NIST Technical Note 1603 

Experimental Study of the Effects of Fuel Type, Fuel 

Distribution, and Vent Size on Full-Scale 

Underventilated Compartment Fires in an ISO 9705 

Room 

Andrew Lock 

Matthew Bundy 

Erik L. Johnsson 

Anthony Hamins 

Gwon Hyun Ko 

Cheolhong Hwang 

Paul Fuss 

Richard Harris 

U.S. Department of Commerce 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive 

Gaithersburg, MD 20899 
ii 

NIST Technical Note 1603 

Experimental Study of the Effects of Fuel Type, Fuel 

Distribution, and Vent Size on Full-Scale 

Underventilated Compartment Fires in an ISO 9705 

Room 

Andrew Lock 

Matthew Bundy 

Erik L. Johnsson 

Anthony Hamins 

Gwon Hyun Ko 

Cheolhong Hwang 

Paul Fuss 

Richard Harris 

U.S. Department of Commerce 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive 

Gaithersburg, MD 20899 

October 2008 

U.S. Department of Commerce 

Carlos M. Gutierrez, Secretary 

National Institute of Standards and Technology 

James Turner, Acting Director 
iii 

DISCLAIMER

Certain companies and commercial properties are identified in this paper in order to specify 

adequately the source of information or of equipment used. Such identification does not imply 

endorsement or recommendation by the National Institute of Standards and Technology, nor 

does it imply that this source or equipment is the best available for the purpose. 

 
iv 

TABLE OF CONTENTS

1 Introduction ............................................................................................................................. 1

1.1 Motivation and Objective ................................................................................................. 1

1.2 Previous Work .................................................................................................................. 2

1.3 Experimental Scope .......................................................................................................... 4

2 Experimental Design ............................................................................................................... 6

2.1 Design of the room ........................................................................................................... 6

2.1.1 Dimensions ............................................................................................................... 6

2.1.2 Materials ................................................................................................................... 6

2.1.3 Doorway Dimensions................................................................................................ 9

2.1.4 The Burners ............................................................................................................... 9

2.2 Overview of equipment .................................................................................................. 11

2.2.1 Heat Release Rate Measurement ............................................................................ 11

2.2.2 Gas analyzers .......................................................................................................... 13

2.2.3 Gas Chromatography .............................................................................................. 16

2.2.3.1 Gas Sample Storage System ............................................................................ 19

2.2.4 Soot Samples ........................................................................................................... 21

2.2.4.1 Gravimetric ...................................................................................................... 21

2.2.4.2 Real time extractive ......................................................................................... 23

2.2.5 Thermocouples ........................................................................................................ 25

2.2.5.1 Aspirated Thermocouples ................................................................................ 25

2.2.5.2 Radiation Effects on Bare Beads ..................................................................... 28

2.2.6 Heat flux gauges ..................................................................................................... 29

2.3 Sampling locations ......................................................................................................... 31

2.4 Data acquisition .............................................................................................................. 33

2.5 Data post-processing ...................................................................................................... 33

2.6 Uncertainty ..................................................................................................................... 35

3 Results ................................................................................................................................... 37

3.1 List of Test Conditions ................................................................................................... 37

3.2 Heat Release Rate ........................................................................................................... 40

3.3 Temperatures .................................................................................................................. 50

3.4 Heat Flux ........................................................................................................................ 60
v 

3.5 Interior Compartment Gas Species ................................................................................ 65

3.6 Soot................................................................................................................................. 73

3.6.1 Gravimetric ............................................................................................................. 73

3.6.2 Real time extractive ................................................................................................ 75

4 Compartment chemistry analysis .......................................................................................... 78

4.1 Mixture Fraction Analysis .............................................................................................. 78

4.1.1 Definition of Mixture Fraction................................................................................ 79

4.1.2 Mixture Fraction Uncertainty ................................................................................. 82

4.1.3 Species Composition Results in terms of Mixture Fraction ................................... 84

4.1.4 Condensed-Phase Hydrocarbon Fuels .................................................................... 87

4.2 Post-Compartment Product Yields ................................................................................. 95

4.3 Carbon Balance .............................................................................................................. 97

4.4 Combustion Efficiency ................................................................................................. 104

5 Scaling from RSE to FSE ................................................................................................... 110

6 Discussion ........................................................................................................................... 114

