peak Heat Flux from

FNHC-25 (#127) on Three Fabrics (over

Polyurethane Foam)

Substrate

Peak Flux

(W/cm2

) b

Washed3 California Fabric/2045 Foam

Washed3 Denim/2045 Foam

Washed3 Splendor/2045 Foam

5.6

4.9 4.6

0.8

0.3 0.5

(a) Fabrics were washed in distilled water to minimize their ignition tendency

(b) Average ± average deviation, four to seven tests per substrate

The narrow range of peak fluxes in Figure 4-19 evidently

reflects, in large part, a narrow range of peak coal surface

temperatures in spite of rather wide variations in the cigarette design parameters. Coal surface temperature is the primary driving variable that dictates the magnitude of the

heat flux. As noted previously, coal surface temperature is determined by a balance between heat generation rate and

heat loss rate; the former is in turn dictated by oxygen

supply rate which is largely fixed by the constant configuration to which all the cigarettes in Figure 4-19 were subjected.

Furthermore, radiation is a major fraction of the coal heat

loss rate and it has a very strong temperature dependence,

permitting small changes in temperature to compensate for larger changes in heat loss rate. Thus coal surface temperature is rather resistant to change and so is the peak incident

flux from the coal surface to a substrate. Repeated temperature measurements were made on ten of the experimental

cigarettes (four cigarettes of a given type with two ther- mocouples per cigarette) placed on a flat horizontal substrate consisting of California fabric over polyurethane

foam; the thermocouples were in the cigarette periphery with the junction at the interface between the cigarette and the

fabric. The average peak temperature ranged over about

50°C (635-688°C) but the average deviation was rather large

(+ 20°C to ± 50°C). The correlation with peak flux (Figure

4-20) is quite rough at best (if it can be said to exist at all); a

result, in part, of the scatter in both variables. There is a further factor which can alter the relation between peak temperature and peak heat flux incident on a

substrate: the conductive (and convective) portion of the

heat flux from the coal (as well as, to a lesser extent, the

radiative portion) is sensitive to the distance between the

coal surface and the substrate surface. This separation

distance appears to vary somewhat with cigarette

parameters; Figure 4-21 (a) and (b) show the results of repeated measurements of the gap between the bottom of a

cigarette coal and the uncharred level of the fabric; the measurements were made with a cathetometer. Note that the

full length gap takes time to develop but it then remains

fairly constant. Comparison of Figure 4-21(a) and 4-21(b)

Table 4-4. Effect of Gap Between

Flux Gage and Coal on Peak Heat

Flux Measured

Cigarette

Additional

(mm)

Gap'' Peak Heat Flux

(W/cm2

) c

BELN-21 (#106)

BELN-21

BELN-21

FNHC-25 (#127)

FNHC-25

FNHC-25

0.50

1.50

0.50

1.50

5.45 ± 0.5

4.81 ± 0.3 3.70 ± 0.2

5.57 ± 0.3 5.36 ± 0.2 4.03 ± 0.2

(a) Substrate is California fabric/2045 polyurethane foam

(b) As noted in the text and shown in Figure 4-21, some gap between

the cigarette coal surface and the substrate surface normally exists; the additional gap here was produced by lowering the flux gage the

indicated amount below the initial level of the substrate surface. The

reduced flux at the 1.5 mm gap probably is due in part to shadowing of the flux gage surface by the edge of the fabric along

the slit in which the flux gage resided.

(c) Average (± avg. deviation) of 3 to 4 cigarettes with six flux scans

per cigarette

Figure 4-20. Peak Coal Surface

Temperature Versus Peak Incident

Flux on a Substrate (Calif. Fabric/2045

Foam)

700

O

d

LU(X

cr

LU

QLU

680 -

660

640

620

600

#

BELN21 FEHN21 l #,0«>

(#1181

FELN21

(#114)

FELC21(#I13)

BNLN21

(#1021 • •

BEHC21

(#107)

5.0 5.2 5.4 5.6 5.8 6.0 AVERAGE PEAK FLUX ON SUBSTRATE (W/cm 2 )

125
Figure 4-2 1a. Measured Gap Between

Coal Surface and Substrate as a

Function of Burn Time on Substrate;

Cigarette FEHC-21(115). Substrate is

Calif. Fabric/2045 PU Foam. Individual

Gap Profiles for Three Cigarettes.

1.6

1.2

0.8

0.4

Time: 1 min

j | Lil

Lit end of cigarette

I 6.0 5.0 4.0 3.0 2.0 HORIZONTAL DISTANCE (cm)

1.0

1.6

1.2

0.8

0.4

Time: 4 min

Lit end of cigarette

I 6.0 5.0 4.0 3.0 2.0 HORIZONTAL DISTANCE (on)

1.0

Lit end of cigarette

6.0 5.0 4.0 3.0 2.0 HORIZONTAL DISTANCE (cm)

shows that, on average, there are significant differences

between these two cigarettes; it suggests that the greater

gap for FEHC-21 (#115) could be due to the expanded

tobacco causing a greater shrinkage in the coal diameter. Diameter shrinkage alone is probably not the whole story

behind the gap; increased heat loss to the substrate (as seen on the inert substrates of high thermal responsivity)

increases the gap and this suggests a role for uneven rates

of heating along the upper and lower surfaces of the cigarette. In any event, the role of this gap in altering the relation between peak incident heat flux and peak coal temperature

is obscured by the fact that the peak temperature lies at a

variable and rather imprecise distance from the paper burn

line (which is at the left end of each measured profile in Figure 4-21); the distance is 1-2 mm typically. The overall gap undoubtedly does alter the flux profile seen on the

substrate surface (as suggested by the results in Table 4-4 where an additional gap was introduced) and the variability

of the gap, for a given cigarette type, probably contributes

appreciably to the scatter seen in these profiles. Return now to the issue of what aspect(s) of the incident heat flux profiles correlate(s) with the measured tendency of the experimental cigarettes to initiate smoldering in upholstery substrates. It was noted previously that the time scales

for coal movement and for heat transfer through the

substrate are comparable. There is a finite dwell time of the

coal on any given point of the substrate surface; the total heat fed into a given point thus will decrease if the cigarette coal moves faster. If the rate of heat input at any given point on the substrate was invariant among the cigarettes (the peak, at least, is nearly invariant, as seen above), the time- integrated or total incident heat becomes potentially a signifi- cant measure of ignition tendency. Once again one expects

Figure 4-2 1b. Measured Gap Between

Coal Surface and Substrate as a

Function of Burn Time on Substrate;

Cigarette FNHC-25(127); Substrate is

Calif. Fabric/2045 PU Foam; Individual

Gap Profiles for Five Cigarettes

I

u

HI w ,

cc

5c °

8 r- o

oE 0.4

HI>

EE

LUCO

rr<o

Time: 1 min

_i_

Lit end of cigarette

5.0 4.0 3.0 2.0 1.0 HORIZONTAL DISTANCE (cm)

1.6

1.2

- Time: 4 min

0.8 -

cc 0.4 -

HI>

_L

Lit end of cigarette

5.0 4.0 3.0 2.0 1.0 HORIZONTAL DISTANCE (cm)

Lit end of cigarette

5.0 4.0 3.0 2.0 1.0 HORIZONTAL DISTANCE (cm)

126
that a series of cigarettes tested on differing substrates or in different configurations will produce a series of steps up

from zero as each critical value of total heat input is reached.

A measure of the total heat input at a point can be

obtained as follows. The passage of the coal over an

arbitrary point on the substrate along the cigarette axis imposes a time-dependent flux at that point; the total heat

input is the integral of that varying flux. Time and space

along the direction of coal movement are related by the smolder velocity so that:

Q F*(t) dt = (1/vs) F(x) dx (4-4)

Here Q is the desired integral that measures the total heat

incident at a point, F*(t) is the time dependent flux seen by

the point, vs is the smolder velocity on the substrate, and

F(x) is the measured axial flux distribution. Of course, one

does not really integrate to infinity but merely to a point

where the flux is quite small. Note that this is a one- dimensional integral; it is the total incident heat per unit area

but it applies only along the cigarette contact line with the

substrate. Calculation of the total incident heat over the

whole width of the coal as the coal moved past a region of

interest would require integration over the distribution normal

to the cigarette axis as well; as noted previously, this lateral distribution was not pursued here. The units of Q, as defined

above, are Joules/cm2. It should be noted that not all of this input heat is retained in the substrate; a good fraction of it is lost from the substrate as a result of heat transfer to the

surroundings (by convection and radiation) as the substrate heats up. Note that this integral is derived from the incident heat flux measurements and is subject to the same sources of error. Once again the data were not obtained for each cigarette on

Table 4-5. Effect of Fabric on Total

Incident Heat From FNHC-25 (#127)

Fabric3

Unwashed Splendor

Washed Splendor

Washed Denim

Washed California

Total Incident Heat

(J/cm2

) b

855 ± 26

1117 ± 154

1033 ± 70

1129 ± 131

Figure 4-22. Total Number of Substrate

Ignitions Versus Total Heat Input

Along Cigarette Axis; Heat Input

Calculated from Flux Profiles on

California Fabric/2045 PU Foam

20 -

g 15 Z

<3

IX. O 10-

d

z

_l<o

-

I I I FN

1 BNHC

(N-2t» • t BNHN-2&

I I I -26 -

FNHC-28

• FNLC-26

FNLH-26

• -

FEHC-

• FEHC-21

25 -

FEHN-21

• 8NIC-2I

• BNLN-21

BEHC-21

BEHN-21

FELC-2I»BELC-21

FELW-21 FELN-2S

Q measured on

Calif. Fabric/2045 foam

Corrected lor cigarette diameter

BELW-21

F-»—

1

1 1 1 I I I I

(a) Fabrics was always on top of 2045 polyurethane foam; horizontal flat configuration

(b) Average of five cigarettes ± average deviation

200 400 600 800 1000 1200 1400 1600 TOTAL HEAT INPUT, Q (J/cm 2

) (measured on substrate, Calif, fabric/foam)

each type of substrate used in Section 3 to measure ignition

tendency; rather they were all obtained with the various

cigarettes placed on flat, horizontal substrates consisting of California fabric on polyurethane foam. The results in Table

4-5 for one cigarette (FNHC-25, #127) imply that this is not a source of error; only the unwashed Splendor fabric, which was not used here, yielded an appreciably different total inci- dent heat for this cigarette.

Figure 4-22 shows the correlation between Q, as obtained

above, and the number of substrate ignitions from Section 3

(primary evaluation). Since the substrate does in fact respond not only to the axial flux distribution but also to the

lateral flux distribution, a simple correction was applied to the values of Q to compensate for cigarette diameter differ- ences; the Q values for 21 mm cigarettes were reduced by

the ratio (21/25) = 0.84 before they were plotted. This

correction does not appear to influence the interpretation of Figure 4-22. The results in Figure 4-22 do not have the

simple upward stepped appearance from left to right that one expects from a perfect correlation. On the other hand,

unlike Figure 4-19, there is at least a tendency for an

increase in the number of substrate ignitions as the abscissa

increases. It should be noted that not only is there scatter in the value of Q, there is also scatter in the number of igni- tions and both of these factors will tend to obscure the ideal stepped appearance of such a plot. The flattening at the top

is expected since the number of ignitions cannot exceed

twenty. In any event, Q is clearly only a rather rough

correlating variable for ignition tendency. The apparent

degree of correlation is not improved by plotting the Q's

against the number of ignitions on each separate type of substrate or configuration so this is not the source of the

scatter in Figure 4-22. Total incident heat is simply not a

wholly adequate measure of the effect of the cigarette on

127
the substrates. Again, this is not entirely unexpected in light of the fact that lateral heat conduction in the substrate is occurring on a time scale comparable to that of coal move- ment over the top of the substrate; Q does not contain any

direct measure of the lateral conduction effect. A variable which does contain some measure of the impact of lateral heat conduction is the size of the "hot spot"

that the cigarette imposes on the substrate; this is in turn proportional to the size of the cigarette coal. For the same

heat flux, increasing the size of the heated area increases

the peak temperature that can be achieved at the center of that area up to a limit achieved with one-dimensional

heating; this limit should not be approached here [4-15]. Data on coal length and cigarette diameter are available. If it

is assumed that the coal is conical and hence its cross- section as seen from the substrate is triangular, one can

easily calculate a measure of the "hot spot" size as the area

of this triangle. Of course, the actual shape of the "hot spot" on the substrate surface is more rounded than a triangle;

the goal here is simply to obtain some roughly proportional measure of the actual spot size. If this variable (triangular

area) provided a perfect correlation with ignition tendency, one would again expect a series of steps upward in the number of substrate ignitions as coal area is increased

beyond some critical minimum. Figure 4-23 shows the correlation obtained here between projected coal area and the number of substrate ignitions from Section 3. Again the

qualitative behavior is correct as it was for the correlation with total heat input; the scatter here is less than with that previous correlating variable. The scatter is still considerable

indicating anywhere from one to sixteen substrate ignitions

at the same coal area of 20 mm2

, for example; again, part

of this scatter is in the number of ignitions. Clearly, coal area

is not the whole story, but it appears to be a major contributor to ignition propensity. This suggests that three- dimensional heat conduction effects in the substrate are more dominant in this ignition problem than is either peak

Figure 4-23. Total Number of Substrate

Ignitions Versus Triangular Estimate of

Planar Projected Coal Area; Cigarettes

Burned on Calif. Fabric/2045 PU Foam

20 I I

l NHC1 FNHC- toBNLN- 250

NIC -24 OBnlC-I

S 08 NMC-21 o

15 o

• ios ofehc-21

fehn-210 o0nln-i1

20«,20S« OBEHC-21 10

•208 • 20120T BELC-JlO OFELC-21 S

n

OrtLN-Jl OFELN-21

• 202 OBCLN-21 —1 '1',. 1 1

1

Figure 4-24a. Correlation Between

Mass Burning Rate of Batch One

Experimental Cigarettes and Substrate

Ignition Propensity Found in the

Bench-Scale Tests of Section 3

cI

COE

LLI

<rz

cc

CDCO

CO<

100

5 10 15 NUMBER OF IGNITIONS

20

Figure 4-24b. Same Correlation as

Above but Restricted to Experimental

Cigarettes Containing Flue-cured

Tobacco Only; line is best fit second

degree polynomial

5 10 15 NUMBER OF IGNITIONS

20

10 20 30 40 PLANAR PROJECTED COAL AREA (mm 2 )

incident heat flux or total incident heat. 13

It is worth noting

that Figure 4-23 suggests that a cigarette with a coal area

less than 15 mm2 would give a great improvement in ignition

tendency.

A3Again, Section 5 assigns a greater potential role to peak heat flux than to coal dimensions. The evidently more dominant role of coal dimensions found here may reflect some correlation between coal size and incident heat flux characteristics not yet discerned.

128
Figure 4-25. Correlation Between Mass

Burning Rate of Batch One

Experimental Cigarettes and Coal

Length (from cigarette burning on

horizontal flat, California fabric over

2045 foam)

c

E

E

LU

ccz

ccD

w

is

5 10 COAL LENGTH (cm)

It has been pointed out that a reasonable correlation exists

I between the number of ignitions and the mass burning rate

'of the first batch of experimental cigarettes [4-19]. Figure 4- 24(a) shows such a plot for all of the cigarettes together; the

correlation looks better if the two tobacco types are plotted

separately as in Figure 4-24(b) showing flue-cured data only.

Mass burning rate is a direct measure of the total rate of heat release from a cigarette. While one can reasonably

expect that a greater rate of heat release could lead to increased heat transfer to a substrate (and, thus, a greater

ignition propensity), in general there is not a sufficiently

'direct coupling between these two items to guarantee a oneto-one correspondence. Interestingly, for the cigarettes

studied here, the coupling that appears to be behind the

correlation in Figure 4-24 is a direct relation between mass

burning rate and coal length; this is shown in Figure 4-25. Thus the mass burning rate correlation and the coal length

correlation are related and the latter indicates the mechanism of increased heat transfer which helps cause a greater

number of substrate ignitions. The existence of such a coupling between coal length and mass burning rate for ^cigarettes is implicit in Eq. 4-1 and also in the cigarette coal

profile model of Gugan [4-20], though both are only approximate descriptions of the relation between oxygen supply rate and tobacco burning rate.

All of the preceding factors (peak flux, total heat input and

I "hot spot" size) count in determining the ignition propensity

of cigarettes, though not equally for the particular set of

: cigarettes and substrates examined here. Furthermore, the

details of the flux history imposed at each point as it moves

over the substrate, count as well. The complexity of these

dependencies is an inevitable consequence of the length

and time scales involved in this problem. The single, simple measures of the flux characteristics considered here provide

useful indications of directions in which to move to decrease

ignition tendency but a definitive picture of the quantitative

role of each variable requires detailed modeling of the igni- tion process of the type discussed in Section 5.

Non-steadiness in the Coal Temperature

It is possible that the preceding picture of an ignition

process dictated exclusively by the measured characteristics

of the incident flux distribution from the cigarette is oversimplified. There may be other factors not accounted for there. Two possibilities come to mind; there may be others. The first has to do with the possible non-steady nature of the

flux from some of the cigarettes. A cigarette resides on a

substrate for several minutes, imposing a moving flux pattern

during all of this time. The flux scans described above take

only 3-4 seconds each; even with six scans per cigarette,

the flux is measured only during a rather small fraction of the total ignition delay. It is possible that some cigarettes

rather regularly and invariably produce, at least once during

the burning of each such cigarette, short-lived increases in their rate of heat generation and, hence, heat flux due to inhomogeneities in paper or tobacco characteristics. Note

that the focus here is not on random fluctuations which may

or may not occur with any given cigarette. It could then be

this occasional (but inevitable) higher heat flux, not the more-likely-measured average flux, that produces substrate

ignition. The necessary characteristics of such deviations

(duration, fractional deviation from the average and lateral extent) are a complex function of the time-average flux and

the nature of the substrate. The simplest approach to assessing their possible importance is to look steadily at the

entire coal of a cigarette during an extended period to deter- mine whether significant temperature deviations from the average occur with some regularity over finite areas of the

coal. The line scan feature of the imaging infrared radiometer was used in a preliminary search for such fluctuating

temperatures. This feature allows continuous monitoring of the emitted radiation along a fixed line which, in this case, was parallel to the longitudinal axis of the cigarette and

included the full length of the coal. The peak emission level was monitored for ten continuous minutes of cigarette

smolder atop a fabric/foam substrate (Calif, fabric/2045

foam); the cigarette/substrate interface could not be monitored but the scan line was on the side of the cigarette.

Three different experimental cigarettes were examined in this manner (with three replicates of each); these were FNLC-21

(#109), FEHN-21 (#116) and FELN-25 (#130). These

cigarettes were chosen because they gave widely differing

numbers of substrate ignitions in spite of having essentially

the same value of projected coal area (Figure 4-23). The

results in all cases showed no short term emission (and thus

temperature) fluctuations. There was in some cases a long term drift in the signal corresponding to temperature

changes of about 40°C, but such slow changes would not

129
have been missed in the normal axial heat flux scans. Thus

this preliminary look for significant surface temperature fluc- tuations that might explain some of the scatter in the preceding correlations was negative. Time did not permit a more extensive examination of this question.

Oxygen Depletion in the Fabric

Another possible source of deviation from the purely heat

flux-dominated ignition process described above was alluded

to previously: the cigarette coal depletes the oxygen in the

substrate. The rate of heat generation in the substrate which

leads to fabric ignition is expected to follow an overall rate law of the form

Q'Z(pox)

a (PcHAR) b exp(-E/RT) (4-5) Here Q' is the heat released per unit mass of fabric char

oxidized, Z is the effective frequency factor, pox is the local mass concentration of oxygen, pchar is the local mass

concentration of fabric char, E is the effective activation energy of the oxidation process, R is the gas constant and T

is the local temperature. Such a rate expression is usual for ignition problems [4-16]. The power dependence on pox is usually less than or equal to first order; the temperature

dependence is thus much stronger than the oxygen dependence. Nonetheless, there is some significant oxygen dependence. As the rate of heat release in the fabric begins to rise rapidly in response to the Arrhenius temperature dependence, it is restrained by the local oxygen depletion due to the oxidation in the cigarette coal; the net effect should be

to increase the necessary temperature that the char must

achieve before its heat release rate reaches the critical level where it is self-sustaining ana the char is actively smoldering. Because of the relative dependencies on temperature and oxygen in the above reaction expression, the

restraint caused by oxygen depletion can be overcome by a

relatively small fractional increase in temperature. For example, assume that the value of E lies in the range from

20 to 40 kcal/mole and that the ignition temperature in the absence of oxygen depletion is 500°C; also assume that the

reaction is first order in oxygen concentration (worst case).

Then depletion of the oxygen level in the char by a factor of two requires a 21 to 43°C (factor of 1.03 to 1.06) increase in temperature to again achieve the same rate of heat release. These are small but not necessarily negligible increases in ignition temperature; if a cigarette is a marginal heat source

for the ignition of a given substrate, this oxygen depletion

effect could make the difference between ignition and nonignition. More relevant in the present context, however, is the

difference in oxygen depletion among cigarettes; one wishes

to know whether such differences are responsible for some

of the scatter in the preceding attempts to correlate ignition

tendency with purely heat transfer-related properties of the

cigarettes.

The technique used to assess the extent of oxygen depletion in the fabric during cigarette ignition was described

previously; recall that the measurements were made

between the fabric and the polyurethane foam in flat, horizontal substrates. Figure 4-26 shows typical results for

Figure 4-26. Oxygen Depletion (as a

function of time) Beneath Fabric

a) FNHC-25 on Splendor Fabric/2045

PU Foam; Igniting Case

b) FNHC-25 on Calif. Fabric/2045 PU

Foam; Non-Igniting Case

LUO

>

DO

LUO

DC

LU

CL

LUCD

>-XO

LU

O

>

>

CD

LUO

DCLU

CL

CD

>-X

o

15

10 h

5

(a)

i i 3 cc/min sampling rate

Cig on E| ec tric heat er as source

Cigarette as

heat source

Fabric ign. Time to move 5mm

@ 0.34 cm/min

I

I

Probe removed

Cig. ' from substrate - removed

J_ 50 100 150

TIME (s) 200

Cig.

removed

0.45 cm/min

I 100

TIME (S)

150 200

the sampled oxygen percentage as a function of time from

just before cigarette contact onward. Figure 4-26(a) shows

the result for a fabric/cigarette combination which gave initia- tion of rapid fabric char oxidation (ignition as defined in this section); Figure 4-26(b) shows the result for a combination

which did not. In both cases, the slow decay in oxygen level after the initial fast transient is caused by the coal moving

over the sampling point. Note that in one case the oxygen

level drops to 12 1/2°/o at the time when the fabric ignites; in the other case the oxygen drops to 11% then begins to recover. The failure of ignition to occur in the second case is not due to the slightly greater oxygen depletion; the

California fabric simply does not sustain smolder on the polyurethane foam even when it is first ignited while off of the foam, with a much more vigorous heat source, and then

placed on it.

130
Table 4-6. Summary of Oxygen Measurements During Ignition

Probe Minimum O2 Before

Gas Flow Ignition Comment3

Cigarette

FNHC-25

Substrate (cc/min)

30

(0/0) Number

(1) SPLENDOR/2045 FOAM -14.5

FNHC-25 SPLENDOR/2045 FOAM 30 = 14.5 // FNHC-25 SPLENDOR/2045 FOAM 30 = 15 // FNHC-25 SPLENDOR/2045 FOAM 13 16.5 a FNHC-25 SPLENDOR/2045 FOAM 14 16-17 n

FNHC-25 SPLENDOR/2045 FOAM 7 = 12 a

FNHC-25 SPLENDOR/2045 FOAM 7.7 = 12.5 a FNHC-25 SPLENDOR/2045 FOAM 3 = 11

n

FNHC-25 SPLENDOR/2045 FOAM 3 = 12.5 a

FNHC-25 SPLENDOR/2045 FOAM 3 = 12 a

BELN-21 SPLENDOR/2045 FOAM 3

16.8 (2) BELN-21 SPLENDOR/2045 FOAM 3 = 17 »

BELN-21 SPLENDOR/2045 FOAM 3 = 16-16.5 //

BEHC-21 SPLENDOR/2045 FOAM 3 15.5 BEHC-21 SPLENDOR/2045 FOAM 3 16.8 -

FNHC-25 SPLENDOR/2045 FOAM 3

b 11.5 -

FNHC-25 CALIFORNIA/2045 FOAM 3 12 (2) FNHC-25 CALIFORNIA/2045 FOAM 3 9.2 » FNHC-25 CALIFORNIA/2045 FOAM 3 10.8 »

FNHC-25 DENIM/2045 FOAM 3 9.2 (3) FNHC-25 DENIM/2045 FOAM 3 8.2 h FNHC-25 DENIM72045 FOAM 3 11.8 (4) FNHC-25 DENIM72045 FOAM 3 12.9 a

FNHC-25 SPLENDOR72045 FOAM 3 = 13 -

FNHC-25 SPLENDOR72045 FOAM 3 = 14 (4) FNHC-25 SPLENDOR72045 FOAM 3 = 14.4 //

(a) Comments: (1) Fabric ign. caused further oxygen decrease subsequently

(2) No fabric ign.

(3) Minimum shown is due to cig. plus fabric smolder

(4) Minimum shown is due to cig. plus fabric smolder

(b) Fine needle probe

(c) Washed fabric

Table 4-6 summarizes the oxygen depletion measurements. There is some dependence of the minimum oxygen

level on both cigarette and fabric. Note that the three

cigarettes differ substantially in their ignition tendency.

FNHC-25 (#127) gave 20 substrate ignitions, BEHC-21 (#107)

gave 11 and BELN-21 (#106) gave one. Close examination of

Table 4-6, comparing these cigarettes for minima due to the

cigarette smolder only, shows that the range of oxygen

minima is from about 11 to 17%. By the same type of calculation procedure done above, one can show that this differ- ence in oxygen levels can cause a difference in ignition

temperature of 13 to 27°C for values of E in the range noted

131
above and with a first order oxygen dependence. Thermal

analysis (TGA) results (air, 0.5 to 5°C/min.) for the fabrics in Table 4-6 give E values in the range from 33 to 36

kcal/mole. The order of the reaction with respect to oxygen

has not been obtained for these fabrics but for another

cellulosic material, tobacco char, Muramatsu found the order

to be one-half [4-17]. With both of these likely parameter

values taken into account, the observed range of oxygen

depletion levels is likely to produce only a 6 to 8°C variation

in ignition temperature. Thus it appears that oxygen depletion effects in the substrate are a secondary source of scatter in the preceding heat transfer correlations, at most. Figure 4-26(a) also shows the oxygen depletion for a

typical case in which the cigarette has been replaced by a

non-oxidative heat source, an electric heater. The source is the end of a 9.5 mm diameter rod heater which is hot enough to glow dull orange; the heater stays about 2 mm

above the fabric surface and provides a peak incident flux on that surface of about 2

1/2 to 3 W/cm2

. The half-height

peak width is about 1 cm. This relatively large heated area

(plus the lack of oxygen depletion) made it possible for this relatively low peak flux to yield the same ignition time as a

cigarette providing a higher peak flux. The drastic decrease

in oxygen depletion when a cigarette is not the heat source

indicates that there is minimal, if any, oxygen consumption in the process of degrading the fabric and foam in the

substrate. Recall that the issue of the thermicity of the

substrate prior to ignition was addressed previously. The

present result is not proof that no exothermicity exists but it does indicate that it must be much less than the rate of heat

release from the cigarette. The depletion that does exist with the electric heater may be due only to local oxygen dilution by the degradation products evolving from the fabric and

foam.

Substrate Temperatures

The differing incident heat flux profiles discussed above

should be reflected in differing temperature distributions in any substrate with which these cigarettes come into contact. This was explored first with an inert substrate to avoid

possible complications due to any reaction heats. The

substrate was chosen for its homogeneity and low thermal

responsivity (to avoid distortion of the cigarette coal): the

material was a calcium silicate insulation board with a

density of 0.22 g/cm3. It was kept in a desiccator prior to

testing; thermal analysis showed a small weight loss (—

10%) over the temperature range from 25 to 500°C, but no

quantifiable heat effect accompanied this loss. The initial measurements were with two thermocouples imbedded in the top surface of the board; these were 0.05 cm diameter

chromel/alumel thermocouples spaced 1.0 cm apart along

the direction of the cigarette axis. Cigarettes previously

ignited and allowed to smolder for a period of two minutes were placed on the board in such a position that the coal would move over the two thermocouples within the succeeding few minutes. The time for the paper burn line to reach the first thermocouple was varied from % to 3

minutes. The results of these measurements are summarized

in Table 4-7. The peak temperatures (except for ther- mocouple #2 with FNHC-25 (#127)) follow the expected

order implied by the number of substrate ignitions. Note that the peak temperature is not simply dictated by the peak flux; FNHC-25 (#127) and BELN-21 (#106) have virtually the same

peak flux in this configuration (see Figure 4-19). Recall that the former cigarette has a coal length that is about twice as

long as the latter and this affects the peak temperature

because of the three-dimensional nature of the heat flow in the substrate. Note that the difference in temperatures

between the two thermocouples does not appear to give a

Figure 4-27. Isotherm Contours on the

Top Surface of a Horizontal Flat

Upholstery Mock-up (California

fabric/2045 foam)

a) Cigarette BELN-21 (#106); time = 226 seconds

b) Cigarette FNHC-25 (#127); time = 368 seconds

ISOTHERMS ON SUBSTRATE

AFTER 2cm OF COAL MOVEMENT

O

COQ

_l<

cc

Coal

0.50

I

(a) —

j

\

- T T

\

250

0.25 300N.

350 \

-0.25 o° / J

-0.50

1

/ 250

Movement

-0.25 0.25 0.50 AXIAL DISTANCE (cm)

-0.50 -0.25 0.25 0.50 AXIAL DISTANCE (cm)

0.75 1.00

132
Table 4-7. Temperatures' on Surface of Calcium Silicate Board

Induced by Cigarettes

Temperature at TC#1

When Burn Line Peak Temperature Peak Temperature (TC#1 - TC#2) When Burn Line No. of Substrate Passes TC#1 atTC#1 at TC#2 Reaches TC#1

Cigarette Ignitions (deg. C) (deg. C) (deg. C) (deg. C)

FNHC-25 20 417 ± 12 470 ± 10 434 ± 10

b 366

BNLN-21 12 418 ± 12 460 ± 8 457 ± 9 378 FEHN-21 12 380 ± 12 420 ± 14 432 ± 16 343 BELN-21 1 355 ± 18 372 ± 30 389 ± 28 314

(a) Temperatures from thermocouples embedded in surface of calcium silicate board 1 .0 cm apart along axis of cigarette coal movement. TC#1 is the

first thermocouple over which the coal passes; TC#2 is the second

(b) Average of two points

good measure of the width of the flux distribution in the

solid, possibly because the times preceding these measure- ments were not held fixed. There does not appear to be a

significant upward trend of peak temperature with time, as seen by comparing the peak values at the two ther- mocouples; this may be because of the relatively long time

at which these measurements were taken. Figure 4-27 shows the isotherms on the top surface of an

upholstery mock-up (California fabric/2045 polyurethane

foam) caused by two of the experimental cigarettes. The two

cigarettes differ substantially in their ignition tendency;

BELN-21 (#106) yielded one substrate ignition out of a

possible twenty in Section 3 (primary evaluation) and FNHC25 (#127) yielded twenty ignitions. At the times shown in the

figure, each cigarette had sat on the substrate just long

enough for the paper burn line to have moved 2 cm. since

the cigarette first came into contact with the substrate. These

times are both sufficient for the temperature patterns to be in a nearly steady state. Recalling the difficulties in obtaining

these types of patterns, one should not regard them as

highly quantitative in an absolute sense; the temperatures

are reasonable, but it is the relative patterns that are of greater interest. The patterns are somewhat irregular due

both to video noise and to random fluctuations in the spatial distribution of the flux incident from the cigarettes. The

400°C isotherm is instructive since the fabric ignition temperatures reported previously were above this level. The area on the substrate surface which is enclosed by the 400°C

isotherm is about 40 times larger in the case of FNHC-25

(#127) than for BELN-21 (#106). There is also a substantial area above 450°C with cigarette FNHC-25 (peak temperature 464°C) whereas the highest temperature with BELN-21

is 25°C below this level (peak temperature 424°C). Thus, no

matter whether smolder initiation in the fabric requires

achievement of a minimum ignition temperature at a point on the fabric or within some minimum volume of the fabric,

it is clear that FNHC-25 will achieve such conditions more

readily than will BELN-21. This is the result that one would

expect on the basis of the preceding measurements of the

incident flux characteristics of these cigarettes.

It is pertinent to note that the small difference in peak

substrate temperatures (40°C) resulting from contact with cigarettes which differ greatly in ignition propensity implies

that the fabric ignition process is only marginally achieved

by the most ignition prone of the experimental cigarettes.

Measurements like those in Figure 27 would have been

useful at several times for any given cigarette type and for more cigarette types as well; this would have provided

further proof of the correspondence between the measured

incident flux characteristics and the temperature buildup in the substrate that leads to smolder initiation. Unfortunately,

time constraints prevented this.

133

Nummary and Conclusions

The studies reported in this section have helped clarify the

relation between the cigarette and the smoldering ignition process it induces in upholstery substrates. It is apparent

that this relation is quite complex even before any rapid

exothermic reactions begin in the fabric. The cigarette coal is altered by the proximity of a substrate and it is altered by

efforts to measure the heat flux incident from the coal to a

substrate. The heat flux that has been measured for a large number

of the experimental cigarettes is the "cold wall" value which

pertains to the very early stages of heat-up of a substrate. The major emphasis has been on obtaining the flux distribution along the longitudinal axis of the cigarettes. The errors

in measuring these flux profiles are such as to make the peak flux values obtained as much as 25-30% lower than

the actual values. The axial heat flux profiles are thus most

useful for comparative purposes. They are found to vary

both with the geometric configuration of the adjacent

substrate (if any) and with the design parameters of the cigarette. The variation with configuration can be largely

explained on the basis of adjustments the cigarette coal makes to its rate of oxygen supply; heat losses appear to

interact with these adjustments. The design parameters of the experimental cigarettes have little impact on their peak

coal surface temperatures and hence their peak heat flux; this latter parameter could not be shown to have a statisti- cally significant correlation with the ignition propensity of the

cigarettes examined here even though there is good reason

to believe that it must if it could be varied significantly

(Section 5).

Cigarette design does substantially affect the smolder

velocity and the coal length. These two parameters combine

to influence the total heat input from a moving cigarette coal

to a fixed point on a substrate surface. Total heat input is found, however, to correlate only approximately with substrate ignition tendency. The best correlation (though by no means perfect) is found between a measure of coal area and ignition tendency; a related correlation exists between mass burning rate and ignition tendency. The partial correlation with coal area implies that the three-dimensional nature

of the heat flow in a substrate in response to local heating

by a cigarette coal is a major factor in determining whether

the fabric beneath the cigarette coal will become hot enough to begin to smolder. There is significant oxygen depletion in the fabric during

its heating by a cigarette coal; this could be sufficient to raise the effective ignition temperature a few tens of degrees.

However, the variation in this depletion among cigarettes of differing design does not appear to be significant as a factor helping to explain their differing ignition propensities. The

limited data on the cigarette-induced temperature distribu- tions on the top surface of both inert and reactive substrates are generally consistent with the conclusions inferred above.

The results here provide both important clues as to how to lower the ignition propensity of cigarettes and an extensive

experimental base on which to build and test models of the

ignition process. For the latter they are particularly important

for clarifying and quantifying the nature and extent of the

cigarette/substrate interaction during ignition, providing flux distributions pertinent to various configurations. The next

section provides further probing of these issues.

135
:~;
References for Section 4

[4-1] Salig, R., "The smoldering behavior of upholstered

polyurethane cushionings and its relevance to home

furnishings fires," Master's thesis, Massachusetts

Institute of Technology Dept. of Mechanical

Engineering, 1978.

[4-2] Behnke, W. "Cigarette Study; Heat Flux and Ember

Temperatures," presented to ASTM, 1969.

[4-3] Damant, G., California Bureau of Home Furnishings,

private communication to J. Krasny, 1975.

[4-4] Ihrig, A., Rhyne, A., Norman, V. and Spears, A., J. Fire Sciences, (1986).

[4-5] Norman, V., "Heat Output of a Burning Cigarette,"

CORESTA Congress, Vienna, Austria, October,

1984.

[4-6] Muramatsu, M., "Studies on the Transport

Phenomena in Naturally Smoldering Cigarettes,"

Research Rept. No. 123, Japan Tobacco Monopoly,

1981.

[4-7] Baker, R., High Temperature Science 7, 236 (1975).

[4-8] Ohlemiller, T., Prog. Energy Combust. Sci. 11, 277

(1985).

[4-9] Palmer, K., Combust. Flame 1, 129 (1957).

[4-10] Moussa, N., Toong, T. and Garris, C, Sixteenth

Symposium (International) on Combustion, The

Combustion Institute, Pittsburgh, PA 1976, p. 1447.

[4-11] Rogers F. and Ohlemiller, T., J. Fire Flamm. 11, 32

(1980).

[4-12] Resnik, F., Houck, W., Geiszler, W. and Wickham,

J., Tob. Sci. 179, 33 (1977).

[4-13] Ohlemiller, T., "Forced smolder propagation and the

transition to flaming in cellulosic insulation" NBSIR

85-3212, National Bureau of Standards, October,

1985.

[4-14] Selke, W., private communication.

[4-15] Thomas, P., Quart. J. Mech. and Appl. Math. 10,

482 (1957).

[4-16] Thomas P., Ignition, Heat Release and NonCombustibility of Materials, ASTM STP 502,

American Society of Testing Materials, Philadelphia,

PA 1972, p.56.

[4-17] Muramatsu, M. and Umemura, S., Beit, zur Tabakforsch. 11, 79 (1981).

[4-18] Touey, G. and Mumpower, R., Tobacco Science 1, p. 33.

[4-19] Spears, A., Lorillard Inc., private communication.

[4-20] Gugan, K., Combust. Flame 10, 161 (1966).

137
!
The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 5

Modeling Ignition

139

Contents for Section 5

Introduction 1 45

Background 147

Cigarette Dynamics 147

Previous Modeling Efforts 148

Modeling the Substrate 151 Thermal Physics 151

Ignition 152

Possible Improvements 152

Modeling the Free Cigarette 1 53

Semi-Empirical Model 1 53

Burning Rate as a Function of Various Parameters 1 53

The Surface Heat Flux 1 54

Correlation Between v and tc 1 55

Detailed Model 1 57

Partial Model 1 60

Equations 1 60

Numerics 161

Initial Conditions 162

Comments 1 62

Interactions Between Cigarette and Substrate 163

Conduction Flux to Substrate 163

Radiation Flux to the Substrate 165

Connection with the Semi-Empirical Model 165

Cigarette Energy Balance in the Presence

of a Substrate 1 67

Summary 1 69

Results from Using the Models 171 Substrate Program 171

Cigarette Program 1 77

Summary and Conclusions; Lessons Learned 181 References for Section 5 1 83

List of Tables

Table 5-1. First Choice of Initial Distributions

of Temperatures, Oxygen Mass Fraction,

and (Relative) Tobacco Density,

Assumed for the Calculation 162

Table 5-2. Calculated and Experimental

Values of Temperatures

at TC#1 and TC#2 1 73

Table 5-B-1. Parameter Values Used for the Sample Run in the Text, Using

Program CIG25 191

List of Figures

Figure 5-1. Schematic of a Smoldering

Cigarette 147

Figure 5-2. Temperature Distributions (in °C) at and near the Hot Coal,

Shortly After a Draw 1 48

Figure 5-3. Gas Temperature (°C) and

Oxygen Concentration in the

Quietly Smoldering Cigarette 148

Figure 5-4. Measured Longitudinal

Surface Temperature Distribution

for Cigarette 105 155

Figure 5-5. Peak Fluxes Measured by

a Thermocouple, for a Representative Sample of Experimental Cigarettes

Smoldering on a California Fabric/Foam Substrate . . . 156

141
Figure 5-6.

Figure 5-7.

Figure 5-8.

Figure 5-9.

Figure 5-10.

Figure 5-1 1a.

Figure 5-1 1b.

Figure 5-1 1c.

Plot of pCv vs t

c

, the Coal

Length, to Test Eq. (5-34) . 156

Average of Several

Measurements of the Flux Emitted by Cigarette

105 Toward the Substrate,

Along the Contact Line . . . 163

Peak Temperatures of the Calcium Silicate Substrate

Surface as a Function of Time, for the Flux Used for Cigarette 105, for Several

Values of a,

Reproduction of Figure F,6b

from Reference [5-12]. Theoretical streamlines for horizontal cylinder

Reproduction of Figure F,6a

from Reference [5-12]. Azimuth

function g(x) giving variation

of local heat transfer coefficient

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 2 sec

166

168

168

173

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 12 sec 173

Calculated Isotherms on a Calcium Silicate Surface,

Resulting from Heating this Substrate with the Flux Shown

in Figure 5-7 (from Cigarette

105), at Time t = 84 sec

Figure 5-1 2a.

Figure 5-1 2b.

Figure 5-1 3a.

Figure 5-1 3b.

Figure 5-1 4a.

Figure 5-1 4b.

Figure 5-1 4c.

Figure 5-1 4d.

Figure 5-1 4e.

Figure 5-1 5a.

Figure 5-1 5b.

Figure 5-1 5c.

Flux Measured Under the Rod Heater Along the Substrate .174

Flux Measured Under the Rod

Heater in the Direction Orthogonal to that Traversed

in the Measurements Shown

in Figure 5-13a 174

Calculated and Predicted

Temperatures at Thermocouples

TC1 and TC2 When the Smolder

Wave from Cigarette 102 is Made to Pass Over Them 175

Calculated and Predicted

Temperatures at Thermocouples

TC1 and TC2 When the Smolder

Wave from Cigarette 102 is Made to Pass Over Them 175

174

Initial Temperature Distribution

(in °C) Chosen for Calculation,

to Simulate Effect of Lighting

Cigarette With a Match 175

Isotherms at t = 2 sec, after

Initiation as in Figure 5-1 4a 176

Isotherms at t = 4 sec 1 76

Isotherms at t = 6 sec 1 76

Isotherms at t = 7.86 sec 1 76

Isotherms for Second Set of Starting Conditions. These

were Taken from Figure 5-2 177

Isotherms Corresponding to Smolder Wave at t = 6 sec 1 77

Isotherms in the Model

Cigarette at t = 1 2 sec 1 77

142
Figure 5-1 5d. Isotherms at t = 1 8 sec 177

Figure 5-1 6a. Contours of Constant Oxygen

Mass Fraction Corresponding

to Figure 5-1 5a (t = 0) 178

Figure 5-1 6b. Oxygen Mass Fractions at

t = 6 sec from the Same

Calculation That Yielded

Figure 5-1 5b 178

Figure 5-1 6c. Oxygen Mass Fractions at t= 12 sec 178

Figure 5-1 6d. Oxygen Mass Fractions at t= 18 sec 178

Figure 5-17. Calculated Velocities of the Upper and Lower Intersections

of the 700°C Isotherm with the Axis, as a Function of Time 179

Figure 5-1 8a. Contours of Constant Radial

Gas Velocity at t = 6 sec from

the Calculation That Yielded

Figures 5-15b-d and 5-16b-d 179

Figure 5-1 8b. Contours of Constant Radial

Gas Velocity at t = 1 2 sec 1 79

Figure 5-1 8c. Contours of Constant Radial

Gas Velocity at t= 18 sec 180

Figure 5-19. Cross Section of Buried

Cable, with Various Distances

and Temperatures Indicated 203

Figure 5-20. Cross Section of Cigarette on

Substrate 205

List of Appendices

Appendix 5-A: A Description of the

Substrate Program 185

Appendix 5-B: The Cigarette Program CIG25 189

Appendix 5-C: Convective and Radiative

Losses from a Freely Burning Cigarette 199

Appendix 5-D. Derivation of the Transverse

Conductive Flux Distribution 203

143

I ntroduction

In Section 3, the results of ignition tests made with a few

selected cigarettes were described. These yielded fluctu- ating but statistically significant results for a few choices of each of five cigarette parameters: tobacco type, cigarette

density, paper permeability, chemical treatment of the paper, and cigarette circumference. In this section, we will consider the mathematical modeling of cigarettes, substrate,

and of their interactions. Among other advantages, a valid mathematical model has the great virtue that not only will it correctly predict the results for such discrete parametric

choices, but that it can correctly predict the results for inter- mediate choices of parameters - i.e. it permits smooth

interpolation of results. Moreover, assuming it does everything right, it can extrapolate — i.e., predict the results for cases outside the parametric bounds of the experiments.

Indeed, it should make correct predictions for the results from entirely novel combinations.

The purpose of this study is to predict theoretically

whether or not an upholstered furniture item will be ignited

to smoldering when a lit cigarette is dropped on it. To do

this, the heating of the substrate when subjected to a moving heat source must first be accurately modeled, and a

criterion established for its ignition. In order to examine how

changing one or more properties of the cigarette will influence its ignition propensity, it is also necessary to understand the behavior of a smoldering cigarette. This

includes knowing how its external heat flux and burning

velocity depend on its various geometrical, physical, and/or

chemical properties, and how these processes are modified

when the cigarette lies on the substrate.

To make such predictions, the physics and chemistry of pyrolysis and of simultaneous heat and gas transport in a

cigarette must be expressed by a set of mathematical equations. Since it is extremely unlikely that analytic solutions of these equations will be possible, procedures must be

devised for solving these model equations numerically, on a computer.

Finally, we need to understand and describe how the

cigarette and substrate influence each other, when in contact. In this section, three models are developed: (1) the computer model TEMPSUB, which yields the time- dependent temperature distribution in a substrate when it is exposed to a moving heat flux; (2) the computer model

CIG25, which gives the time-dependent distributions of temperature, oxygen concentration, gas velocity, and

burning rate in a freely-smoldering cigarette with user- prescribed properties; and (3) a model for the interaction of the cigarette and substrate when they are in contact; this gives the heat flux from a cigarette to the substrate. The next sections present the details pertaining to substrate heating, modeling a freely-smoldering cigarette,

modeling the interactions, and the procedure to be used for getting the flux to use in the substrate program. The results obtained with, and a partial validation of, the models are given last. In order to place the cigarette-modeling effort into perspective, the next subsection gives a brief account of the physics of cigarette smoldering and a description of earlier cigarette models.

145

ackground

Understanding the smoldering cigarette has received a good deal of effort, both experimental and theoretical. In this section, a brief, qualitative discussion of the dynamical

processes which occur will be presented, the salient results from earlier experiments noted, and some of the principal

efforts made to model a cigarette, discussed. It is not intended to be an exhaustive review.

Cigarette Dynamics

A cigarette consists of small strands of cured tobacco leaf, held in a cylindrical shape by a paper wrapping. The

cylinder has a circumference of 20 to 25 mm; it is usually

circular in cross-section, with radius R. The paper is chemically treated to burn at about the same rate as the tobacco,

and has permeability within specific limits. Often there is a

filter at one end. A schematic illustration of a smoldering

cigarette in its quiescent phase is given in Figure 5-1. The

section marked C in this figure is char, most of which is oxidizing at a rate sufficient to make it glow. The peak

temperature in this region is about 800 to 850°C, i.e. 1 100

± 25 K. The glowing coal is shaped more or less like a

thick cone. The cone length varies, but is usually (see

Section 4) on the order of 1 cm in length. Some of the heat

from this reaction is carried back towards the virgin tobacco

(the zone marked VT in the figure); this occurs partly by

thermal diffusion, partly by radiation, and partly by convection of hot gases. This heat dehydrates and decomposes

the tobacco behind the char - this is the (shaded) region

marked P in the figure (P for "pyrolyzing"). This is the region

from which a visible plume of smoke (marked S) rises. At

the very front of the cigarette is the residual and evanescent

ash, marked A and EA, respectively, in the figure. For all commercial cigarettes, the paper decomposes and

burns at the same velocity as the tobacco; this occurs in a

thin region, on the order of 1 mm in width. Although the paper is permeable, most of the oxygen which is needed to sustain combustion diffuses into the cigarette in front of the paper burn line. That it must diffuse inward is clear, since

the volume of air needed to consume the cigarette is about

1000 times the volume of the solid. This study only

considers the quiescent phase of smoldering — i.e., between puffs — since that is the situation when it lies on

the substrate. The measured temperature distribution in the smoldering

cigarette is shown by the isotherms in Figure 5-2, taken

from Baker [5-1]. Figure 5-3, taken from the same reference,

shows the (measured) volume percentage of oxygen. Note

that this value is essentially zero in the region of maximum

temperature, so that the reaction (oxidation) rate there is low, in spite of the high temperature.

It can be seen that the smoldering is (as might be

expected) cylindrically symmetric. Also — consistent with an

oxygen-diffusion-controlled process — the oxygen concentration in the center drops to very low values. Generally, the peak reaction rates occur in the region where the mole frac- tion of oxygen, x(02), is less than one percent. If the reaction rate is described by an Arrhenius expression, then it must be highly peaked in the high-temperature region.

Indeed, the simple approximation of an infinitely high reaction rate occurring over a surface which is a paraboloid (or conoid) of revolution might be expected to have some

Figure 5-1. Schematic of a Smoldering

Cigarette. The region marked EA is "evanescent"

ash, which normally falls off. It remains in place only

when resting on the substrate. For the meaning of the

other symbols, see the text. Note that the orientation

is the reverse of that shown in Figures 5-2 and 5-3.

147
Figure 5-2. Temperature Distributions

(in C) at and near the Hot Coal,

Shortly After a Draw. The Upper Figure Shows

the Temperatures in the Solid; the Lower Figure, that in the Gases. The Shaded Region in Explained in the

Text. From Baker [5-1].

DISTANCE FROM LINE OF PAPER BURN (mm)

-2 +2 +4 +6 +8 +10

DISTANCE FROM LINE OF PAPER BURN (mm)

validity (see Ref. [5-15]). In reality, this "surface" is a thin region. Since the oxygen concentration increases as the

outer surface is approached, we would expect that this region is thickest at the periphery, where the peak surface

temperature is 550-600°C, and grows thinner towards the

center, with a slightly higher temperature; this region is shown in the lower of the two figures in Figure 5-2 by the shaded paraboloid. The highest temperatures occur behind

the highly active shell. Thus, suppose an observer were

positioned at x = - i.e., at the paper burn line. As time

progresses and the smolder wave moves to the left (to the

right, in Figure 5-1), the peak reactions occur in a

contracting ring, starting at the periphery and contracting to a point, leaving ash on the outside of the ring.

The distribution of surface temperature is a central question for our study, since the heat flux delivered to the

substrate depends on it. Perhaps most important is the peak

surface temperature there, Tp

. Unfortunately, it is not an

easy quantity to measure. Indeed, it is not even a well- defined quantity, since (as we see from Figure 5-2) the gas

and the solid temperatures are not quite the same. Moreover, the result depends on the measurement technique.

Baker's measurements yielded a peak surface temperature

of about 550°C. Measurements reported in Section 4 yield

peak temperatures in the range 650-700°C; however, these

measurements are made with a thermocouple inside the paper wrapping, so that the surface temperature must be

lower. Egerton et al. [5-7] found 616°C for Tp. Lendvay and

Laszlo [5-8], using an IR technique, found that Tp for their cigarettes was approximately 600°C. Since peak surface

temperatures may well vary by 50°C among cigarettes, it is clear that Tp = 600 ± 50°C.

Cigarettes vary within a factor of about 3 in the speed of propagation of the smolder wave: the average commercial

cigarette is 6 to 7 cm long, and it takes between 10 and 30

minutes to be consumed, without drawing or puffing on it. The variations depend on the radius, on the packing

density, on whether the tobacco leaf has been expanded or

not, on the kind of tobacco, on the moisture content of the tobacco, on the cut width, and on the kino of paper, its permeability, and how it has been chemically treated. Note

that, contrary to what is predicted by Muramatsu's model

(see below) Samfield states that the moisture content does

not affect its peak temperatures (Ref. [5-14]); rather, it affects the burning velocity, because it takes time (and

energy) to evaporate the water.

Previous Modeling Efforts

A number of attempts have been made to model smoldering cigarettes or analogous systems. All of them make

some simplifying assumptions in order to make the problem

tractable. Figure 5-3. Gas Temperature (°C) and

Oxygen Concentration in the Quietly

Smoldering Cigarette. From Baker, ref. [5-1].

(a) Gas Temperature

i

(b) Oxygen

148
One of the early ones is that of Moussa, Toong, and

Garris [5-2]. They experimented with, and then modelled,

the smoldering and extinction of a cellulose cylinder without

any paper wrapping. They assumed the smoldering to be

steady-state, and they treated the problem as one- dimensional (hence, no radial gradients). They found: (a) (Experimentally) that the smoldering velocity is closely

related to the maximum temperature in the cylinder, (b) reasonable agreement between theory and experiment for the extinguishment limit, (c) that the rate-limiting step in the combustion and hence in the rate of propagation is the

diffusion of oxygen to the char, which is in good accord

with experiment. They also (d) calculated values for v, the propagation velocity of the smolder wave. However, the

calculation depends on an uncertain parameter, and the

quantitative accuracy of the model is questionable.

A much more detailed model of a cigarette was produced

by Summerfield et al. [5-3], It considers a two-step process:

| pyrolysis to a char, followed by its oxidation. It ignores water

evaporation. The char-oxidation reaction is assumed to be a

[ linear function of the oxygen concentration. The combustion

model is time-dependent rather than steady-state, and

j considers the paper covering, though only indirectly, via a

I varying surface permeability to oxygen. It has a sophisticated treatment of heat transfer inside the cigarette: it

I includes heat transfer by radiation, as well as by solid phase

! conduction. It is also a one-dimensional model. The model

! consists of ten simultaneous, coupled partial differential

; equations (PDEs), and the starting condition assumes the

| presence of fixed amounts of ash, char, and tobacco. The

calculation predicts the burning velocity fairly well, as a

; function of draw rate. However, the dependence on oxygen

mole fraction in the atmosphere is not so well predicted,

although this is not important for the current purpose. The

calculated gas temperature profile is fairly good: the peak is about right; but the width of the distribution is too narrow

(see Section 4). Perhaps the main limitation for this project is that it is a steady-draw model, so that diffusion and natural convection within the cigarette are ignored.

The most elaborate model is that due to Muramatsu et al. [5-4,5]; it was developed in two stages. In Ref. [5-4] they

develop a model for the pyrolysis of the cigarette. Their

model is best described by quoting from their abstract:

"A one-dimensional mathematical model for heat and mass

balance has been proposed to elucidate the changes occurring in the temperature and density of the evaporationpyrolysis zone in a naturally smoldering cigarette. The model

considers: (1) pyrolysis of tobacco obeying Arrhenius

kinetics, (2) evaporation of water from tobacco following a

mass-transfer- and rate-determined process, (3) weight loss

|' of tobacco due to pyrolysis and evaporation, (4) internal heat transfer characterized by effective thermal conductivity,

(5) heat loss attributable to free convection and radiation from the outer surface of the cigarette and endothermicity of

the evaporation process, and (6) smoldering speed. These

processes are expressed in a set of simultaneous ordinary

differential equations that can be solved numerically by the Runge-Kutta-Gill method.

Furthermore, they assume the process is steady state, and,

at this stage, impose the propagation velocity, v. They also ignore the convection or diffusion of gases other than water

vapor. They take the existence of the paper wrapping into account only through its effect on the loss of water vapor. These approximations are evidently adequate, as it yields

good agreement between theory and experiment (see Ref.

[5-1]) for the temperature and density along the axis in the pyrolysis-evaporation region. Position along the axis is given

by x, where x = is the boundary between the pyrolysis

region and the char-oxidation region. Thus, the agreement

for T(x) and p(x) is good for x<0 - i.e., before the char- oxidation region (not considered in this part of their model). For x>0, the calculated temperature profiles deviate

substantially from measured ones, as might be expected.

The dependence of the profiles on the imposed velocity, on

the other hand, is not so well reproduced — there is only

semi-quantitative agreement. Since this pyrolysis-zone model

is one-dimensional, it does not give an R-dependence of the

results.

In Ref. [5-5], Muramatsu developed a char-oxidation

model which describes the processes occurring in the region x>0; this complements the pyrolysis/evaporation

model developed in [5-4]. The model is quite detailed; it takes two char-oxidation reactions into account and is two- dimensional (cylindrically symmetric). Like all the other models it is a homogeneous model, i.e., it does not take the

point-to-point heterogeneity of the cigarette (i.e., the fact that there are solid particles and a gaseous medium) into account directly. Energy loss is through radiation and

convection at the outside surface of the cigarette. It is assumed that there is no temperature difference between

the solid and gaseous phases. This is not a bad approximation, and simplifies the problem considerably. Heat transport

by thermal radiation inside the cigarette is taken into account in a somewhat different way than is done in Summerfield er al. The thermal conductivity at any point is assumed to be isotropic. Similarly, the temperature dependence of the gaseous diffusivity is taken into account

explicitly.

Finally, the pyrolysis/evaporation model and the char- oxidation model are tied together through an energy-flow

matching condition at the pyrolysis/char-oxidation boundary

to obtain the appropriate smolder velocity. There are still a few weaknesses in this formulation:

1. Any pyrolytic reactions in this region (x>0) are ignored:

2. The burning is assumed to be steady state;

3. The paper burn line must be coincident with the (forcibly)

plane end of the pyrolysis zone:

4. Prior to decomposition, the paper wrapping is assumed

to be impervious to oxygen; this should result in the cigarette going out, according to experiment;

5. Perhaps in order to be consistent with the above

assumption, radial convection of gases is ignored; and

149
6. If the calculation has not converged after 1000 iterations, the unconverged result is accepted as correct, nevertheless.

The results of calculations made by Muramatsu for six representative cigarettes are:

1. The peak temperatures, when expressed in °C, are only

2.7% to 5.7% higher than experimental data.

2. The smolder velocities are 14% high, on the average,

varying between 4% low and 26% high.

3. The calculated variations of smolder rate (v) and peak

temperature (Tm) with R (the cigarette radius), the packing density pp

, and the moisture content in the tobacco shreds are indistinguishable from the experimentally observed variations.

The dependence of v and Tm on ambient oxygen partial pressure is not well predicted (this is not an important

consideration in this study).

4. The calculated distribution of temperature and oxygen

concentration (in the char oxidation region) is in agree- ment with measurement, except for a scale factor (the predicted distribution is narrower than observed).

Because of this last point, Muramatsu et a/.'s model cannot be used directly to obtain the flux emitted to the substrate: the too-narrow temperature distribution would substantially

underpredict the energy output of the cigarette to the

substrate. However, the model is excellent for some

purposes; in particular, to estimate cigarette smolder velocities. The velocity is used in conjunction with a correlation found in this section (also see Eg. (4-1)) to obtain the axial width of the distribution of heat flux from the cigarette.

150
Modeling the Substrate

(x.y.t) = h(Ts -Ta ) + £s a(Ts 4 -Ta (5-3)

Thermal Physics

Smoldering ignition of a flammable substrate (i.e., furniture) results from that material being subjected to a sufficiently

high heat flux for a sufficient length of time. The substrates of interest are fabric-covered padding. For

the sake of simplicity, however, this analysis assumes the

substrate to be homogeneous, uniform, and inert. Thus, the

model begins with a representation of the diffusion of the energy (supplied by the ignition source) within the substrate; the latter is a specified, external, slowly-moving flux; the presence of a cigarette is taken into account via appropriate

boundary conditions. The general equation for heat diffusion through a solid medium is [5-6]

pC § = div(k grad T) + S

at (5-1

;

This equation relates the time rate of change of temperature

(the left-hand side) at a point, to the temperature gradients

at that point. Here S is any internal heat source (or sink), and the thermal conductivity k is a function of temperature,

and hence a function of position. If the substrate is inert and

does not contain water, then S = 0, and any heat sources or sinks will appear only on the boundaries. Using a Cartesian

coordinate system, z is the coordinate normal to the surface,

with the origin on the surface. That is, z = is the surface. Thus the boundary condition is that the net flux into the surface is, at any point,

^net(x,y,t) = -k dT(x,y,z,t)

dz z =

(5-2)

= ^in(x,y,t) - O z = 0, t>0

where in is the flux from the moving heat source (cigarette)

into the substrate normalized to ambient (see Eq. (5-81)), and ^oui is the (net) flux from the horizontal substrate to the

overlying medium (cigarette or air):

k =

Ta =

h =

and

Here Ts = T(x,y,0,t) is the surface temperature

thermal conductivity of the substrate

the ambient temperature

the convective heat loss coefficient, for points away from the cigarette

emissivity of the substrate surface

(assumed uniform) o = Stefan-Boltzmann constant

For surface points under the cigarette, the first term on the

right hand side of Eq. (5-3) represents conduction rather than convection. From the measured initial conduction flux from cigarette to substrate, 3.7 W/cm2

, one can infer that along the line of contact between the cigarette and

substrate, the effective value of h is 74 W/m2 °C; over the

entire heated region (about 1 cm2 in extent) the average

value is 40 W/m2 °C. Thus, as the surface of the solid is being heated by the

flux, it is being cooled by heat transfer through the solid; some of that heat is transported to other parts of the surface

where it is lost to the atmosphere via convection and

radiation. The source flux at the surface, 0i„(x,y,t), is prescribed. For a source at the surface whose shape f(x,y) is fixed, but which moves at constant velocity v along the x axis, it is expressed as

0in(x,y,O,t) = f(x-vt,y).

If the source is stationary, then analytic solutions of the problem are possible, assuming a linear rate of heat loss at the z = boundary (s s = 0). However, there is no simple

analytic solution for a moving source, nor for the cases where radiative (T4

) cooling is taken into account. Hence a numerical procedure is required in general. When the source moves, the problem must be treated in three (spatial)

dimensions. When the heated spot moves in a straight line along the surface, the problem simplifies slightly, because of the bilateral symmetry.

For the numerical solution, the substrate is subdivided by

a grid; the source is a flux distribution over the surface

mesh, and the movement of a source simply becomes a

time-varying source over each grid point. The computer

151
program TEMPSUB has been written, which solves Eq. (5-1) numerically, with the boundary condition (5-2). See

Appendix 5A for details. This program has been checked for accuracy and

correctness for some special cases for which we have

analytic solutions. It has also been checked for global

energy balance; that is, the temperature distribution in the

solid must be such that

t df in (x,y,t')dxdy = pCf Ti)dxdydz +

(5-4)

df Wx,y,t')dxdy

l °d where Tj is the initial temperature of the solid (assumed to be constant). With a grid size of 1.5 mm or less, and a suffi- ciently short time interval (see Appendix 5A), the maximum

errors found in the calculated temperatures are about 1%,

compared to the exact analytic expressions.

The program assumes that the impinging heat flux is of the form

0in(x,y,t) = <t> m exp

r ~\ X -x vt

V.

_y^

J

(5-5)

The user must input the peak flux <f> m (in W/m2

), the initial peak position x , the standard deviations ax and ay , and the

velocity v, all in meters (or m/sec). The program also requires a thermal conductivity k and a thermal diffusivity a

for the substrate material. The volume is divided into parallelepipeds whose size is user-chosen. The smallest practicable size is 1.5 mm on a side, for a substrate of size 6x6x3 cm deep. The user must be certain to choose a

time interval At for the calculation such that

At < (Ax)2 /12a (5-6)

The results will be shown later, and more detailed descriptions given in Appendix 5A.

Ignition

The simplest ignition criterion is that a point on the surface

reaches an "ignition temperature" Tig , characteristic of that material; this is adequate for our purposes. It is then necessary to know whether, when (smoldering) ignition of the substrate occurs, this is shortly followed by self- extinguishment, or whether it is self-sustaining. The

experimental observation is that the smoldering is usually

self-sustaining under the circumstances with which we are concerned (see section 4). When there is ignition, the term S in Eq. (5-1) ceases to be zero, and the calculation ceases to be valid thereafter. However, since all that is wanted to be determined is whether the substrate ignites, this is of no consequence.

Possible Improvements

Although the program TEMPSUB is adequate, it could

usefully be generalized in several ways. First, it assumes

that the thermal diffusivity,

a = k/pC,

is constant, whereas for most materials, at least the specific

heat and thermal conductivity vary with temperature. If the

variation is not large, this can be taken into account

reasonably well by using some appropriate average value

for a. For porous media such as fabrics and foamed

plastics, there will be substantial heat transfer by (internal) radiation, so that there will be a significant nonlinear temperature dependence of k. Second, the fact that the thermal

characteristics of the padding are different from those of the

fabric should be taken into account. Third, since most

fabrics are fibrous/porous, they should be treated as diather- manous slabs — i.e., heating and cooling by radiation should

be treated in depth. Fourth, moisture evaporation and move- ment should be taken into account.

It may also be that melting and/or charring of the fabric and the padding should be considered; in fact, foam

padding can (locally) shrink away from the fabric prior to the

latter's ignition. Still another complication is that generally

neither the fabric nor the padding is homogeneous. Finally,

if either material is not inert, so that it pyrolyzes as its temperature rises, then the term S in Eq. (5-1) must be

included; S<0 for endothermic pyrolysis, S>0 for exothermic pyrolysis. This would complicate the solution somewhat, assuming no material or oxygen depletion. If the

pyrolytic process(es) do involve oxygen, then the problem

becomes enormously more complicated, as the PDE's

describing gas diffusion and convection must be solved

together with the PDE (5-1).

152
Modeling the Free Cigarette

The model of a cigarette must predict (a) the external heat

flux from it, and the extent of the heating zone, (b) the

velocity of smolder propagation, and (c) how these depend

on: the radius of the cigarette (R), the tightness of packing

(via the void fraction <t>), the type of tobacco (via its ther- mophysical and kinetic parameters: heat of gasification Hv , heat of combustion Hc , activation energies and pre- exponential factors, density p, thermal conductivity k, specific heat Cp

, etc.), and the wrapping paper (its thick- ness, chemical composition, permeability, kinetic parameters, etc). Two alternative modeling approaches were

pursued in parallel, intending that at least one would

succeed in yielding the desired objective. The development

of each benefitted from insights gained with the other. The

first is a global, semi-quantitative model which borrows

heavily from earlier modeling work. The second is a more

detailed model based on first principles.

Semi-Empirical Model

The first approach is to utilize existing experimentally or

theoretically determined correlations in order to get the temperature and flux distributions, smolder velocities, etc.

Burning Rate as a Function of Various Parameters

From Figures 9-4 to 9-7 of Section 9 of Muramatsu [5-5], we

find the following experimental dependencies for smolder

rate ( rh, in mg/min and v, in cm/min) and maximum interior temperature Tm (in °C); bear in mind that these are for a

cigarette in free burn, not on a substrate. As was shown in Section 4, however, the smoldering rate on a substrate is (to a first approximation) a constant fraction of the rate in free burn. Dependence on cigarette radius:

rii(R) = 17.2 (2ttR) mg/min,

with R in cm; since

fin = 7iR 2pv,

(5-7)

(5-8)

then with p = 0.259 g/cm 3 (their reference value), 1

, DN 2(17.2 x 10~ 3) 0.133 . . v(R) = l a259R

; - —cm/mm

and Tm(R) = const. = 815°C

Dependence on packing density pP :

with 2ttR = 2.5 cm,

m(p P) = const. = 43 mg/min

and Eq. (5-7) yields

v(p P) = 0.0865 /pP cm/min

Also, Tm(pT) = const. = 815°C

(5-9)

(5-10)

(5-11)

(5-12)

Muramatsu also gives the dependence on moisture content and ambient oxygen partial pressure. The latter is of no

interest to us, for our present purpose.

In Figures 9-8(a) - (e) of Ref. [5-5], a sensitivity analysis

for some other parameters is given, but derived from the model rather than experimentally. These results show that the smolder velocity v and peak (interior) temperature Tm

are very weak functions of the pre-exponential factor for pyrolysis (Zp), solid-phase thermal conductivity (ks ), and

specific heat of tobacco (Cv ). On the other hand, there is a

perceptible dependence of v and Tm on Zco . the pre- exponential factor for the char-oxidation reaction:

v(ZC o) = 0.168 + 0.178(Z/Zo ) cm/min (5-13)

where Z is the reference value of Zco , Z the actual value

used. Similarly,

Tm(Zco) = 687 + 181 Z/Z °C (5-14)

: The coefficients in Eqs. (5-7) to (5-24) are given to three significant figures for calculation only; the final results are only valid to two

significant figures. Note that cm/min must be converted to m/sec for use in the substrate program.

153
The dependence on the mass transfer coefficient Kg is very

strong:

v(Kg) = 0.240 + 1.94x10 -4 exp(6Kg/Kgo) cm/mm (5-15)

and

Tm(Kg) = 696 + 3.113 exp(3.6 Kg/Kgo) °C (5-16)

where Kgo = 4.45 cm/sec is the reference value. The

dependence they found on the diffusion coefficient is even

steeper; it is also rather more complicated, for v; a crude

(but perhaps adequate) approximation to v(D) is

f 0.6 D/D - 0.276 0.86 < D/D < 1 v(D)= ] (5-17)

I 1.38 D/D - 1056 1 < D/DD < 1.24

where D = 0.112 cm2/sec is the reference value of D. For

the peak temperature,

Tm(D) = 262 + 548 D/D °C (5-18)

The dependencies on thermal conductivity of the solid phase in the burning zone, ks , are

v(ks ) = 0.355 - 0.025 ks /kso cm/mm (5-19)

and

Tm(ks ) = 958 - 132 ks /kso °C (5-20)

where kso = 3.16 x 10~ 3 W/cm°C is the reference value.

The dependencies on the radiative emissivity from the outer surface burning zone, es , are

v(ss) = 0.711 - 0.38 £s/eso cm/min (5-21)

and

Tm(ss) = 1085 - 270 £s/eso °C (5-22)

-where e = eso is the reference value (e so = 0.73).

Finally, the dependencies on Qh = Hc , the heat evolved by

smoldering, are

v(H c) = 1.6 Hc/H C o - 1.269 cm/min

and

Tm(Hc) = 1060 Hc/HCo - 237 °C

(5-23)

(5-24)

where Hco is the reference value of the heat of combustion

(Hco = 4200 cal/gm = 17570 J/gm).

These expressions are only approximate, because they were

obtained by the author from Muramatsu's figures by a

curve-fitting exercise. One might possibly do better by refer- J ring to Muramatsu's original figures. A possible drawback to J this formulation (not actually inherent in Muramatsu's model)

is that the nonlineanties of the system are ignored. That is, it must be assumed that the factors are independent. This

may still be adequate. That possible drawback can be

entirely avoided by using the cigarette model CIG25

described earlier; that involves extensive computations,

however.

We now have expressions for v and Tm for almost any

cigarette for which the thermophysical parameters can be

specified. These do not yet (quite) satisfy what is required

for the problem, as will be seen in the next subsection.

However, a correlation is then found which enables one to

find the heat flux to the substrate (to a first approximation),

from a knowledge of v (or m) alone.

The Surface Heat Flux

In this section, the heat fluxes and the energy balance for the cigarette are discussed, and how they are related to its measured surface temperature distribution. The detailed calculations appear in Appendix 5C. In order to find the heat flux from a cigarette to the substrate, it is useful to see what the heat fluxes are in free burn, and then calculate how they are modified by contact with the substrate. The

isolated cigarette is first considered here, and the cigarette on a substrate in the next section. A cigarette contains m grams of tobacco, which release mHc joules of energy when it smolders. A fraction Xs of this

is required to heat up the solid and to pyrolyze it to char. A

fraction Xc is convected away, and a fraction Xr is radiated

away. When it lies on a substrate these fractions change,

and there is an additional loss by conduction; that fraction is

Xcd- Xs, Xc. Xcd, and Xr may be functions of local conditions,

such as the partial pressure of ambient oxygen, the rate at which the cigarette burns, and whether or not it is in contact

with a substrate. They may each be a function of time, as

well. From conservation of energy,

Xcd(t) + Xs(t) + Xc(t) + Xr(t) = 1 (5-25)

Thus, in the time required to burn the entire cigarette, it releases XcmHc joules via convection and Xi-mH c via radiation (where %c and Xr are the time-averaged values). The

total energy output for a particular (experimental) cigarette

will now be found from its measured smolder velocity. The

separate convective and radiative loss rates will then be

inferred from the surface temperature measurements, and

the energy production and loss compared.

At any moment, the surface temperature of the smoldering cigarette is, (as can be seen from Figure (5-2)), a

function with a single peak. This is displayed in Figure (5-4)

for one of the experimental cigarettes used in this study

(#105). However, these measurements were made inside the cigarette wrapping (as close to the periphery as was

instrumentally practicable). The actual peak surface temperature was lower than this, as discussed in the next section. This curve must therefore be appropriately modified before it

is used for any calculations. The modification is discussed in detail in Appendix 5C.

154
Figure 5-4. Measured Longitudinal

Surface Temperature Distribution for

Cigarette 105

10 20 30 40

DISTANCE (mm)

The total energy output rate of the cigarette is

Et = rhHc

70

(5-27)

Measurements made by Muramatsu et al. [5-4] (Table 5-5) showed that when the enthalpy lost from a representative

sample of cigarettes by outgassing is excluded, the average

net heat of combustion is

Hc = 1440 cal/g = 6010 J/gm. (of tobacco)

With the packing density and burning velocity measured for

this cigarette, the energy production rate

E, t = 4.52 watts

can be inferred.

The net radiative flux from this surface is

0r(X,t) = £ctf[T4(X,t) - Ta4

] (5-28)

while the net convective flux is

^c(x.t) = h[T(x,t) - Ta] (5-29)

In these expressions, T is in Kelvins, Ta is the ambient

temperature (in K) and ec is the emissivity of the cigarette

surface.

In Appendix 5C, it is shown that from the longitudinal

temperature distribution T(x) measured near the surface of cigarette 105 (shown in Figure (5-4)) and Eqs. (5-28) and

(5-29), one can infer that when it burns in the open air, the convective and radiative losses are about

Ec = 2.02 watts

and

E r = 2.49 watts,

respectively.

There is a small difference E, - E r - Ec between the production and loss rates, due to the energy deposited in the cigarette, averaged over the smolder period. Thus, the energy leaves by convection and radiation in comparable

amounts, in free burn. The analogous results for the case where the cigarette lies on the substrate will be analyzed in the section on interactions.

It would be useful to measure the emitted flux directly, so as to check these theoretical estimates. When a flux gauge

is run along the cigarette, however, what is measured is the

radiative plus the conductive flux to the gauge. Therefore, a

direct comparison is not possible, and a detailed analysis is required. The results of these flux gauge measurements and

their analysis are given in the next section. It will also be

shown there how the heat fluxes in the open relate to the heat flux to the substrate. Before doing that, however, a

very useful result can be obtained as shown in the following

section.

Correlation Between v and i,

The heating flux from the cigarette will be expressed in the (approximate) form, Eq. (5-5). Therefore we need to know

the four parameters m , v, ctx , and oy

. The flux used as a heat source for the calculation of the substrate temperature

has been taken to have a peak value, m , which should be

taken to be a function of time; however, the cigarette

surface temperature will quickly stabilize, so that except for a brief and unimportant initial transient, it is indeed

appropriate to choose m as a constant. As pointed out in Section 4, the (similar) cooling of the cigarette by the cold gauge in its brief passage past the cigarette reduces the peak flux by 20-25%. We assume that this is about the same as the reduction due to the substrate; this assumption

is borne out by the approximate consistency of the calculations made in subsection Interactions Between Cigarette and

Substrate and Appendix 5C. The peak fluxes, P

, measured

while the cigarettes smoldered on a substrate, are plotted in Figure 5-5. It appears from this figure that ^p

is insensitive to the cigarette burned (from among the experimental

cigarettes); a simple unweighted average of these data yield

P = 5.60 ± 0.38 W/cm2

(0.38 W/cm2

is one standard deviation; however, the error flags are large, and ± 0.8 W/cm2 is a better reflection of

reality). We shall return to this later. If P

is constant, it might

be expected that the longitudinal (axial) width of the flux distribution (roughly, the length Cc of the coal) should correlate closely with m (this is similar to the connection made in Eq. (4-1)). This correlation is readily demonstrated. First, note that

rti = pP A v (5-30)

155
Figure 5-5. Peak Fluxes Measured by a

Thermocouple, for a Representative

Sample of Experimental Cigarettes

Smoldering on a California Fabric/Foam

Substrate

20

1 1 FNHN-21 ,FNHC-26 BNHM-25

-I • f^-i- -I • FNHN-25-* BNHC-26

FNLC-25

PEAK FLUX (W/cm^)

where A is the cross sectional area of the cigarette. Usually,

A = tiR 2.

Also, Q = it) Hc is the power produced. The power lost while smoldering freely is

QL = 2ttR \ 0(x)dx

In the steady state, they are equal, and therefore

pp 7iR 2 v Hc = 2ttR ( ^(x)dx, (5-31)

where v is the free-smolder velocity. Assume that the energy

loss per unit length along CL (the line of contact with the

substrate),

E'P = I 0(x)dx, (5-32)

is proportional to the length of the coal and to the peak

value of the heat flux measured by the gauge (in free space). That is,

^(x)dx - I, fc 0p (5-33)

where £, is the proportionality constant. (It is not obvious that Eq. (5-33) should hold, since <t> v measures the peak flux of radiation plus conduction to a cold surface, whereas 0(x) is the flux distribution of radiation plus convection while smoldering freely). Substituting Eq. (5-33) into (5-31), one obtains

pPCv = r-p Z, P 4, (5-34)

where C is the circumference. When A = tcR 2

, C = 2nR.

The left hand side of Eq. (5-34) (where pP , C, and v were

found from measurements on the cigarettes) were plotted vs the (measured) coal lengths lc . If P were indeed constant, we should find that the values lie on a straight line going

through the origin. The plot is shown in Figure 5-6, and it is clear that a good correlation indeed exists. If we ignore

sample 27, which is an outlier, then the data can be fitted reasonably well with a straight line which goes through the

origin; this is the line marked 0L, and it corresponds to

pCv = 5.12 x 1CT 3 4.

With Hc = 6010 J/gm and szS P =

(5-35)

5.60 W/cm2

, therefore, % = 0.437.

If the measured peak fluxes were used, rather than the averages, the scatter is reduced, but only very slightly. Finally, investigation has shown that using the integrated

values of the flux — i.e.,

J' m(x)dx — rather than P4, does

not improve the correlation (indeed, the scatter is worse).

Thus it has been shown that to a first approximation, the peak flux can indeed be taken to be constant. Moreover,

Eqs. (5-6) to (5-24) can then be used to obtain v for any set

of cigarette parameters, and Eq. (5-35) yields 4. Later it will be shown how to relate ox to 4, and how to estimate oy

. If one chooses <t> v for <j> m , therefore, all four parameters

needed to characterize the heating flux (via Eq. (5-5)) are

available. This is the simplest quantitative model of cigarette- substrate interaction; an example of its use will be given

later.

Figure 5-6. Plot of pCv vs fc , the Coal

Length, to Test Eq. (5-34). The Data are Given with Error Flags.