6.1 Behavior of different fuels ........................................................................................... 114

6.1.1 Liquid Fuels .......................................................................................................... 114

6.1.2 Solid Fuels ............................................................................................................ 120

6.1.3 Comparison ........................................................................................................... 125

6.2 Effect of fuel distributions ............................................................................................ 125

6.3 Ventilation effects ........................................................................................................ 130

6.4 Heat release rate ramp .................................................................................................. 135

7 Summary ............................................................................................................................. 137

8 Future Work ........................................................................................................................ 139

9 References ........................................................................................................................... 140

10 Acknowledgements ............................................................................................................. 143

A. Channel Lists ...................................................................................................................... 145

B. Equipment List .................................................................................................................... 147

C. Micro-GC Method Report ................................................................................................... 148
vi 

LIST OF FIGURES

Figure 2.1 Internal dimensions of ISO 9705 enclosure used in these experiments 

including multiple door widths and gas sample and temperature probe 

locations. All dimensions have an uncertainty of ± 2 cm. ........................................ 7

Figure 2.2 Photograph of the actual ISO 9705 room used for experiments. The structural 

construction of sheet steal on steel studs can be seen along with the internal 

surface covering of ceramic fiber blanket. ................................................................ 8

Figure 2.3 Ceramic insulation retainers used to secure the ceramic fiber blanket to the 

sheet steel walls. The actual retainer is shown (left) as well as its installed 

configuration (right). ................................................................................................. 8

Figure 2.4: Free-burn and spray burner pan construction and dimensions. The dimensions 

of 50 cm, 70.7 cm, and 100 cm are all internal burner dimensions. All 

burners had a lip height of 10 cm. ........................................................................... 10

Figure 2.5: Positioning of free-burn pan burners. The burners of different size were 

placed at the geometric center of the floor and/or along the centerline 

against the back wall. Pans in either position were mounted on load cells to 

measure the mass loss (or gain in the case of the spray burner) to determine 

fuel loss rate. For the spray burner cases only a single 70.7 cm x 70.7 cm 

pan was used in the center of the floor to catch the fuel spray. Both the 

pump fed pool burner and the gravel filled natural gas burner were located 

at position 1 inside the room. .................................................................................. 10

Figure 2.6: Schematic drawing of 6 m square hood and exhaust stack instrumented for 

calorimetry measurements. Taken from Ref. [29] .................................................. 12

Figure 2.7: Exhaust gas sampling system used for heat release rate measurement. ..................... 13

Figure 2.8: Schematic drawing of gas sampling system. .............................................................. 15

Figure 2.9: Schematic diagram of gas sample storage system in position B-A. ........................... 20

Figure 2.10: Positions of the control valves for the gas sample storage system. .......................... 20

Figure 2.11: Schematic drawing of gravimetric soot sampling system. ....................................... 22

Figure 2.12: Schematic of real time extractive soot measurement probe. .................................... 25

Figure 2.13: Detailed drawing of aspirated thermocouple using NACA design [34]. ................ 27

Figure 2.14: Schematic drawing of aspirated thermocouple measurement hardware. ................ 28

Figure 3.1: Heat release rate for test ISONG3 comparing the ideal heat release rate, as 

imposed by gas flow rate, by the red dashed line and the measured, by 

oxygen loss calorimetry, solid blue line. ................................................................. 39

Figure 3.2: Heat release rate for test ISOHept5 comparing the ideal heat release rate, as 

imposed by pump flow rate, by the red dashed line and the measured, by 

oxygen loss calorimetry, solid blue line. ................................................................. 39
vii 

Figure 3.3: Heat release rate for test ISOHept9 (Heptane) comparing the ideal heat 

release rate, as measured by the burner mass loss rate, by the red dashed line 

and the measured, by oxygen loss calorimetry, solid blue line. .............................. 43

Figure 3.4: Heat release rate for test ISOProp15 (Iso-Propanol) comparing the ideal heat 

release rate, as measured by the burner mass loss rate, by the red dashed line 

and the measured, by oxygen loss calorimetry, solid blue line. .............................. 43

Figure 3.5: Heat release rate for test ISOHeptD12 (Heptane) comparing the ideal heat 

release rate, as measured by the burner mass loss rate, by the red dashed line 

and the measured, by oxygen loss calorimetry, solid blue line. .............................. 44