COo

4 6 8 10 COAL LENGTH, w c (mm)

156
Detailed Model

The motivation for constructing a computer model of smoldering cigarettes has already been explained. In this section, the assumptions and equations required for a good

cigarette model are outlined. The model which has actually

been developed is only a subset of it. The complete model

is outlined here nevertheless, in order to enable a user to add the missing pieces in the future, if desired. We have seen that a good deal of detail is lost when the model is assumed to be one-dimensional. Therefore the time

spent on making it two-dimensional (i.e., assuming cylin- drical symmetry) was well spent. If a steady state were

assumed, then the equations would simplify; however, it would then be necessary to choose the smolder velocity

correctly (i.e., as an eigenvalue.) Moreover, if the equations

are taken to be time-dependent, the heat and mass-transfer

equations are parabolic partial differential equations (PDEs)

which are easier to solve, in some ways: The convergence

for the steady state equations is very slow (indeed,

Muramatsu found that one thousand iterations would not

suffice, at times), and it might actually be computationally

faster to do the time-dependent problem. Also, this formulation yields v directly, whether or not it is constant. Finally, it

is desirable to have a unified model, rather than separate

pyrolysis and char-oxidation models, as Muramatsu has. For

these reasons, it was decided to solve the time-dependent

equations.

The following simplifying assumptions are made:

1 . The cigarette is modeled with only one pyrolysis reaction and one char-oxidation reaction, rather than the six reactions chosen by Muramatsu.

2. Since the (internal) gas flow velocities depend on the pressure gradients, axial convection is neglected, as being much smaller than radial convection (since the

axial gradients must be much smaller than the radial gradients).

3. The water (pre-existing or produced during combustion)

in the tobacco column is also ignored. This may or may

not be a good assumption, but it avoids yet another

complication.

4. The tobacco column can be treated as a continuum -

i.e., as a homogeneous, uniform mixture.

5. The tobacco shreds do not shrink as they lose mass.

6. The gas and solid phases are at the same temperature,

locally, in the cigarette.

7. Species or temperature gradients within the tobacco

shreds will be neglected, consistent with assumption

No. 4.

8. Radiation transfer within the cigarette can be incorporated into an effective thermal conductivity.

9. The paper behavior appears only in the boundary

conditions.

10. The gases generated or heated by combustion move

radially outward to the side boundary (aside from diffu- sion). Thus there is a radial flow calculated strictly by mass conservation: The gas pressure within the cigarette is assumed to be only negligibly different from

atmospheric, and therefore no momentum equations

need be written.

1 1

.

The gas phase is quasi-steady. That is, dpj'd\ = 0.

12. Consistent with assumption #9, any (axial or radial) gradients in the paper are ignored; an effective mass

transfer coefficient is used to model diffusion through

the paper.

13. Assumption #8 is complemented with the assumption

that the thermal conductivity is the same function of temperature throughout the cigarette - i.e., whether in ash, char or tobacco.

When the cigarette interacts with a substrate, two additional assumptions are made:

14. The cigarette combustion zone retains its cylindrical

symmetry (observed to be approximately correct on

fabric/foam substrates).

15. Prior to its ignition, the presence of the substrate has

two effects on the cigarette, both of which can be

assumed to apply symmetrically (on the average) to the

entire cigarette periphery:

(a) The oxygen supply to the cigarette is reduced by some factor

(b) The thermal effects (e.g., as a heat sink) can be

calculated in a decoupled manner (this assumption is weak, and may have to be dropped eventually).

The equations which describe the mass and energy trans- port in a smoldering cigarette will now be presented. Any

additional simplifying assumptions will be indicated as each

equation is discussed.

First, however, it is necessary to clarify some of the terms appearing in the equations. Consider the decomposition of the tobacco: one gram of tobacco, upon pyrolysis,

produces nc grams of char. Assuming no reactions (with

oxygen, nitrogen, etc.) the other 1-nc grams will be gaseous

products. Each gram of char reacts with n 2 grams of oxygen to produce some heat, n A grams of ash, and

1 -nA + n 2 grams of gaseous products of combustion.

Since the combustion process mostly proceeds at very low

oxygen concentrations, it can be expected to be inefficient - i.e., incomplete; and nQ2 is smaller than the stoichiometric

value.

157
lass Conservation:

[(1 - n c)R P + (1 at n A)Rco] (5-36)

where ps is the mass density of the solid, R p

is the pyrolysis

rate (in gm/cm3 sec) and Rco the char oxidation rate. The

equation of continuity in cylindrical coordinates is

-Jp

[ps (1 -4>) + Pz <t>\ + ) -|r (0pg u r r) = (5-37)

where r is the radial coordinate, pgis the mass density of gases, <j> is the void fraction in the cigarette (i.e., the volume

fraction of gas, rather than of tobacco shreds), and u r is the

radial (convective) gas velocity. Axial convection has been

dropped, by assumption #2. Since the shreds are assumed

not to shrink, remains constant. Because of assumption

#11, one can write &<»»-*% = '

and using Eg. (5-36), the equation for gas results:

d

r dr

(pg

r u r ) = (1 -0[(1 -nc)RP + (1 -nA)Rco]

(5-38)

(5-39)

One might define pA , pc, and pt as the ash, char, and

tobacco densities and take them to be constant. Then if the

total volume of solid is Vs (Vs = (1 -^)Vtotai), while those of ash, char, and tobacco are VA , Vc , and VT , respectively, it would follow that

1 tt- [Pt Vt + pA VA + pc Vc ]

However, it is more convenient to define the bulk densities

pi = mi/Vs

i = A, C, T (5-40)

where mA = total mass of ash, etc. Then

Ps = pA + Pc + Pt (5-41)

and each of these bulk densities varies with time.

The equations for tobacco and char densities are very

simple:

dpi

at

and

dpc

at

= -FL

ncRp - Re

The equation for pA ,

dPA _ R p.. - nA nco

(5-42)

(5-43)

(5-44)

is not needed, since the ash is inert and simply accumulates. In the following equations, x is the axial coordinate.

Rather than dealing with the oxygen density p 2, the equations are written in terms of the oxygen mass fraction y:

y = Po2/pg

Then mass conservation for oxygen is

d(^Pg y) _, _d , a. s 1 a

(5-45)

at ax

1 A.

r 3r

qx) (r q r ) r 3r

(r u r y pg) - nQ2(1 -^)RC

(5-46)

where q x and q r are the axial and radial oxygen mass

fluxes from diffusion; that is,

q, = - ^ De pg

(Zi De Pg

ax

iY_

ar

^

> (5-47)

J

where De is the oxygen diffusion coefficient. Inserting Eqs.

(5-47) into (5-46) and using the overall gas continuity equation, (5-46) becomes

ay_ at ?U r ay . d_ r

ar ax PgDe ^_ ax

.J

r 3r

r ~\

rpg D,

v.

ay_

: ar J

(5-48)

^_

{y(1 -nc )R P + [y(1 -nA) + nOJ] Rco }

Next, consider the energy eguation:

Assuming that the gas is quasi-stationary, as in Eq. (5-38), and that the specific heats of all gases are the same and

independent of temperature, then the energy conservation

equation can be written in terms of the temperature; it is

<

1 -«">c,f + AvAf-l; +

1 !-

r ar rar J

(5-49) + (WXQcoRco - QpRp)

where Cs = specific heat of the solid

Cg = specific heat of the gases

k = thermal conductivity of the cigarette (see

assumption #13)

Qco = energy released from char oxidation (lower

heat of combustion)

and Qp = energy absorbed in (endothermic) pyrolysis

158
The internal heat transfer has a radiative and a conductive

component, as described earlier. The expression used here

is the same as that used in Ret. [5-4] and is due to Kunii

[5-10]; for porous materials,

k(T) = (1 -

2/3

) ks +

1/3 (kg + \ h r Dp)

where h r is a heat transfer coefficient for radiation,

h r = 8T 4ctT3

, (5-51)

Dp is the mean pore diameter, O is the total void fraction (including the void space in the shreds, and is therefore

larger than <t>), 8t is the emissivity of the shreds, kg is the thermal conductivity of the gas, and ks that of the solid shred (and depends on the mass density of the shred).

Also, the diffusion coefficient is assumed to be the same

for all the gases; it is given as

De = D (T/273)

7 (5-52)

where D depends on the gas and the background material. Muramatsu gives D = 0.112 cm2 /sec. Since the gas pres- sure in the quiescent cigarette is very nearly the ambient

pressure, the ideal gas law permits one to write the gas

density in the form

pg = Pgo(T /T)

where T is the absolute temperature.

(5-53)

Finally, expressions for the reaction rates are needed. It is assumed that each is given by an Arrhenius relation; thus

Rp = (pT) m Zp exp(-Ep/RT) (5-54)

where the exponent m is to be determined experimentally, as is the "frequency factor" (or "pre-exponential factor") Zp

. Ep

is the activation energy for the pyrolytic reaction, and R

is the universal gas constant. The tobacco density pr may

be expressed as

Pi = PsyT (5-55)

where yT is the tobacco mass fraction.

Similarly, the char-oxidation reaction rate is taken to be

Rco = pc n Pol Zco exp(- Eco/RT) (5-56)

where (again) the exponents n and p are to be determined

experimentally, and the densities are written in terms of the

respective mass fractions,

pc = Ps yc and po2 = pg y (5-57)

The initial conditions are (before ignition of the cigarette)

ps(x,r,0) = pso = Pto

pc(x,r,0) = pA(x,r,0) =

T(x,r,0) = T

y(x,r,0) = ya {= yam biem = 0.232)

(5-58)

(5-50) The boundary conditions are:

on the axis,

dr dr = for all x and t. (5-59)

At the lit end of the cigarette, the temperature boundary

condition is

x = r

~~\

.ax , = eAa(T4 -V) + he(T-Ta (5-60)

for all r and t. T = T(0,r,t) and Ta = Tamb i e nt.

Here, too, h e = convective heat transfer coefficient (at the

end), o is the Stefan-Boltzmann constant, and eA = emissivity of the cigarette at the x = end (we are assuming a grey body - i.e., no wavelength dependence). The value to be used here should be that of the ash. Here, we are assuming that the ash never falls off the cigarette — a

realistic assumption for the case when the cigarette rests on

a substrate, but not realistic for free-air burning; however,

this simplifying assumption will probably be adequate. Moreover, if it were not made, the geometry would be continually

changing, and the boundary conditions would become

exceedingly complicated.

There is usually a filter at the other end. However, this (again) is of minor importance for the cases examined here; 2 thus, for the temperature boundary condition at the other end,

x = L-» -k 3T

3x

eTa(T<-Ta4

) + h e (T-Ta)

x = L

for all r and t (where now T = T(L,r,t)).

Next, the oxygen boundary conditions must be considered.

It is assumed, for the sake of simplicity, that the filter prevents any oxygen diffusion at the cold end2 (x = L): r ^\

_9y_ ax

v. j

(5-62) x= L

where D is the diffusion coefficient for oxygen within the

cigarette. At the other end, the conditions must be

2 The filter is shown in Section 3 to have a substantial impact on

ignitions that happen only after the full length of the cigarette is burned; for such cases this boundary condition would have to be

changed.

3Also referred to as kt

, by Muramatsu.

159
D

ax v. J

= Yb(ya -ye) (5-63)

where ye = y(0,r,t) is the oxygen mass fraction at the "hot" end of the cigarette and ya is the ambient fraction, defined

in Eq. (5-58). D is a function of temperature; for the sake of simplicity, it is assumed that it is the same function for ash

as it is for virgin tobacco and for char, y is the mass transfer

coefficient. 3 Muramatsu [5-5] gives it as

Yb = 6.38 x 10

-1 V4 T

z - /a (T-Ta) (T+ 123.6)

R

cm/sec, (5-64)

for the effect of the boundary layer, where T is the mean

value between Tc (the local cigarette surface temperature)

and Ta (the ambient temperature), all temperatures in Kelvins.

Finally, the cigarette's side surface must be considered. It is covered by paper; the paper wrapper in principle should

also be included with its own set of equations, which will include its reaction kinetics. However, the amount of energy

released when it burns is negligible in comparison to that released by the tobacco. If a unique paper decomposition

(or ignition) temperature can also be specified, then the paper (kinetic) equations can be replaced by (two)

appropriate boundary conditions. This simplifies the problem

considerably, though it may omit some potentially interesting

physics.

If there were no paper, then the temperature boundary

condition at the sides would be

-k(x.R)

dr

v. _y = EC (X)<T(T« 4

) + h(T-Ta) (5-65)

The emissivity of the cylinder surface will depend on

whether it has turned to ash, is still pyrolyzing, or still virgin

tobacco; therefore the emissivity has been explicitly shown

to be a function of x. Also, the thermal conductivity at the surface will in general depend on whether it is ash, char, or

virgin tobacco. The assumption which is made here is that k

is the same for all three (assumption #13).

Similarly, although the heat transfer coefficient at the sides,

h, will be different from what is at the ends, we simplify by

assuming that

he = h (5-66)

The emissivity ec has one value for the virgin tobacco

region, another for the char region, and a third for the ash

region. However, these refer to "char" and "ash" for the paper, and may occur at different temperatures, and there- fore different locations, than for the tobacco. That is, conditions must be chosen for ec(x). The simplest approximation

that can be made is that the paper pyrolyzes/ignites/ disappears at some paper ignition temperature Tip . Then there are just two values for sc - that for the virgin paper, and

that of ash. These meet at the paper burn "line." Experiments have shown (see Figure 5-2) that

Tip = 450 ± 100°C

For oxygen, the equation is the analogue of Eq. (5-63):

Y(ya - ys ; D

ay

dr Yb(ya - ys )

x > xD

x < xc

(5-67)

where x p = xp

(t) is the position of the paper burn line at time t.

The paper resistance to oxygen diffusion can be expressed

as

YP Dp/8

where Dpis the diffusion coefficient in the paper and 8 is the mean paper thickness. The total resistance of both

paper and boundary layer is then

Y = (Yb

1 + Yp (5-68)

Eqs. (5-67) express the simplification that where the paper

has burned, its remains present no barrier at all, and the

radial oxygen diffusion at the boundary depends only on the

properties of the boundary layer.

Thus for the "ideal" model, there are the nine coupled

nonlinear PDE'S (36), (39), (42), (43), (48), (49), (53), (54), and (56), in terms of the nine unknowns pc, pg , Ps, Pt, y, T, ur , Rp , and Rc0 .

Partial Model

The model outlined above is quite complex; it was therefore decided to consider a subset of the equations which still contains much of the essential physics, but which is more

tractable.

Equations

The simplifications that were made are the following: first, it was assumed that pg = constant and ps = constant. A onestep reaction was assumed - i.e., no pyrolysis, just tobacco

oxidation. Thus, Rp = 0. It was assumed, (as by Summerfield et at. [5-3]), that the char-oxidation reaction is second

order — that is, linear in both oxygen and tobacco; i.e., that n = p = 1 in Eq. (5-56). Finally, the radiation losses at the boundary were linearized, so that an effective heat transfer

coefficient which is the sum of the convective part and the

linearized radiative part was used. That is,

h(T-Ta) + sc a(T4 -Ta

4

) -+ h'(T-Ta (5-69)

160
where

h' = h + £cCT(T + Ta)(T2 + Ta 2

)

T being some appropriate average of the surface temperature. The value used by us is given in Table A-1 (Appendix 5B).

Eqs. (5-49) and (5-48), the diffusion equations for temperature and oxygen, simplify to

(1 -0)ps Cs — + 0PgU rCg — (5-70)

k V2 T + (1-0) Qco Re

and

3y

t + u r fjf - De V2 y (i^) [no2 + y(1-nA)]R C0 (5-7T

where V2 =

ax2 drdr

r -\

ar (5-72)

(many of which could not be obtained from direct measurement).

Thus, this simplified model has four equations for the four variables pc , y, T, and u r

. It was felt prudent to insert global

balance checks for heat and oxygen. These take the form

0pg ydV = Y(ya-ys )dS pg yu rdS

(5-76)

n 2 (1-0) RcodV

and

[(1-0)psC s + 0pg Cg] TdV

The char-oxidation source term (5-56) becomes

Rco = PcPgyZco exp(-Eco/RT) g/cm3 sec (5-73)

The approximation pg = const has two immediate conse- quences:

1

.

In order to get a given reaction rate, the oxygen concentration must be (incorrectly) calculated to be smaller than

it really is, at any temperature higher than ambient.

2. The radial outflow velocities u r will be calculated to be

smaller than they really are. This in turn results in easier

inward diffusion of oxygen from the surface, and somewhat smaller convective energy loss.

In the one-step approximation, the equation for pT(t) disappears: each gram of tobacco is replaced by nc grams of char, and Eq. (5-43) becomes

dpc at Re (5-74)

Muramatsu [5-5] found that a best fit to the data was

obtained with p = 1/2 in Eq. (5-56). Therefore, one version of the program was written using that dependence; that version has had difficulties in converging, however, and so

J this attempted improvement was dropped.

Eq. (5-39) simplifies to

3& + f-|r(pgurr) = (W)(1-nA)R c (5-75)

As long as pg = const, the first term on the left hand side of Eq. (5-75) vanishes. The velocity u r is valuable as a check

on the program, since it is a sensitive marker of the local reaction rate. This permitted "tuning" the model parameters

h'(Tc -Ta) dS -

pg u rCgTg dS (5-77)

(1-0) Qco Rco dV

where the integrations are over the entire surface and

volume of the cigarette. The second term in the left hand

side integral of Eq. (5-77) can be dropped, since pg is constant and pg « ps

. Also, consider the middle term on

the right hand side of Eq. (5-77): we note that the ideal gas

law permits us to write pgTg = paTa , in the integrand. (When

a pyrolytic reaction is introduced, terms involving Rp

will have to appear in the last integrals of Eqs. (5-76) and

(5-77)). Insertion of these global checks was very useful in uncovering a number of theretofore-unexpected errors. The computer program which implements the solution of these four equations is called CIG25.

Numerics

These equations were approximated by a set of difference

equations for numerical solution; three-point central differ- ence formulas have been used for the spatial derivatives. The reaction rate is a very sensitive function of temperature, and therefore it follows that the differential equations

are "stiff' — i.e. there is a wide variation in reaction rates. This means that very short time steps would be required in the numerical integration of the equations, if an explicit tech- nique were used. In order to permit longer time steps while

maintaining stability, therefore, an implicit solution method was used. After a number of other choices proved inadequate (partly because of the complicated boundary conditions), the Crank-Nicolson method was settled on. Since it is

161
an implicit method, some method has to be used to converge to the correct solution. One of the things that was

learned during the development of the program is that the oxygen diffusion rate is one to two orders of magnitude

faster than the temperature diffusion rate. Therefore one can

"decouple" the equations for oxygen and heat diffusion. That

is, they can be solved by an iterative procedure of successive approximations, starting with oxygen diffusion. The

Gauss-Seidel successive substitution technique was used for both the y and T equations, with a relaxation parameter.

That is, the value to be used for variable y after the ith itera- tion yields yi, is

y = (1-X) yi- X yi. (5-78)

Numerical experiments showed that for this subset of equations, a sharp peak of efficiency occurs with X = 0.9

(i.e., under-relaxation). 4

Initial Conditions

Two sets of initial conditions have been used. First, rather than using Eqs. (5-58), it was assumed that a match had

been applied to the x = end of the cigarette, producing some reactions; these used up only a small amount of tobacco, but most of the oxygen that had been in situ. The

initial temperature distribution was assumed to be very high

at the tip, then linearly decreasing to ambient temperature.

The oxygen mass fraction behaves in complementary

fashion. For the numerical calculations, the cigarette was divided

into ten cylindrical shells, i.e., Ar = 0.4 mm, and into slices

of the same thickness, Ax = Ar. The temperature at node n

is as given in Col. 2 of Table 5-1

.

If we assume that the combustion of char proceeds

according to

C +

(l±a> 02 a C02 + (1 -a)CO,

it is clear that 16(1 +a)/12 grams of oxygen are needed to burn one gram of carbon (char). It follows that if combustion

lowers the local mass fraction of oxygen from ya to y, it will lower the relative density of char (and hence tobacco) from

1 to x, where

4(1 +a)nc

r ~\

Pi 7a - y)

Therefore, when the initial oxygen distribution is taken to be

as given in Col. 3 of Table 5-1, the resulting relative density

of tobacco is given in Col. 4 (to three significant figures). pQ

is the actual mean tobacco density in the virgin cigarette. It became clear during the development of the program that it would be desirable to also have an alternative set of starting conditions. This second set is described later.

'Many of the numerical techniques mentioned here are discussed in Ret. [5-13].

Comments

During the development of this model, we have confirmed

what has already been known for some time, both from

experiment and from earlier modeling efforts; to wit, that the

rate at which oxygen is allowed to diffuse into the cigarette

is the principal determiner of the burning rate. So that if a

"fire-safe" cigarette is wanted, without any other consideration (e.g., flavor, tar and nicotine toxicity of products, etc), one need merely use a paper with marginal permeability

e.g., 4 Coresta units- and this will just about guarantee that the cigarette will go out when dropped on upholstered

furniture. Because this is only a "partial" model, we would expect

the results obtained with the current values of input

parameters to be somewhat unrealistic. The input

parameters therefore have to be modified, in order to

(partially) compensate for this. The parameter values used in the calculation are given in Appendix 5-B. The results obtained with CIG25 are given later, and are

there seen to be at least semi-quantitatively reasonable.

Nevertheless, there are a number of additions which would

improve the accuracy of the model. These are:

1. Introduction of the ideal gas law (Eq. (5-53)),

2. Inclusion of the radiation loss at the boundaries,

3. Inclusion of a pyrolysis reaction,

4. Use of the nonlinear dependence on y, for Rco .

Beyond these, it would be desirable to take some more

physics into account, such as:

5. Inclusion of axial gas flow,

6. Inclusion of the evolution of H2O vapor and its recondensation downstream,

7. Possibly, the paper kinetics,

8. More than one pyrolytic and/or char-oxidation reaction. Table 5-1. First Choice of Initial

Distributions of Temperatures, Oxygen

Mass Fraction, and (Relative) Tobacco

Density, Assumed for the Calculation

T is in degrees Kelvin.

Plo/Pc

1 1000 .01 .999 2 1000 .01 .999

3 1000 .01 .999 4 1000 .01 .999 5 1000 .01 .999 6 860 .02 .999

7 720 .04 .999

8 580 .08 .999

9 440 .16 1.000

10 300 .232 1.000

162
Interactions Between

Cigarette and Substrate

Conduction Flux to Substrate

In this section the effects which take place when the lit cigarette and the substrate are in intimate contact are outlined. Since the principal effect of the cigarette is to heat the

substrate, how to find the heat flux from the cigarette to the

substrate (when the cigarette has already been influenced

by the substrate) is then considered in detail. Finally, the

effects of the cigarette on the substrate are touched on. As we have seen, the substrate is a fairly complicated

system, and the cigarette a more complicated one still. The

situation when the two are in contact is describable by a still more complex set of equations; we have not attempted to set those up for solution. Instead, let us consider the probable effect of each on the other, in a qualitative way. First, consider the effects of a cigarette on a horizontal substrate,

in order of importance. The principal effect is the heating by

a hot spot; the cigarette also affects the boundary conditions: it interferes with convective cooling, over its entire length. Moreover, if any oxidative reaction takes place in the

substrate, the cigarette "competes" with the substrate for oxygen. Finally, some of the water vapor and tar which are

emitted by the cigarette may recondense on the surface of the substrate, and change its thermal characteristics. The effects of the horizontal substrate on the cigarette are

the mirror image of the above, in a sense: first, the cold

substrate initially provides a substantial extra heat sink (by

conduction). As it heats up, the magnitude of this sink

declines. Second, the convective and radiative heat losses are reduced as well. Moreover, this effect varies with time, as the substrate heats up. If the substrate begins to have

exothermic reactions, it may change from a heat sink to a

heat source. (The results quoted in Section 4 indicate that

this probably will not be the case before ignition, however).

Finally, it is evident that just from the geometry, the

substrate interferes with the uptake of oxygen by the cigarette. Moreover, if the substrate begins to react with oxygen,

then the oxygen depletion for the cigarette would become

still more severe.

In accordance with the above lists, we begin by

calculating the heating flux delivered to the substrate by the influenced cigarette.

First consider the flux to the substrate. The flux from the various cigarettes was measured with a small, water-cooled

flux gauge (see Section 4). The face of the flux sensor (ther- mopile) was placed flat against the surface of the cigarette, either in free space or flush with the surface of a substrate. The gauge is moved back and forth past the hot region

several times; sufficiently slowly that the gauge comes to equilibrium, but fast enough that the cold gauge does not lower the cigarette temperature very much (the typical

temperature depression is indeed only momentary, and of about 50-70°C-see Section 4). The heat transfer from the

cigarette surface to the sensor is given by

- ec a(V-Ts «) + h(Tc -T,), (5-79)

Figure 5-7. Average of Several

Measurements of the Flux Emitted by

Cigarette 105 Toward the Substrate,

Along the Contact Line. The Substrate in this

Case was Laundered California Fabric 2045, with Foam

Padding. The Dashed Curves Indicate the Probable

Errors. This Distribution Corresponds to the

Temperature Distribution Shown in Figure 5-4.

10

c\j

X

=3

<

111 I

8

-

6

-

4 -

2

-

-

I i i i -

- -

_

i\ ''A

v\

_

-

1: \

-

-

1

/II -

-

•

,y/i

' 1

1 I*"**—

-

-30 -20 -10 10 20

DISTANCE RELATIVE TO PEAK (mm)

30

163
where Tc is the cigarette surface temperature, Ts that of the

sensor, sc is the emissivity of the cigarette surface, and h is an effective heat transfer coefficient. The second term corresponds to conduction through a thin air space between

the cigarette and gauge surfaces. Thus

q"(0,y,0) = q'(0,0,0)

h = k/5, (5-80)

where k is the thermal conductivity of air at T = (Tc + Ts )/2, and 8 is the mean spacing. A typical result is shown in Figure 5-7, corresponding to the temperature distribution shown in Figure 5-4, for cigarette 105. The measured flux is the initial (and momentary) flux from the cigarette to the cold

substrate at the (very small!) area of contact between them.

How is one to use or interpret this result? If the substrate

starts out cold, and is in good thermal contact with the cigarette, this flux represents the initial heat flux to it, along the

line of contact (LC). It is interesting to see what the total energy loss rate is; the flux ^(x) shown in Figure 5-7 was

first integrated numerically, and yielded

a

2 + y2 (5-84)

is derived there, where q'(0,0,0) is the (peak) conduction

flux on the axis; this flux drops rapidly with time. The parameter a is determined via Eqs. (5D-8) and (5D-9); it is of the order R/2. The total conductive loss (at t = 0) is then found

to be

Ecd (0) = 2a(tan" 1 ya) q"(x,0,0)dx,

JO

where £, is another characteristic distance for which a

reasonable value is i, - R. With a peak initial flux of 5.6 W/cm2 to the substrate, of which 1.9 W/cm2

is radiative and

3.7 is conductive (see Appendix 5D), we find that for R = 0.4 cm, a = 0.226 cm; then £, = R implies Ecd (0) =

2.1 watts as an estimate for the initial energy transfer to the substrate via conduction.

L

^(x)dx = 6.07 + 1.17 -0.90 W/cm.

With this large flux, the substrate heats up rapidly, so that the net flux, given by Eq. (5-79), falls rapidly to lower

values.

The flux distribution 0(x) is that along the line of contact; i.e.,

it is i^(x,0); the transverse dependence must also be known.

Moreover, we must know 0(x,y) as a function of time. The

latter is in fact readily found, if it is assumed that the cigarette surface temperature profile stays (relatively) constant. For then the flux given by Eq. (5-79) holds at all times; i.e.,

0(x,t) = ec CT[Tc 4(x,t) - Ts 4

(x,t)] + h[Tc(x,t) - Ts (x,t)],

just as given in Eqs. (5-2) and (5-3) (assuming also that h is constant). That is, we use

>o(X,t) = ec a[Tc 4

(x,t) - Ta4

] + h[Tc (x,t) - Ta] (5-81

;

as the source flux for the substrate program, and the net heat flux from cigarette to substrate (along CL) is

flx.t) = ^o(x.t) - &(x,t),

where

^,(X,t) = EcCT[Ts 4

(X,t) - Ta

4

] + h[Ts (x,t) - Tj.

(5-82)

(5-83)

(It has been assumed that the initial substrate surface

temperature is the ambient temperature - i.e., Ts (x,0) = Ta). o(x,t) is given by experiment, as in Figure 5-7, and ^s (x,t) is calculated by the substrate program.

The conductive flux distribution q"(x,y,t) in the transverse

direction is calculated in Appendix 5D. The (approximate)

expression

Experimental measurements (see Section 4) have shown

that the flux from a cigarette can be (very crudely) fitted with a distribution of the form (5-5). If expanded as a power

series, this evidently agrees with Eq. (5-84), to lowest order

in y

2

. The total energy output from the distribution (5-5) is

^(x.y)dxdy = n<JxOy n (5-85)

Reasonable agreement with experiment is obtained with

CTx = 0.6 cm; also, oy > 0.32 cm. For the conductive part, however, we must modify these values to oxc = 0.67 and ayc = 0.30. Then with ^m = 3.7 W/cm2

, Ecd is found to be

Ecd (0) = ti(.67)(.30)3.7 = 2.3 watts.

With time, this energy loss term must fall according to

Eed(t) - Ecd (0) Tc - Ts (t) Tc - Ta

(5-86)

where Tc is the mean cigarette surface temperature and Ts (t) the (rapidly rising) mean surface temperature. In Appendix

5D it is shown that we can use the peak (rather than the average) temperatures in Eq. (5-86);

EC d(t) « Ecd (0) Tp - Ts (t) Tp - Ta (5-86a)

The temperature difference Tp - Ts in the steady state is such that

Ecd (oo) = 0.7 Watts

164
Radiation Flux to the Substrate

Assume an infinite cylinder of uniform temperature Tc resting on the flat substrate. For some area of the substrate of temperature Ts , the net radiative flux going into the

substrate is

is = es [Q </>c + (1 -Q)*. - ctTs 4

] (5-87)

where es = emissivity/absorptivity of the substrate (assumed constant)

C = radiation flux from cigarette

a = ambient radiation flux = cjTa

4

and Q is the fraction of energy emitted by the given

substrate area which would be intercepted by the cylinder.

If'Es = ec = 1, then Eq. (5-87) becomes

is = Q ctTc 4 + (1 -Q)0a - tfTs 4

More generally, an expression for C is written, and then one solves simultaneously for C and S . The result is that the flux from the cigarette, C , is given by

Ec aTc4 + (1 -so*

(5-88)

1-SC nR

dx Q(x)(es aTs 4 (x) + (1 -es )[Q(x)0c + (1 -Q)0a]|

The configuration (view) factor Fsc = Q must then be found.

From Sparrow and Cess [5.11], we find that for an

infinitesimally thin but infinitely long strip on the substrate,

parallel to the cylinder axis and a distance y from it, the view factor is

Q(y) =

R

2 R

2 + y2 (5-89)

<rTs 4

(y) = <t>*

where

R

2 + y2

K = aTs 4 (0)

(5-92)

(5-93)

is the maximum surface black-body emission. Carrying out the integration in Eq. (5-90), the last integral takes on the values

Ss 7lR .dx =

(5-94)

respectively. These are then to be used in the expression

for C , Eq. (5-90), and that in turn is to be used in Eq.

(5-87), for the flux (locally) absorbed by the substrate.

From Eqs. (5-87) and (5-89), it can be seen that the radiation flux from the cigarette to the substrate has precisely the same functional form as the conductive flux distribution, Eq.

(5-84). Thus our theoretical expression for the transverse dependence of heat flux is

0(y) - C R

2

'a2 + y

2 R

2 + y2 (5-95)

where C o and ro are the (initial) peak convective and radiative fluxes.

To sum up: an explicit expression for the transverse dependence of the cigarette flux [Eq. (5-95)] has been found,

which supplements the generic longitudinal dependence

given by Eq. (5-81). Thus, if the longitudinal dependence at the cigarette surface is known, the flux 0(x,y) can be found

by substituting the radiative part of Eq. (5-81) for ro and the

conductive part for CO , in Eq. (5-95).

where R is the cylinder radius. All but one of the integrals in Eq. (5-88) can now be carried out exactly, and

0cA = ec aTc 4 + (1 -ec) x

(5-90)

5-s.

4 TtR Q(x) aTs 4 (x) dx

where ec is the emissivity/absorptivity of the cylinder, and

A = 1 - (1-Ec)(1-6s)/4 (5-91)

There are two interesting cases:

I. Initially, T,(y) = Ta

II. In the steady state, a reasonable approximation to

T,(y) is

Connection with the Semi-Empirical Model

Alternatively, we may consider the above calculations to give a theoretical justification for using a Gaussian as a

lowest-order approximation to the transverse dependence of the heating flux. When the example values found above for

0co, 0ro and a are used in Eq. (5-95), it is found that

0(R)/0(O) = 0.30.

This corresponds to using

CTy ~ R/1.1 = 0.36 cm.

As can be seen from Figure 5-7, the longitudinal dependence of the heating flux also appears to be Gaussian (to lowest order), as has been observed earlier. Thus, Eq. (5-5) should be a fair approximation to the cigarette flux, and it can be used as input for the substrate-heating program.

However, <rx and oy are then needed. Note that oy can be

expected to be proportional to R, simply from geometry.

165
Since oy ference,

0.36 cm for the cigarette of 2.5 cm circumav = 0.36

2tiR 2.5 = 0.905 R cm (5-96)

in general. For the 2ttR = 2.1 cm cigarette, this yields ay =

0.30 cm, in good agreement with the value estimated in Appendix 5D. From the correlation between smolder

velocity and coal length given by Eq. (5-35), the value of ax can be connected with the cigarette parameters because cr x should be proportional to lc - Using the data available from

cigarette 105, one finds: v = 0.668 cm/min, (c = 6.5 ± 0.5 mm, p = 0.16 g/cm3

, and C = 21 mm. In Appendix 5D, it

is shown that ax = 0.62 ± 0.1 cm. Then

ax = F pCv (5-97)

with 165 ± 27 cm2 sec/g.

The semi-empirical model and the correlation described

above can now be used explicitly. Thus, suppose that the packing density for a particular cigarette is p = 0.259

g/cm3

, that C = 2.5 cm, and that all but one of the other parameters for this cigarette also have their base (reference) values; but that its diffusion coefficient for oxygen is 10%

greater than the reference value: D/D =1.1. Then Eq. (5- 17) implies that the smolder velocity is

v = 0.435 cm/min = 7.25 x 10

"

3 cm/sec,

and Eq. (5-97) yields

ax - 165 (0.259) 2.5 (7.25 x 10~ 3

) = 0.77 cm.

Similarly, the transverse width of the distribution is given by

Eq. (5-96):

civ = 0.36 2_5

2.5 = 0.36 cm.

These can now be used, along with fa = 5.6 W/cm2, in Eq. (5-5). Later it is shown (see Figure (5-8)) that the peak

temperature reached by a substrate, Th i, is only weakly

dependent on ct x or ay: an increase in ctx leads to a (small) increase in Thi, for a given velocity. On the other hand, the increase in ox here is due to an increase in velocity (over the base value). But a higher velocity means that the total energy injected into the substrate, in a given time, is reduced, and one would expect that to lead to a decrease

in Thi. Indeed, a separate calculation has shown that for the ox = 3 mm case plotted in Figure 5-8, a velocity v = 4 x 10~ 3 cm/sec leads to Th i - Ta = 425. 7°C, while a fourfold increase to v = 16 x 10" 3 cm/sec leads to Th ; - Ta =

402. 2°C. Thus these two effects on Th j very nearly cancel

each other. This is rather startling; it seems to suggest that

all cigarettes would produce the same peak surface temperature Thi, and therefore have the same ignition propensity;

whereas as seen in Section 3, this is not at all the case: it was shown there that the expanded-tobacco cigarettes

produce fewer ignitions. In fact, our semi-empirical model

does indeed predict the same result: suppose that the reference cigarette (v = 0.334 cm/min, pp = 0.259 g/cm3

) is once again used, and consider the effect of expanding the tobacco leaf. This lowers the bulk density of the cigarette; if

it is lowered by 39%, to p = 0.158 g/cm3

, then according

to Eq. (5-12), the smoldering velocity jumps to v = 0.548

cm/min. At the same time, the axial length of the flux distri- bution, according to Eq. (5-97), is entirely unchanged, in view of Eq. (5-12). For reasons which will become apparent

momentarily, ^p was taken to be 5.76 W/cm2 for the refer- ence case, rather than 5.60 W/cm2

. The substrate program

then shows that for the calcium silicate substrate, Th i =

489. 3°C for the reference case. For the cigarette with expanded tobacco and the same flux, Th i = 483. 9°C. Thus

if 483.9 < Tig < 489. 3°C (and if there were no fluctuations

in properties), there would be no ignitions with the "expanded" cigarettes, and all ignitions with the non- expanded cigarettes. This is a very narrow temperature

range, however.

We now return to the observation made earlier that there

is no obvious dependence of flux on cigarette type. A more

careful inspection of Figure 5-5 reveals two correlations; first,

it can be seen that the average peak flux from the expanded cigarettes (the second letter in the identifying labels is E) is 5.46 W/cm2

, while for the non-expanded ones

(the second letter is N), it is 5.76 W/cm2

; this is why the flux was taken to be 5.76 rather than 5.60 W/cm2

, above. This

also suggests a density dependence for the peak fluxes. When the peak fluxes are plotted against the bulk densities, a crude correlation can in fact be established, though the

scatter is very large. If the two worst outliers are omitted, the

following relationship is found by linear regression:

fa - 4.982 + 3.085 pp W/cm2 (5-97a)

The correlation coefficient is r = 0.54. A second observation

is that the Burley cigarettes (identified with B as the first letter) averaged fa — 5.85 W/cm2

, while the cigarettes

made with flue-cured tobacco (identified with F as the first letter) averaged fa - 5.29 W/cm2

. Indeed, a least-squares

fit was made to the data for the two sets of cigarettes, and it was found that

Figure 5-8. Peak Temperatures of the

Calcium Silicate Substrate Surface as

a Function of Time, for the Flux Used

for Cigarette 105, for Several Values

Of <7x

500 ' I I

400 A> \\ oxIf \V

12 mm

300 . II Y—6 mm / '—3 mm

200 7

100

i i i i i i i i 50

t(s)

166
^F(n) = 4.95 + 0.0336 n W/cm2

^n(n) = 5.53 + 0.0316 n W/cm2

,

where n is the number of ignitions

(5-97b)

(5-97c)

Consider the second observation first: the fact that the peak fluxes for the Burley cigarettes are, on average, 0.56

W/cm2 greater than for the flue-cured cigarettes, ought to be

reflected in a clearly greater ignition propensity for the Burley cigarettes. In fact, it is not (see Section 3). That it is not implies that

(a) The peak heating flux is irrelevant to the ignition process,

or (b) Although the fits for Burley and flue-cured appear

to be separate and distinct, the actual separation

between them is negligible,

or (c) There are some other factors which compensate

for the flux difference.

Aside from the fact that we know (from the equations of physics) that the peak flux does play a central role, Eqs. (5- 97b) and (5-97c) themselves clearly indicate that the peak

flux correlates with ignition. Thus hypothesis (a) must be

dropped. Hypothesis (b) is dubious. This leaves us only with

(c). There is in fact a difference in the densities of B and F

cigarettes, but that difference is minor, and it only accounts

for a small part of the 0.56 W/cm2 difference. The rest of the

difference remains a puzzle.

One final observation must be made: it is quite remarkable that the slopes in Eqs. (5-97b) and (5-97c) are nearly

identical. This is surely not a coincidence. Moreover, with the maximum density of 0.32 gm/cm3 among the cigarettes

used in this study, Eq. (5-97a) yields ^p = 5.94 W/cm2

. The

difference is 0.53 W/cm2

, nearly the same as that given by

Eqs. (5-97b) or (5-97c) for An = 20. Thus if this density

difference corresponded to zero to 20 ignitions, the slope

d^p/dn from Eq. (5-97a) would be nearly the same as that of the other two lines! Now consider the mean density of the expanded-tobacco

cigarette: it is pp = 0:158 g/m3

, and Eq. (5-97a) suggests

that the flux to be used should be 5.47, rather than 5.76

W/cm2

. Carrying out the substrate-heating calculation again

with this lower value of ^p yields Thi = 467. 0°C — a

substantially lower peak temperature. This temperature is sufficiently lower (22°C) than the peak temperature calculated for the non-expanded tobacco (489. 3°C) that the

results found in Section 3 become entirely understandable.

(Except for the lack of difference between Burley and

flue-cured).

Cigarette Energy Balance in the

Presence of a Substrate

Next, it is necessary to see how the presence of the

substrate affects the cigarette, particularly its energy

balance. Two of the principal effects are, loss of energy to the substrate by heat conduction, and reduction of the

oxygen supply. Before explicit calculations of the change in energy loss by the cigarette due to the presence of the substrate are made, the following needs to be pointed out: The burning rate is principally controlled by the rate at which oxygen can diffuse into the cigarette, as has been

seen earlier. When the cigarette is placed on a substrate,

the availability of oxygen declines because of the interfer- ence of the substrate with the (air) flow field. Experimental

measurements have shown (Section 4) that the decline in burning rate is about 17% (an average over all cigarettes

examined on a flat horizontal substrate). The fluctuations about this average value are substantial, however.

If a steady state is achieved, then the rate of production

of heat must also decline by 17%, just as the heat loss rate does. We can now make theoretical estimates of the heat

losses by the interacting cigarette.

Figure 5-9 is a reproduction of Figure F,6b from Ostrach

[5-12]. It shows the calculated streamlines during free convective cooling of a heated horizontal cylinder. It is apparent that at large distances, the flow is inward; near the

cylinder, it all becomes upward. When a surface is placed

under it, the flow is affected substantially: to zeroth order,

the convective cooling will be diminished by the fact that the

flow is eliminated in the lower region (where we now have

conductive cooling, instead). Since that is a strip of width

2£, it corresponds to an angular wedge of central angle 20,

where

tanG as ^/rG ;

with \ = 0.75ro , 6 = 36.9°, while ^ = r yields 9 = 45°. I might be still larger.

For the infinite, uniform-temperature cylinder in free space,

the local heat transfer coefficient h(0) decreases monotonically from a broad peak at the lower stagnation point, to zero at the upper one, as shown by Figure 5-10 (Figure

F,6a, in Ref. [5-12]. The g(x) in this figure is proportional to

h(9); the proportionality constant is unimportant). This near- constancy can also be seen in a striking way from Figure 7- 4 of Ref. [5-9]. The average h is

h = —

71 h(8)d8,

and its value is given by Eq. (5C-4). If £, = r is assumed,

the integration should only extend from tc/4 to tc; then the

integral is only 69% of the original. Assuming that the convective losses from the cigarette behave in a way similar to those from the constant-temperature infinite cylinder, the convective cooling by air when the cigarette is placed on

the substrate is only about 0.7 (or less) of what it is in the open.

One must also ask how the radiative cooling is changed.

Without the substrate, the radiative energy loss from a "cigarette" of length L, temperature Tc , is

Eout = 2nRLec aTc 4

,

while the feedback from the environment is

167
Figure 5-9. Reproduction of Figure F,6B

from ref. [5-12]. Theoretical

Streamlines for horizontal cylinder. The

scale is for Gr = 104

E, n = 27lRL£c CTTa4.

With the substrate present, the radiation energy feedback

Ein increases, while the surface temperature decreases, so

that the net loss is smaller. It is easy to show that the energy input to the cylinder from the lower half space is

Figure 5-10. Reproduction of Figure F,6a

from ref. [5-12]. Azimuth function g(x)

giving variation of local heat transfer

coefficient. The other curve is of no relevance

here.

2.5

2.0 3 l5

J?

X

CT

1.0

0.5

~v ^Sfy

V

1 2 3 1

.. .--i—l

0.8

0.6

0.4 3

en

0.2

30 60 90 120 150 1! Azimuth x, degrees

oo (5-98) E L - 2 Lec l dxQ(x)|Es <rTs

4

(x) + (1 -es )[Q & + (1 -&)M

(where fa is given by Eq. (5-90)). Thus, including the upper

half-space,

E in = 7tRL£c0a + E L

The result depends on Ts (x). Two cases are again

considered:

Case I: T,(x) = Ta (t = 0)

Case II: Ts (x) is given by Eq. (5-92)

For case I, Eq. (5-99) yields

TtR

(5-99)

Ein L Ec [4 fa + (1 -£s )(0c-0a)], (5-100)

while case II yields

Ei„ = kRL

ec [2es m + 20a + (1 -Es )(fa + fa)]. (5-101)

The peak value of the substrate temperature will generally

be in the neighborhood of its ignition temperature. That is, it

is assumed that Ts (0) in Eq. (5-93) is Ts (0) = Tig . Ignition

temperatures for substrates lie in the range T;g = 400 ±

100°C.

Explicit calculations can now be made in order to find how much the radiation loss is changed, when the cylinder

is placed on the surface. The reference values ec = 0.73, es = 0.8, Ta = 27°C, and Tmax = 400°C are used. The new

peak surface temperature Tcs has yet to be determined; assume that

I cs — I c 600°C. Then

fa = 0.0459 W/cm2

, ec aTc 4 = 2.404 W/cm2

, Eq. (5-91

)

implies A = 0.9865,

and e,fa

Then:

0.931 W/cm2

Case I (t = 0): fa = 2.455 W/cm2 (only slightly higher than

EcCTTc4

)

and Enet/ E&t = 0.963

Thus, there is a 3.7% decline in net radiation loss (due to reflections from the cold substrate).

Case II (steady state): fa = 2.456 W/cm2

and Enet/ E&t = 0.824;

that is, the decline in the net radiation loss rate is 18%, "late"

in the substrate-heating process.

168
There is one more effect to be included: when a cigarette

is placed on a substrate, its surface temperature distribution changes: its peak temperature drops from Tc = 600°C to Tp

, and its width along the axis rises from ctx to ct'x , in proportion to the increase in the length of the coal from (c to

fc

'. The total energy loss for cigarette 105 smoldering on the

substrate is estimated (Appendix 5C) to be E = 3.75 W

and in the open, at a rate 17% higher:

E° = 3.75/0.83 = 4.52 watts. It was also found that this

is divided into Ec° = 2.02 W and E° = 2.49 W. From the

estimates made just above, therefore, when the cigarette is dropped onto the substrate, the convective loss must go

from Ec° to

Ec = 0.69

873 - Ta

where Tp

is the new peak value.

; The radiative loss must go from Er° to V

Er J^ - B/4a

Tc Ta Er°,

where Tc is the peak surface temperature while in the air (currently, we take Tc = 600°C) and B is the square

bracket in Eq. (5-101).

Finally, Eq. (5-86a) is used for the conductive flux. It is then

found that a drop of only 10°C, to TP = 590°C, requires a 5% increase in cone length: 2c'lic = 1.049) to yield the

observed energy loss rate; a drop of 20°C requires a 10%

increase (fc 7fc = 1.105). Assuming a drop to 580°C, one

obtains

E r = 2.03, Ec = 1.01, and Ecd = 0.71 watts.

These three values are not very sensitive to the various

assumptions made for Tp

, Tc , etc.

Summary

In this section it has been shown that some reasonable esti- mates for the reduction in convective and radiative losses of a cigarette when it is dropped on a substrate can be made;

for the case under consideration, 50% and 19%, respectively. A reasonable estimate for the additional loss due to conduction to the substrate can also be made: about 0.7

watts. Together, these yield the observed decline of about

17% in the cigarette burning rate.

I

169

Results from Using

the Models

The use of the semi-empirical model to find the four parameters needed in Eq. (5-5) for the cigarette flux has

already been discussed. In this section the results which are obtained from using the substrate program with a given flux,

will first be examined. Then, the results of using the

smoldering-cigarette program CIG25 will be examined.

Substrate Program

It is important to validate the computer model against

experiment. The following experiment was carried out: 5 a

smoldering cigarette was placed on a porous, low-density

calcium silicate insulation block. This material is fairly homogeneous, and is essentially inert, as determined by

differential scanning calorimetry (DSC). Two thermocouples were embedded right at the surface, 10 mm apart. The

cigarette was placed so that the line connecting the ther- mocouples was also the line of contact with the substrate,

and with the paper burn line about 7 mm from TC #1. A

continuous record was made of the temperatures recorded

by TC's 1 and 2. The flux distribution that was used was

that shown in Figure 5-7, and the values (from the literature) used for p, C, and k for the calcium silicate were p = 216

kg/m 3

, C = 1.12 J/gm°C, and k = 0.0715 W/m°C. With

these inputs, v = 0.5 cm/min = 8.33 x 10" 5 m/sec, and

es = 0.95, the program gave temperatures considerably

higher than the measured temperatures. It was noted that k and C could both be expected to increase with temperature,

and so another run was made, using k = 0.10 W/m°C, but keeping a the same (i.e., C was increased to 1.12

(0.1/.0715) = 1.57 J/gm°C). This gave the improved, but

still inadequate, results shown on the next page, at t = 84

sec. That is the time at which the paper burn line should

have traveled the distance vt = 7 mm, and have been

located right above TC #1 . This is indicated by the first dash

mark in the computer output shown on the next page. The

first column indicates the temperature above ambient, along

s This is also described in Section 4, but the redundancy will perhaps be

useful here.

the substrate center line. The second column shows the temperatures at the adjacent mesh points (1.67 mm to the

right), and so on. The top row is at zero, because that

(vertical) face is kept at ambient (the boundary condition).

Thus, the calculated temperature at TC #1 , at the moment

the peak flux passes over it, is 495.98°C above ambient, or 516°C. Six mesh points below corresponds to the distance

6 x 1.67 = 10 mm, so TC #2 is located there, as is indi- cated by the second dash mark. The temperature calculated there is 145.88 °C above ambient, or about 166°C. The

temperatures measured at that moment, by contrast, were 420°C and 54°C, respectively. Two minutes later, the calculated temperatures at TC's nos. 1 and 2 were 167°C and

518°C, respectively, vs measured temperatures of 269°C

and 413°C. Thus, at t = 84 sec, the calculated temperatures were 96° and 112°C too high; while at 204 sec, they were low by 102°C and high by 105°C, respectively.

Three of the four readings are much lower than the calculated values, and the question is "why?" The "anomaly" at TC

#1 at t = 204 sec will be explained presently. There are

several possibilities:

a. The substrate contains water (absorbed, or of hydration)

which must be driven off.

b. The substrate is not inert, and experiences endothermic

pyrolysis.

c. The assumed input flux is too high.

d. The thermophysical values used for the calculation are

inaccurate.

e. The program is incorrect.

f. The cigarette produces water and/or tars which

condense onto the substrate, acting thereafter as a heat

sink.

g. The heat transfer coefficient (for convective cooling of the

surface) is larger than assumed.

As for hypothesis (a): the calcium silicate was kept in a

dessicator for more than 24 hours before the test. As for (b): as pointed out above, DSC analysis showed that this is not the case.

171
X LENGTH Y MESHES ALPHA K H EMS DT TIME DELTA

.0667 20 295E-06 .07|7? 10 .00 .950 .200 84.000 .00167

FMAX VX SIGX SIGY XZRO SIZE RATIO EMS LOSS(J.)

56000 . .833E-04 .00700 . 00360 01932 .33333 6.22

# OF STEPS SUBSTRATE HEAT. JOULES INTEG. FLUX. JOULES CONVECT LOSS. JOULES

420 96.33 353 . 79 128.77

SURFACE TEMPERATURE, (X-Y PLANE). LEFT HALF

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

2.20 2.12 1.90 1 .59 1 .26 .93 .66 .44 .28 .17

4.89 4.71 4.20 3.50 2.73 2.02 1 .41 .94 .59 .36

8.65 8.30 7.34 6.04 4.67 3.41 2.37 1 .56 .98 .59

14.32 13.65 11 .91 9.63 7.32 5.27 3.61 2.36 1 .47 .88

23.19 21.93 18.73 14.77 10.96 7.74 5.22 3.37 2 .08 1 .23

37.38 34.97 29.04 22.11 15.89 10.94 7.24 4.61 2 .81 1 .65

60.10 55.51 44.55 32.46 22.41 14.96 9.68 6.06 3 .66 2 .13

95.33 86.91 67.24 46.67 30.72 19.78 12.48 7.67 4 .57 2 .63

145.63 131.22 98.12 65.12 40.84 25.27 15.51 9.35 5 .49 3 .13

204.96 1 82 . 79 1 32 . 79 86.76 52.35 31 .16 18.59 10.99 6 .36 3 .58

229.54 202.05 1 42 . 87 108.22 64.61 37.14 21.50 12.44 7 .09 3 .94

305 . 37 267.91 186.08 136.96 78.26 42.99 24.04 13.58 7 .61 4 .18

386.02 339.29 234.30 166.74 91 .34 47.98 25.89 14.27 7 .86 4 .26

451 .49 398 . 00 274 . 75 190.93 101 . 18 51.15 26.71 14.37 7 .79 4 .17

490.16 432.79 298 . 55 204.07 1 05 . 44 51 .67 26.25 13.83 7 .38 3 .91 — 495.98 437 . 53 300 . 42 202 . 77 102.76 49.18 24.44 12.67 6 .67 3 .51 467.26 410.60 279.17 186.51 93. 17 43.86 21 .47 11 .00 5 .74 3 .00

406.68 355.04 238 . 05 157.86 78. 16 36.50 17.73 9.03 4 .69 2 .44

322 . 60 279 . 45 1 84 . 68 122.15 60.38 28.23 13.73 6.99 3 .63 1 .89

229.85 197.77 1 29 . 37 85.97 42.84 20.25 9.95 5.10 2 .66 1 .39 — 145.88 125.05 81.56 54.97 27.91 13.49 6.76 3.51 1 .85 .97

82.54 70.73 46.39 32.02 16.75 8.37 4.31 2.28 1 .22 .65

41 .93 36.02 23.94 17.10 9.32 4.86 2.59 1 .41 .76 .41 19.30 16.67 11 .31 8.46 4.85 2.66 1.47 .82 .46 .25

8.14 7.09 4.95 3.92 2.39 1.38 .80 .46 .26 .14

3.19 2.81 2.04 1.72 1 .12 .69 .42 .25 .14 .08

1 .18 1 .05 .80 .73 .51 .33 .21 ^3 .07 .04

.42 .38 .31 .30 .23 .15 .10 .06 .04 .02

.15 . 14 .12 .12 .10 .07 .05 .03 .02 .01 .05 .05 .05 .05 .04 .03 .02 .01 .01 .01 .02 .02 .02 .02 .02 .01 .01 .01 .00 .00

.01 .01 .01 .01 .01 .01 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

.00 .00 .00 .00 .00 .00 .00 .00 .00 .00

An attempt was made to test possibility (c), by changing

Ox from 7 mm to 6.1 mm. The results at t = 2, 10, and 84

sec are displayed in Figures 5-11 a to 5-1 1c, in a graphical

form. The isotherms at multiples of 50°C are displayed;

these make the gradual heating up of the substrate obvious.

The movement of the temperature peak, approximately

tracking the movement of the flux peak, is also clear. The

results, however, are only marginally better than for the previous run. Next, hypotheses (c) and (f) were tested together, by

using a different heat source: a thin, electrically-heated

vertical rod, with one end held stationary about 2 mm

above the substrate. This heat source produces no water, and the flux from it can be measured unambiguously. The

flux is shown in Figures 5-1 2a and 5-1 2b, in two orthogonal

directions. The average was fitted with a sum of two Gaussian curves such as given by Eq. (5-5), with v = 0. ax = oy (the flux must be cylindrically symmetric).

The calculated (Tca i) and the measured (Tex i) values of the temperature at the surface, at the origin, are given in Cols. 2 and 3 of Table 5-2, respectively. As before, there is a second thermocouple 1 cm from the center; the calculated

(Tca2) and the experimental (TeX 2) values are given in Cols. 4 and 5. The errors are still substantial, but only about half

172
Figure 5-1 1a. Calculated Isotherms on

a Calcium Silicate Surface, Resulting

from Heating this Substrate with the

Flux Shown in Fig. 5-7 (from Cigarette

105), at Time t = 2 sec. Solid and dashed

curves alternate to facilitate distinguishing among

adjacent isotherms.

what they were for the cigarette as a source. If we assume

that the program is correct, then the only remaining explanations are (d) and (g): the thermophysical constants used

for calcium silicate were incorrect, and/or h is larger than 5. One can expect that with increasing temperature, k and

Cp would both increase. It was found that the experimental

results could be reasonably well matched by using k = 0.10

W/m°C, p = 205 kg/m 3 (the substrate lost 10% of its mass

in the D S Calorimeter), Cp = 2.57 J/gm°C, es = 0.9, and

a heat transfer coefficient h = 18 W/m2 °C. The resulting calculated values at TC1 and TC2 are shown in Cols. 6 and

7 as T'cai and T'ca2. No choice was found which would yield

the experimental value for TC2 at t = 180 sec, while also giving reasonable values for the other thermocouple at other

times. The experiment should have been rerun with the heater centered over TC2, in order to test the correctness of the initial experimental run; but there was not enough time

to do this. The inadequacy of the literature values of k and Cp to

yield the observed results indicates that without adequate

input data, the models will not give reliable results. The program was then rerun, using these effective values

of k, p, Cp , etc, for the substrate. For the input flux, that corresponding to cigarette 102 was used: ax = 6.1 mm, oy = 3.0 mm, (j) m = 5.6 W/cm2

, and v = 0.38 cm/min. The

results are shown in Figure 5-1 3a. As is seen there, the peak temperature read by TC1 is well reproduced, though

the calculated temperature rises too quickly at first, and falls too slowly beyond the peak. Similarly, the temperature at

Figure 5-11b. Calculated Isotherms on

a Calcium Silicate Surface, Resulting

from Heating this Substrate with the

Flux Shown in Figure 5-7 (from

Cigarette 105), at Time t = 12 sec. Solid

and dashed curves alternate to facilitate distinguishing

among adjacent isotherms.

TC2 appears to rise too rapidly. The reason for the too- rapid-rise lies in the asymmetry of the input flux: as seen in Figure 5-4, the temperature rise along the cigarette is very

rapid at the front end, and elongated behind; the flux must

follow the same pattern. Eq. (5-5) prescribes a flux with fore- and aft-symmetry, however, so that the asymmetry cannot be modeled at present. 6 In order to obtain the observed

temperature dependence at TC1, therefore, a smaller value

of ax was used: ox = 4 mm. This choice results in a good

fit at TC1, as is seen in Figure 5-1 3b. The calculated temperature at TC2 lags the measured temperature;

presumably, this is because the Gaussian distribution has

Table 5-2. Calculated and

Experimental Values of Temperatures

(in degrees C) at TC1 and TC2, as a

Function of Time.

t(sec) Teal Texl TC a2 Tex2 T'cal T'ca2

10.8 403 298 105 79 296 75

22.8 447 335 136 89 347 95

82.8 486 388 189 113 395 130

180 497 405 211 126 408 147

173
Figure 5-1 1c. Calculated Isotherms on

a Calcium Silicate Surface, Resulting

from Heating this Substrate with the

Flux Shown in Fig. 5-7 (from Cigarette

105), at Time t = 84 sec. Solid and dashed

curves alternate to facilitate distinguishing among

adjacent isotherms. The flux peak has travelled 7 mm

in this time.

Figure 5-12a. Flux Measured Under the

Rod Heater, Along the Substrate

855

.020

.025

.023

.020

.018

.015

.013

.005

.003

.050 .055 .068

the flux falling off too rapidly at large distances. However,

this inadequacy is of minor significance for our purposes. The more important fact is that the magnitude of the temperature peak was found, within 14°C.

The paper burn line reached TC1 at t = 95 sec; this is marked point A on the figure. The peak flux arrives 20 sec

later; this is marked as point B. At the given burn velocity,

this difference corresponds to about 1 .3 mm.

Instead of finding the temperature at a fixed location (such as at a thermocouple), one can ask what the peak surface

temperature is at any moment, regardless of where on the substrate it is. If the substrate had an ignition temperature Tig , this would permit one to see whether Tg is reached (or exceeded) anywhere. The results for three such runs are shown in Figure 5-8, where the only change from one curve

to another was to lengthen the flux distribution (by

increasing ax). The peak temperature approaches an

asymptotic value fairly rapidly, for each choice. As we might

have expected, the asymptote is higher, the larger ax is, but the affect is relatively small: a 100% increase in the axial length of the distribution (from ax = 3 mm to 6 mm)

produces only an 8.7% increase in the (asymptotic) temperature rise, while a further doubling (to 12 mm) produces

only a further 3.8% rise. On the other hand, the asymptotic

''The reason for the inadequate fit in Figure 5-1 4a only became clear during the writing of this report, and there was no time to generalize

the input flux.

Eo

X

z>

<

111 I

-30 -20 -10 10 20

DISTANCE RELATIVE TO PEAK (mm)

temperature rise, ATmax , is directly proportional to the peak

flux, so that the variations in the peak flux will influence ATmax much more strongly. For a given type of cigarette,

peak fluxes may vary by as much as 10% from one to another; this would lead to 10% differences in the temperatures developed in the substrate. If the ignition temperature

is near the calculated peak temperature, therefore, fluctua- tions among the cigarettes may lead half the cases to ignite. The same effect can cause the ignition tendency to have an

apparently strong dependence on crx in spite of the weak

dependence of ATmax shown here; Figure 4-23 implies such an effect. The corollary is that to ensure no ignitions, we

must have ATg be 10% or more above the predicted

*-J I max •

Figure 5-1 2b. Flux Measured Under the

Rod Heater in the Direction Orthogonal

to that Traversed in the Measurements

Shown in Figure 5-12a

10

*T 8

Eo£ 6rx

5W

I

-

! -

, .,

l 1 ... , ...

-

-

-

-

i i i 1 1

-

30 -20 -10 10 20 30

4 -

2

-

DISTANCE RELATIVE TO PEAK (mm)

174
Figure 5-13a. Calculated and Predicted

Temperatures at Thermocouples TC1

and TC2 When the Smolder Wave from

Cigarette 102 is Made to Pass Over

Them. The Point A Corresponds to the Paper Burn

Line Crossing TC1; Point B Corresponds to the Flux

Peak Passing Over It

500

400

I 200

Ox " 6.1 mm

Calculation •'

100 1 120 140 A B

180 200

Cigarette Program

During the development of the program, radial and temporal

oscillations were observed in the output, especially for the oxygen results. The cause of the first was (too) large spatial

gradients. This was corrected by reducing the mesh size from Ax = Ar = 0.04 cm to Ax = Ar = 0.02 cm. Also, the time step was reduced to 5 ms. Finally, the conver- gence criterion was tightened from 1% to 0.1%; this gave

smoother results and therefore better values for the

derivatives. Some graphical routines have also been incorporated into the program, so that the results can be more readily visualized. The results of running the program, starting with the

initial conditions for T(x) given earlier, are shown in Figures

Fig. 5-1 3b. Calculated and Predicted

Temperatures at Thermocouples TC1

and TC2 When the Smolder Wave from

Cigarette 102 is Made to Pass Over

Them. The Point A Corresponds to the Paper Burn

Line Crossing TC1; Point B Corresponds to the Flux

Peak Passing Over It. The Flux Distribution Has Been

Taken to be Narrower than in Figure 5-1 3a.

500

400

O 300

200

100

- Ox " 4mm

Experiment

i —

'Calculat

r

on

r r— i

/TC#1

JS

TC#2

Experimenl/^^-'

.^'

'

i —

i

—7-rrr.

5-1 4a to 5-1 4e; the results are shown for t = 0, 2, 4, 6, and

7.86 sec. The results are plotted here as isotherms (with

temperatures in degrees Celsius). Contours of constant oxygen mass fraction are also obtainable from the program,

but are not given here in the interest of saving space. We

note that the peak temperatures occur in a torus which

gradually approaches the axis - this is where the reaction

rates peak. With time of course the peak temperatures will

lie on the axis.

If the program were permitted to run long enough (30-60

sec), the solution would "relax" to the quasi-steady state. This

would have been very costly in computer time, however.

Moreover, it would not have been very useful, since it is the

(quasi) steady state that is compared with experiment and

with other models. Much more sensible, therefore, is to use

a starting condition for the cigarette which is already close

to a steady (or quasi-steady) state. It is also the condition

which prevails when the cigarette is dropped onto furniture. Therefore, an alternative "initial" condition was chosen, which

corresponds to the experimentally observed distributions of y and T, shown in Figures 5-2 and 5-3. The approximations

to those distributions used here, are shown in Figures 5-1 5a

and 5-1 6a (corresponding to t = 0). The peculiar appear- ance of some of the contours in Figure 5-1 6a is an artifact of the graphical-display computer package: it sometimes

connects points which should not be connected. The subsequent figures show the evolution of the distributions in the model "cigarette" with time, out to 18 sec. We note that the temperature diffuses rather more, in this submodel, than it does in reality. That is, the temperature distribution becomes

too broad (perhaps because water vaporization has been

Figure 5-14a. Initial Temperature

Distribution (in °C) Chosen for

Calculation, to Simulate Effect of

Lighting Cigarette With a Match. Solid

and dashed curves alternate to facilitate distinguishing

isotherms.

20 40 60 80 100 120 140 160 180 200

t(s) A B

.800

U«C CQUfiLS

SEC. .700

.600

.500

I -«00

i0O

.200

. 100

III. I

| !••.!

1

1,1 1

0.000

0.

1

.'0 100 .let S00 .4M

SAOIUS - Cn

175
Figure 5-1 4b. Isotherms at t=2 sec,

after Initiation as in Figure 5-14a

Figure 5-14d. Isotherms at t=6 sec.

.900

TIME EOUALS

2.8 SEC. .700

.600

.S00

T .400 Z

.300

IM "-]

.200 "- 5»e - -" ~-^

\

.100

5 : 1976.1 ' .

\'

^ \\]S/,'J/ , Li 0.000 .100 .200 .300

RfiOlUS - CH

.499

1 1 me: equals

Figure 5-14c. Isotherms at t=4 sec. Figure 5-1 4e. Isotherms at t=7.86 sec

TIME EQUALS

.200 .500 POO I US - CM

neglected). This result is the opposite ot that obtained with Muramatsu's model, where the temperature distribution is too narrow. By following the intersections of a specific isotherm on the

axis — say, that for 700°C - we readily infer the velocity of the smolder wave. (This can also be done by following the 450°C point on the surface, which is the paper burn line.) We find that for another set of parameters, the velocities (using the 700°C isotherm) vary with t as shown in Figure

5-17. vu is the velocity of the upper intersection, vL that of

.800

TIME EQUALS

7.66 SEC.

.700

.600

.500 ~ ~ --_ i

£

'—----- ' i .100 ------T^x "** N. |

.300 - -"• —~-^T\ s i

.200 """/^S'W!

/ B86. / 1 \ \ "

.100

0.000 .100 .200 .300 .400 wnoius - CH

the lower intersection. The smolder velocity may be taken to be the (arithmetic) mean. We see that the velocities drop

rapidly to nearly asympotic values. These values are not the same, however, and since vL > vu beyond t = 17, the hot zone is apparently shrinking; if this continued, the cigarette

would go out. A steady state is obtained with the parameter

values shown in Table A1, Appendix 5B. The peak interior temperatures are on the axis, and are

quite reasonable. The peak surface temperatures (at the

sides) are of the order of 550°C, essentially what is

176
Figure 5-15a. Isotherms for Second Set

of Starting Conditions. These were

Taken from Figure 5-2. The reason for alternating solid curves and dashed curves is explained in the captions for Figures 5-11a and 5-14a.

Figure 5-15c. Isotherms in the model

cigarette at t=12 sec.

5.001"

"I

1. 60

time;. .00 SEC 5.60

TEMP. N C. 2.40

J.J0

2.00

1.60 E

, 1.60 Iz 1 .40 J

1.20'

1.00-

1

.600 ^-—> |

.600

"''».

>

.400

1 II

.200

0. W\00 .200 .400 ROD I US - CM

5.00 1

2.60 1

TIME- 12.00 SEC 2.60 1

TEMP. IN C. 2.40

2.20

2.00.

1.60

1

1

1

1

1

1

1

1

, 1.60-

1 ~~ "" ^ | x

Z 1.40

1

' "v. 1

1.20 C

S '

1 .00

.600 'Am

M'

.600

.400

.200 ^ ' 1 -.<'. .A

0.000 .200 .400 RADIUS - CM

Figure 5-15d. Isotherms at t=18 sec

Figure 5-1 5b. Isotherms corresponding

to smolder wave at t=6 sec. These result from calculations made with CIG25.

5.001

2.69 1

TIME- 6.00 SEC 2.60 1

TGKP. IN C. 2.40

2.20

2.00

1.60-

1

1

1

1

1

1

1

1

, 1.60

1

Z 1.40

-1

1

1 .20 -~0

1 .00 "••••CV

.600 "•nV 1

.600

.400

.200 -y,\

0.000 1 1

. .^i f\ 0.000 .200 .400 BOOIUS - CM

5.00i n

2.60

TIME- 16.00 SEC 2.60

TEMP. IN C. 2.40-

2.20

2.00

1 .60 c" 1-60 I

Z 1.40

"" 1

1 .20

1 .00 ^XA- \\\

.600 \\

'

.600

.400

.209

0.000

0. -r,'</\

300 .200 .400 eooius - cm

observed. In Figures 5-18a-5-18c, the outflow velocities are

plotted, again as contours. It is interesting to note that there

are two tori with peak rates; presumably one corresponds to a region where the oxygen concentration is relatively high, even though the temperature is not a peak, and the other

reaction peak, to a region where the temperature is relatively high, although the oxygen is low. This result may be

an artifact of CIG25, however; gas outflow from pyrolysis

would tend to suppress oxidation behind the coal — i.e.. in the upper part of Figure 5-1 5d. The results are quite sensitive to the input parameters,

especially (of course) the paper permeability. The program

runs much more smoothly with the second set of initial conditions, as is evidenced by the much shorter computer

time required to make a run of given length. Thus, the

"partial" model runs well, and gives results which appear to be reasonable.

177
Figure 5-16a. Contours of constant

oxygen mass fraction, corresponding

to Figure 5-1 5a (t=0). See the text for

discussion.

Figure 5-16c. Oxygen mass fractions at

t=12 sec.

3.B8

i.ee

2.6B

2.40

2.20

2.8B

1.80^

rV I .6B

§ I.4BI .28

I -BB

_ _ _ J?

I

.808 ^%i

')^

.600

tee l^J C ^

.288

8.808

e.

^^^——^

see .200 .400 MO I US - CM

5.00 i

2.80

2.60

2.48

7. 28

2.BB

1 .88

3E

, 1.68 H

I

l-'B- ^s 1 .28 — ^s. sJ~-Jj^>-V V ^j

1 .88 r5>^\v

.688

.EBB ll/l '/'/

.4BB

.20B 'r^y\

t^'a

0.000 .200 .'00 enoius - en

Figure 5-16b. Oxygen mass fractions at

t=6 sec, from the same calculation

that yielded Figure 5-15b.

Figure 5-16d. Oxygen mass fractions at

t=18 sec.

5.00 1

2. 88

2.60

2. 48

2.2B'

2.00

i .ea E

, 1. 68 X

I l.4B<

1 .20- r>Ti

1 .88

.888 \\V'

.600 ill!

i if

.408 S/'/d

.200 S^z^

- ^^^ '

8.800

8. rr^r./i)00 .2BB . 4BB

CHOI US - CM

.000 .200 .<0 RADIUS - CH

178
Figure 5-17. Calculated Velocities of

the Upper and Lower Intersections of

the 700°C Isotherm with the Axis, as a

Function of Time. These were Obtained by

Starting with the Second Set of Initial" Conditions.

40 p^ri 1 1 1 1 f

-. 24

COo

> 16

i—i r "i—

r

Figure 5-18a. Contours of constant

radial gas velocity at t=6 sec, from the

calculation that yielded Figures

5-15b-d and 5-16b-d.

5.00 ->

2.80

2.60

2.40-

2.20

2.00-

I .80

u

, 1.60- X

1 .20

1 .00

.800- T

}

.800

.400

.200 M

0.000 .200 .400

8001 US - CM

Figure 5-1 8b. Contours of constant

radial gas velocity at t=12 sec. The values

are in cm/sec.

5.00 . n

2.80

2.60

2.40-

2.20-

2.00-

I .80-

, 1.60-

NGTH si

->

1 .20

1.00

.000- T"1

.600

.400 <<M - _ .let'3

.200-

0.000

0. )00 .200 .400 8H01US - CN

179
Figure 5-18c. Contours of constant

radial gas velocity at t=18 sec.

000 .200 .<0 600 1 US - Cn

180
Summary and Conclusions;

Lessons Learned

A smoothly-running computer program (TEMPSUB) has

been produced, which yields the temperature distribution in an inert substrate, when subjected to a heating flux. This

heating flux is Gaussian with an elliptical cross section, and

can be taken to be a moving source (with arbitrary velocity).

The peak flux and the widths of the distribution are also

user-specified. The program has been checked against

known analytic solutions, and has produced answers which

are correct (within the limitations of the numerical procedures). When realistic inputs are supplied, it predicts

temperatures in good accord with experiment.

A smoothly-running computer program (CIG25) has also been produced, which incorporates a major fraction of the known physical/chemical processes occurring in a naturallysmoldering cigarette, as outlined earlier. This model is an advance over previous models in that it is two dimensional,

time-dependent, and takes into account the effects of the paper wrapping on oxygen diffusion. Running this program

produces fairly realistic temperature and oxygenconcentration profiles, as well as yielding a realistic smolder

velocity.

The key variables which have been identified pertain to oxygen transport: the permeability of the paper to oxygen,

the temperature at which the paper burns, and the diffusion coefficient in the tobacco column.

Following an independent line, a semi-quantitative analysis

which directly yields the widths of the heating flux distribu- tion from a cigarette smoldering on a substrate has also been carried out. This flux can then be used in the

substrate-heating program. The analysis is based on empirical correlations of burning velocity vs some cigarette

parameters, and on similar correlations based on Muramatsu's model. It also depends on a new correlation developed here. This semi-empirical model works well. The

detailed model is potentially even better, but it is (currently)

difficult to make the lengthy computer runs needed to carry

out parametric studies. A conclusion of central importance is that the very best

substrate and cigarette models are not very useful unless

reliable thermophysical data, especially for the substrate, are

available. To be sure, if a particular cigarette on a particular substrate does not succeed in igniting it, then the cigarette

model will serve to tell us what changes can be made

without increasing the ignition propensity on that substrate, even with inadequate data. Vice versa, if a cigarette does

ignite some substrate, the cigarette model will serve to tell us what changes can be made without lowering the ignition

propensity. But the intermediate cases, which are more

interesting, could not then be analyzed.

The problem — i.e., modeling a cigarette, a substrate,

and their interactions - is exceedingly complicated. The

(sub-)model, as it stands now (CIG25), neglects some nonnegligible aspects of the physics - such as axial flow, the gas continuity equation, the ideal gas law, pyrolysis, the production and transport of water, radiation loss at the boundary, a more complete paper model, etc. Nevertheless,

it is already sufficiently realistic that it can manifest a number

of the features of cigarette behavior, including realistic temperature and oxygen-concentration profiles, realistic velocities for the thermal wave, etc. For example, if one

wants to lower the smoldering rate of a cigarette, one can:

a. Decrease the permeability of the paper, as already

pointed out above,

b. Increase the heat transfer rate at the surface (this could

be done by increasing the emissivity of the paper, for example),

c. Increase the tobacco packing density (see Eq. (5-12)).

In fact, almost every parameter affects v. Items a-c are,

of course, qualitatively obvious; but the model permits quantification of these effects. Note that decreasing the smoldering velocity of a cigarette

without making any other changes in its properties (not

possible, of course!) would increase the ignition propensity

However, decreasing the smoldering velocity also decreases

the length of the coal; the combined effects are to slightly

lower the ignition propensity. If the decrease in velocity

results from an increase in packing density, then there is an accompanying increase in peak heat flux to the substrate,

which increases the ignition propensity more dramatically.

These results agree with the experimental findings in Section 3. As pointed out in the introduction, a good mathematical

model permits one to not only interpolate properly between

experimental results, but also to extrapolate to new situa181
tions. Thus the model can also allow one to investigate the

effects of changing other parameters which may be

amenable to control in industrial production, and which have

important impacts on smoldering, such as changing the void

fraction (and thereby the packing density), changing the tobacco type (which would affect the reaction kinetics, and

therefore the rate, directly), changing the cigarette radius,

etc. Much of this is also obtainable from Muramatsu's

model; those results are given by Eqs. (5-6) to (5-24). The amount of physics left to introduce into the program

should not require a prohibitive amount of effort and should

also not increase the computation time significantly. Thus, we have an interesting computer model which — with perhaps another year's effort - could become excellent. Just as the cigarette model requires further work, so does

the substrate model. Perhaps the most significant improvement which still needs to be made in the latter is the

introduction of a second layer.

Another important consideration is that this cigarette

program could have some important non-cigarette applications — to wit, in studying smoldering in other materials and

configurations. Thus, one could rewrite the code in Cartesian coordinates with relatively little effort, and examine the smoldering of a non-inert substrate in a variety of configurations. To the extent that CIG25 is inadequate, the semiquantitative approach used earlier can serve as an interim

solution.

Finally, as to the approaches used in modeling the cigarette: it is not clear that the best numerical method for solving the equations have been used; for example,

quasilinearization of the equations might make the problem more tractable. Another item which became clear during the analysis is that the H2O produced during combustion might have an

important effect that has not been at all considered, in writing down the equations: it may condense on the inner portions of the cigarette and/or on the paper wrapper,

changing the characteristics of the paper. By the same

token, the free water in the tobacco would also be

important.

Similarly, the substrate may (a) absorb water from the

cigarette, and (b) not be inert. Both of these make the

substrate-heating calculation less reliable than it could be. The substrate-heating calculation can nevertheless be useful

in a relative sense: if the calculated temperatures (which are

too high) indicate that the surface temperatures do not quite

reach Tig , then it is certain that ignition will not take place.

Another "lesson" is the importance of choosing appropriate

initial conditions: the first set of initial conditions was

perfectly reasonable, but it takes 60 sec or longer of smoldering for the "cigarette" to relax to some approximation of a steady state; the present model numerics made that attempt

impractical. Using, instead, an approximation to an

experimental steady-state-distribution of oxygen and temperature permitted the program to run much more smoothly,

and to relax to its steady state. Aside from the numerical difficulties, the sheer magnitude

of the calculation is impressive: An 18-sec "burn" on a 3-cm

"cigarette" required 21 hours of calculation on a Perkin- Elmer 3252 "mini" computer. On a Cyber 855 the same

calculation took about 4000 CPU seconds; a 30-sec "burn" took 7000 CPU sec, and a more "difficult" parameter set required 18000 CPU sec for a 60-sec burn. A vectorized

version of the program should run quite a bit faster on a Cyber 205. A final observation regarding the cigarette models: the basic output required of the cigarette model(s) for this study,

is the heating flux to the substrate. The best model available heretofore (that of Muramatsu) fails in that respect, within a

scale factor. The present computer model (CIG25) has the same weakness (with a different scale factor). The model will have to be completed and improved, before it is thoroughly

reliable. CIG25 can be used reliably for comparison calculations, however; that is, if the relevant parameters are avail- able for a given cigarette, the changes in its output flux resulting from varying one or more of its characteristics can

readily be found. If the flux emitted by the original cigarette

is known, therefore, the flux emitted by the altered cigarette can be predicted.