Figure 3.6: Heat release rate for test ISOHeptD13 (Heptane) comparing the ideal heat 

release rate, as measured by the burner mass loss rate, by the red dashed line 

and the measured, by oxygen loss calorimetry, solid blue line. .............................. 44

Figure 3.7: Fire leaving the door of the ISO 9705 room during test ISOHeptD12. It was 

not possible to view the inside of the room during this test. ................................... 45

Figure 3.8: Heat release rate for test ISOStyrene17 (Polystyrene) comparing the ideal 

heat release rate, as measured by the burner mass loss rate, by the red 

dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

The mass loss reading was lost during the experiment due to warping of the 

burner pan. The ideal HRR values were smoothed because of excessive 

signal noise. ............................................................................................................. 45

Figure 3.9: Images of the burner warping and moving during test ISOStyrene17. The 

burner was observed to be as much as 20 cm off of the floor in one corner. 

The burner warped because of its large size, 1m2, and the excessive heat 

transfer to the burner in the room. This caused a loss of the mass loss 

measurement in this experiment. ............................................................................. 46

Figure 3.10: Heat release rate for test ISOPPD18 (Polypropylene) comparing the ideal 

heat release rate, as measured by the burner mass loss rate, by the red 

dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

The mass loss reading was lost during the experiment due to warping of the 

burner pan. The ideal HRR values were smoothed because of excessive 

signal noise. ............................................................................................................. 46

Figure 3.11: Heat release rate for test ISOHept22 (heptane) comparing the ideal heat 

release rate, as measured by the spray burner pump flow rate, by the red 

dashed line and the measured, by oxygen loss calorimetry, solid blue line. ........... 47

Figure 3.12: Heat release rate for test ISOHept27 (heptane) comparing the ideal heat 

release rate, as measured by the spray burner pump flow rate, by the red 

dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

This test featured a linear increase in the fuel delivery rate to observe the 

effects of a HRR ramp. ............................................................................................ 47

Figure 3.13: steady state heat release results. The dashed line indicates ideal or complete 

burning. ................................................................................................................... 48
viii 

Figure 3.14: Comparison between temperatures measured from bare bead and aspirated 

thermocouples at front sampling location as a function of time for test 

ISONG3. .................................................................................................................. 52

Figure 3.15: Comparison of averaged temperatures measured from bare bead and 

aspirated thermocouples at front sample location for test ISONG3. ....................... 53

Figure 3.16: Comparisons of averaged temperature measured at front and rear 

thermocouple trees for test ISOHeptD12 and ISOHeptD13. .................................. 53

Figure 3.17: Histories of temperature at front and rear sampling locations for test 

ISOHept22 (heat release rate measured from calorimeter was included to 

show fire condition). ............................................................................................... 55

Figure 3.18: Histories of temperature at front thermocouple trees for test ISOHept9. ................ 55

Figure 3.19: Histories of temperature at rear thermocouple trees for test ISOHept9. .................. 56

Figure 3.20: Averaged temperatures as a function of heat release rate at front sample 

location for all fuels tested. ..................................................................................... 57

Figure 3.21: Averaged temperatures as a function of heat release rate at rear sample 

location for all fuels tested. ..................................................................................... 57

Figure 3.22: Comparison of heat flux measurements made in the ceiling for 1/4 width (20 

cm) doorway heptanes fuel test ISOHept9. ............................................................. 62

Figure 3.23: Comparison of the heat flux gauges positioned in the floor for 1/4 doorway 

(20 cm) heptanes fuel case ISOHept9. .................................................................... 62

Figure 3.24: Photograph of the center (front) and rear burners immediately after fire test 

ISOPropD14. ........................................................................................................... 63

Figure 3.25: Comparison of heat flux gauge measurements for heat flux gauges 

positioned in the floor for 1/4 doorway (20 cm) distributed fuel isopropanol 

case ISOProp14. ...................................................................................................... 63

Figure 3.26: Comparison of heat flux gauge measurements for heat flux gauges 

positioned in the floor for 1/4 doorway (20 cm) distributed fuel isopropanol 

case ISOProp14. ...................................................................................................... 64

Figure 3.27: Transient gas volume fraction s and soot mass fraction of test ISOHept9 

(Heptane). ................................................................................................................ 67