A simple alternative is to use the semi-quantitative model,

which uses Muramatsu's model results, together with the

correlation described by Eqs. (5-48) or (5-49). This proce- dure is simple and quick.

182
leferences for Section 5

[5-6]

[5-1] Baker, R., "Temperature Variation Within a Cigarette

Combustion Coal During the Smoking Cycle," High [5-7] Temperature Science 7, 236, 1975.

[5-2] Moussa, N.A., Toong, T.Y., and Garris, C.A., "Mechanism of Smoldering of Cellulosic Materials," 16th [ 5"8] Symposium (International) on Combustion, p. 1447,

The Combustion Institute, Pittsburgh, PA, 1977.

[5-3] Summerfield, M., Ohlemiller, T.J., and Sandusky, [ 5" 9] H.W., "A Thermophysical Mathematical Model of Steady-Draw Smoking and Predictions of Overall [5-10]

Cigarette Behavior," Combustion and Flame 33, 263, t 5" 11 ] 1978.

[5-4] Muramatsu, M., Umemura, S., and Okada, T., "A [5-12]

Mathematical Model of Evaporation - Pyrolysis Processes Inside a Naturally Smoldering Cigarette,"

Combustion and Flame 36, 245, 1979. I 5

" 1 3]

[5-5] Muramatsu, M., "Study of Transport Phenomena

Which Occur During Unforced Smoldering of Cigarettes," Res. Report No. 123 of the Japan [5-14]

Tobacco and Salt Monopoly, 1981. I 5

" 15]

Carslaw, H.S., and Jaeger, J.C., "Conduction of Heat in Solids," (2nd ed), Oxford University Press, 1959.

Egerton, A., Gugan, K., and Weinberg, F.J., "The

Mechanism of Smoldering in Cigarettes," Combustion and Flame 7, 63, 1963.

Lendvay, A.T., and Laszlo, T.S., "Cigarette Peak

Coal Temperature Measurements," Beitrage zur Tabakforschung 7, 276, 1974.

Holman,

1963.

Kunn, D. Sparrow,

Transfer,

Ostrach,

J. P., "Heat Transfer," (5th ed.), McGraw-Hil

Chem. Eng. (Japan) 25, 891, 1961

E.M., and Cess, R.D., "Radiation Heat

" McGraw-Hill, 1978.

S., "Laminar Flows with Body Forces," in Theory of Laminar Flows (ed, F.K. Moore) Princeton

Univ. Press, 1964.

Vemuri, V., and Karplus, W.J., "Digital Computer

Treatment of Partial Differential Equation," PrenticeHall, 1981.

Samfield, M., personal communication, 1986.

Gugan, K., Combustion and Flame, p. 161, 1966.

183

Appendix 5A.

A Description of the

Substrate Program

Program TEMPSUB has been written in ANSI 77

FORTRAN, and is therefore machine-independent, in that sense. However, it has been DIMENSIONEd so that it requires at least 132,000 words of memory. Thus, it will run

(for example) on a CYBER 855. However, CDC machines

have a 60-bit word, and there are no truncation-error problems. That should still be the case on a 36-bit machine.

But for machines with a 32-bit word, double precision might

be required.

TEMPSUB consists of a main routine and a set of subroutines. The main routine provides an interface between

the user and the numerical computations performed by the subroutines FLUXFT, CTRLBC, and CENTDIFF. FLUXFT

calculates the impinging flux (according to Eq. (5-5)) for each grid point on the heated surface of the substrate. A

correction for the emissivity of the substrate is also made.

CTRLBC calculates the surface temperature using a central difference approximation for the boundary condition (Eqs.

(5-2) and (5-3)). Finally, CENTDIFF uses a central difference

approximation to Eq. (5-1) to find the temperatures at all grid points within the substrate volume for as many time

steps as desired. Other subroutines calculate the global

energy balance for the substrate (Eqs. (5-4)). When TEMPSUB is run, the user is presented with a menu as shown below. The values shown are default values; all values are in the MKS system, and the user can change any of the numbered items. A detailed explanation

follows.

LIST OF PARAMETERS

Numbered Parameters Can Be Changed

1. x/y substrate length/width ratio, 1 or 1.5

y substrate width in meters = .2 z substrate depth in meters = .1

2. # of meshes in y direction = 10 (25 = maximum)

ambient temperature = 293 degrees kelvin

3. alpha (k/rho*c) = 1 E-7 M*.2/sec

4. thermal conductivity = .1 watts/(m*degree kelvin)

5. H(convective) = 10 watts/(m**2* degree kelvin)

6. EMS(surface emissivity) = 0.9

7. peak flux = 10000 watts/m**2

8. X velocity = .0 m/sec

9. sigma x = .04 m

10. sigma y = .04 m

1 1

.

size ratio = 1

.

12. x-sub-zero = x/2 m

Enter # for parameter change, or for no more changes

?

When the question mark (?) prompt appears, the user chooses a single parameter to change by entering the appropriate item number. The program responds with a request to the user to enter the desired value. After entry of the number, the program prompts again for further changes; entering halts further parameter changes for this run.

(1) allows a choice of the square or rectangular top

surface. (The aspect ratio of the latter is 3:2). Note that y =

20 cm, z = 10 cm, are set here; they can be changed via item (1 1), below.

(2) sets the number of meshes in the y direction (perpendicular to the axis of the cigarette). For an x/y ratio = 1 , the maximum number of meshes is 25; for an x/y ratio = 1.5 the maximum number of meshes is 18. The limit of the number of meshes is imposed by the current memory

limit on the Cyber 855, (approximately 130,000 words per program).

Items (3) through (10) are self-explanatory.

(11) sets the size for the x, y, and z dimensions of the

substrate. Thus a ratio of 0.5 resets all three dimensions to

half the value chosen in item (1). (12) sets the x starting position at time t = 0, assuming

the end of the substrate is at x = 0. After the parameter entries have been completed, the mesh width (Ax = Ay = Az) and At(max) are calculated

internally via Eq. (5-6), and the user is prompted to enter At, (At < At(max) for numerical stability). 7 Further prompts ask

''Although taking At = At(max) guarantees stable convergence, it does

not guarantee accuracy. For numerically accurate results, one should choose At = At(max)/10.

185
for the total number of time steps (of size At) and the number of steps until temperature data is to be sent to the screen and to a permanent file. When the prescribed

number of time steps have elapsed, the program returns

control to the user for further changes in parameters.

TEMPSUB can be run either interactively or in batch

mode. For a batch run a SUBMIT file must be prepared

which duplicates the user replies in interactive mode. This is a system-dependent procedure, and hence it will not be

described here. The following is a listing of program

TEMPSUB.

PROGRAM TEMPSUB (SUBSEC . TAPE6=SUBSEC . TS . TAPE7=TS . PTEM. TAPE8=PTEM)

THIS PROGRAM CALCULATES THE TEMPERATURES AT CRID POINTS IN A SUBSTRATE WITH AN IMPINGING FLUX ON THE (HEATED) SURFACE. THE FLUX IS SPECIFIED IN A FUNCTIONAL FORM AND CALCULATED IN SUBR

.

FLUXFT. SUBR. CTRLBC CALCULATES THE BOUNDARY CONDITION SURFACE

TEMPERATURE. SUBR. CENTD1FF USES AN EXPLICIT CENTRAL DIFFERENCE APPROXIMATION TO FIND TEMPERATURES AT ALL OF THE INTERIOR GRID

POINTS. SUBR. HMAT SETS VALUES FOR THE CONVECTIVE LOSS COEFFICIENT MATRIX FOR THE HEATED SURFACE (X-Y PLANE). CURRENTLY

THERE ARE TWO VALUES. HUNDR (H UNDER THE CIGARETTE). AND

H (H ELSEWHERE). GLOBAL ENERGY BALANCE IS CALCULATED BY SUBRS

.

CNLOSS. EMLOSS. AND HEAT. HEAT TRANSFERS AT SURFACES OTHER THAN

THE HEATED SURFACE ARE NOT INCLUDED IN THE GLOBAL ENERGY CALCULATION. CROSS SECTIONS STORED IN SUBSEC

T( I .2.1) VS. TIME STORED IN TS BINARY NAME BTEMP

USE WITH SUBCIG SUBMIT FILE COMMON T( 55. 29. 28) .WT( 55. 29.28 ).FLUX( 55.29 ).HM( 55. 29) CHARACTER ASTR.60

ASTR=' • •

- DEFAULT VALUES

XL=X SUBSTRATE SIZE IN M. YL=Y SUBSTRATE SIZE IN M ZL=Z SUBSTRATE SIZE IN M. R=SUBSTRATE SIZE RAT 10: DEFAULT = 1 XL=.3

YL=. 1 ZL=.1

r=i .e XZRO = INITIAL X POSITION FOR FLUX PEAK

XZRO=. 15 XLR=X/Y SUBSTRATE LENGTH/WIDTH RATiO

XLR=1 .5 NMESHY = # OF MESHES IN Y DIRECTION, MAX=2S NMESHY=10 STAB=STABILITY FACTOR MAXIMUM TIME STEP IS CALCULATED AS 1/2 OF COURANT CRITERION

IN ORDER TO ENSURE A STABLE SOLUTION. FOR ACCURACY IN THE FINITE DIFFERENCE CALCULATION THE CHOSE TIME STEP (DT) SHOULD BE LESS THAN 1/5 OF THE MAXIMUM TIME STEP. STAB=1/12. ALPHA = K/(RHO"C)

ALPHA=1 .E-7 THERMAL COND. . EM I SSI VI TY. CONVECTION

TC=. 180 EMS=0 .

9

H=10.0

LENGTH AND WIDTH OF CIGARETTE

HOT END FALLS ON XZRO CIGLEN=.04 CIGWID=.00334

H FACTOR UNDER CIGARETTE

HUNDR=ie

FMAX=PEAK FLUX

FMAX=10000 VX=VELOCITY OF FLUX IN X DIRECTION

VX=0 SIGX=FLUX WIDTH IN X DIRECTION SIGX=.086

SIGY-=FLUX WIDTH IN Y DIRECTION SIGY-.03

START INTERACTIVE SCREEN PRINT BLOCK

CC

60

20

C

PRINT.

PRINT'

PRINT.

PRINT. PRINT.

PRINT.

PRINT.

PRINT.

PRINT.

PRINT.

PRINT.

PRINT.

PRINT.

PRINT'

PRINT.

PRINT.

PRINT.

. 'LIS

(A)

1

T OF PARAMETERS, NUMBERED PARAMETERS CAN BE CHANGED' ASTR

X/Y SUBSTRATE LENGTH/WIDTH RATIO, 1 OR 1.5'

Y SUBSTRATE WIDTH IN METERS = .2'

Z SUBSTRATE DEPTH IN METERS - .V

I OF MESHES IN Y DIRECTION *= 10 (25 = MAXIMUM)' AMBIENT TEMPERATURE «= 293 DEGREES KELVIN' ALPHA (K/RHO-C) - 1.0E-7 M««2/SEC

THERMAL CONDUCTIVITY - .1 WATTS/(M«DEGREE KELVIN)' H(CONVECTIVE) - 10 WATTS/(M..2-DEGREE KELVIN)' EMS(SURFACE EMISSIV1TY) -= .9' PEAK FLUX « 10000 WATTS/M..2'

X VELOCITY IS 0.0 M/SEC

SICMA X IS .04 M' SIGMA Y IS .04 M' SIZE RATIO - 1.

X-SUB-ZERO = X/2 M'

PRINT.. '13 H(LOSS UNDER CIGARETTE) = 10 WATTS/(M. .2.DEG-K . )

' PRINT'(A)' ,ASTR PRINT', 'ENTER # FOR PARAMETER CHANGE OR FOR NO MORE CHANGES'

READ". IP IF(IP.EQ.1)THEN

PRINT., 'ENTER LENGTH/WIDTH RATIO, 1 OR 1.5' READ..XLR

IF(XLR.LT.1 .2)THEN XL=XL/1 .5 XZR0=XL/2

END IF ELSE IF(IP.EQ.2)THEN

PRINT., 'ENTER | OF MESHES IN Y DIRECTION, <=25' READ" .NMESHY ELSE IF(1P.EQ.3)THEN

PRINT. ,' ENTER VALUE FOR ALPHA' READ*. ALPHA

ELSE IF(1P.E0.4)THEN

PRINT., 'ENTER VALUE FOR THERMAL CONDUCTIVITY' READ..TC

ELSE IF(IP.EQ.S) THEN

PRINT., 'ENTER VALUE FOR CONVECTION COEFFICIENT'

READ. ,H HUNDR=H

ELSE IF(IP.E0.6) THEN

PRINT., 'ENTER VALUE FOR EMISSIVITY'

READ.. EMS ELSE 1F(IP.E0.7)THEN

PRINT*. 'ENTER VALUE FOR MAXIMUM FLUX' READ..FMAX

ELSE IF(1P.EQ.8)THEN

PRINT. , 'ENTER VALUE FOR X VELOCITY'

READ. ,VX ELSE IF(IP.E0.9)THEN

PRINT., 'ENTER VALUE FOR SIGMA X' READ..SIGX

ELSE IF(1P.EQ.10)THEN

PRINT. . 'ENTER VALUE FOR SIGMA Y' READvSIGY

ELSE IF(IP.EQ.11)THEN

PRINT., 'ENTER VALUE FOR SIZE RATIO' READ..R

XL=XL.R YL=YL«R

ZL=ZL«R XZRO=XZR0»R

ELSE IF(IP.E0.12)THEN

PRINT., 'ENTER VALUE FOR X READ. .XZRO ELSE 1F(IP.EQ.13)THEN

PRINT.. 'ENTER VALUE FOR H LOSS UNDER CIGARETTE'

READ.. HUNDR

ELSE 1F(IP.EQ.0)THEN GO TO 60 END IF GO TO 50 T.WT.FLUX MATRIX DIMENSIONS = GRID POINTS

ONE EXTRA FOR Y FOR IMAGE PLANE NY=NMESHY+2

NZ=NMESHY+1 NX=NMESHY»3+1

IF(XLR. LT. 1 .2)NX=NMESHY.2+1 AMBT=AMBIENT TEMPERATURE

AMBT=293

SET T AND WT = 293 DO 20 1 = 1 .NX DO 20 J=1 .NY DO 20 K=1 ,NZ

T( I , J.K)=AMBT

WT(I . J,K)=AMBT CONTINUE

DELTA=MESH WIDTH DELTA=YL/NMESHY

DTMAX= (STAB" DELTA.. 2 )/ALPHA

PRINT', 'MAX TIME STEP = '.DTMAX PRINT. , 'ENTER VALUE FOR DT

READ..DT

PRINT., 'ENTER # OF TIME STEPS' READ.. NOT PRINT. . 'ENTER | READ..NSTEP

ZERO'

OF STEPS BEFORE PRINT'

ENO INTERACTIVE SCREEN PRINT BLOCK NLO0P=1 CONVECT=0

EM I SSV=0

DO=0 CALCULATE THE BOUNDARIES OF THE INSULATED AREA UNDER

THE CIGARETTE

REAL POSITIONS

CXLO=XZRO-.001 CXHI=XZRO+CIGLEN+001

CYHI=CIGWID

CALL HMAT(CXLO,CXHI ,CYHI . HUNDR . H .DELTA , NX. NY) DO 500 ITIME=1 .NOT TIME=DT.ITIME

PTIME=DT.(ITIME-1)

XCTR=XZRO+VX.PT IME CALL FLUXFT(NX, NY, DELTA. FMAX, VX.SIGX.SIGY, XZRO. T IME, DOOT, EMS) SUM THE INTEGRATED FLUX DQ1=DQDT»DT

D0=D0+DQ1 CALL CTRLBC( ALPHA . DT . DELTA . TC , EMS , NX . NY , NZ . AMBT

)

186
lee c...

cc...

CALL CENTDI F( ALPHA . DT , DELTA , NZ , NY , NX

)

CALL CNLOSS ( AMST . NX , NY , DELTA . CONV , DT

)

SUM THE CONVECTIVE LOSSES FOR EACH STEP C0NVECT=C0NVECT4C0NV

CALL EMLOSS( EMS , AMBT . NX . NY . DELTA . EMLS . DT

)

SUM THE EMISSIVE LOSSES FOR EACH STEP EMISSV=EMISSV+EMLS

FILE WRITE BLOCK

,N1)

IF(NLOOP.GE.NSTEP.OR. ITIME.GE .NDT)THEN CALL HEAT ( TC . ALPHA , DELTA . NX . NY , NZ , T I ME . HTOT . AMST

)

WRITE(6.200)

200 FORMAT(1X,//'X LENGTH' ,2X, 'Y MESHES' ,3X. 'ALPHA -

. 4X.-K- , •7X. 'H- .5X. -EMS' ,7X. 'DT' ,5X, -TIME - .4X. 'DELTA') WRITE(6.205)XL.NMESHY, ALPHA. TC.H. EMS, DT. TIME, DELTA

205 FORMAT ( 2X . F6 . 4 . 3X . 1 4 . 2X , E 1 8 . 3 . 1 X . F5 . 3 . 2X , F6 . 2

.

•F6.3.3X.F8.3.F8.3.F8.5)

WRITE(6,210)

210 FORMAT (1X.//4X, 'FMAX' ,7X, 'VX' .5X. 'SIGX' ,4X, 'SIGY'

.

•4X. 'XZRO' ,4X, "SIZE RATIO' ,3X. ' EMS LOSS(J.)') WRITE(6.215)FMAX.VX.SIGX,SIGY,XZRO,R.EMISSV

2 1 5 FORMAT (1X,F8.1,E10.3,F8.5,F8.5.F8.5.3X.F8.5.6X,F7.2)

WRITE(6,225)

225 FORMAT ( 1 X .//' # OF STEPS' .2X. 'SUBSTRATE HEAT, JOULES', 2X, •'INTEG. FLUX, JOULES' ,2X, 'CONVECT LOSS. JOULES') WRITE(6,230)iTIME,HTOT.DO, CONVECT

230 FORMAT ( 3X , 1 5 . 1 2X , F7 . 2 . 1 5X . F7 . 2 . 1 0X . F7 . 2

)

WRITE(6,112)

112 FORMAT(1X, //'SURFACE TEMPERATURE. (X-Y PLANE), LEFT HALF') N1=NY/2

DO 62 I 1 = 1 .NX WR]TE(6.100)((T(1I.J,1)-AMBT).J=2,

62 CONTINUE WR1TE(6,220) • 220 FORMAT(1X,/' SURFACE TEMPERATURE, (X-Y PLANE). RIGHT HALF') DO 64 11=1 ,NX WRITE (6, 100) ((T( I 1 , J . 1 )-AMBT) , J=N1+1 .NY)

64 CONTINUE

1C=XCTR/DELTA+1.5 WRITE(6.114)

114 FORMAT(1X. //'CROSS-SECTION AT PEAK IN X. (Y-Z PLANE)')

DO 70 K=1 ,NZ WR1TE(6.100)((T(IC.J.K)-AMBT),J=2,N1)

70 CONTINUE WR!TE(6.116)

116 FORMAT (IX. //'LONGITUDINAL SECTION. Y=0, (X-Z PLANE) - ) N2=NZ/2

DO 72 11 = 1 .NX WRITE(6.100)((T(II ,2.K)-AMBT).K=1 ,N2)

72 CONTINUE

WR1TE(6.118)

118 FORMAT (1X.//' FLUX ON SURFACE. (X-Y PLANE)')

DO 74 I 1=1 .NX WRITE(6.100)(FLUX(II.J).J=2.N1)

74 CONTINUE WR1TE(6.120)

120 FORMAT (1X.//' CONVECTIVE MATRIX. (X-Y PLANE)') DO 300 11=1 ,NX WRITE(6.310)(HM(II.J).J=2.NY)

310 FORMAT(1X.25(F3.0,2X))

300 CONTINUE

END IF F0RMAT(1X.15(F8.2.1X))

PLOT FILE WRITE BLOCK

I F(NLOOP.GE.NSTEP. OR. ITIME.GE. NOT) THEN NHORZ=NX

NVERT=NY-1 WRITE(8..)NHORZ,NVERT. TIME. DELTA

C SURFACE TEMPERATURE

DO 800 15=2. NY WRITE(8.600)((T(I6.15.1)-AMBT).I6=1 .NX) 800 CONTINUE

600 FORMAT (20F6.0)

END IF SCREEN PRINT BLOCK

1F(NLOOP.GE.NSTEP.OR.IT1ME.GE.NDT)THEN TIME=DT«ITIME

!2=(NX-1)/2+6

11=12-10 CALL SFLUX(I1 .12.2.6.DODT.ITIME.TIME) CALL STEMP(I1 .12.2.6, ITIME. TIME) CALL CSECT (XCTR. 2, 6, 1,1 0,1 TIME, DELTA, TIME) CALL HEAT( TC. ALPHA. DELTA. NX. NY, NZ. TIME. HTOT. AMBT) PRINT., 'CONVECTIVE LOSS = '.CONVECT NLOOP=1 IF(ITIME.LT.NDT)THEN

PRINT.. 'ENTER # OF STEPS BEFORE PRINT' READ..NSTEP

END IF ELSE NLOOP=NLOOP+1

END IF MAKE A FILE OF T( I .2.1) FOR EACH TIME STEP IF(ITIME.E0.1)THEN NDD=NDT/5

WR I TE ( 7 . •

) NX . NY . NZ . DELT A . R . VX , DT , XZRO , NOD .ALPHA . H . TC . S I GX

END IF IF(MOD(ITIME,5).EO.0)THEN

PTIME=1TIME»DT WRITE(7,-)PTIME

WR1TE(7.490)( (T(I.2,1)-AMBT).I=1 .NX) 490 FORMAT ( 1 5F7. 1) END IF 500 CONTINUE

PRINT.. 'DO ANOTHER CALC? 1 = YES' READ..NNN

IF(NNN.EQ. 1 ) GO TO 50 STOP

END

C SUBROUTINE SFLUX(I1 . 12. J 1 .J2.DQDT, ITIME. TIME) COMMON T (55. 29. 28 ).WT( 55, 29. 28). FLUX (55. 29) .HM(55.29) PRINT.. 'FLUX DISTRIBUTION'

PRINT.. 'STEP = '.ITIME,' TIME= '.TIME.' DODT= '.DODT DO 50 1=11.12 PRINT 10, (FLUX(I . J)

.

J=J1 . J2) 50 CONTINUE

10 FORMAT(1X.8(F8 2.1X)) RETURN

END SUBROUTINE STEMP(11.I2,J1 .J2, I TIME. TIME) COMMON T(55,29.28).WT(55.29.28).FLUX(55.29).HM(55.29)

PRINT., 'SURFACE TEMPERATUREPRINT.. 'STEP = -.ITIME.' TIME = '.TIME DO 50 1=11.12 PRINT 10,(T(I.J.1).J=J1 ,J2) 50 CONTINUE

10 F0RMAT(1X.8(F8.2.1X))

RETURN

END SUBROUTINE CSECT(XCTR.J1 .J2.K1 ,K2 , 1 TIME, DELTA. TIME) COMMON T (55. 29. 28). WT (55. 29. 28). FLUX (55, 29 ).HM( 55, 29) PRINT.. 'CROSS SECTION AT XCTR' PRINT., 'STEP = '.ITIME.' TIME = '.TIME,- XCTR = '.XCTR

C TEMPORARY FIX FOR XCTR(REAL)

I=XCTR/DELTA+1 .5 DO 50 K=K 1 . K2 PRINT 10,(T(I ,J,K).J=J1 ,J2) 50 CONTINUE

10 F0RMAT(1X.8(F8.2, IX)) RETURN

END

C « SUBROUTINE CENTDI F( ALPHA, DT . DELTA. NZ . NY. NX) C SUBROUTINE FOR CENTRAL DIFFERENCE CALCULATION

C ALPHA=K/(RHO«C).DT=TIME STEP . DELTA=MESH SIZE IN METERS

C ENTER WITH BC'S IN K=1 PLANE OF T MATRIX

COMMON T(55.29.28).WT(55.29.28).FLUX(55.29).HM(55.29)

C FILL IMAGE PLANE (J=1) WITH J=3 VALUES

DO 50 1=2. NX DO 50 K=2.NZ T(I.1.K)=T(I.3.K) CONTINUE

SET CONSTANTS

C1=ALPHA«DT/(DELTA..2)

C2=1-6«C1

C CALCULATE NEW VALUES OF TEMPERATURE

DO 100 K=2.NZ-1

DO 100 J=2.NY-1

DO 100 I=2,NX-1 AVG6=T(I+1 , J.K)+T(I-1 ,J.K)+T(I ,J+1.K)+T(I .J-1 ,K)+

>T(I ,J.K+1)+T(I .J.K-1) WT(I ,J,K)=C2.T(I,J,K)+C1.AVG6

T00 CONT I NUE C PUT WT IN T FOR NEXT ITERATION

DO 200 K=2.NZ-1

DO 200 J=2.NY-1

DO 200 I=2.NX-1 T(I,J.K)=WT(I.J.K)

200 CONTINUE

RETURN

END

C • ....'. SUBROUT I NE CTRLBC( ALPHA . DT . DELTA , TC . EMS . NX . NY . NZ . AMBT

)

C SUBROUTINE FOR CENTRAL DIFFERENCE BOUNDARY CONDITIONS

C H=CONVECTION, DELTA=MESH SIZE

C TC=THERMAL COND. . EMS=SMISS1VITY

C EXIT WITH T(I .J.I) FILLED

COMMON T( 55. 29. 28) .WT(55 , 29 . 28) . FLUX(55. 29) .HM(55. 29) SBC=5 . 67E-8 TA]R=AMBT C1=ALPHA.DT/(DELTA..2)

C3=2«DELTA/TC B=-C1«EMS.SBC«C3

C=C1«C3

D=C1 E=C1.C3«EMS.SBC.TA1R..4

C FILL IMAGE PLANE

DO 50 1=1 .NX DO 50 K=1 ,NZ T(I.1.K)=T(I,3.K)

50 CONTINUE

DO 200 J=2.NY-1

DO 200 I=2.NX-1 F=E+C1«C3.HM(I

,

J).TAIR AA=1-6«C1-C1.C3«HM(I ,J) AVG5=T(I+1 ,J.1)+T(I-1 . J . 1 )+T( I ,J+1 ,1)+T(I ,J-1 .1) •+2.T(I.J,2) WT(I,J.1)=AA.T(I .J.1)+B"T(I.J,1)..4+FLUX(I.J).C

•+D.AVG5+F

200 CONTINUE

C FILL T(I.J.I) PLANE

50

C

187
DO 360 J=2,NY-1

DO 368 I=2,NX-1 T(I,J.1)=WT(I,J, CONTINUE

RETURN

END SUBROUTINE HEAT (TC. ALPHA, DELTA, NX, NY, NZ.TIME.HTOT, AMBT) COMMON T(55.29.28).WT(55.29.28).FLUX(55.29).HM(55.29)

C CALCULATE TOTAL HEAT IN JOULES FOR ENTIRE SUBSTRATE

SUMT=0

DO 50 1 = 1. NX1

DO 50 J=2.NY-1

DO 50 K=1.NZ-1 T1=T(1,J,K)+T(I+1.J.K)+T(I.J+1 ,K)+T(I.J,K+1)

T2=T(I+1 ,J+1 ,K)+T(I+1 ,J+1.K+1)+T(I+1 , J ,K+1 )+T( I , J+1 ,K+1) SUMT=SUMT+(T1+T2)/8.-AMBT

50 CONTINUE HTOT=SUMT.(TC/ALPHA).2«DELTA..3

PRINT., -TOTAL HEAT IS .HTOT.' TIME IS '.TIME

PRINT., •SUMT='. SUWT

RETURN

END

C SUBROUT I NE CN LOSS ( AMBT .NX. NY, DELTA, CONV , DT

)

C CALCULATE CONVECTIVE LOSS PER STEP FOR ENTIRE SURFACE

COMMON T(55.29.28) ,WT(55.29 .28) . FLUX(55.29) ,HM(55.29) CONV=0

DO 50 1=2. NX1

DO 50 J=3.NY-1 CONV=CONV+HM( I , J

) • (T( I . J . 1 )-AMBT)

50 CONTINUE

C TAKE CARE OF J=2 DIVIDE BY 1/2 FOR FLUX 1/2 ON GRID POINT

DO 55 I=2.NX-1 CONV=CONV+HM( I . J). (T( I ,2,1)-AMBT)/2.

55 CONTINUE CONV=C0NV»DELTA«.2'0T.2

RETURN

END

C SUBROUT I NE EMLOSS ( EMS . AMBT .NX.NY.DELTA.EMLS.DT) C CALCULATE EMISSIVE LOSS PER STEP FOR ENTIRE SURFACE COMMON T(55.29.28),WT(55,29.28).FLUX(55.29).HM(55.29) SB05.67E-8

EMLS=0 TAIR=293

DO 50 I-2.NX-1 DO 50 J=3.NY-1 EMLS=EMLS+EMS«SBC.(T(I . J . 1 )-TAIR)..4

50 CONTINUE

C J=2. 1/2 FLUX ON GRID POINT

DO 55 1=2. NX1

EMLS=EMLS+(T(I ,2.1)-TAIR)/2.

55 CONTINUE EMLS=EMLS.DELTA..2«DT.2

RETURN

END

SUBROUTINE FLUXFT(NX,NY,DELTA.FMAX.VX,SX.'SY,XZRO.TIME.FSUM,EMS) COMMON T(55.29,28).WT(55.29,28).FLUX(55.29).HM(55.29)

C FIND FLUX FOR EACH I ,J C MULTIPLY EACH FLUX BY EMS DO 50 1=1 .NX DO 50 J=2.NY

C X.Y COORDINATES OF I.J GRID POINTS

XP=(I-1).DELTA

YP=(J-2). DELTA X=XP-XZRO-VX«TIME

C FUNCTION

C WATCH FOR UNDERFLOW

EA=(X/SX).«2 EB=(YP/SY)..2 IF(EA.GT.25..0R.EB.GT.25.)THEN

FLUX(I.J)=0

ELSE PA-EXPf-EA)

PB-EXP(-EB) FLUX(I.J)=PA.PB.FMAX.EMS

END IF 50 CONTINUE

C INTEGRATED FLUX.DQ/DT. INCLUDING IMAGE 1/2 PLANE

FSUM=0 DO 100 1-1. NX

DO 100 J-2.NY C CORRECT FOR IMAGE BOUNDARY 1/2 AREA UNDER FLUX IF(J.E0.2)THEN

FSUM=FSUM+FLUX( I , J )/2 ELSE FSUM=FSUM+FLUX(I.J)

END IF 100 CONTINUE

FSUM=FSUM.2«DELTA.«2

RETURN

END C SUBROUTINE HMAT(CXLO,CXHI ,CYHI .HUNDR, H.DELTA. NX, NY) C CALCULATES CONVECTIVE LOSS MATRIX FOR USE

C CTRLBC AND CNLOSS COMMON T(55.29.28).WT(55.29.28).FLUX(55.29).HM(55,29)

C CALCULATE THE GRID POSITIONS. LOCK TO NEAREST GRID NXLO-CXLO/DELTA+1 .5 NXHI-CXHI/DELTA+1.5

NYHI«=CYHI/DELTA+2.5

C FILL HM MATRIX WITH H AND HUNDR VALUES

DO 50 1 = 1 .NX DO 50 J=1 ,NY 50 HM(I,J)=H

C NOW FILL THE RECTANGLE UNDER THE CIGARETTE WITH HUNDR DO 100 I=NXLO.NXHI DO 100 J=2.NYH1

100 HM(I.J)=HUNDR

RETURN

END

188
Appendix 5B.

The Cigarette Program CIG25

This appendix contains a brief description of the cigarette

code CIG25 and describes the procedure required to operate the code on the CYBER 855 computer. This

program, too, is in standard FORTRAN. A version of CIG25

will also operate on the CYBER 205 and on the Perkin

Elmer 3252 minicomputer. The physics contained in CIG25

includes thermal diffusion with a temperature-dependent

diffusion coefficient, oxygen diffusion with a temperaturedependent diffusion coefficient, gas flow in the radial direction, combustion with a one-step Arrhenius equation,

convective thermal boundary conditions, and oxygen

porosity at the boundary which includes the effects of paper. The resulting nonlinear partial differential equations

are solved using the implicit Crank-Nicolson method with a Gauss-Seidel over-relaxation solver. The program structure consists of a main program with twelve subroutines and two function routines. The main

program handles the input of program variables, calling of the subroutines to calculate the physics, testing for convergence after each iteration loop, and calling of the output subroutines.

Subroutines TEMP and OXY calculate the heat and

oxygen diffusion, respectively; subroutine VELOCR

calculates the radial velocity of the gas flow, and subroutine

REACT calculates the reaction rate of the combustion

occurring in the cigarette.

The initial data file for temperature, oxygen fraction,

density fraction, and velocity is generated by subroutine

INITIAL, or read from an external data file by subroutine

INITD. The results of the calculations are output to an

external file by the subroutines OUTPUT and OUTPUTP.

The other four subroutines in the code: TEST, TESTT,

TRAPE, and OTRAPE, were used to test the diffusion calculations and calculate energy and oxygen conservation

for earlier versions of the code. The present code has been

changed sufficiently that these subroutines will need some

coding changes before they will work with the additional physics now included. They must therefore be bypassed,

which is accomplished with the indicated answers to questions 1 and 2 of the input, as will be shown below.

The procedure detailed below enables a user to operate

the cigarette program CIG25 on the Cyber 855. When run, the program will output the results of the calculation to file

TEM25. This output file may then be listed out to a printer or plotted by a laser printer using the graphics code

PLOTT25.

There are several options available to the user when

CIG25 is submitted to the computer. While the code can be

operated interactively, usually a batch submission is more

desirable since the CPU time required to complete a job can exceed one hour on a Cyber 855. The user has an

option to use an internally generated initial input file to define the initial temperature, oxygen fraction, density

fraction, and radial flow velocity, or to input an external set

of values using the data file ITEM1. The first option

corresponds to the "initial" condition, meant to simulate the

result of using a match to light the cigarette, and shown in Figure 5-1 4a. At present, ITEM1 contains an initial condition

corresponding to the data on temperature and oxygen

fraction from an experiment by Baker (see Ref. [5-1]). An

assumed density fraction distribution is used along with a

zero initial velocity distribution. A second user option is to select either an input mode

where most of the constant variables are input using the keyboard or to use an input mode where the variables are submitted in a batch file. A variation on this mode of input is a second mode where only those variables which are likely to change are input externally, with the other variables being initialized within the program. Examples of both input

modes are given below.

To run the cigarette code interactively, the compiled code

must be attached to the users' job using the command

"GET,BCIG25A". To run the code, the command "BCIG25A"

is entered on the terminal. The following list of prompts will appear with either suggested or required responses. PROMPT ANSWER

Enter 1 to test gasdiff routines

Enter 1 to test temp diff routines Enter 1 if standard

input values

Enter 2 if changed

input values

2 (required)

2 (required)

2 if you only wish to change a limited set of variables,

3 if you wish to change

most of the variables.

189
If choice 3 is selected, a series of prompts for virtually all the variables used in the program will appear with a request

for input values. If choice 2 is selected, a limited number of prompts will appear with a request for input. Generally, most

of the prompts will be self-explanatory. The few that need some explanation are: PROMPT

Enter number of grids in R,

Enter number of timesteps

for energy balance check.

Enter length ratio Z to R

ANSWER

20 (for consistency: the first value of the DIMENSION

and PARAMETER state- ments equals no. of grids + 1 and is currently 21).

This routine has not yet

been updated, therefore

enter a number larger than

the desired number of timesteps.

7.5 (This input determines

the length of the "cigarette,"

relative to its radius. The

second value in the DIMENSION and

PARAMETER statements must equal NG*RATIO+1,

and is currently 151).

An example of a batch SUBMIT file, SUB25A, is given

below. The SUBMIT file is specific to the CYBER, but the equivalent control file for some otner machine or operating

system should be readily prepared by your system operator.

The SUBMIT file supplies the operating set of parameters for the machine, such as the operating class, the maximum

(CPU) time the program should run, the user ID and

password, the name of the program to be run, the names ;of the data files to be used, and the name(s) of the output

file(s). Then the "data stream," consisting of the answers to the prompts (questions) which would appear on the screen

if the program were being run interactively, is given. Some

of those prompts are shown above, but the list was not complete. We now list the complete set of prompts, followed

by a batch SUBMIT file (SUB25A). The input parameters

given in SUB25A after the end-of-record mark correspond to the following prompts:

Enter 1 to test gasdiff. routines. Enter 1 to test temp diff routine. Enter 1 if standard input values are desired. Enter 2 if improved input values are desired. Enter the number of grids in R. Enter the number of timesteps and num timesteps data out. Enter number of timesteps for energy balance check.

Enter the value for oxy diff coef, def. val. = 1 .2. Enter the value of GAR and GARP. default values = 5.4,

2.7. Enter H = HR/K.

Enter B to change pre-exponential factor. Default value =

3.8 E13

Enter 1 to read an existing data file. Enter timestep for first 50 iterations in seconds.

Enter timestep for iterations gt. 50 in seconds.

Enter err for iterations. Enter IT and TIM

To run the SUBMIT file, type SUBMIT, SUB25A, E An example SUBMIT file for a run is: SUB25A,SCI1,T= 11000.

USER, HEN, CIGAR.

GET.BCIG25A.

GET, ITEM 1. DEFINE, TEM25.

BCIG25A.

EXIT. DEFINE, TEM25.

2

2

220

6000

400

8000

.70000

1.00

.500

1.50

9.25E12

1.005

.005

.001

0. The data used for the run shown in the text is given in Table A-1 below,

followed by the listing for CIG25.

190
Table 5-B-1. Parameter Values Used for the Sample Run in the Text,

Using Program CIG25

Physical parameter

pso = 0.74 g/cm3 pg = 1.18 x 1 "

3 g/cm3

pco = 0.252 g/cm3

pao = 0.0962 g/cm3

n02 = 1.64

R = 0.4 cm

Cs = 1.043 J/g°C

Do = 0.112 cm2 /sec

Hc = Qh = 4200 cal/gm = 17570 J/gm

^ = 0.65

Eco = 1.7 x 105 J/g mole

cm3 3.78 x 10 11 g sec

yg = 0.8 cm/sec

YP = 0.089 cm/sec

Tp = 450°C

50.6

W

m2 °C

Description

Density of shred

Density of air

Density of char

Density of ash

Oxygen mass

|p tobgcco combust|0n Char mass

Cigarette radius

Specific heat of solid

Diffusion coefficient for oxygen in the tobacco column, at ambient temperature

Heat of combustion of char

Void fraction

Activation energy for char oxidation

Pre-exponential factor for char oxidation

Mass transfer coefficient, through boundary

layer

Mass transfer coefficient through (virgin)

paper

Temperature at which the paper disintegrates

Effective heat transfer coefficient

kg = 4.514 x 10 -4 W/cm°C

ks = 3.16 x 10" 3 W/cm°C

Dp = 0.0575 cm

£, = 0.98

<D = 0.82

Parameter value used in program

D1 = pJPg = 627

D2 pJpso = 0.341

AN = pao/p w = 0.13

CN = n02 = 164

(normalizing constant)

A (pso Cs R

2 )" 1 = 8.1 cm°C/J

D = D /R 2 = 0.7 sec" 1

C m-^k. = 16800 K

Cs

PH <t> = 0.65

E =

RB 20400 K (Eco in terms of the gas constant)

2.8 x 1011 sec" 1 B = Pso Zc<:

GAR e= Yg/R = 2.0 sec

-1

GARP =; -^(— + —)" 1 =0.2 sec" 1 R Yp Yg

Thermal conductivity of the gas

Thermal conductivity of the solid

Pore diameter

Emissivity of smoldering coal

Total void fraction

The last five items above are used in Eq. (5-50), for the effective thermal conductivity in the cigarette.

At = 0.005 sec Size of time steps TS = At A X;

TP = 723 K

H =. h

' R

= 1.9 k(300)

GK = kg W/cm K

KF ks W/cm K

DP - Dp ET = Et PH1 =

<£ Convergence criterion ERR s e = 10-

191
1 PROGRAM CIG25(TEM25. ITEM1 , TAPE6=TEM25. TAPE7=1 TEM1

)

DIMENSION T(21.151).Y(21.151).R(21.151),W1(21.151).W2(21,151)

1.GA(151).W3(21.151).RR(21.151).Y1(21.151).R1(21,151).T1(21.151)

2,U(21.151).W4(21.151).U1(21.151).RR1(21 ,151),RRW(21 .151)

C PROGRAM SOLVES PDE" EQUATIONS USING CRANK-NICHOLSON TECHNIQUE

C OXYGEN PDE IS SOLVED ITERATIVELY USING GAUSS-SEIDEL TECHNIQUE

C TEMPERATURE PDE IS SOLVED ITERATIVELY USING A GAUSS-SEIDEL

C TECHNIQUE

C THE VELOCITY IS CALCULATED BASED ON THE ASSUMPTION THAT THE

C GAS DENSITY IS CONSTANT. THE RESULTING DIFFERENTIAL EQ. IS C INTEGRATED USING THE TRAPEZOID RULE.

C TWO TIME STEPS CAN BE CHOSEN. THE FIRST TIME STEP IS USED FOR

C THE FIRST 50 T1MESTEPS AND THE SECOND TIMESTEP IS USED FOR C ALL SUBSEQUENT TIMESTEPS.

C PAPER IS CONSIDERED POROUS WITH POR0SITY GARP

C PROGRAM HAS THE SAME PHYSICS AS CIG21A AND ALSO INCLUDES

C A TEMPERATURE DEPENDENT THERMAL DIFFUSION COEFFICIENT.

C CONVECTIVE COOLING AT THE SURFACE

NNN=0

PRINT.. 'ENTER 1 TO TEST GASDIFF. ROUTINESREAD' ,NNN IF(NNN.EQ.I) CALL TEST

IF(NNN.EQ. 1) GO TO 50 PRINT.. 'ENTER 1 TO TEST TEMP DIFF ROUTINEREAD' . MMM

IF(MMM.EQ.I) CALL TESTT IF(MMM.EQ.1)GO TO 50 PRINT.. 'ENTER 1 IF STANDARD INPUT VALUES ARE DESIRED- PRINT. .- ENTER 2 IF IMPROVED INPUT VALUES ARE DESIRED.'

READ* ,NN IF(NN.GT.2) GO TO 5 1F(NN.EQ.2) GO TO 2 D=.7 A=.028 B=5.5E16 C=1.68E04

E=2.266E04

D1=220. D2=.341 PH=.65

TP=723.

BE=.01

GAR=1 .0 GARP= .

5

AN=. 13 CN=1 .6428 RIZR=8

H=.50 SPHGS=.5 GO TO 3

2 D=1 .2 C THE OXY DIFF COEF HAS BEEN DECREASED BY A FACTOR OF 2 C OVER THE IMPROVED INPUT VALUE. IT IS NOW MURAMATSU VALUE.

C NOTE THAT A=1/DS«CS.R..2 WHICH DIFFERS FROM CIG21 A=8.0964

B=3.7E13

C=1 .68E04 E=2.266E04

C D1 HAS BEEN RECALULATED FROM A VALUE OF 1220 TO PRESENT

C BY CONSIDERING THE TOBACCO SHRED POROUS

D 1=627 D2=.341 PH=.65

TP=723

.

GAR=5 .

4

GARP=2 .

7

AN=. 13 CN=1 .6428 RIZR=7.5

SPHGS= .

5

H1=1 .386 DP=.0575 GK=4.514E-4

FK=3. 16E-3 ET=.98 PH1=82

3 ERR=.001 PRINT.. -ENTER NUMBER OF GRIDS IN R' READ..NG

PRINT. . 'ENTER NUMBER OF TIMESTEPS AND NUM TIMESTEPS DATA OUT

READ*. ISP.INP

PRINT.. 'ENTER NUMBER OF TIMESTEPS FOR ENERGY BALANCE CHECKREAD.. IEB PRINT.. 'ENTER THE VALUE FOR OXY DIFF COEF, DEF . VAL.=1.2' READ..D

PRINT., 'ENTER THE VALUE OF GAR AND GARP. DEFAULT VALUES = 5.4.2.7'

READ. .GAR. GARP

PRINT., 'ENTER H =HR/K

READ..H

PRINT. , -ENTER B TO CHANGE PRE-EXPONENTI AL FACTOR. D. V.=3. 8E13' READ..B

PRINT., 'ENTER E TO CHANGE EXPONENTIAL. D.V.=2 . 266E04

READ..E

PRINT., 'ENTER 1 TO READ EXISTING DATA FILE- READ". I DATA GOTO 8

5 PRINT., -ENTER GAS AND DEN. SPECHT/R.. 2. D/R>«2. 1/DS-CS.R..2

READ" ,0.A PRINT. . 'ENTER THERMAL RELEASE RATE/GAS DEN RC/DG RC=DS.DC«ZCREAD. .

B

PRINT., 'ENTER HEAT/GM/SPECIFIC HEAT O/CS AND REACTION EXP E/R- READ..C.E

PRINT. , 'ENTER RATIO SOLID/GAS DEN, CHAR/SOLID DEN D1.D2- READ.. D1 .02 PRINT.. 'ENTER VOID FRACTION PHI=PH. IGNIT TEMP FOR PAPER TP - READ. .PH.TP PRINT.. 'ENTER BETA=BE . GAMMA/R=GAR , GARP WHICH IS PAPER POROSITYREAD. .BE, GAR, GARP

PRINT.. -ENTER G ASH/G TOB=AN AND G OXY/G GAS CN'

30

40

READ.. AN. CN

PRINT*. 'ENTER MAXIMUM CHANGE FOR STEADY STATE CONDITIONS. ERR' READ.. ERR PRINT., 'ENTER NUMBER OF GRIDS IN R AND NUMBER OF TIMESTEPS ISP' READ.. NG. ISP PRINT., 'ENTER GRID RATIO Z TO R' READ..RIZR

PRINT., 'ENTER CONVECTION COEF H=HR/K, NUM TIMESTEP FOR DATA INP' PRINT., 'K IS THE THERMAL CONDUCTIVITY AT 300K' READ., H1.INP

PRINT., 'ENTER RATIO SPEC. HEAT OF AIR TO SPEC. HEAT OF TOB.' READ..SPHGS

PRINT.. 'ENTER DIAMETER OF VOID SPACE(CM)DP. RAD. EMISSIVITY ET

READ. ,DP.ET PRINT., 'ENTER THERMAL COND OF GAS GK . THERMAL COND OF SOLID FK

READ. .GK.FK

3 IT=0 TIM=0.

ISKIP=1 NTEST=0 W=9

K1 = 1 K=1 TA=293. YA=.232 A1=(1-PH1..(2./3.)).FK+GK.PH1..(1./3.)

A2=1 ,5109E-11.ET.DP.PH1..(1 ,/3.)

I EBN=0

A3=1 .133E-11.DP«ET.PH..(1 ./3.

)

IN=0 NR=NG+1 NZ=NG«RIZR+1

PRINT.. 'ENTER TIMESTEP FOR FIRST 50 ITERATIONS IN SECONDS' READ..TS1

PRINT., 'ENTER TIMESTEP FOR ITERATIONS GT 50 IN SECONDS' READ..TS2

TS=TS1 PRINT., 'ENTER ERR FOR ITERATIONS- READ. , ERR INITIALIZE MATRIX

1F(IDATA.E0.1) THEN

PRINT., 'ENTER IT, TIM- READ* , IT. TIM CALL INITD(T.Y.R.U.W1 ,W2 .W3.W4 .GA.GAR) ELSE CALL INITIAL(TA,T.Y.R.NR.NZ.GA,W2.W3.W4.U)

END IF

IF (1T.EQ.0) THEN WRITE(6.124) FORMATC INITIAL CONDITIONS')

CALL 0UTPUTP(D.A.B.C.E.D1 ,D2 .PH.TP. GAR .GARP, AN. CN.H.NG. 1RIZR.IN.TS.TIM) CALL OUTPUT(NR,NZ,T,Y.R,U)

END IF CALCULATE REACTION RATE FROM DIFFERENTIAL^ EQ CALL REACT (T,R,NR.NZ,W1 ,B , D1 , Y , TS . E . W2 . W3 . RR ,K1 .RRW) CALCULATE OXYGEN DIFFUSION

CALL OXY (NG . D . TS . PH . B . AN , E , D2 . CN , Y , T , R , GAR . W2

,

1 NR , NZ . G A . TP , YA . RR . D 1 . U , W4 , RRW , W3 . TA . I SK I P . GARP , W) CALCULATE TEMPERATURE

CALL TEMP(NG.A.B.C,D1 .02 .NR . NZ .PH. TS. E. T .HI . TA.R. Y.RR ,W3. 1U.W4.SPHGS.RRW. ISKIP.W.A1 .A2.A3) CALCULATE VELOCITY/R0

CALL VEL0CR(PH.AN,D1 .02 .NG.NR.NZ .RR.W4.U.RRW)

TEST FOR CONVERGENCE

RES 1 0=0. DEL=0.

DO 40 1=1 ,NR DO 30 J=1 ,NZ IF(K1 .EQ.1) THEN RR1(I.J)=RR(I.J)

Y1 ( I ,J)=W2fI ,J) Rlfl ,J)=WWI ,j) THI.J)=W3(I.J)

U1(I.J)=W4(I.J)

ELSE 1F(W2(I.J).GT.0.) THEN RESID=ABS((Y1(1,J)-W2(I.J))/W2(I.J))

ELSE IF(Y1(I.J).GT.0.) THEN RESID=ABS((Y1(I.J)-W2(I.J))A1(I.J))

END IF IF(RESIO-DEL.GT.0.) DEL=RESID

RESID=ABS((T1(I ,J)-W3(I ,J))/T1(I ,J)) IF(RESID-DEL.GT.0.) DEL=RESID

IF(U1(I,J).GT.0.) THEN RESID=ABS((U1(I.J)-W4(I.J))/U1(I,J))

ELSE IF(W4(1.J).GT.0.) THEN RES1D=ABS((U1(I.J)-W4(1.J))/W4(I.J))

END IF IF(RESID-OEL.GT.0.) DEL=RESID IF(RR1(I.J).GT0.) THEN RESID=ABS((RR1(I.J)-RRW(I.J))/RR1(I.J))

ELSE IF(RR(I.J).GT.0.) THEN RESID=ABS((RR1(I.J)-RRW(I.J))/RRW(I,J))

END IF 1F(RESID-DEL.GT.0.)DEL=RESID

Y1(I.J)=W2(I.J) Rl(l,j)=WHI.j)

U1(I,J)=W4(I.J)

RR1(I.J)=RRW(I ,J) T1(I.J)=W3(I.J)

END IF CONTINUE

CONTINUE

IF(K1 .EQ.1) THEN

K1-2

DEL=1

.

END IF IF(K.GT300) GO TO 400

192
102

85

90

109

50

C

101 102 103

104

105 106

C

110

C120

C130

C140

150

K=K+1 ISKIP=2 IF(DEL.GT.ERR) GO TO 10 IT=1T+1 1EBN=IEBN+1

1F(1EBN.E0. IEB) THEN

TEST FOR ENERGY AND OXYGEN BALANCE

! EBN=0 CALL TRAPE(I . J.T,W3.NR.NZ.TS.PH,A.H,R.Y.E.TA.B,C.D1 .D2) CAL L OTRAPE ( I . J . T . W3 . NR , NZ . TS , PH . CN . GAR , R , Y . E . TA . B . C , GA , W2

)

END IF UPDATE VARIABLES FOR NEXT TIMESTEP

DO 80 1 = 1 .NR DO 75 J=1 .NZ R(l ,J)=W1(1.J) Y(l.J)=W2(I,J)

T(l.j)=W3(I.J)

U(I.J)=W4(I.J) CONTINUE CONTINUE

ISKIP=1

IN=IN+1 IF(IT.EO.50) TS=TS2 INTERMEDIATE OUTPUT

IF(IN.EO.INP) THEN IF(IT.GE.50) THEN TIM=50.TS1+(IT-50)«TS2

ELSE TIM=IT«TS1

END IF IF(IN.EO.INP) IN=0 WRITE(6,102) TS.TIM FORMAT('TIME STEP =' . E9 .3, 'TIME ='.E9.3) CALL OUTPUT(NR.NZ.T.Y.R.u) VALT=0

.

DO 90 1=1. NR DO 85 J=1.NZ

IF(T(I,J).GT.VALT) VALT=T(I.J) CONTINUE CONTINUE

IF(VALT.GE.1500.) THEN PRINT.. 'TEMP EXCEEDS 1500 K' STOP

ELSE IF(VALT.LT.700.) THEN

PRINT.. 'MAXIMUM TEMP BELOW 700. K' STOP

END IF END IF FINAL OUTPUT

IF(IT.GE.ISP) THEN PRINT.. 'PROGRAM REACHED LAST TIME STEP!!'

IF(IT. GE.SB) THEN TIM=50.TS1+(IT-50).TS2

ELSE TIM=IT«TS1

END IF WRITE(6,108) FORMAT('CIG25A OUTPUT') CALL OUTPUT(NR,NZ.T,Y,R,U)

STOP

END IF K-1

K1 = 1 GO TO 10 PRINT.. 'FAILED TO CONVERGE IN GLOBAL SCHEME' WRITE(6,109) IT. DEL CALL OUTPUT(NR.NZ,T,Y,R,U)

FORMAT( 'TIMESTEP WHICH C1G25A DIDNT CONVERGE' . 15. 'DEL= \F7.3)

STOP CONTINUE

END SUBROUTINE INITD(T,Y,R.U.W1 ,W2 ,W3 ,W4 .GA.GAR) PARAMETER (NR=21 ,NZ=151

)

DIMENSION T(NR.NZ).Y(NR.NZ).R(NR.NZ).U(NR,NZ),W1(NR.NZ)

1 .W2(NR.NZ) .W3(NR.NZ) .W4(NR,NZ) .GA(NZ) PROGRAM READS A DATA FILE AT TIMESTEP IT AND TIME TIM. FORMATfI3,21F6.0)

FORMAT (20F6.0) FORMAT(I3.21F6.3)

FORMATf20F6.3) FORMAT(13,21F6.1)

FORMAT(20F6.1)

DO 110 J=1.NZ READf7.10l)jJ.(T(l.J).I=1 .21) READ(7.102)(T(I.J).I=22.41)

CONTINUE

DO 120 J=1.NZ READ(7,103)JJ.(Y(1.J),I=1 .21) READ(7.104)(YO , J). 1=22.41) CONT I NUE

DO 130 J=1 ,NZ READ(7.103)JJ. (R( I. J). 1=1, 21) READ(7.104)(R(I . J), 1=22.41) CONTINUE

DO 140 J=1 .NZ READ(7.105)jJ, (U( I. J), 1 = 1 ,21) READ(7.106)(U(I.J).I=22.41)

CONTINUE

DO 160 J=1 .NZ IF(J.LT.28) THEN

GA(J)=GAR

ELSE GA(J)=0.

END IF DO 150 1=1. NR W3(I,J)-T(I.J)

W2CI.jJ«Y(I.J)

WHI.Jl-Rfl.J)

W4(I.J)-U(I .J) CONTINUE

160 CONTINUE

RETURN

END SUBROUT I NE I N I T I AL ( TA . T , Y , R . NR . NZ . GA , W2 . W3 . W4 . U) DIMENSION T(21.15l).R(21.151),Y(21.151).GA(151).W2(21,151)

1 .W3(21 ,151) ,U(21 . 151 ).W4(21 .151) DO 20 1=1 ,NR DO 18 J=1 ,NZ U(I,J)=0.

W4(I ,J)=0. IF(J.LT.9) THEN R(I,J)=999

ELSE R(I.J)=1 .0 END IF IF(J.LT,6) THEN

Y(I,J)=.01 W2(I,J)=.01

ELSE IF (J.EQ.6) THEN

Y(I,J)=.01 W2(I.J)=.01

ELSE IF(J.E0.7) THEN Y(I,J)=.02 W2(I.J)=.02

ELSE IF (J.EO.8) THEN

Y(I ,J)=04

W2(I ,J)=.04

ELSE IF(J.E0.9) THEN

Y(I ,J)=.08 W2(I.J)=.08

ELSE IF (J.EQ.10) THEN Y(I,J)=.16

W2(I ,J)= 16 ELSE

Y(I ,J)=.232 W2(I.J)=.232

END IF IF(J.LT6) THEN

T(I ,J)=1000. W3(I , J)=1000.

ELSE IF(J.GE.6.AND.J.LE.9) THEN

T(I .J)=1000 -140. .(J-5) W3(I.J)=T(I.J)

ELSE T(I.J)=TA W3(I.J)=TA

END IF

18 CONTINUE

20 CONTINUE

DO 22 J=1 .NZ GA(J)=0.

22 CONTINUE

RETURN

END SUBROUTINE REACT(T.R.NR.NZ.W1 ,B,D1 . Y. TS, E.W2 ,W3 ,RR . K1 ,RRW) DIMENSION T(21.151).R(21.151).Wl(21.15l).Y(21,151)

1 .W2(21 ,151).W3(21 ,151),RR(21.151).RRW(21.151)

C CALCULATES REACTION RATE/MAX CHAR DENS I TY(RR/DCMAX) DO 20 1 = 1 .NR DO 18 J=1 .NZ IF(K1 . EO. 1) THEN

RR(I ,J)=B.R(I ,J).Y(I,J).EXP(-E/T(1.J))/D1 RRW(I,J)=RR(I,J)

ELSE

RRW(I ,J)=B.W1(I.J)-W2(I,J)>EXP(-E/W3(I ,J))/D1 END IF W1(I.J)=R(I.J)-(RRWfI .Jl+RR(I ,J)).TS/2. IF(W1(I.J).LT.0) W1(I.J)=0.

18 CONTINUE

20 CONTINUE

RETURN

END SUBROUT I NE T EMP ( NG . A . B . C . D 1 . D2 . NR , NZ . PH . TS . E . T . H1 . TA . R .

Y

1 .RR.W3.U.W4.SPHGS.RRW. ISKIP.W.A1 .A2.A3) DIMENSION T(21.151).R(21 . 151 ) . Y(21 . 151 ) .S(21 , 151 ) ,RR(21 . 151

)

1 .W3(21,151).U(21.151).W4(21 .151).RRW(21 ,151) DT(A1 .A2,TT)=A1+A2»TT..3 GM1=A«TS«NG.NG/(2 . •

( 1-PH)

)

A4=A3-GM1

TT=300. HH=H1.DT(A1 .A2.TT) B1=C.D2«TS/2. GD=PH«SPHGS.NG'TS/(4 . -D1 •

( 1 .-PH)

)

IF(ISKIP.E0.2)G0 TO 131 DO 100 I=2,NR-1

GPL=1 +1 ./(2..(I-1))

GMI=1 -1 ./(2..(I-l))

DO 95 J=2.NZ-1 TT-T(I.J) GM=GM1«DT(A1 .A2.TT)

S(! ,J)=(1 .-4..GM).T(I.J)+CM.(T(I . J+1 )+T( I . J-1 )+GPL«T( 1+1 . J

)

14CMI.TM-1 ,J))+B1«RR(I ,J)-GD.U(I . J) • (T( 1 + 1 . J)-T( 1-1 . J)

)

2+A4.(T(I.J).(T(I+1.J)-T(I-1.J)+T(I.J+1)-T(I.J-1)))..2

95 CONTINUE

100 CONTINUE

TT=T(1.1)

CM=GM1 .DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT)

S(1 ,1) = (1 ,-6..GM-GM.2..H/NG).T(1 . 1 )+2 . «GM. (T ( 1 .2) + 2 . «T(2 . 1 ) 1+H.TA/NG)+B1»RR(1 . 1)+A4.(T(1 .

1

).2.«H.(T(1 . 1 )-TA)/NG)- «2 TT=T(1 ,NZ) GM=GM1.DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT)

S(1 .NZW1 -6 .GM-2 «GM.H/NG).T(1 .NZ)+4 . .GM.T(2 ,NZ) 1+2.«GM.T(1 ,NZ-1)+GM.2.«H.TA/NG+B1.RR(1 ,NZ) 2+A4.(T(1,NZ)«2..H.(T(1 ,NZ)-TA)/NG)«.2 GPL-1.+1./(2..(NR-1))

TT-T(NR.I)

193
GM=GM1 -DT(A1 ,A2.TT) H=HH/DT(A1 .A2.TT) S(NR.1)=(1 .-4..GM-(2.+2..CPL).GM.H/NG).T(NR,1)+CM.(2.«

1T(NR-1 , 1)+2.«T(NR.2))+(2.+2. -GPL) .GM.H.TA/NG+B1 «RR(NR. 1

)

2+CD.U(NR,1).(2.«H.(T(NR.1 )-TA)/NG) TT=T(NR,NZ) GM=GM1«DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT) S(NR.NZ)=(1 .-4..GM-(2.+2. .GPL).GM.H/NG)«T(NR,NZ)+GM.(2.«

1T(NR-1 .NZ)+2..T(NR.NZ-1))+(2.+2..GPL)«GM.H.TA/NG+B1.RR(NR,NZ) 2+CD.U(NR.NZ).(2..H.(TfNR.NZ)-TA)/NG) 3+A4.(T(NR.NZ).4..H.(T(NR.NZ)-TA)/NG).»2

DO 128 I=2,NR-1

GPL=1 .+1 ./(2..(I-1))

GMI=1 .-1 ,/(2 » ( 1-1 )

)

TT=T(I.1)

GM=GM1 »DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT) S(I,1)=(1 .-4.«GM-2.»GM«H/NG)»T(1 , 1 )+GM«(GPL«T(I+1 .1) 1+GMI »T( 1-1 . 1 ) )+2 . »GM.T( I . 2)+2 . .CM.H.TA/NG

2+B1.RR(I

.

1)-GD«U(l.1)»(T(l+1 . 1 )-T( 1-1 . 1 )

)

3+A4.(T(I . 1).(T( 1+1,1 )-T( 1-1,1 )+2.«H.(T( 1,1 )-TA)/NG))««2

TT=T(1 .NZ) GM=GM1«DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT)

S(I ,NZ)=(1 .-4..GM-2..GM.H/NG)«T(I . NZ)+CM« (GPL.T ( 1+1 ,NZ) 1+GMI «T( 1-1 .NZ)+2..T(l.NZ-1))+2 . .GM.H.TA/NG+B1 «RR( 1 .NZ) 2-CD»U(I .NZ)«(T(I+1.NZ)-T(I-1 .NZ)) 3+A4.(T(I ,NZ).(T(1 + 1 ,NZ)-T(I-1 ,NZ)-2..H.(T(I.NZ)-TA)/NG))««2

120 CONTINUE

GPL=1 .+1 ,/(2.«(NR-1))

DO 138 J=2,NZ-1

TT=T(1 .J) GM=GM1«DT(A1 .A2.TT)

S(1 .J)=(1 ,-6..GM).T(1.J)+CM. (T(1 . J+1 )+T( 1 , J-1 )+4. .T(2 . J)

)

1+B1»RR(1 ,J)+A4«(T(1 ,J).(T(1 ,J+1)-T(1 ,J-1))).«2 TT=T(NR.J) GM=GM1>DT(A1 ,A2,TT) H=HH/DT(A1 .A2.TT) S(NR.J)=(1 .-4..GM-2..GM.H.GPL/NG).T(NR.J)+CM.(2.«T(NR-1 ,J) 1+T(NR.J+1)+T(NR.J-1))+2..GM.H.TA«GPL/NG

2+B1«RR(NR.J)+CD.U(NR,J).(2. «H. (T(NR, J )-TA)/NG) 3+A4.(T(NR.J).(-2..H.(T(NR.J)-TA)/NG+T(I,J+1)-T(I.J-1)))..2

130 CONTINUE

131 CONTINUE

00 140 1=1 ,NR

IF(I GT.1) THEN

GPL=1 .+1 ./{2. • (1-1 )

)

GMI=1.-1 ,/(2..(I-1))

END IF DO 138 J=1 .NZ TT=W3(I ,J) GM=GM1«DT(A1 .A2.TT) H=HH/DT(A1 .A2.TT)

IF(I .GT. 1 .AND. I .LT.NR.AND.J.GT.1 . AND. J . LT.NZ) THEN VAL=(GM.(GPL«W3(I+1 ,J)+GMI.W3(I-1 ,J)+W3(I ,J+1)+W3(I ,J-1))

1+S(I ,J)+B1-RRW(I ,J)-GD»W*(I.J).(W3(1+1 , J)-W3( 1-1 . J)) 2+A4«(W3(I.J)«(W3(I+1.J)-W3(I-l .J)+W3(;.J+1)-W3(I.J-1)))»»2

3)/(1 .+4..GM) ELSE IF(J.EO. 1 .AND. I .LT.NR.AND. I .GT. I ) THEN VAL=(GM.(2.«W3(I . 2)+CPL>W3(I+1 , 1 )+GM! .W3( 1-1 . 1 )+2 . •H.TA/NG)

1+S(I ,1)+B1«RRW(I .J)-GD«W4(I .1).(W3(I+1 , 1)~W3(I-1 .1)) 2+A4.(W3(I ,J).(W3(1+1 ,J)-W3(I-1 ,J)+2.«H.(W3(I ,J)-TA)/NG))..2

3)/(1 .+4..GM+2.«H'GM/NG)

ELSE IF(J. LT.NZ. AND. J. GT. 1 .AND. I .EQ.NR) THEN VAL=(GM»(2..W3(NR-1 ,J)+W3(NR.J+1)+W3(NR.J-1)+2..H.TA.GPL/NG)

1+S(NR . J )+B1 .RRW( I

. J )-GD«W4 (NR , J

) .2 . .H.TA/NG

2+A4.(W3(I ,J).(-2.»H.(W3(I ,J)-TA)/NG+W3(I , J+1)-W3(I ,J-1)))..2

3)/(1 .+4. .GM+2. .GM.GPL.H/NC-GD.W4(NR. J). 2. .H/NG) ELSE IF (I .EG. 1 .AND. J .LT.NZ. AND. J. GT.1) THEN VAL=(GM. (4..W3(I+1 ,J)+W3(I ,J+1)+W3(I ,J-1))+S(I ,J)+B1.RRW(I ,J) 1+A4.(W3(] ,J).(W3(t.J+1)-W3(I .J-1))). .2 2)/(1.+6..GM)

ELSE IF(J. EO.NZ. AND. I .LT.NR.AND. I .GT. 1) THEN VAl=(GM.(CPL.W3(I+1 .J)+GMI.W3(I-1 ,J)+2..W3(I .J-1 )+2. .H.TA/NG

1)+S(I ,J)+B1«RRW(I .J)-GD.W4(I.J).(W3(I+1 . J )-W3( 1-1 , J)

)

2+A4.(W3(I .J).(W3(I+1 ,J)-W3(I-1 .J)-2..H.(W3(I . J)-TA)/NG) ) ..2 3)/(1 .+4. .GM+2. .GM.H/NG)

ELSE IF (J.EO. 1 .AND. I .EQ.1 ) THEN VAL=fGM.(4..W3(I+1 ,J)+2.«W3(I .J+1)+2..H.TA/NG)+S(I.J)+B1

1«RRW(I ,J)+A4.(W3(I ,J).2..H.(W3(I.J)-TA)/NG).«2

2)/(1 .+6. "GM+2. -GM.H/NG)

ELSE IF(I. EQ.1 .AND. J. EO.NZ) THEN VAL=(GM.(4..W3(I+1 ,J)+2..W3(I , J-1 )+2 . .H.TA/NG)+S( I .J) 1+B1«RRW(I ,J)+A4.(W3(I ,J).2.«H.(W3(I . J)-TA)/NG) .«2 2)/(1 .+6. .GM+2. .GM.H/NG)

ELSE IF (J. EQ.1 .AND. I .EQ.NR) THEN VAL=(GM.(2..W3(I-1 ,J)+2..W3(I . J+1 )+(2 .+2 . .GPL). H.TA/NG)

1+S(I ,J)+B1«RRW(I .J)-GD.W4(I .J). 2.« H.TA/NG)

2/(1 .+4..GM+(2.+2. .GPL).GM.H/NG-GD.W4(I . J).2.«H/NG)

ELSE IF (1 .EQ.NR. AND. J.EQ.NZ) THEN

VAL=(GM.(2.«W3(I-1 ,J)+2..W3(I . J-1 )+(2. +2. «GPL) .H.TA/NG)

1+S(I .J)+B1.RRW(I.J)-CD.W4(I.J).2..H.TA/NG

2+A4.(W3(I .J). 4. «H.(W3(I ,J)-TA)/NG)..2 3)/(1.+4..GM+(2.+2..GPL).GM.H/NG-GD«W4(I ,J).2..H/NG)

END IF W3(I.J)=W.VAL+CC.W3(I .J) 138 CONTINUE

140 CONTINUE

RETURN

END SUBROUT I NE OXY ( NG . D . TS . PH . B , AN , E . D2 . CN , Y , T , R , GAR . YY2

1 ,NR,NZ.GA,TP,YA.RR.D1 .U.W4 .RRW.W3.TA. ISKIP.GARP.W) DIMENSION Y(21.151).T(21.151).R(21.151).GA(151).C(21.151)

1 ,W2(21 ,151).RR(21 ,151).U(21.151),W4(21 . 151).RRW(21 . 151 ) .W3(21 . 151

)

GM1=TS<NG»NG/2.

8B=TS. ( 1 .-PH) «D1 .D2/(2 . .PH) CC=1 .-W GV=NG.TS/4. 1F(ISKIP.EQ.2)G0 TO 21

DO 20 1=1 ,NR IF(l.GT.I) THEN

GPL=1 .+1 ,/(2..(I-1))

CMI = 1 .-1 ,/(2. .(1-1))

END IF DO 10 J=1 .NZ

I F( I. GT.1 .AND. I .LT.NR.AND.J.GT.1 .AND. J . LT.NZ) THEN GM=GM1*DC(I,J.T,D)

CM=1 .-4. «GM C(I.J)=CM.Y(I.J)+GM.(Y(I.J+1)

1+Y(I . J-1)+CPL«Y(I+1 ,J)+GMI.Y(I-1 .J))-BB«(Y(I.J).(1 ,-AN)+CN) 2.RR(I.J)-GV«U(I ,J).(Y(I+1 ,J)-Y(I-1.J)) ELSEIF(J.EQ.NZ.AND.I.GT.1.AND.I.LT.NR)THEN

GM=GM1.DC(I, J.T.D)

CM=1 .-4..GM

Cf I , J )=CM. Y( I . J )+GM. (2 .

1Y(I,J-1)+GPL.Y(I+1 ,J)+GMI.Y(1-1 , J ) )-BB- (Y( I . J

) . ( 1 .-AN)+CN)

2«RR(I ,J)-GV.U(I .J)«(Y(I+1,J)-Y(I-1 ,J)) ELSE IF (J. EQ.1 .AND. I. GT.1 . AND. I . LT .NR) THEN GM=GM1.DC(I.J,T.D)

CM=1 .-4..GM

DF=GM/GM1

C(I .J)=CM.Y(I.J)+GM.(2..Y(1.J+1)+2..GAR.(YA-Y(I.J))

1/(DF.NG)+GPL«Y(I+1 ,J)+GMI.Y(I-1 .J))-BB.(Y(I.J)

2.(1 .-AN)+CN).RR(I . J)-GV.U(I ,J)«(Y(I+1 ,J)-Y(I-1 ,J)) ELSE IF (I EQ.1 .AND. J. GT.1 .AND. J. LT.NZ) THEN GM=GM1«DC(I . J.T.D) C(I.J)—(1 .-6.«GM).Y(I ,J)+GM.(Y(I.J+1) 1+Y(I.J-1)+4.«Y(I+1 ,J))-BB.(Y(I,J).(1.-AN)+CN).RR(I.J)

ELSE IF(I . EQ.NR. AND. J. GT. 1 .AND. J. LT.NZ) THEN GM=CM1.DC(I .J.T.D)

CM=1 .-4. .GM DF=GM/GM1

1F(GA(J) EQ.0) THEN C(I,J)=CM.Y(I ,J)+GM.(Y(I.J+1)+Y(I.J-1)+2..Y(I-1 ,J) 1+2..GARP.GPL.(YA-Y(I.J))/(DF.NG))+2..GPL.U(I . J ).Y( 1 . J )/(DF.NG)

2-BB«(Y( I

. J)>(1 .-AN)+CN).RR(1 ,J) 3-GV-U(I .J).2..GARP«(YA-Y(I.J))/(DF.NG)

ELSE

C(I ,J)=CM.Y(I ,J)+GM.(Y(I.J+1)+Y(I.J-1)+2..Y(I-1 ,J)+2..GAR.

|.Y(I ,J)/(DF.NG)-BB

|.2.«GAR.(YA-Y(I.J))

1GPL-(YA-Y(I .J))/(DF.NG))+2..GPL«U(I.J

2»(Y(I ,J).(1 ,-AN)+CN).RR(I ,J)-GV.U(I.J 3/(DF.NG)

END IF ELSE IF (I. EQ.1 .AND. J.EO. 1) THEN GM=GM1.DC(I .J.T.D) DF=CM/GM1 C(I.J)=(1 -6..GM).Y(I,J)+GM.(2..Y(I.J+1)+2..GAR.(YA-Y(I.J))/

1(DF.NG)+4..Y(I+1 .J))-BB«(Y(I.J).(1.-AN)+CN).RR(I .J) ELSE IF(I.E0.1 .AND. J. EO.NZ) THEN GM=GM1.DC(I .J ,T.D)

C(I ,J)=(1 .-6..GM).Y(I.J)+GM.(2..Y(I.J-1)+4..Y(I+1 ,J))-BB 1«(Y(I.J)'(1 -AN)+CN).RR(I ,J) ELSE IF(I EQ.NR. AND. J. EQ.1) THEN GM=GM1.DC(I .J.T.D)

CM=1 .-4. .GM DF=GM/GM1

C(I ,J)=CM.Y(I .J)+GM.(2..Y(I,J+1)+2.«Y(I-1 ,J)+GAR. 1(2.+2..GPL).(YA-Y(I ,J))/(DF.NG))+2..GPL.U(I.J).Y(I.J)/(DF.NG) 2-BB.(Y(I.j).(1.-AN)+CN).RR(I.J)-GV.U(I.J).2..GAR.(YA-Y(I.J))

3/(DF«NG)

ELSE IF (I. EQ.NR. AND. J. EO.NZ) THEN GM=GM1.DC(I.J.T.D)

CM=1 .-4. »GM DF=GM/GM1 C(I.J)=CM.Y(I ,J)+GM.(2..Y(I.J-1)+2.«Y(I-1.J))-BB 1.(Y(I.J).(1.-AN)+CN).RR(I ,J)-GV.U(I.J).2..GAR.(YA-Y(I.J))

2/(DF.NG)

END IF

10 CONTINUE

20 CONTINUE

21 CONTINUE

DO 50 1=1 ,NR

IF (I. GT.1) THEN

GPL=1 .+1 ./(2..(I-1)) GMI=1.-1 ./(2..(I-1))

END IF DO 40 J=1 ,NZ

IF (I. GT.1 .AND.

I

.LT.NR.AND.J.GT.1 .AND. J. LT.NZ) THEN GM=GM1.DN(I . J .W3.D)

CP=1 .+4..GM VAL=W.(GM.(W2(I .J+1)+W2(I.J-1)+GPL.W2(I+1 . J)+CMI»W2( 1-1 ,J)) 1-BB»(W2(I ,J).(1 -AN)+CN).RRW(I.J)

2+C( I . J )-GV.W4 ( I . J ) . (W2( 1+1 . J )-W2( 1-1 . J ) ) )/CP

ELSE I F( J. EO.NZ. AND. I .GT. 1 . AND. I . LT .NR) THEN GM=GM1.DN(I.J.W3,D)

CP=1 .+4..GM VAL=W.(GM.(2.«W2(I.NZ-1)+GPL.W2(I + 1.NZ)+GMI.W2(I-1.NZ))

1 -BB> (W2 ( I . J

) •

( 1 .-AN)+CN) .RRW( I.J) 2+C(I ,NZ)-GV.W4(I ,J).(W2(I + 1 ,J)-W2(I-1 ,J)))/CP

ELSE IF(J. EQ.1. AND. I. GT.1 . AND. I . LT .NR) THEN GM=GM1.DN(I.J,W3,D)

CP=1 .+4..GM DF=GM/GM1 VAL=W. (GM. (2 . •W2( I . 2)+2 . .GAR.YA/(DF.NG)+GPL.W2( 1+1 . 1 )+GMI

.

1W2( 1-1 . 1))+C(I.1)-GV.W4(I .J).(W2(I+1 ,J)-W2(I-1.J)) 2-BB«(W2(I . J)«(1 -AN)+CN).RRW(I . J) )/(CP+2 . «GAR.GM/(DF.NG))

ELSE IF(I .EQ.1 .AND. J. GT.1 .AND. J. LT.NZ) THEN GM=GM1.DN(I ,J .W3.D) CP=1 .+4..GM VAL=W«(GM»(W2(1 .J + 1 )+W2(1 , J-1 )+4. «W2(2 . J) )+C( 1 . J) 1-BB«(W2(I ,J)»(1 .-AN)+CN).RRW( I .J))/(1 .+6.-GM) ELSE IF(I .EQ.NR. AND. J. GT.1 .AND. J. LT.NZ) THEN GM=GM1.DN(I .J.W3.D)

CP=1 .+4..GM DF=GM/GM1 1F(GA(J).EQ.0) THEN IF(T(NR,J).LT.TP) THEN VAL=W.(GM.(W2(NR. J+1)+W2(NR.J-1)+2.«W2(NR-1 ,J) 1+GPL.2.«GARP.YA/(DF.NG))+C(NR.J)

194
2-GV.W4(l ,J).2.«GARP«YA/(DF.NG) 3-BB«(W2(I,J)»(1 .-AN)+CN).RRW(1.J))/(CP-2.«GPL«GM.W4(I .J)/(DF.NG) 4+CPL«2.«GARP.GM/(DF.NG)-GV.W4(I,J).2..GARP/(DF.NG))

ELSE GA(J)=GAR

VAL=W«(GM«(W2(NR. J+1 )+W2(NR. J-1)+2. »W2(NR-1 .J)+GPL«2. »GAR«YA 1/(DF.NG))+C(NR,J)-GV«W4(I . J)«2.«GAR.YA/(DF.NG)

2-B8 •( W2 ( I. J

) .