Figure 3.28: Transient gas volume fraction s and soot mass fraction of test ISOPP18 

(Polypropylene). ...................................................................................................... 67

Figure 3.29: Transient gas volume fractions and heat release rate of test ISOPP18 

(Polypropylene). ...................................................................................................... 68

Figure 3.30: Gas species volume fractions from GC analysis of front sample location in 

ISOHept27 at t=1375 s. ........................................................................................... 68

Figure 3.31: Steady state average oxygen volume fraction measurements at front sample 

probe location. ......................................................................................................... 69
ix 

Figure 3.32: Steady state average oxygen volume fraction measurements at rear sample 

probe location. ......................................................................................................... 69

Figure 3.33: Steady state average CO2 volume fraction measurements at front sample 

probe location. ......................................................................................................... 70

Figure 3.34: Steady state average CO2 volume fraction measurements at rear sample 

probe location. ......................................................................................................... 70

Figure 3.35: Steady state average CO volume fraction measurements at front sample 

probe location. ......................................................................................................... 71

Figure 3.36: Steady state average CO volume fraction measurements at rear sample probe 

location. ................................................................................................................... 71

Figure 3.37: Steady state average THC volume fraction measurements at front sample 

probe location. ......................................................................................................... 72

Figure 3.38: Steady state average THC volume fraction measurements at rear sample 

probe location. ......................................................................................................... 72

Figure 3.39: Steady state gravimetric soot mass fraction measurements at front sample 

probe location. ......................................................................................................... 74

Figure 3.40: Steady state gravimetric soot mass fraction measurements at rear sample 

probe location. ......................................................................................................... 74

Figure 3.41: Soot mass concentration and heat release rate during polystyrene fire test 21. ....... 75

Figure 3.42: Comparison of the optical and gravimetric soot mass fraction at the rear of 

the compartment in test #21. ................................................................................... 76

Figure 3.43: Soot mass concentration and heat release rate during heptane fire test 26. ............. 77

Figure 3.44: Soot mass concentration and heat release rate during heptane fire test 28. ............. 77

Figure 3.45: Comparison of the optical and gravimetric soot mass fraction at the rear of 

the compartment in test #28. ................................................................................... 78

Figure 4.1: The equivalence ratio as a function of mixture fraction for nonpremixed 

flames burning methane and n-heptane. .................................................................. 83

Figure 4.2: The mass fraction vs. the mixture fraction calculated by the single-parameter 

mixture fraction model. ........................................................................................... 83

Figure 4.3: Mass fractions of front and rear compartment gas species for the natural gas 

fire tests #1-#3, and #32: (a) transient measurements, (b) time-averaged 

measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. ............. 86

Figure 4.4. Mass fractions of front and rear compartment gas species for the heptane fire 

tests #5, #9, #12, #13, #19, #22-#26 and #28: (a) transient measurements, 

(b) time-averaged measurements as a function of mixture fraction without 

soot, and (c) time-averaged measurements as a function of mixture fraction 

including soot. ......................................................................................................... 89
x 

Figure 4.5: Mass fractions of front and rear compartment gas species for the toluene fire 

tests #20 and #29: (a) transient measurements, (b) time-averaged 

measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. ............. 90

Figure 4.6: Mass fractions of front and rear compartment gas species for the 

polypropylene fire tests #11 and #18: (a) transient measurements, (b) timeaveraged measurements as a function of mixture fraction without soot, and 

(c) time-averaged measurements as a function of mixture fraction including 

soot. ......................................................................................................................... 91

Figure 4.7: Mass fractions of front and rear compartment gas species for the polystyrene 

fire tests #16, #17 and #21: (a) transient measurements, (b) time-averaged 

measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. ............. 92

Figure 4.8: Comparison of mixture fraction calculated with and without soot using the 

time-averaged species measurements when the HRR was quasi-steady. ................ 93

Figure 4.9: Mass fractions of front and rear compartment gas species for the iso-propanol 

fire tests #14, #15 and #30: (a) transient measurements, (b) time-averaged 

measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. ............. 94

Figure 4.10: The CO2 volume fraction, CO2 X , in the exhaust stack as a function of the fire 

heat release rate during the periods when the HRR was quasi-steady for 

each of the fuels tested (DF indicates the doorway fraction of 80 cm). .................. 96