( 1

. -AN ) +CN ) • RRW ( 1

, J )

)

3/(CP+CPL«2.»GAR«GM/(DF.NG)-2.^GPL»GM.W4(I ,J)/(OF.NG) 4-GV.W4( I . J

) «2 . .GAR/(DF.NG)

)

END IF ELSE VAL=W.(GM. (W2(NR. J+1 )+W2(NR. J-1 )+2. «W2(NR-1 ,J)+GPL>2. «GAR«YA 1/(DF.NG))+C(NR.J)-GV.W4(I, J).2.^GAR-YA/(DF.NG)

2-BB.(W2(I ,J)«(1 .-AN)+CN).RRW(] ,J)) 3/(CP+GPL«2.»GAR.GM/(DF.NG)-2. •GPL«GM^W4(I ,J)/(DF.NG) 4-CV.W4(I ,J)»2.»GAR/(DF.NG))

END IF ELSE IF(I.EQ.1 .AND.J.EQ.1) THEN GM=GM1.DN(I .J.W3.D) DF=GM/GM1 VAL=W.(GM«(2.«W2(1 . J+1)+2. • GAR.YA/(DF«NG)+4 . «W2( 1 + 1 , J)) +

1C(I ,J)-BB"(W2(1 ,J)»(1 .-AN)+CN).RRW(I.J))/(1 .+6.«GM+2. .GAR.GM 2/(DF»NG))

ELSE I F ( I . EQ . 1 .AND.J.EO.NZ) THEN GM=GM1»DN(I ,J.W3,D) VAL=W.(GM.(2.«W2(I.J-1)+4 , W2(I+1.J))+C(I.J)

1-BB«(W2(I.J)»(1 .-AN)+CN).RRW(I.J))/(1 .+6.-GM) ELSE IF (I-EQ-NR. AND.J.EQ.1) THEN GM=CM1.DN(I ,J,W3.D)

CP=1 .+4.»GM

DF=GM/GM1 VAL=W.(GM.(2.»W2(I.J+1)+2.«W2(I-1.J)+(2.+2.«GPL)«GAR«YA/(DF«NG))+

1C(I,J)-CV.W4(I,J).2.«GAR.YA/(DF.NG)-BB«(W2(I.J)«(1.-AN)+CN) 2.RRW(I.J))/(CP+(2.+2..GPL).GAR.GM/fDF.NG)-GV.W4(I,J)

3.2 . .GAR/(DF«NG)-2 . •GPL»GM«W4( 1 . J )/(DF«NG)

)

ELSE IF(I.EO.NR. AND.J.EO.NZ) THEN GM=GM1«DN(I .J.W3.D)

CP=1 .+4..GM VAL=W«(GM»(2.«W2(I,J-1)+2.«W2(I-1 ,J))+C(I .J) 1-BB. (W2 ( I . J ) • ( 1

. -AN)+CN ) »RRW( I . J ) )/CP

END IF C W IS MISSING IN FRONT OF VAL SINCE IT IS INCLUDED EARLIER IN EO W2(I ,J)=VAL+CC»W2(1 . J) 48 CONTINUE

50 CONTINUE

YNEG=0. DO 68 1=1 ,NR DO 55 J=1 ,NZ IF(W2(I.J).LT.e.) THEN

C IF(W2(I.J).LT.YNEG) YNEG=W2(I ,J) W2(I,J)=8.

END IF 55 CONTINUE

60 CONTINUE

RETURN

END SUBROUTINE VELOCR(PH.AN,D1 ,D2 .NG ,NR .NZ ,RR ,W4 .U.RRW) DIMENSION RR(21,151).W4(21,151),U(21,151) ,RRW(21 .151)

C CALCULATES RADIAL VELOCITY DIVIDED BY R0 (W4/R8)

C ASSUMES CONSTANT GAS DENSITY.

C INTEGRATION IS DONE BY THE TRAPEZOID RULE

DO 20 J=1.NZ

DO 18 1=2. NR

W4(l .J)=(1.-PH).(1 -AN).D1«D2.((I-2).RR(I-1 . J )+( 1-1 ) .RR( I . J ) )/ 1(2..PH.NG.(I-1))+W4(I-1,J).(I-2)/(I-1)

18 CONTINUE

28 CONTINUE

RETURN

END FUNCTION DC(I.J.T.D) DIMENSION T(21 .151) DC=D«(T(I .J)/273.)««1 .75 RETURN

END FUNCTION DN(I.J.W3,D) DIMENSION W3(21 ,151) DN=D.(W3(I.J)/273.)..1.75

RETURN

END SUBROUT I NE OUTPUTP (D.A.B.C.E.D1.D2.PH.TP. GAR . GARP . AN . CN . H , NG

1 .RIZR.IN.TS.TIM) WRITE(6.184)D.A.B.C

WRITE(6.185)E.D1 .02. PH

102 FORMATCTIME STEP = '

. E9 . 3. 'TIME =' .E9.3)

183 FORMAT (-POINTS IN R = •,I3. P POINTS IN Z = \I3)

104 FORMAT ('D=' . E9.3.'A=' ,E9.3, 'B=' .E9.3. 'C='.E9.3)

185 FORMAT('E=' .E9.3. 'D1*=.' .E9.3, '02=' ,E9.3. 'PH=' .E9.3)

186 FORMAT ('GAR=' . E9 . 3

. 'GARP=' . E9 . 3, ' AN=' . E9 .3 , 'CN=',E9.3)

187 FORMAT

(

- TP=- . E9 .3. 'H= ' . E9 . 3, 'NG=' ,13, 'RIZR=' . F6. 2. ' IN=' . 13) WRITE(6. 106)GAR,GARP,AN,CN WRITE(6,187)TP,H.NG.RIZR.IN WRITE(6.102)TS.TIM

WRITE(6,183)NG+1 ,NC«RIZR+1 RETURN

END SUBROUTINE OUTPUT(NR.NZ. T . Y .R.U) DIMENSION T(21.151),R(21,151),Y(21.151).U(21.151)

181 F0RMAT(I3.21F6.1)

182 FORMAT(I3.21F6.3)

183 FORMAT(I3.21F6.8)

104 FORMAT(3X,20F6.1)

185 FORMAT (3X.20F6. 3) 106 FORMAT f3X. 20 F6.8)

121 FORMAT? 'TEMPERATURE')

122 FORMAT ('OXYGEN')

123 FORMAT ('DENSITY FRACTION')

124 FORMAT? 'RADIAL VELOCITY') WRITE(6.121)

DO 175 J=1 ,NZ

U

WRITE(6.103)J.(T(I , J). 1=1. 21)

C WRITE(6.106)(T(I. J). 1=22.41)

175 CONTINUE

WRITE(6.122)

DO 188 J=1 .NZ WRITE(6.102)J,(Y(I ,J) ,1=1 .21) C WRITE(6.185)(Y(I.J),1=22.41)

188 CONTINUE

WRITE (6.123) DO 190 J=1 .NZ WRITE(6,102)J.(R(I .J), 1=1. 21)

C WRITE(6.105)(R(1.J).I=22.41)

198 CONTINUE

WRITE(6.124)

DO 200 J=1.NZ WRITE(6,181)J.(U(I . J). 1=1. 21)

C WRITE(6,ie4)(U(I.J).I=22.41)

200 CONTINUE

RETURN

END SUBROUT I NE TRAPE ( I

. J . T . W3 . NR . NZ . TS . PH . A . H , R , Y , E , TA

1 .B.C.D1.D2) DIMENSION T(21.151).W3(21.151).Y(21,151).R(21.151)

C W3 IS THE TEMP. AT THE PRESENT TIMESTEP.

C T IS THE TEMPERATURE AT THE LAST TIMESTEP.

C INTEGRATION METHOD RESEMBLES TRAPEZOID METHOD IN THAT THE

C CYLINDER IS DIVIDED UP INTO SMALL CONSTANT TEMP. PIECES.

C VOLUME INTEGRALS

NG=NR-1 H1=8

H2=0

H3=8

H4=0

DO 20 I=2.NR-1

DO 10 J=2.NZ-1

H4 =H4+2 . • ( 1-1 ).(T( I .J)-TA) H1=H1+2.»(I-1).(W3(I .J)-T(I.J))

10 H3=H3+2.«(I-1)«R(1.J).Y(I ,J)«EXP(-E/W3(1 ,J)) 20 CONTINUE

DO 30 J=2.NZ-1 H4=H4+NG« (T (NR . J )-TA) H1=H1+NG«(W3(NR.J)-T(NR.J))

30 H3=H3+NG«R(NR,J).Y(NR. J).EXP(-E/W3( I ,J)) DO 40 I=2.NR-1 H4=H4+(I-1)»(T(I ,1)-TA+T(I ,NZ)-TA) H1=H1+(I-1).(W3(I , 1)-T(I,1)+W3(I ,NZ)-T(I ,NZ)) 40 H3=H3+(I-1).(R(I ,1).Y(I.1).EXP(-E/W3(I . 1 ) )+R( I ,NZ)» 1Y(I.NZ)«EXP(-E/W3(I .NZ))) DO 50 J=2.NZ-1 H4=H4+.25»(T(1 .J)-TA) H1=H1 + .25.(*V3(1.J)-T(1 ,J)) 50 H3=H3+.25«R(1 .J)-Y(1 , J)«EXP(-E/T(1 .J)) H4=H4+.5«NG«(T(NR,1 )-TA+T(NR,NZ)-TA) H1=H1+.5»NG»(W3(NR.1)-T(NR.1)+W3(NR,NZ)-T(NR.NZ))

H3=H3+ . 5«NG. (R(NR . 1 ) .Y(NR . 1

) • EXP(-E/W3 (NR . 1 ) )+R(NR ,NZ)

•

1Y(NR,NZ)«EXP(-E/W3(NR.NZ)))

H4=H4+(T(1 . 1)-TA+T(1 .NZ)-TA)/8. H1=H1+(W3(1 ,1)-T(1.1)+W3(1 ,NZ)-T(1 ,NZ))/8. H3=H3+(R(1 . 1)«Y(1 . 1).EXP(-E/T(1 . 1 ) )+R( 1

, NZ) -Y( 1 .NZ) LEXP(-E/W3(1 ,NZ)))/B. H4=H4«(1 .-PH) H1=H1«(1 .-PH) H3=H3»(1 .-PH)«C«D2«B«TS/D1

C SURFACE INTEGRALS

H2Z=8. DO 60 J=1 .NZ

IF (J.GT.1 .AND.J.LT.NZ) THEN H2Z=H2Z+(W3(NR.J)+T(NR.J)-2.«TA)/2.

ELSE H2Z=H2Z+(W3(NR.J)+T(NR.J)-2.«TA)/4.

END IF 68 CONTINUE

H2=H2Z»2 . .TS^NG^NG'A^H

C TOP SURFACE

H2R=0

.

DO 70 I=2.NR-1

70 H2R=H2R+2.-(I-1)»(W3(I .1)+T(I . 1 )-2 . »TA)/2

.

H2R=H2R+ . 25« ( W3( 1 . 1 )+T ( 1 . 1 )-2 . «TA)/2 . +NG« (W3 (NR . 1 )+T (NR . 1

)

1-2.»TA)/2. H2=H2R«A.H.TS«NG+H2

C BOTTOM SURFACE

H2R=0

.

DO 88 I=2.NR-1

80 H2R=H2R+2 . • ( 1-1 ) • (W3( I .NZ)+T( I ,NZ)-2 . «TA)/2

.

H2R=H2R+.25«(W3(1 .NZ)+T(1 ,NZ)-2. »TA)/2 .+NG« (W3(NR.NZ) 1+T(NR.NZ)-2.«TA)/2. H2=H2+A.H.TS«NG»H2R

WRITE(6.108)

188 FORMAT('VALUE OF THE HEAT INTEGRALS ARE:') WRITE(6.181)H1 .H2.H3

101 FORMAT ('VOLUME TERM H1=' . F9 . 3

, 'CONVECT ION H2=' . F9 . 3, 'SOURCE

1 H3= ' .F9.3) WRITE(6.102) H4

102 FORMAT( 'TOTAL HEAT CONTAINED IN SOLID'. F9. 3) WRITE(6.103) 100..(H1+H2-H3)/H4

103 F0RMAT('?5 HEAT UNACCOUNTED FOR IN CALCULATIONS' . F9 .3) RETURN

END SUBROUT I NE OTRAPE( 1 . J . T . W3 . NR , NZ . TS . PH . CN . GAR , R . Y . E . TA

.

1B.C.GA,W2,YA) DIMENSION T(21 .151).W3(21 . 151).Y(21 ,151).W2(21 .151),R(21 .151)

1 .GA(151)

C W2 IS THE OXYGEN CONCENTRATION AT THE PRESENT TIMESTEP

C Y IS THE OXYGEN CONCENTRATION AT THE LAST TIMESTEP

C INTEGRATION IS IDENTICAL TO THAT IN TRAPE

C VOLUME INTEGRATION

NG=NR-1 H1=8

H2=0 H3=0

195
1020

(Y(l.J)-YA)

.(W2(I.J)-Y(I.J)) R(I.J).Y(I.J).EXP(-E/W3(I.J))

50

60

C

C

100

101

102

103

H4=0

DO 20 I=2.NR-1 DO 10 J=2.NZ-1

H4=H4+2. «(I-1] H1=H1+2.«(I-1

H3=H3+2.-(I- CONTINUE

DO 30 J=2.N2-1 H4=H4+NG«(Y(NR. J)-YA) H1=H1+NG.(W2(NR.J)-Y(NR,J))

H3=H3+NG«R(NR.J)-Y(NR.J).EXP(-E/W3(NR,J))

00 40 I=2.NR-1 H4=H4+( 1-1 )• (Y( I

. 1 )+Y( I .NZ)-2 . «YA) H1=H1+(I-1).(W2(I.1)-Y(I , 1)+W2(I ,NZ)-Y(I .NZ)) H3=H3+(I-1).(R(I.1).Y(I.1).EXP(-E/W3(I.1))+R(I.NZ)

1.Y(I.NZ)«EXP(-E/W3(I .NZ))) DO 50 J=2.NZ-1 H4=H4+.25«(Y(1 , J)-YA) H1=H1+.25«(W2(1 ,J)-Y(1.J)) H3=H3+.25-Y(1 .J)«EXP(-E/W3(1.J)) H4=H4+.5«NG.(Y(NR. 1 )+Y(NR. NZ)-2 . .YA) H1=H1+.5.NG .(W2(NR.1)+W2(NR.NZ)-Y(NR.1)-Y (NR.NZ)) H3=H3+.5.NG.(R(NR.1).Y(NR,1).EXP(-E/W3(NR.1))+R(NR,NZ).Y(NR,NZ)

1»EXP(-E/W3(NR.NZ)))

H4=H4+(Y(1 ,1)+Y(1 , NZ)-2..YA)/8. H1=H1+(W2(1 . 1)+W2(1 ,NZ)-Y(1 ,1)-Y(1 ,NZ))/8. H3=H3+(R(1.1).Y(1.1).EXP(-E/W3(1 , 1))+R(1 ,NZ)»Y(1 ,NZ)» 1EXP(-E/W3(1 ,NZ)))/8. H3=H3«(1 .-PH).CN»B/PH SURFACE INTEGRALS

H2Z=0.

DO 60 J=1 .NZ IF(J.GT.1 .AND.J.LT.NZ) THEN H2Z=H2Z+GA(J).(W2(NR.J)+Y(NR. J)-2..YA)/2.

ELSE H2Z=H2Z+CA(J).(W2(NR,J)+Y(NR, J)-2..YA)/4.

END IF CONTINUE H2=H2Z.2..NG«NG.TS

TOP SURFACE

H2R=0

.

DO 70 I=2.NR-1 H2R=H2R+2 . .GAR. ( 1-1 )

• (W2( I

. 1 )+Y( I. 1 )-2 . «YA)/2

.

H2R=H2R+.25«GAR.(W2(1 .

1

)+Y(1 . 1 )-2. »YA+NG.(W2(NR, 1 )+Y(NR, 1 )- 12..YA))/2. H2=H2+H2R«NG«TS

BOTTOM SURFACE NO DIFFUSION THROUGH THE FILTER WRITE(6,100) FORMAT('VALUE OF THE OXYGEN INTEGRALS ARE:') WRITE(6,101)H1 .H2.H3 FORMAT ('VOLUME TERM H1=' . F9 .3, 'CONVECTION H2 =', F9 . 3, 'SOURCE

1 H3= ' .F9.3) WRITE(6,102) H4 F0RMAT('TOTAL OXYGEN CONTAINED IN SOLID'. F9. 3) WRITE(6,103) 100..(H1+H2-H3)/H4

FORMAT('% OXYGEN UNACCOUNTED FOR IN CALCULAT IONS ' . F9 . 3) RETURN

END SUBROUTINE TEST DIMENSION Y(21.151).R(21.151).T(21.151).GA(151),W2(21.151)

1 ,RR(21 .151) ,W3(21 .151) PRINT., 'ENTER NR AND NZ

REAO». NR.NZ

PRINT..' NUMBER OF TIME STEPS' REAO..NTP

NG=NR-1

D=1. PRINT. , 'ENTER NUMBER OF TIMESTEPS FOR OXYGEN BALANCE'

C

C40

25

30

60

101

102

104

90

100

READ.. 108 IOBN=0 C PRINT.. 'ENTER TIME STEP' READ..TS

10 PH=1

B=1 . AN=1 . E=0. D1=220.

D2=1 . CN=1 . GAR=2

.

TP=300

YA=0. DO 20 1=1. NR DO 18 J=1.NZ

GA(J)=2.

T(I ,J)=. 00001 W3fI.J)=. 00001

W2(I ,J)=. 00001 R(I.J)=0

RR(I ,J)=0. IF(J.EO.I) THEN

Y(I ,J)=. 00001 ELSE

Y(I ,J)=0.00001

END IF

20

18

C

C

C

C

40

18 CONTINUE

20 CONTINUE

PRINT.. 'ENTER I .J VALUES FOR ' r(i,,J)=100.

25 READ.. I,

J

30

Y(I ,J)=100. DO 60 K=1 .NTP 60 CALL OXY(NG.D.TS.PH.B,AN E.D2 ,CN, Y.T.R. 1GAR.W2.NR.NZ.GA,,TP.YA,RR .01) 101 I06N-I06N+1 IF(IOBN.EO 106) THEN 102 IOBN=0 CALL OTRAPEO .J T.W3.NR.NZ.TS ,PH, CN.GAR.R.Y, E.TA. B.C .GA.W2.YA) 104 END IF C USE NEXT THREE STATEMENTS ONLY TO RUN Y=100. TEST CASE

C DO 40 1-1 .NR 80

Y(I,1)=100.

Y(I,NZ)=0. CONTINUE

IF(K.LT.NTP) THEN

DO 30 1=1. NR DO 25 J=1.NZ Y(I,J)=W2(I,J)

CONTINUE

END IF CONTINUE

WRITE(6,101) NR.NZ FORMAT('OXYG NR = '.14.' NZ = ',14) WRITE(6.102) TS.NTP.TS.NTP FORMAT('TIMESTEP = '.E9.3.' NUM STEPS=' . 14. ' TIME= '.E9.3) WRITE(6.104)

FORMAT ( 'OXYGEN FOR LAST TIMESTEP')

DO 80 J=1 .NZ WRITE(6.100)J.(Y(I ,J).I=1.NR) CONTINUE

WRITE(6.103)

FORMAT ('OXYGEN FOR PRESENT TIMESTEP')

DO 90 J=1 ,NZ WR]TE(6,100)J. (W2(I ,J). 1=1 .NR) CONTINUE

F0RMAT(I3.11(F9.3))

RETURN

END SUBROUTINE TESTT

TO TEST DIFFUSION PART OF CIG. THEN DO LOOP OVER Z MUST BE RESET NOT TO INCLUDE Z=1 AND Z=NZ SUCH THAT THE TEMPERATURE VALUES REMAIN 100 AND 001C. FAILURE TO DO THIS WILL LEAD TO TEMPERATURE VALUES THAT ARE TOO LOW COMPARED TO THEORY. DIMENSION T(21.151).R(21,151).Y(21.151).W1(21.151),W2(21,151),

1W3(21 ,151).GA(151).RR(21 .151) PRINT. . 'ENTER NR AND NZ

READ*. NR.NZ

PRINT. , 'ENTER NUMBER OF TIME STEPS' READ. .NTP PRINT.. 'ENTER NUMBER OF TIMESTEPS FOR ENERGY BALANCE' READ..IEB

NG=NR-1

I EBN=0

A=1 . PRINT.. 'ENTER TIMESTEP' READ..TS

PH= . 65

D1 = 1 . C=0.

8=0. TA=0. 02=0.

H=2.

E=0. CN=0. YA=232

AN=0. GAR=5

.

ERR=0001

NTEST=1

DO 5 J=1.NZ

GA(J)=0.

DO 18 1=1 ,NR DO 20 J=1 .NZ Y(I.J)=.232

R(I.J)=0-

RR(I,J)=0. W2(I.J)=.232

W1(I .J)=0. IF(J.EQ.1) THEN

SET T AND W3=100. IN NEXT TWO LINES IF RUN T=100 CASE. T(I.J)=. 00001

W3(I .J)=. 00001 ELSE T(I,J)=. 00001

W3(I .J)=. 00001

END IF CONTINUE

CONTINUE

W3(11 .11)=. 00001 PRINT. , 'ENTER I.J VALUES FOR T(I.J)=100.'

READ.. I.J T(I.J)=100.

00 60 K=1 .NTP CALL TEMP(NG,A,B.C.D1 .02 .NR ,NZ .PH.TS. E.T.H.TA.R, Y.RR.W3. ERR) IEBN=IEBN41

IF(IEBN.EO. IEB) THEN

IEBN=0 CALL TRAPE(I , J.T.W3.NR.NZ.TS,PH.A,H,R.Y,E.TA,B.C.D1 ,D2) END IF USE NEXT THREE STATEMENTS ONLY TO RUN T=100 TEST CASE. 00 40 1=1 .NR T(I,1)=100.

T(I ,NZ)=,001 CONTINUE

IF(K.LT.NTP) THEN

DO 30 1 = 1 ,NR DO 25 J»1 ,NZ T(I,J)=W3(! .J) CONTINUE

END IF CONTINUE

WRITE(6.101) NR.NZ

FORMAT (' TESTT - TEMP NR = '

. 14. ' NZ = ', 14) WRITE(6, 102)TS.NTP.NTP.TS

FORMAT( 'TIMESTEP = ' . E9 . 3 .

' NUM STEPS = '.14,' TIME - '.E9.3) WRITE(6.104)

FORMAT(' TEMPERATURE FOR LAST TIMESTEP')

DO 80 J=1 .NZ WRITE(6,100)J.(T(I.J).I=1 .NR) CONTINUE

196
WRITE(6,103)

FORMAT( -TEMPERATURE FOR PRESENT TIMESTEP - ) DO 90 J=1 ,NZ WR1TE(6,100) J,(W3(1.J), 1=1 ,NR) CONTINUE

FORMAT(I3. 11F9.3) RETURN

END

197
':'

- h

use
Appendix 5C

Convective and Radiative Losses from

a Freely Burning Cigarette

If the cigarette burns in the open, then the total radiative energy output at time t is

Xr(t)rti(t)H c = 2tiR r(x,t)dx (5C-1;

where r is given by Eq. (5-28). (This negiects radiation from

the ends which is unimportant except at the beginning

(t = 0)); similarly for convection,

L

Xc(t)m(t)H c = 2ti R c (x,t)dx (5C-2)

c

where <z> c is given by Eq. (5-29). Let us estimate %c - In order

to find the convective cooling flux ^c , the heat transfer

coefficient h is needed. The Nusselt number for the heat

transfer by natural convection from a uniform-temperature,

long horizontal cylinder in air is (Ret. [5-9], p. 275)

Nu = 0.53 Ra° 25 (5C-3)

when the Rayleigh number is in the range 104 -109 (here Ra

== 2.8 x 10"). Hence the heat transfer coefficient for an

infinite cylinder of radius R at uniform temperature T is

h =s 3.43 x 10" 4 T - T

R

W/cm2 °C (5C-4)

with R in cm. [See Muramatsu [5-4], Eq. (8-19)]. It is assumed that the same expression will hold for the cigarette

(even though the temperature is not constant and is distributed over a narrow band, rather than a uniform

temperature over an infinite band).

The simplest way to evaluate the integral in Eq. (5C-2) is to use the mean-value theorem:

nL L

c dx = h AT(x)dx (5C-5)

If the temperature distribution were Gaussian, with standard

deviations, i.e.,

T(x) - Ta = AT(x) = ATP exp-(x-x ) 2 /s2. (5C-6)

then the integral would be

„ L ,.oo AT(x)dx = sVn ATP (5C-7)

The integral can also be expressed in terms of the half-width w (the total width at half the peak value, which is easily

measured).

ATdx = 1.0645 w ATC (5C-8)

If the distribution is asymmetric but still Gaussian on each

side of the peak, with different values for the standard

deviations on each side, then Eq. (5C-8) still holds. The temperature distribution in Figure 5-4 is not symmetric, but it is (roughly) Gaussian on each side. The

halfwidth is w = 0.96 cm; and assume that the actual peak

temperature is 80° lower than measured, as suggested

earlier: Tp = 555°C. Since Ta = 27°C, Eq. (5C-8) would

yield 540 cm-deg for the integral. The Gaussian

approximation cannot be very good, however: a numerical

integration of the area under the curve in Figure 5-4 yields

lATexpdX 763 ± 14 cm-deg (5C-9)

We assume that the real curve is geometrically similar to the one shown, but scaled down, with a reduced peak of Tp

. That is,

AT(x)r Tn T, 635 Ta AT(x) (5C-10)

Then with Tp = 555°C, the integral falls to 663 ± 13 cm

deg. Thus the Gaussian approximation to the integrated flux underestimates the result by 18%. Nevertheless, as will be

seen shortly, the Gaussian approximation is useful. The

199
value 663 cm-deg holds for the cigarette on the substrate;

for the free-burning cigarette, the value will be different. We

will come back to this. Next.we need to find h in Eq. (5C-5). From Eq. (5C-4),

this is h(T), and the appropriate average T is required. If T is defined in the usual way, the result depends on the interval over which T is averaged. One way to avoid this difficulty is to note that if Eq. (5C-6) held, then

[AT(x)] 5/4 = (ATP) 5/4 exp-(x-xo) 2/0.8s2

and therefore

j[AT(x)]

5/4 dx = yfn (ATP) 5/4 sV0\8

(5C-n;

(5C-12)

The Gaussian approximation to the integral has been shown

above to be inaccurate. However, a large part of that error can be removed by expressing sATp

in Eq. (5C-12) in terms

of the actual integral, via Eq. (5C-7). That is,

j[AT(x)]

5/4 dx = (ATP) 1/4 V08 JAT(x)d) (5C-13)

Then the experimental value can be used for the last integral. This method of estimating |^c (x)dx in effect yields

AT= 0.64ATP. With Tp = 555°C, ATP = 528°C and

therefore AT= 338°C, so that Eq. (5C-4) yields8 h = 19.3 x 10" 4 W/cm2 deg.

With the (corrected) value of ]AT(x)dx, the integral (5C-5)

becomes

j<z5c (x)dx = 663(19.3 x 10

"

4

) = 1.28 W/cm,

and therefore

Ec = 27tRUc(x)dx = 2.69 watts

while on the substrate. In the air, the coal is shorter, and

this must be reduced. The reduction is by the factor l£llc , where l£ is the coal length in free air (neglecting any

change in surface temperature). Again, we will soon return

to this. Now

rh Hc

Measurements of cigarette 105, smoldering on a substrate,

made at the CFR, gave v = 0.668 cm/min

and

Therefore

p = 0.16 g/cm3 (±3°/o)9

m = 7tR2 p v = 37.5 ± 1.1 mg/min = 6.25(19) x 10

"

4 g/sec,

Thus Eto,ai = 6.25 x 10" 4 (6010) = 3.75 watts.

*This cigarette has 2nR = 2 1 cm.

9Note that Muramatsu's cigarette has pp - 0.259 g/cm3

This is while smoldering on a flat substrate, however.

Experiments (Section 4) have shown that being on the

substrate slows down the burning rate by about 17%, on

the average. Therefore away from the substrate, we expect

E,°o, = 3.75/0.83 = 4.52 W,

and thus

Xc = 2.69/4.52 = 0.595

Next, Xr is obtained. Using the approximation (5C-7),

f[T

4 (x) - Ta 4 ]dx = Vtt as x

4V3

+ -^ a

2 Ta + 3V2 aTa2 + 4Ta3 (5C-14)

where a = ATP

.

The factor in front of the bracket is just JAT(x)dx, as is evident from Eq. (5C-7). This has already been found to be,

after adjustment, 663 cm-deg. Also, Ta = 27°C = 300 K

and a = 528°C. Then

E r = 2rcR £c <rj[T(x)4 -Ta 4 ]dx = 3.32 W,

and therefore %r = 0.734. Adding the value of Xc to it, the

result is

Xr + Xc - 1329

Clearly, this sum cannot be greater than 1 . Before

attempting to rationalize this result, let us determine %s — i.e., the fraction of heat left in the solid:

Es = JCP p AT dV

From Figure 5-2, we estimate that

JAT dV = 171.5 cm3 deg.

About % of the volume involved at any moment is in ash,

Pa - 0.13 pp , and Vb in char, pc = 0.34 pp

. Then with Cp = 1 J/gm°C and pp = 0.16, we find

Es = (171.5)(1)[%(0.13) + V3 (0.34)]0.16 = 5.5 Joules.

Finally, Es = Es /x,

where t is the time required to burn the entire cigarette. At the velocity v = 0.668 cm/min., and with a cigarette length L = 7 cm, t = 10.5 min = 630 sec. on the substrate, or 630 (0.83) = 523 sec. in free space.

Thus Es = 0.0105 W

0.0105

Xs —

4.52 = 0.0023

200
Thus we require %r + Xc = 0.9977, negligibly different from away from the substrate, the decline in length would have to

1.00. It was found above that assuming Tp = 555°C, the be still greater. The source of this discrepancy is not clear. sum is 1.33, which is outside the bounds of experimental However, this reduced length yields (in open air) error. It was seen in Section 4 that the length of the coal is smaller in the open then on the substrate. Suppose the Ec° = 2.02 W and E r° = 2.49 W,

overestimates of energy loss are attributable entirely to this

factor. Then the width of the (longitudinal) distribution must or decrease from 663 cm-deg to (663)(0.9977/1.329) = 497

cm-deg in order to get the correct energy loss rates. This Xc = 0.447 and Xr = 0.551

25% decline in length is rather larger than any of the experimentally measured declines [see Figure (4-1 1b)]. Thus, the energy leaves the cigarette by convection and

Moreover, since the surface temperatures will be higher radiation in comparable amounts.

201

Appendix 5D

Derivation of the Transverse

Conductive Flux Distribution

Consider the transverse flux distributions; first, that for the conductive flux. This will be found in a simple analytic

approximation. The simplest approximation is to treat the

cigarette as if it were an infinitely long cylinder at uniform

temperature. This further suggests treating it as a "buried cable" (buried in air, which is assumed to be entirely

quiescent - i.e., all boundary layer - between the

cigarette and the substrate). Since the rest of the air is not

static, this treatment can only be a crude approximation, of course. 10 The situation is as shown in Figure 5-19. The

"cable" is of radius r . Its center is the distance N from the

surface, which is at the uniform temperature Ts . The cable can be replaced by an equivalent line source, a distance a < N from the surface. In the steady state, the surface

temperature of the cable can also be specified to be T . The line-source approximation for the transient case is done

in Carslaw and Jaeger [5-6], p. 261 . For the line source, they take the heat liberated to be at the (possibly variable)

rate

T(r,t) = Ta +

Q'

4rck E,-1 frO - E, Gffl

4at

-1 HJ (5D-4)

rj is the distance to the sink (the image line). In the limit

t -» oo, Eq. (5D-4) yields the steady-state solution,

T(D - T. + ^In y

2 + (a + z) 2

y

2 + (a-z)2 (5D-5)

where z is the (normal) distance from the point to the plane, y the orthogonal distance, as shown in Figure 5-19. The

isotherms are cylinders, and the "cable" surface is one of them.

The transient heat flux towards the surface is easily found

from Eq. (5D-4); it is

flx.z.t) = k |I

pC#) = Q' (5D-1)

per unit length. This source is in a static material at an

initially uniform temperature Ta ; the heat is turned on at t = 0.

If (Z>(t) = const = q, then the temperature in the surrounding

material at any point P a distance r from the source is given

by

r

T(r,t) = Ta +

4rtx Ei v

rz 4at (5D-2)

at time t, where a is the thermal diffusivity and E1 is the first exponential integral. From Eq. (5D-1),

a

" k (5D-3)

By using the image method, we find that for the case where we have the source in a semi-infinite space, with the surface

kept at Ta ,

10/4n alternative analysis was also carried out, but was no better.

Figure 5-19. Cross Section of Buried

Cable, with Various Distances and

Temperatures Indicated. The Distance n-r Between the "Cable" Surface and the Shaded Substrate

Above is Grossly Exaggerated for the Purpose of

Clarity.

V///////////////T

. T

N

203
2k

(a + z) expf- r, 2/4«t) + (a

, exp(-r2/4gt) (5D-6)

Note that with this line-source approximation, the cigarette

surface is an imaginary surface around the source, and

therefore the initial cigarette temperature, in this approximation, is Ta ; it only rises because of conductive

heating by the line source.

The steady-state flux towards the surface can be obtained

either by taking the t -» oo limit of Eq. (5D-6), or by

differentiating Eq. (5D-5) with respect to z. Then the flux at the boundary - i.e., the surface z = — is

q"(y.O) =

Q'n a

2 + y: = q"(0,0) a2 + y2 (5D-7)

Since this is a steady-state result, it is important that we

know how close to the steady state the system really is. One

can easily estimate how long it would take to achieve steady

state, if the air were everywhere static: it is (roughly) the time it will take to heat up the air space between the source and the boundary to the mean temperature between them

(about 280°C). The volume of air between the cigarette and

the substrate is (2 - 7t/2)rQ

2 per unit length. Taking

reasonable values for the cigarette energy output, air density, and specific heat, this time is about 5 milliseconds. When the cigarette is first dropped on the substrate, the

principal heat flux from it to the substrate is radiative only,

and therefore the mean heating flux is about 2 W/cm2

. Therefore, for a typical substrate, the surface temperature

will only rise by 15-20°C in the 5 ms calculated above. In that time, the air has just about reached its steady value for that substrate temperature. Since the substrate response is relatively slow, the steady-state solution for the "buried cable" can be used to obtain a fair approximation to the initial conduction flux. Indeed, the dependence given by Eq. (5D7) agrees (semi-quantitatively) with measurements

(Section 4). Thus, the form of the desired transverse dependence has

been found. One can either use the knowledge of the initial conduction flux along CL to get the initial solution everywhere (via Eq. (5D-7)), or the fact that the cigarette

surface temperature is known, using Eq. (5D-5). In either case, the parameter a is needed in order to get an explicit answer; in order to find it, the transcendental equation

Co = 1 +

8k(Tc -Ta) VC,

q"(0,0) r fri Co

emissivity of ec = 0.73, a surface temperature of 550°C

radiates at the (net) rate of 1 .87 W/cm2

, so that the conduction flux to the surface must be 3.73 W/cm2

. With

this flux, if r = 0.4 cm, we find (from Eq. (5D-9)) that a =

0.23 cm, and an effective minimum distance 5 = 0.6 mm

between the cigarette and the substrate along CL, is inferred. With this value of a, the instantaneous (but calculated as if this were a steady state!) conduction flux at the distance y = r Q would be about 24% of the value at the

centerline (y = 0). If 8 is given, then so are a and Cc ; hence

Eq. (5D-9) relates Tc and the peak conduction flux, q"(0,0).

A more accurate analysis is necessary in order to obtain more realistic results.

In the remainder of this appendix, the total rate of conduction to the substrate is estimated. First, assume the

results of the above analysis: assuming that Eq. (5D-7) gives

the transverse dependence for all x, the total conductive

energy flow Ecd is

: Cd - q"(x,y)dxdy

= I dx q"(x,0) dy^I = an q"(x,0)dx

It was found that for the total flux, J^,(x)dx = 6.07 ± 1 .0 W/cm; hence for the conduction flux,

q"(x,0)dx =—(6.07 ± 1) = 4.05 +73 W/cm;

5.6 -- 60

With a = 0.226, therefore,

Ecd = a;t(4.05 ± . . .) = 2.87 + ^ watts.

(However, see Eq. (5D-13)). This can be approached

another way: Experimental measurements have shown that the flux from a cigarette can be fitted with a distribution of the form (5-5). This agrees with Eq. (5D-7), to lowest order

in y

2

. The total energy output from this distribution is

(5D-8)

(x,y)dxdy = noxoy 0„ (5D-11)

must be solved for CQ ; then

„ = 4k(Tc -Ta ) q"(0,0) CnC

(5D-9)

An explicit estimate for a can now be made. The cigarette

surface temperature is depressed by the presence of the cold substrate (or cold gauge); suppose that the peak

temperature drops to about 550°C; at that point, the measured (peak) flux is about 5.6 W/cm2

. With a measured

The average central peak has been measured to be

about 5.6 W/cm2

, of which about 1.9 W/cm2

is radiation; therefore <t> m - 3.7 W/cm2

. Moreover, ox - 0.61 to 0.7 cm,

CTy = 0.32 to 0.36 cm. A Gaussian distribution would then

yield

x,0)dx = ^(0,0) VTt(CTx) = 5.6 Vtt ctx

204
Then crx = 0.62 ± 0.1 cm yields 6.15 + 1.0 W/cm for the

integral. This agrees very well with the measured 6.07

W/cm, and suggests that Eq. (5D-11) will also give an

accurate result; with oy = 0.36 cm, it yields

EC d(0) = 2.58 watts,

in close agreement with the earlier estimate. This, then,

purports to be the total initial convective flow to the substrate from the cigarette.

There are two effects which must modify these calculations

of Ec (0): First, a convective flow is set up around the

cigarette, as shown by the streamlines in Figure 5-20

(labelled by arrowheads). The shaded region under the

cigarette is (relatively) quiescent and is principally involved

in conduction; conduction through the convective region is much smaller. Hence Eq. (5D-7) is to be integrated only for the region -£,<y<£,. That is, the absorbed convective

energy is

The second effect relates to radiation, and works in the opposite direction: the radiative component falls as T

4

, whereas the conductive component falls linearly with T. Thus the ratio of r to C is highest at the peak: 1.87/3.73 =

0.5, and falls outside the peak. It is not difficult to show that the ratio of the standard deviations of the two distributions (assuming each is Gaussian) is about 1.48. It follows that j^rdx = 1.52 and j^c dx = 4.55, so that the mean ratio is 0.33, rather than 0.5. Thus, while the total distribution has ax = 0.61 cm, the radiative and conductive distributions separately have ar = 0.45 and oQ - 0.67 cm. Thus the expression (5D-13) must be increased by the factor 0.67/0.61 =1.1, and the integral in this equation must be

increased from 4.05 to 4.45; then Eq. (5D-13) yields

Ecd(0) = 8.90 a tan' 1 J2. a

For £, = r Q = 0.4 cm, Ec (0) = 2.13 w. This corresponds to oy = 0.30 cm, rather than 0.36 cm. Thus the overall effect

is to reduce the conductive loss.

Ecd = 2 L q"(y)dy =

^

2aLQ' 2La q"(0,0) tan 1 A (5D-12)

(where Eq. (5D-7) was used in the form Q' = 7taq"(0,0)).

h More properly, integrating along the CL,

EC d(0) = 2a tan ii q"(x,0)dx (5D-13)

This is the generalization of Eq. (5D-10); for E, < <x, therefore, the convective loss rate will be smaller than what was calculated above, from this effect alone.

At later times, the conductive flux falls: If the mean surface

temperature of the substrate at time t is Ts (t), then at later times

Ecd(t) - Ecd (0) Tc - T5 (t) Tc Ta (5D-14)

where Tc is the mean cigarette surface temperature.

Assuming the substrate temperature profile resembles that

of the fluxes, it is easy to see (since the conduction loss is linear in T) that we only need the peaks of the temperatures

to find the total conduction flux. Hence Eq. (5D-14) may be

replaced by

E'cd(t) = EC d(0) Tc JM

Tp - Ta (5D-14)

where Tpis the peak cigarette surface temperature. This

concludes the discussion of convective heat transfer to the

substrate.

Figure 5-20. Cross Section of Cigarette

On Substrate. Heat Conduction from the Cigarette

Occurs Mainly Within the Shaded Region. The Curves

with Arrows Indicate the Air Streamlines.

y//////^\//////

S

205

The Effect of

Cigarette

Characteristics

on the Ignition of

Soft Furnishings

Section 6

Evaluation of

Test Methods for

Cigarette Ignition

Propensity

207

Contents for Section 6 List of Tables and Figures

Introduction 207

Methods Suggested in the Literature 21 1 Weight Loss of Polyurethane Foam 215

Procedure 215

Comparison of Weight Loss Results and

Number of Ignitions 215

Cigarettes Burning on an Alpha-Cellulose

Substrate 219

Cigarettes Smoldering on a Glass Plate 221

Methods 221

Results 221

Tentative Test Method Using Fabrics

and Padding Materials 223

General Considerations 223

Outline of Suggested Tentative Test Method 223

Summary 225

References for Section 6 227

Table 6-1 .

Figure 6-1.

Weight Loss of Polyurethane

Blocks Caused by Smoldering

Cigarettes, Five Blocks with 5 Cigarettes Each 217

Relationship of Polyurethane/

Cigarette System Weight Loss and Number of Ignitions

Obtained in Primary Evaluation 216

209

I ntroduction

A key task commissioned by the Technical Study Group was

the development of a suitable measurement for cigarette

ignition propensity. Such a test method would serve as a

tool in research and development, for quality control in manufacturing, and as a test for regulatory efforts. The initial approach to this task was to evaluate test methods

suggested in the literature. Since no fully satisfactory method was found, a few new concepts were investigated. This work

could not be completed in the time period allowed, but

insight into the problems and chances of success of various

candidate test concepts was gained. Consequently, this section is a progress report, documenting the development

efforts as an aid to future research. Various candidate

methods are evaluated in Sections 6.1 to 6.4; the most

promising concept is described in more detail under 6.5. This work could not be started until cigarettes with varying

degrees of ignition propensity, including very low levels, had

been identified. Section 3 shows that the relatively low igni- tion propensity of such cigarettes found in the primary evaluation (consisting of testing cigarettes on three substrates and

noting the total number of ignitions) was validated by extensive further evaluations. These additional evaluations were conducted on numerous substrates, ranging in cigarette igni- tion resistance from intermediate to very low. This range was

due to variations in fabric/padding (and in some cases, welt- cord) variations and configurations, as well as fabric contamination; it included substrates with near worst case

cigarette ignition resistance. It thus seems reasonable to assume that the observed differences in cigarette ignition

propensity during screening on these substrates would

prevail in most real life scenarios in which a cigarette falls on

soft furnishings, and that the primary evaluation ignition results provided a credible basis for test development. The

scope of this project did not include the extension of this work to wildland substrates, such as forest or grassland

covers. With the present state of the art, evaluation of the ignition

propensity of a given cigarette would have to be carried out on a variety of substrates with graduated cigarette ignition

resistance, including very low values, to assure testing under

near worst case conditions. (This is essentially the methodology of the above mentioned "primary evaluation" and vali- dation.) The substrates should consist of commercial fabrics

and cotton batting or polyurethane foam padding, in a

variety of configurations. The problem with this approach

has been the limited degree of reproducibility of commercial

materials; strict quality control at every production step may

overcome this deficiency A general outline suggesting means to minimize this problem is given in Section 6.5. Such

a test procedure would resemble the approval testing of new

drugs and cosmetics, where no standard protocols in the

strict sense exist but general guidelines have to be followed. Before much experimental work with the ignition propensity of cigarettes had been performed, it was assumed that a

cigarette with a low burn rate in air would have low ignition

propensity [6-1]. Well-developed methods for measuring burn

rate of cigarettes in air exist [e.g., 6-2]; however, as discussed in Section 3, these burn rates do not appear

predictive of ignition propensity. In fact, a good overall correlation between mass burning rate measured in air by one of the cigarette company laboratories and ignition propensity was found for the first series of experimental cigarettes (no

data were furnished for the second series). However, at the low ignition propensity range, the range of interest, the mass

burn rate in air did not predict ignition propensity accurately.

Also, the correlation was improved when calculated separately for the Burley and flue cured cigarettes. It would

have to be established whether the relation ship between mass burning rate and ignition propensity is tobacco type

dependent; the ignition propensity results did not show such

a dependency in the present experiments. Temperatures of cigarettes burning in air have been measured in our and

other laboratories (Section 4) [e.g., 6-3,4]. They require rather sophisticated equipment, and their ability to predict ignition

propensity is questionable.

The reason that these and other measurements of cigarette properties in air do not seem to be sufficiently predictive of their ignition propensity on substrates may be the

strong interaction between cigarette and substrate [6-5.6]. More specifically, there are changes in cigarette burn rate and heat output which depend on the nature of the

substrate in contact with the cigarette. The effects of the

substrate on temperature/time relationships inside a cigarette were discussed in detail in [6-5] and are briefly reviewed

here. The temperature measured in the center of a cigarette was highest and the time/temperature peak sharpest when

the cigarette burned in air. The peak was lower and broader

when the cigarette was placed on a substrate on which

211
smoldering occurred in the area near the cigarette but did report, with the emphasis on the time period prior to self- not spread (no self-sustaining smoldering ignition). The sustaining ignition of the fabric. temperature was initially still lower, and for a longer period of It thus appears that, because of this potential for signifi- time, on a substrate which ignited, i.e., the smolder spread cant interaction between the burning cigarette and the continuously from the cigarette area. After full involvement of substrate, any method for the measurement of cigarette igni- the fabric and polyurethane foam, the temperature in the tion propensity should be based on its smoldering behavior

cigarette rose. Similar effects of substrates on cigarette on one or several "standard" substrates,

temperature and burn rate are discussed in Section 4 of this

212
lethods Suggested in the

Literature

Several methods for measuring cigarette ignition propensity were discussed in a recent paper by Norman [6-7]. Differ- ences in ignition propensity had been defined for four experimental cigarettes varying in packing density and

circumference by testing them on almost 200 substrates (33

fabrics, 2 paddings, 3 configurations). About a dozen

methods to measure the heat output of these cigarettes were

considered, and four were explored in greater depth. Two of these selected methods tested the cigarettes in air and two on substrates. The author concluded that the heat output of the experimental cigarettes varied widely when the cigarette

burned in air, but that the nature of the substrate became

dominant when they were burned on substrates. For the

record, the methods explored in some depth by Norman

were:

a. The measurement of the surface heat flux/time relation- ships from cigarettes smoldering in air by means of a

heat collector. The resulting plots were analyzed in terms of maximum heat flux, time above certain heat

flux values, etc.

b The measurement of the total heat release from

cigarettes suspended in air near a water bath covered

with aluminum foil. The rise in water temperature was

recorded.

c. The determination of the weight loss rate of various

cigarette/substrate systems which smoldered. Since this was found to be mostly substrate dependent, Norman

did not consider it promising. Similar conclusions were drawn in our earlier work [6-8].

d. Measurement of the volume of the smolder imprints

and the time of burning of smoldering cigarettes on

polyurethane blocks. (Without the fabric cover, the polyurethane does not smolder but melts and partially

chars when a cigarette is placed on it.) This method

seemed promising, and was further pursued in our

laboratories, as described below.

213

Weight Loss of

Polyurethane Foam

Following the above lead, the weight loss of polyurethane

foam exposed to cigarettes varying in ignition propensity was investigated. Most polyurethane foams do not continue

smoldering after the cigarettes burn out, but leave a visible imprint. Norman suggested the measurement of the volume

of such imprints by filling the imprints with small beads of known packing density and weighing the beads as a measure of the cigarette ignition propensity. We found it more convenient to measure the weight loss per unit length

of cigarette. However, we found later that this method lacks

in precision. Perhaps the volume measurements would have

been more precise, because part of the polyurethane foam

does not pyrolize but melts and shrinks back from the cigarette, creating a cavity. It is possible that the cavity sizes

correlate better with cigarette ignition propensity than the

weight loss which only depends on the amount of pyrolized

material. However, in a recent communication to the TSG it was pointed out that polyurethane foams on the market vary widely in cigarette ignition resistance, and that it may be

difficult to obtain a standard foam for the purposes of this test [6-9], This is discussed in greater detail below.

Procedure

Polyurethane foam (HD 2045, 51 mm (2 in.) thick) was cut

into 127 x 203 mm (5x8 in.) blocks. The blocks were

dried at 100°C for 3 hours and placed in a desiccator over

silica gel until ambient temperature was reached (30-60

mm.). The blocks were removed from the desiccator and

immediately weighed on a balance with 0.01 g resolution. The blocks were placed on recording balances to obtain

weight loss curves. Five conditioned cigarettes were sampled from each of the 41 experimental cigarettes, the patented cigarettes and their controls, and the three commercial controls. These were weighed, then lighted and

placed on the block such that the cigarette paper seam was

not in contact with the foam. After all cigarettes were on the block the weight loss recording program was started. If a

cigarette self-extinguished it was removed from the block,

lighted again and placed back on the block in the same

spot that it had previously occupied. If any, or all, of the five

replicate cigarettes repeatedly self-extinguished, it was noted

and the partial weight loss value was recorded. After all of the cigarettes on a block had burned to completion, the program was stopped and the weight-loss curve was printed

out. The residue from the burned cigarettes was discarded

and the blocks were again dried and weighed as previously

described. The weight loss of the foam blocks was

recorded.

Comparison of Weight Loss Results

and Number of Ignitions

Figure 6-1 shows a comparison of the weight loss values

and the corresponding number of ignitions on the substrates obtained in the primary evaluation discussed in Section 3. While a weak correlation exists (correlation coefficient =

0.69), this did not appear an acceptable predictive test for cigarette ignition propensity, at least with the limited sampling used in this comparison. This holds particularly in the range of interest, the low ignition propensity range. The above results were obtained by use of only one foam

block with five cigarettes on it. Table 6-1 shows the results obtained with selected cigarettes when five foam block repli- cates, each with five cigarettes smoldering, were exposed.

Statistical analysis of the results indicates that even with 50

replicates, the correlation coefficient would only be 0.76

[6-10]. Obviously, this evaluation method in its present form

shows little promise. However, Norman's original suggestion,

to measure the volume of the cigarette imprints, should be

tried. Several possible reasons for this lack of precision come to mind. One was that we were operating at the limits of the balance; furthermore, the polyurethane foam lost some

weight during the heating (for conditioning purposes, as described above) after exposure of the cigarettes. This

heating would be unnecessary if the foam imprint volume

rather than the weight loss were measured. Variability of the foam chemistry or cell configuration was also suspected as a reason for the lack of precision of the results-assuming,

of course, that the experimental cigarettes are consistent in their effect on the foam substrate.

It is well known that different production lots of polyurethane foam vary in their response to burning cigarettes.

215
Figure 6-1. Relationship of Polyurethane/Cigarette System Weight Loss and

Number of Ignitions Obtained in Primary Evaluation

E

E

0.35

CVJ 00 0.30

O)

o

0.25

10

O) 0.20

CO

CO

o

_J

0.15

X

O

HI

5

0.10

0.05

I I I I

_ • mm •

• • • •3

• • • • • • 02

_ • • _ • • 2o • • 2 •

• • • • • • 3o • • o2 • • - •2 • • • •

•

• • • •

I

.

10 15

NUMBER OF IGNITIONS

20 25

NOTE: Numbers adjacent to a symbol refer to .multiple points at that location

The CPSC has repeatedly returned shipments of the "Stan- dard UFAC" foam because they did not behave like earlier shipments when tested with certain fabrics [6-11]. UFAC

suspected that vertical position in a foam bun (production

unit of extruded foam roughly 1 m thick) may be a cause for such variable results. However, ignition/non-ignition tests at the UFAC laboratories did not show this difference [6-12]. Close control of foam chemistry and cell configuration in foams over small distances or even among production lots has probably never arisen as a practical problem. Thus an improvement may not be of interest to the foam industry,

and it may be difficult to find a foam producer who would

be prepared to make a more reproducible foam.

It may be possible to characterize the foam by using an

electric heating element resembling cigarettes. Such heaters have been tried in connection with attempts to develop a

"standard cigarette," with inconclusive results [6-13]. In practice, one could test a set of cigarettes on one side of the foam block, and later apply the heat source to the other. The results could then be expressed as the ratio of the weight loss due to the smoldering cigarettes to the weight

loss due to the standard heating source. Alternatively, one

could use a commercial cigarette as the standard,

assuming, of course, that they are closely controlled in heat

output. Time did not permit exploring these approaches.

216
Table 6-1. Weight Loss of Polyurethane Blocks Caused by Smoldering Cigarettes

Five Blocks with 5 Cigarettes Each

Cigarette Circumference N

Total umber

Foam Weight Loss

Average Range Std. Std. Error Number

106

(mm) ig

1

mtionsd (9) (g) (Dev.

0.03

(0/0)

21 0.08 0.04-0.12 35

107 21 11 0.10 0.08-0.12 0.01 10

112 21 20 0.16 0.13-0.20 0.03 19

130 25 4 0.09 0.05-0.12 0.03 31 122 25 7 0.09 0.06-0.10 0.02 22

127 25 20 0.22 0.19-0.26 0.03 14

201 21 0.05 0.03-0.07 0.01 20

(a) In primary evaluation

217

Cigarettes Burning on an

Alpha-Cellulose Substrate

In earlier work, ignition propensity rankings were obtained

for six commercial cigarette packings by testing them on a

variety of substrates [6-14]. Similar rankings were obtained in tests in which the weight loss rate of cigarettes smoldering on alpha-cellulose paper (used in chromatographic analyses)

of the cigarettes was determined. This paper smoldered

along with the cigarettes but did not sustain the smolder

after the cigarettes burned out. However, when this test was

applied to the low ignition propensity cigarettes from the present series, the alpha-cellulose did not smolder and no

weight loss occurred. Consequently, no cigarette ranking at the lower end of the ignition propensity scale was possible

However, treatment of the paper with alkali metal ions may

decrease its cigarette ignition resistance, allowing its use as

a standard material for measuring ignition propensity in the low range. This possibility could not be explored under the present program.

219

Cigarettes Smoldering

on a Glass Plate

An inert substrate, such as a glass plate, would have the advantage of retaining its response to heat emanating from

the cigarette in repeated tests. This could overcome the

reproducibility problems of fabric/padding substrates. On the

other hand, the thermal characteristics of the glass plate are

very different from those of fabric substrates, and may not produce the same effect on the cigarette with respect to heat sink action and oxygen blocking. Our work with glass

plates indicated early on that differentiation between

commercial and low ignition propensity cigarettes was

possible, but for differentiation between intermediate and low

ignition propensity cigarettes, the system would have to be

heated.

Methods

A piece of plate glass 1.6 x 152 x 152 mm (Vie x 6 x 6

in.) weighing 137 g and a brass block 25 x 152 x 152 mm

(1x6x6 in.) weighing 5.4 kg were placed on a Thermolyne Type 1900 hot plate with the brass plate directly on the

hot plate surface and the glass plate resting on the brass

surface. A type K thermocouple was placed at the center of

i the top of the glass plate and held in place with a 100 g

i weight. The perimeter of the glass plate was surrounded by

: a 25 mm (1 in.) thick fiberglass insulation with the glass surface 51 mm (2 in.) below the top of the fiberglass frame. The thermocouple was connected to a Doric Trendicator

415A meter. The hot plate was placed in series with a Powerstat Variable Autotransformer. The temperature control on the

1 hot plate was set to maximum and the temperature was

regulated with the Autotransformer. This system controlled

| the measured temperature within a range of 5°C. The low ignition propensity cigarettes BELN-21, No. 106,

! FELN-21, No. 114, and 201, the intermediate ignition propensity cigarette FELN-25, No. 129, and the commercial cigarette No. 6 were selected to provide a wide range of ignition

propensities. The cigarettes were lit and allowed to burn in air for one minute. The entire group of cigarettes was then

placed on the glass surface. The temperature was increased

slowly and observations for each group of cigarettes at the

increasing temperatures were reported with respect to which

cigarettes continued to smolder on the heated surface.

In a few experiments, the glass plate was replaced with a piece of heavy duty aluminum foil. At ambient temperature

the high ignition propensity cigarette failed to burn to completion. Because of a limited time for experiments, it was

decided not to pursue the experiments on aluminum foil at increased temperatures, because the thermal responsivity of aluminum is even more different from that of fabric than that

of glass.

Results

At ambient conditions, the commercial cigarette smoldered

along its entire length and the others self-extinguished. The

temperature of the glass plate was then raised as described

above. Not until the temperature reached 86.5°C did any of the cigarettes except the commercial No. 6 smolder to completion. Between a temperature of 86 and 97°C, repli- cates of the other cigarettes smoldered in a random fashion,

i.e., some smoldered to completion, others partially. No

difference between the low and moderate cigarettes was

evident. One could hope that very tight temperature control of the experimental environment could lead to better differentiation between cigarettes. A closely controlled oven comes to mind. All the cigarettes exposed at one time on the glass

plate should be the same kind, to avoid simultaneous

exposure of cigarettes with different response to heat. Rather

than relying on visual inspection of smoldering, cigarette

weight loss could then be determined. This would permit one to account for cigarettes which smoldered only partially. Finally, sintered glass plates should be considered since

their thermal responsivity would be closer to that of fabrics than that of ordinary glass. However, reproducibility of sintered glass surfaces and feasibility of removal of condensation products would have to be established.

221

Tentative Test Method Using

Fabrics and Padding Materials

General Considerations

In previous work, a series of substrates varying in cigarette

ignition resistance was obtained, often by trial and error

[e.g., 6-14,15,16] and cigarette ignition or non-ignition

observed. The ignition propensity of various cigarettes could

then be determined by the number of substrates ignited.

This worked reasonably well for any set of fabric/padding

combination; but as soon as a new roll of supposedly identical fabric or lot of padding material was used, reproducibility problems often arose [e.g., 6-8,17]. One could expect

problems even within a lot or shipment of these materials,

because they are generally poorly controlled. Even different shipments of the UFAC and California Bureau of Home

Furnishings standard fabrics and UFAC standard foam have

been found to vary in ignition propensity [6-11,17]. This

section explores means to minimize the effects of such variability in substrate characteristics. Among the reasons for the lack of reproducibility of substrate materials is the fact that upholstery fabrics are produced primarily with control of appearance in mind. The

best controlled property may be dye shade and not even

that is always the same, as one can sometimes observe by

comparing chairs and sofas sold in sets. We also have found

backcoating thickness to occasionally vary over a short length of fabrics. In one case, we found differences in fiber content (100 percent cotton vs. polyester/cotton yarns) in supposedly identical fabrics. Similarly, yarn size and twist, number of yarns per unit area, crimp, pile height, etc, can

vary, and the effect of these and other construction variables on cigarette ignition resistance has never been systematically

investigated. However, while one can expect poor quality control of furniture cover fabrics, certain industrial fabrics,

such as cotton ducks, are produced to fairly close construction specifications. One such fabric was used in the study of fabric contamination discussed above; it only smoldered

when contaminated with alkali metal ions. To prepare substrates for cigarette ignition propensity

testing one would have to control the smolder promoter

(e.g., alkali metal ions) or inhibitor content of fabrics. Controlling such concentrations in fabric manufacture may go a

long way towards obtaining reproducible standard fabrics as

well as reducing cigarette initiated fires. One could choose

industrial fabrics produced in large volumes to certain specifications such as cotton ducks, very thoroughly desize

and scour them, and then treat them with varying concentrations of alkali metal ions to obtain fabrics with systematically

varying cigarette ignition resistance. However, very accurate

control of the concentration of any finishing agent is difficult even in closely controlled laboratory experiments. Full exploration of the effect of normally occurring process variations

affecting alkali metal concentrations on cigarette ignition

resistance of fabrics could not be carried out under the present program.

Ihrig et al. [6-15] identified fabric density and weight per

unit area as parameters which affect cigarette ignition resis- tance. They also developed a method of defining another

such parameter, the "smoldering proclivity" by observing the smoldering characteristics of yarns taken from the fabrics. Smoldering was initiated by means of an electric heater, at the bottom end of vertical yarns taken from the fabric, and

the progress of the smolder observed. This correlated well with the sodium and potassium ion content of the fabrics. These methods could be used to check the quality control

of fabrics used for cigarette testing.

The choice of a "standard" padding material could

proceed along similar lines. Cotton batting is innately very

variable, and polyurethane foam chemistry and cell distribu- tion are not adequately controlled, as shown in the above

described weight loss experiments which were conducted

without fabric. It may be possible to use multiple layers of one well defined fabric as the substrate, obviating the need

for a separate padding.

Outline of Suggested Tentative

Test Method

To be able to measure the ignition propensity of cigarettes

by testing over a period of time, the following is suggested:

a. Acquisition of several hundred yards of a very well desized and scoured industrial, 100 percent cotton duck fabric or similar fabric and a single, optimally

controlled batch of polyurethane foam. In mockup

form, this fabric/foam combination should not ignite

223
with commercial cigarettes. (If pilot experiments show

that multiple layers of one fabric can be used as stan- dard substrates, the foam would not be needed.)

b. Treatment of the fabric with various concentrations of compounds containing alkali metal ions or other smolder promoters. At the lowest level, it should ignite with the commercial cigarettes. At the highest level, it should ignite with the lowest ignition propensity

experimental cigarettes available. Intermediate levels should ignite with the commercial cigarettes but not the

lowest ignition propensity cigarettes. If cigarettes with even lower cigarette ignition propensity are developed, even higher smolder-promoter concentrations would

have to be applied. (It remains, however, to be deter- mined that cigarette ignition resistance decreases

infinitely with increasing alkali metal concentrations. It may be necessary to change the base fabric to one

with lower cigarette ignition resistance or use multiple

layers of one fabric to vary substrate ignition

resistance.)

c. The fabric pieces should be sampled at frequent

intervals along their length. The sample specimens

should be characterized by the standard textile measurements of their weight, density, yarn size and twist, number of yarns per unit length, and air permeability, as well as by determination of the smolder-promoter

concentration and by the above mentioned yarn smoldering test [6-15]. Similarly, thermogravimetric analysis

and perhaps other characterization tests of foam

specimens should be conducted. If large variations of these properties are encountered, fabric areas and

polyurethane foam sheets ought to be arranged into groups of similar properties, and only the largest of those should be used for cigarette evaluations. Similar procedures are used in cigarette testing, where the weight distribution of a large sample is determined and

only cigarettes in the median weight group are tested

[6-18], Cigarette comparisons should then be carried out on fabric and foam specimens of similar ignition resistance.

d. As an alternative to the alkali metal treatments, one

could obtain yardage of fabrics with innately varying

cigarette ignition resistance, and use them in the manner described in a. The production of such fabrics should be strictly quality controlled at each step, to assure piece-to-piece reproducibility.

e. Measurement of relative char damage by cigarettes

varying in ignition propensity on substrates which

smolder along with the cigarettes but do not sustain smoldering when the cigarettes burn out may supplement the above ignition/non-ignition evaluations. Weight

loss measurements along these lines have shown poor

reproducibility in previous work [6-8], but this may not be the case if the substrates (and cigarettes) were more closely controlled.

f. The sensitivity of ignition propensity measurements to fabric smolder promoter concentration and variations in foam thermogravimetric results should be investigated.

Similarly, the effect of ageing on these properties

should be established.

The smoldering propensity of experimental cigarettes could

then be investigated on such substrates. During such tests, relative humidity and temperature in the test room, and air velocity and direction with respect to the smoldering front movement of the cigarette in the immediate area of the test should be closely controlled. As more experience is obtained with this method, pass-fail criteria could be established. These could then be checked against the results obtained on laboratory mockups of low cigarette ignition

resistance fabric/padding combinations, as well as on

discarded, soiled furniture. In many cases, both flat surface

and crevice tests should be undertaken. (Work described in Section 3 shows that for the low ignition propensity,

experimental cigarettes, crevices may be equally cigarette

ignition resistant as flat cushions, while for commercial

cigarettes, crevices always had lower cigarette ignition resis- tance [6-19].) Consequently, tests for measurement of the

ignition propensity should be conducted in both configurations.

224
Nummary

A number of candidate test methods for the propensity of cigarettes to ignite upholstered furniture have been evaluated. It appears that such a test method would have to consist of a cigarette on a substrate rather than with the

cigarette in air, because of the substrate-cigarette interaction (heat sink effect and blocking of oxygen).

Two types of substrates were considered: (1) upholstered

type combinations of fabric and padding, and (2) more

permanent, re-usable substrates such as glass plates. Upholstery materials present a problem in their lack of reproducibility. Procedures to minimize this are discussed; they involve close cooperation with the material producers.

A number of test methods which would not have to rely on use of fabrics and padding have been investigated, albeit not in depth because of the short period available for this work. None of these could be recommended without further evaluation. These include measurement of the weight loss or imprint volume of polyurethane foam blocks on which smoldering cigarettes have been placed; determination of full length burning or self-extinguishment of cigarettes placed on

a glass or pyrex plate held at various temperatures; and

perhaps some of the measurements discussed in Section 4. This work has not produced a test method. It may have

narrowed the field from a large number of potential candidates, and pointed towards the next steps to be taken in further development of the more promising approaches.

225

References for Section 6

[6-1] Spears, A.W., Technical Analysis of the Problems

Relating to Upholstered Furniture and Mattress Fires Relative to Proposed Cigarette Legislation Including a Review of Relevant Patents, Testimony, Subcommittee

on Health and the Environment, Committee on Energy

and Commerce, U.S. House of Representatives

(March 21, 1983).

[6-2] Resnik, F.E., Factors Effecting Static Burning Rate, Presented at the Coresta Symposium, Montreux, Swit- zerland (September 1974).

[6-3] Egerton, A., Gugan, K., and Weinberg, F.J., The

Mechanism of Smoldering in Cigarettes, Combustion

and Flame 7, 63-78, (1963).

[6-4] Baker, R.R., Temperature Variation Within a Cigarette

Combustion Coal During the Smoke Cycle, High

Temperature Science 7, 236-247 (1975).

[6-5] Salig, R., The Smoldering Behavior of Upholstered

Polyurethane Cushionings and its Relevance to Home

Furnishings Fires, Master's Thesis, Massachusetts Insti- tute of Technology, Cambridge, MA (1982).

[6-6] Ortiz-Molina, M., Salig, R., Tesoro, G.C, and Toong,

TY, Smoldering in Cotton Upholstery Fabrics and

Fabric/Cushioning Assemblies, Org. Coat. Plast. Chem., 43, 189-194 (1980).

[6-7] Norman, V., Some Considerations Concerning the Heat Output of Cigarettes, Presentation to the Technical Study Group (March 1985).

[6-8] Krasny, J.F, and Gann, R.G., Relative Propensity of Selected Commercial Cigarettes to Ignite Soft Furnishings Mockups, NBSIR 86-3421, [U.S] Nat. Bur. Stand. (1986).

[6-9]

[6-10]

[6-11]

[6-12]

[6-13]

[6-14]

[6-15]

[6-16]

[6-17]

[6-18]

[6-19]

Ihrig, A.M., and Rhyne, A.L., Presentation to the Technical Study Group, (1987). Dixon, W.J., and Massey, F.J., Introduction to Statistical Analysis, 3rd ed., pp. 202-206, New York: McGraw-Hill

Book Co. (1969).

Fairall, R, Consumer Product Safety Commission,

personal communication (1980).

Briggs, R., Upholstered Furniture Action Council,

personal communication (1980).

Suga, S., Simulated Cigarette Test, Report to the Research Committee on Fire Defense, Tokyo, Japan

(1984). Krasny, J.F, Allen, P., Maldonado, A., Juarez, N., Development of a Candidate Test Method for the Measurement of the Propensity of Cigarettes to Cause

Smoldering Ignition of Upholstered Furniture and

Mattresses (NBSIR 81-2363) [U.S] Nat. Bur. Stand.

(1981).

Ihrig, A.M., Rhyne, A.L., Norman, V., and Spears,

A.W., Factors Involved in the Ignition of Upholstery

Fabrics by Cigarettes, Journal of Fire Sciences, 4, 237-260 (1986). California State Department of Consumer Affairs, Bureau of Home Furnishings, Connecticut Fire-Safe Cigarette Study, Final Report, California Bureau of Home Furnishings, North Highlands, CA (June 1986).

Williams, S., California Bureau of Home Furnishings,

personal communication (1985).

Samfield, M., personal communication (1986). Babrauskas, V. and Krasny, J., Fire Behavior of Upholstered Furniture, Monograph 173, [U.S.] Nat. Bur. Stand. (1985).

227

The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 7

Conclusions

229

conclusions

The following are the principal findings of this research. The

reader is referred to the individual sections for further details.

• In furniture mock-up tests involving a wide range of fabrics and paddings, the best of the experimental

cigarettes tested had considerably lower ignition propensities than previously-tested commercial cigarettes.

• Three cigarette characteristics were found to reduce igni- tion propensity significantly: low tobacco density, reduced

circumference, and low paper permeability. Even larger

reductions were achieved with some combinations of these. The tobacco column length, the presence of a filter

tip, and citrate content of the paper had effects in limited cases. The tobacco blend had minimal impact on ignition

propensity.

• Non-ignitions were often achieved without the cigarette

self-extinguishing during the test; i.e., many cigarettes

burned their full length without igniting the substrate.

• Some of the best performing experimental cigarettes had

tar, nicotine, and CO yields that were comparable to typical commercial cigarettes.

• Single embodiments of each of five patented cigarette

modifications also reduced ignition propensity. These

included variations in the paper, an additive to one location of the tobacco column, an additive throughout the tobacco column, and an additive to the exterior of the

paper.

• Ignition results from the mini-mockup apparatus correlate very well with corresponding data from experiments with chairs made with the same fabrics and padding materials.

• The physics of the ignition process is a function of both

the cigarette and the substrate. Therefore, an accurate

ignition propensity measurement apparatus must involve the two components.

• Intrusive probes of the ignition process (e.g., ther- mocouples, heat flux gauges) perturb the delicately

balanced system; but, if they are small and well-selected, the induced errors can be estimated. With care, (nonintrusive) infrared imaging can be used to study the thermal profiles on non-igniting or igniting substrates.

An approximate correlation exists between the coal area and ignition propensity. Peak coal surface temperatures

(and thus peak heat fluxes) did not vary sufficiently to demonstrate a correlation with ignition tendency for the

cigarettes tested. Oxygen depletion in the vicinity of the ignition site is important during the ignition process, but is sufficiently similar for all cigarettes examined so as not to account for their relative ignition propensities.

It is possible to construct a complex computer model of the smoldering combustion of a cigarette and the response of an idealized substrate. With all its simplifications, this model is sufficiently realistic to manifest key

physical features of the ignition process and to reproduce some of the cigarette characteristics that do and do not

affect ignition propensity. Thus, the model could potentially be used to screen possible combinations of (included) characteristics that offer increased fire safety. At present, however, the model is very slow and not userfriendly.

The current, mini-mockup methods are valid for research

measurements of the ignition propensity of cigarettes.

However, their use in a standard test method of cigarette

performance is compromised by the variability in the commercial fabrics and paddings used in the mockup.

Several alternative candidate test methods for measuring

the cigarette ignition propensity of soft furnishings were

evaluated; none were usable in their current state of development. Two viable approaches to cigarette testing are proposed. The first modifies the existing mini-mockup

procedure using specially-prepared, well-controlled fabrics. The second uses a non-reactive substrate at variable temperature to determine the minimum needed cigarette heat-loss rate for extinguishment. Both need further development.

231

The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 8

Priority

Further Research

Directions

233

Contents for Section 8

Test Method Development and Baseline Data 237

Experimental Cigarette Testing 237

Baseline Performance Data 237

Broader Investigation of Ignition Physics 237

Ignition Model Predictions 238

235

Priority Further Research

Directions

In any closed-end research effort such as this one, there are many ideas that cannot be pursued and others that evolve

during the project. The following is a tabulation of those

studies whose results are important to a sound understanding of the cigarette/furniture ignition phenomenon and

to realization of the research into practical usage.

would then be calibrated using cigarettes of varied and

known ignition propensity. Testing would be performed

using mini-mockups. This area reguires a more detailed study of the correlation between alkali metal ion content and smoldering ignition propensity of a fabric

Test Method Development and

Baseline Data

Both cigarette manufacturers and the public need a test to determine how well improved cigarettes perform. The test should be simple enough to be used as part of a quality assurance program. The development of such a test was

intended to be part of the Technical Study Group program.

This research has indicated directions for such a method;

however, the time frame was too short for complete develop- ment. Three promising approaches are: • Non-smoldering (inert) substrate testing. Studies with cigarettes laid on non-reactive surfaces indicated the

potential for differentiating between moderate and low

ignition propensity cigarettes. Heating of, e.g., a glass

plate or frit allows adjusting the pass/fail criterion. The

glass plates could be easily standardized and re-used

after cleaning.

• Surrogate reactive substrate testing. The weight loss of multiple layers of a-cellulose paper had appeared

promising. However, the paper did not differentiate well among the moderate and low ignition propensity

cigarettes. Some addition of smolder-enhancing ions could make this approach work.

• Controlled substrate testing. The poor reproducibility with

this system has been due to inter- and intra-bolt variation

in the fabrics and paddings. Selected fabrics could be

scoured and then treated with controlled levels of smolder-enhancing ions. For readily-ignitable fabrics, the

fabric dominates the substrate ignition potential. Padding

materials would, however, still be carefully selected. The

performance of the resulting "standardized" substrates

Experimental Cigarette Testing

The current research has indicated positive directions for reducing cigarette ignition propensity. Research is needed

on more combinations of these factors, especially lower

tobacco content and modified paper permeability and thick- ness. Variations selected using the computer model should

also be studied.

Baseline Performance Data

When a test method is completed, performance data for current market cigarettes should be generated as a baseline. These data could then be compared to analogous future- year cigarette performance data.

Broader Investigation of Ignition Physics

Extensive research is needed to better measure and define the effect of the substrate on the cigarette's ignition propensity. Specific aspects are:

• characterization of the kinetics of the substrate/cigarette

interaction and its impact on ease of ignition, and determination of the thermophysical properties of various

substrates;

• more detailed measurement of the heat generation of smoldering cigarettes and components of heat transfer

237
(radiation, convection, conduction);

examination of a wider range of experimental cigarettes

and substrates; and

measurement of cigarette ignition in crevices of soft furnishings.

Ignition Model Predictions

The studies of the physics of the ignition process have been

used to guide the development of a first-cut computer model

of the ignition process. The model itself is operational, but would benefit from key improvements to correct expedient,

but necessary simplifications.

The desirable upgrades to the cigarette model include:

• multi-step tobacco pyrolysis and combustion, rather than

simply one-step char combustion, including changes in the kinetics that result from paper modification;

• inclusion of free moisture and combustion-generated

water;

• more realistic movement of air and combustion gases

within the cigarette; and

• detailed paper behavior (changes in permeability and

combustibility) as a function of temperature.

Beneficial improvements to the substrate model are:

• two-layer (fabric plus padding) construction;

• heat-induced reactivity; and

• crevice geometry capability.

The computer programs should then be made more timeefficient to permit a large series of runs with parametric vari- ations of cigarette and substrate variables.

238
The Effect of

Cigarette Characteristics

on the Ignition

of Soft Furnishings

Section 9

Acknowledgements

239

Acknowledgements

Successful completion of a project of this magnitude and

duration requires the enthusiastic contributions of a large

number of participants. The authors are pleased to cite the

efforts of their colleagues within the Center for Fire Research: Emil Braun, Newton Breese, Robin Breese, Karen

Davis, Jeffrey Didion, Darlene Dorsey, Wanda Duffin, Paula

Garrett, Lisha Glinsman, Daniel Gross, Barbara Houston,

Nora Jason, Takashi Kashiwagi, Randall Lawson, Richard

Peacock, Susan Riggin, Randy Shields, Brenda Thompson,

Kay Villa, and Maureen Wood; colleagues from the NBS

Center for Applied Mathematics: Keith Eberhardt and Ronald

Rehm; associates from Montgomery College: William Davis

and Donald Day; and external consultants Max Samfield and

William Selke. In addition numerous discussions were held

with the members of the Technical Study Group, and these

played a significant role in the course of this research. Many other persons and organizations cooperated by

supplying experimental materials and services. Thanks are due to Dr. Alexander Spears of Lorillard, A Division of Loews

Theatres, Inc., who coordinated the production of the

experimental cigarettes. They were produced by the American Tobacco Company, the Brown and Williamson

Tobacco Corporation, Philip Morris U.S.A., and the R.J. Reynolds Tobacco Company. The production of the full-scale furniture was coordinated by Roy Briggs, of the Upholstered

Furniture Action Council.

The following people supplied measurements of the physical and chemical characteristics of the experimental

cigarettes and their components: measurement of the tar, nicotine, and CO yields: Harold Pillsbury, Federal Trade

Commission; tobacco analysis: Dr. Wesley Weeks, Department of Crop Science, North Carolina State University; paper

porosity: Dr. Charles Mattina, Kimberly-Clark Corporation;

paper citrate content: Dr. S. Sahu, U.S. Consumer Product

Safety Commission; alkali metal ion analysis of the fabrics and cotton batting used in the ignition experiments: Dr. K. Gupta, of the U.S. Consumer Product Safety Commission.

Soil was extracted from discarded furniture cover fabrics by Ms. Cindy Busier, International Fabricare Institute. The soil extract, as well as alkali metal ions, were applied to other

fabrics by Prof. Kwan-nan Yeh, Department of Human

Ecology, University of Maryland.

241
L S D FP T. Cf C OMM. BIBLIOGRAPHIC DATA

SHEET (See instructions

1. PUBLICATION OR

REPORT NO.

NBS/TN-1241

2. Ferforr-ing Orga-1

. Report No. 3. Publication Date

January 1988

4. TITLE AND SUBTITLE

THE EFFECT OF CTGARETTE CHARACTERISTICS ON THE IGNITION OF SOFT FURNISHINGS

5. A'JTHOR(S)

R.G. Garm, R.H. Harris, J.F. Krasny, R.S. Levine, H, Mitler and T.J. Ohlemiller

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions; NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. Stote. ZIP)

10. SUPPLEMENTARY NOTES

3 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This research was performed by the NBS Center for Fire Research under the Cigarette

Safety Act of 1984. Cigarette-initiated furniture fires are the leading cause of fire

deaths and injuries in the United States. The objectives of this project was to

determine those properties of cigarettes that have an impact on their ignition of

furniture. Experiments were performed on small-scale representations of furniture

as well as actual chairs. Experimental cigarettes, varied parametrically in six

different characteristics, were used, along with some patented ( fire-sate ) and

representative commercial cigarettes. These experiments demonstrated significant

differences in performance among the cigarettes used and led to further understanding

of the features of the burning process that affect energy transfer to (and subsequent

ignition of) furniture. Four cigarette characteristics were found to reduce ignition

propensity: filter tip, low tobacco density, reduced circumference, and low paper

permeability. Each of the patented cigarettes showed reductions as well. Within

the ranges studied, tobacco column length, tobacco blend, and citrate content of the

paper had minimal impacts on ignition propensity. Computer modeling of the _ cigarette/furniture system was also pursued, with a goal of allowing interpolation

within and extrapolation beyond the currently used cigarettes. Further priority

research needs are listed.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

cigarette; cigarette fires; fire; fire research; ignition

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15. Price

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