Figure 4.11: The CO volume fraction, XCO *, in the exhaust stack as a function of the fire 

heat release rate during the periods when the HRR was quasi-steady for 

each of the fuels tested. ........................................................................................... 96

Figure 4.12: The values of FCO and Fsoot as a function of the local equivalence ratio for 

the time averaged measurements during the period when the HRR was 

quasi-steady. .......................................................................................................... 100

Figure 4.13: The CO and soot yields as a function of the local equivalence ratio for the 

time averaged measurements during the period when the HRR was quasisteady. .................................................................................................................... 102

Figure 4.14: The ratio of the CO to soot yield as a function of the local equivalence ratio 

during the period when the HRR was quasi-steady. ............................................. 103

Figure 4.15: The CO yield as a function of the soot yield during the period when the HRR 

was quasi-steady. Also shown is a line representing the results of Koylu [2]. ..... 103

Figure 4.16: The combustion efficiency in the exhaust stack as a function of the ideal heat 

release rate for natural gas and heptane fuels under the condition of full 

doorway size (DF=1.0). The indicated uncertainty includes the 14% 

uncertainty of the calorimetry used to make the measurements. .......................... 106

Figure 4.17: The combustion efficiency in the exhaust stack as a function of the ideal heat 

release rate for various fuels under the condition of DF=0.25. The indicated 
xi 

uncertainty includes the 14% uncertainty of the calorimetry used to make 

the measurements. ................................................................................................. 106

Figure 4.18: The combustion efficiency in the exhaust stack as a function of the ideal heat 

release rate for various doorway sizes in heptane fires. The curve fit lines 

are for illustrative purposes only. .......................................................................... 107

Figure 4.19: The local combustion efficiency at the front and rear sample locations as a 

function of the ideal heat release rate for various doorway sizes in heptane 

fires. The curve fit lines are for illustrative purposes only. ................................... 107

Figure 4.20: The burning fraction inside compartment as a function of ideal heat release 

rate under the condition of DF=0.125 in heptane fires. The curve fit line is 

for illustrative purposes only. ................................................................................ 108

Figure 5.1: Example normalized scaling quantities with * Qd = 0.17, φ = 0.1, and H/D* = 

12.23, on the left (ISONylon10) and a * Qd = 12.74, φ = 7.53, and H/D* = 

2.17, on the right (ISOPropD14). .......................................................................... 113

Figure 6.1: Comparison of measured heat release rate for three different liquid fuels, 

Heptane, Iso-Propanol, and Toluene. .................................................................... 116

Figure 6.2: Plot of heat of combustion of each fuel verses measured and ideal heat release 

rate for three liquid fuels. ...................................................................................... 116

Figure 6.3: Comparison of measured front (solid lines) and rear (dashed lines) 

temperatures for three different liquid fuels, Heptane, Iso-Propanol, and 

Toluene. ................................................................................................................. 117

Figure 6.4: Comparison of measured front (solid lines) and rear (dashed lines) oxygen 

volume fraction as a function of time for three different liquid fuels, 

Heptane, Iso-Propanol, and Toluene. .................................................................... 117

Figure 6.5: Comparison of measured front (solid lines) and rear (dashed lines) CO 

volume fraction as a function of time for three different liquid fuels, 

Heptane, Iso-Propanol, and Toluene. .................................................................... 118

Figure 6.6: Comparison of measured front (solid lines) and rear (dashed lines) CO2

volume fraction as a function of time for three different liquid fuels, 

Heptane, Iso-Propanol, and Toluene. .................................................................... 118

Figure 6.7: Comparison of measured front (solid lines) and rear (dashed lines) total 

hydrocarbon (THC, on a CH4 basis) volume fraction as a function of time 

for three different liquid fuels, Heptane, Iso-Propanol, and Toluene. (Note: 

Front Iso-propanol results are not shown as the analyzer failed during this 

test. ........................................................................................................................ 119

Figure 6.8: Comparison of the measured radiative heat flux at the front ceiling location, 

channel ID:HFFCE, for heptanes, toluene, and isopropanol. ................................ 119

Figure 6.9: Comparison of the measured radiative heat flux at the front floor location, 

channel ID:HFFFL, for heptanes, toluene, and isopropanol. ................................ 120
xii 

Figure 6.10: Comparison of the measured heat release rate for polystyrene and poly 

propylene solid fules. ............................................................................................ 122

Figure 6.11: Comparison of measured front (solid lines) and rear (dashed lines) 

temperature as a function of time for two different solid fuels, polystyrene 

and polypropylene. ................................................................................................ 122

Figure 6.12: Comparison of measured front (solid lines) and rear (dashed lines) oxygen 

volume fraction as a function of time for two different solid fuels, 

polystyrene and polypropylene. ............................................................................ 123

Figure 6.13: Comparison of measured front (solid lines) and rear (dashed lines) CO2

volume fraction as a function of time for two different solid fuels, 

polystyrene and polypropylene. ............................................................................ 123

Figure 6.14: Comparison of measured front (solid lines) and rear (dashed lines) CO 

volume fraction as a function of time for two different solid fuels, 

polystyrene and polypropylene. ............................................................................ 124

Figure 6.15: Comparison of measured front (solid lines) and rear (dashed lines) total 

hydrocarbon volume fraction (on a CH4 basis) as a function of time for two 

different solid fuels, polystyrene and polypropylene. ........................................... 124

Figure 6.16: Comparison of heat release rate for heptane fires with a single burner and 

two distributed burners. ......................................................................................... 127

Figure 6.17: Comparison of front (solid line) and rear (dashed line) temperatures for 

heptane fires with a single burner and with two distributed burners. ................... 127

Figure 6.18: Comparison of front (solid line) and rear (dashed line) O2 volume fraction 

for heptane fires with a single burner and with two distributed burners. .............. 128

Figure 6.19: Comparison of front (solid line) and rear (dashed line) CO2 volume fraction 

for heptane fires with a single burner and with two distributed burners. .............. 128

Figure 6.20: Comparison of front (solid line) and rear (dashed line) CO volume fractions 

for heptane fires with a single burner and with two distributed burners. .............. 129

Figure 6.21: Comparison of front (solid line) and rear (dashed line) total hydrocarbon 

volume fraction for heptane fires with a single burner and with two 

distributed burners. ................................................................................................ 129

Figure 6.22: Comparison of front floor (solid line) and center ceiling (dashed line) heat 

fluxes for heptane fires with a single burner and with two distributed 

burners. .................................................................................................................. 130

Figure 6.23: Comparison of heat release rates for three different ventilation conditions of 

a heptane spray burner fire operating at a nearly steady state of 1000 kW. .......... 132

Figure 6.24: Comparison of front (solid likes) and rear (dashed lines) temperatures for 

three different ventilation conditions of a heptane spray burner fire 

operating at a nearly steady state of 1000 kW. ..................................................... 132
xiii 

Figure 6.25: Comparison of front (solid likes) and rear (dashed lines) O2 volume fraction 

for three different ventilation conditions of a heptane spray burner fire 

operating at a nearly steady state of 1000 kW. ..................................................... 133

Figure 6.26: Comparison of front (solid likes) and rear (dashed lines) CO2 volume 

fraction for three different ventilation conditions of a heptane spray burner 

fire operating at a nearly steady state of 1000 kW. ............................................... 133

Figure 6.27: Comparison of front (solid likes) and rear (dashed lines) CO volume fraction 

for three different ventilation conditions of a heptane spray burner fire 

operating at a nearly steady state of 1000 kW. ..................................................... 134

Figure 6.28: Comparison of front (solid likes) and rear (dashed lines) total hydrocarbon 

volume fraction for three different ventilation conditions of a heptane spray 

burner fire operating at a nearly steady state of 1000 kW..................................... 134

Figure 6.29: Comparison of ideal heat release rate, determined from fuel flow rate, and 

measured heat release rate measured from oxygen loss caloremetry for test 

ISOHept27, where the heat release rate was ramped linearly with time.. ............. 136

Figure 6.30: Comparison of temperature and various species mole fractions for 

ISOHept27 test with a linear heat release rate ramp. ............................................ 136

Figure 6.31: Comparison of various gas species from both gas analyzers and GC analysis 

with heat release rate for heat release rate ram test ISOHept27. ........................... 137
xiv 

LIST OF TABLES

Table 2.1: Total delay times for the three gas sample probes used in the experiment. All 

delay times have an expanded uncertainty of ±2 s. ................................................. 15

Table 2.2. List of micro-GC columns, specifications, and GC parameters used during FSE 

experiments. ............................................................................................................ 17

Table 2.3. List of calibration standards and precision analyzed gases that were utilized for 

GC calibration. ........................................................................................................ 17

Table 2.4: Sequence of controls for storing and then analyzing gas samples in the gas 

sample storage system. ............................................................................................ 21

Table 2.5. Location of measurement probes inside of the enclosure. ........................................... 32

Table 2.6: Uncertainty of measurements ...................................................................................... 35

Table 3.1: List of test conditions considered in this report. .......................................................... 38

Table 3.2: Description of calorimetry measurement labels. ........................................................ 40

Table 3.3: Summary of averaged steady-state results of HRR and exhaust stack species 

measurements. U indicates the standard deviation in each steady state 

measurement. ........................................................................................................... 49

Table 3.4. Description of interior gas temperature measurement labels. ..................................... 52

Table 3.5: Summary of averaged steady-state results of temperatures at front locations. ............ 58

Table 3.6: Summary of averaged steady-state results of temperatures at rear locations. ............. 59

Table 4.1. Stoichiometric Value of the Mixture Fraction (Zst) for different fuels. ..................... 81

Table 4.2: Average fractional soot, CO and CO/soot ratio at the front and rear 

compartment measurement locations. ..................................................................... 99

Table 4.3: Average yields of soot, CO and CO/soot ratio at the front and rear 

compartment measurement locations. ................................................................... 101

Table 4.4: Summary of averaged steady-state results of combustion efficiency in the 

exhaust stack. The steady state periods here are the same used for all steady 

state measurements and are listed in Table 3.5. The uncertainty, U, 

indicated here only reflects the statistical variation .............................................. 109

Table 5.1: List of Normalized Scaling Parameters for Compartment Fires and the Range 

of Values Examined in this Study. ........................................................................ 111

Table 5.2: Scaling comparison between the reduced scale enclosure (RSE) and the full 

scale enclosure (FSE) for heptane fires. The heat release rate values (Q) are 

taken as the heat release measured when CO began to be measured in the 

room. ..................................................................................................................... 113

Table 6.1: Heat of combustion and measured and ideal heat release rates for liquid fuels. ....... 115

Table 6.2: Fuel Properties (r is the stoichiometric ratio of fuel to air). ..................................... 125
1 

1 INTRODUCTION

This report describes new full-scale compartment fire experiments, which include local 

measurements of temperature, heat flux and species composition, and global measurements of 

heat release rate and mass burning rate. The measurements are unique to the compartment fire 

literature. By design, the experiments provided a comprehensive and quantitative assessment of 

major and minor carbonaceous gaseous species and soot at two locations in the upper layer of 

fire in a full scale ISO 9705 room [1]. 

Fire protection engineers, fire researchers, regulatory authorities, fire service and law 

enforcement personnel use fire models (such as the NIST Fire Dynamics Simulator, FDS[2]) for 

design and analysis of fire safety features in buildings and for post-fire reconstruction and 

forensic applications. Fire field models have historically showed limited ability to accurately 

and reliably predict the thermal conditions and chemical species in underventilated compartment 

fires. Formal validation efforts have shown that for well ventilated compartment fires, with the 

exception perhaps of soot, field models do quite well in predicting temperature and species when 

experimental uncertainty is accounted for. Inaccurate predictions of incomplete burning and soot 

levels impact calculations of radiative heat transfer, burning rates, and estimates of human 

tenability. High-quality (relatively low, quantified uncertainty) measurements of fire gas 

species, temperature, and soot from the interior of underventilated compartment fires are needed 

to guide the development and validation of improved fire field models. 

The experimental results provided in this report are the continuation of a long-term National 

Institute of Standards and Technology (NIST) project to generate the data necessary to test our 

understanding of fire phenomena in enclosures and to guide the development and validation of 

field models by providing high quality experimental data. The experimental plan was designed 

in cooperation with developers of the NIST FDS model to assure that the measurements would 

be of maximum value. Advanced development of FDS and other field models is extremely 

important, since it will lead to improved accuracy in the prediction of underventilated burning, 

typical of fire conditions that occur in structures. Improving models for under-ventilated burning 

will foster improved prediction of important life safety and fire dynamic phenomena, including 

fire spread, backdraft, flashover, and egress (involving the presence of toxic gas and smoke), 

which are critically important for application of fire models for fire safety. 

1.1 Motivation and Objective

Field models, such as the NIST Fire Dynamics Simulator (FDS)[2] are widely used by fire 

protection engineers to predict fire growth and smoke transport for practical engineering 

applications. Many field models numerically solve the conservation equations of mass, 

momentum and energy that govern low-speed, thermally-driven flows with an emphasis on 

smoke and heat transport from fires. Among the various assumptions used in the development of 

early versions of FDS, all chemical species were tied to a single mixture fraction variable by use 

of a set of mixture fraction state relations. A single mixture fraction variable cannot be used for 

the prediction of carbon monoxide and soot, and the yield of these species was prescribed in FDS 

4, rather than predicted. In fact, the yield of these species is usually not constant, but a complex 

function of their time-temperature history. In practice, an knowledgeable user would attempt to 

pick yields that would reflect the anticipated ventilation condition of the simulation from 
2 

literature values for well-ventilated burning, using data from a bench-scale apparatus [3] or from 

other sources such as the full scale experimental results presented here. Using this approach, the 

CO volume fraction for pool fire burning in an under-ventilated compartment can be 

underestimated by as much as a factor of ten. 

FDS 5 [2] has included a simple predictive method for CO production. This revised method 

breaks the mixture fraction calculation into two parts resulting in a two-step chemistry model. 

This change in the chemistry of the model is an improvement over the prescriptive method used 

in FDS 4, however still under predicts CO substantially. A recent paper [4] by the developers of 

FDS reported on the model validation of the reduced scale enclosure (RSE) experimental results 

[5]. They found that FDS 5 has improved its prediction of fires in this configuration. The best 

agreement was observed with methanol, a very low sooting fuel. In general good agreement was 

observed with velocity and temperature data from these experiments. The CO production model 

was improved substantially, however there is still significant difference between the experiments 

and the model. As more soot was produced by the fuels and the fires became more 

underventilated an under prediction of CO and an over prediction of CO2 was observed. The 

authors attributed these effects to the specific assumptions being made in the FDS CO prediction 

scheme. 

In an effort to validate current fire models and to further the development of better predictive 

methods for fires, the current report presents new and unique data on full scale underventilated 

compartment fire experiments which builds on the previous data concerning reduced scale 

enclosures (RSE) [5]. The experiments are presented with analysis and experimental modeling 

results as a method of explaining the fire behavior and aiding in analysis. 

1.2 Previous Work

Experimental research on enclosure fires has been on-going in fire research laboratories and 

academic institutions over the last 50 years. The motivation has varied from applied 

investigations studying particular fire scenarios to more fundamental work with the goal of 

understanding toxic species production behavior in fires. Some of the fundamental research that 

tried to ascertain ventilation and upper-layer effects on enclosure fire chemistry was conducted 

in well-controlled hoods. Sometimes, the main objectives of this research was to generally 

develop and validate fire models or particular structural fire simulations, while much of the 

research was conducted to acquire a better understanding of complex enclosure fire dynamics 

with a focus on chemical and thermal conditions. This section provides an overview of some of 

the recent research efforts in enclosure fires and highlights some of the more pertinent 

experimental work. 

Research conducted at Harvard University and the California Institute of Technology in the 

1980s explored fires burning under an exhaust hood (false ceiling) to simulate the layer effect of 

an enclosure fire, e.g. [6, 7]. The relative distance of the fire below the hood was adjusted to 

vary the entrainment of air into the plume before it entered the upper layer. These experiments 

focused on underventilated burning, pathways for air to enter the upper layer, and the validity of 

the concept of “global equivalence ratio” (GER) which is the fuel-to-air mass ratio normalized 

by the mass ratio required for stoichiometric burning. Some recent modeling work by Cleary 

and Kent [8], has also focused on experimental data from hoods. In a recent study, Brohez et al. 
3 

explored the use of a bench-scale calorimeter to measure fire properties of materials burning in 

underventilated conditions [8, 9]. 

Research at NIST by Bryner et al. further explored the global equivalence ratio concept and 

carbon monoxide production in a reduced (2/5) scale enclosure with natural gas as the principal 

fuel [9]. The results showed that the upper layer in enclosure fires is not homogeneous, and that 

CO can be produced in greater quantities than predicted by the GER concept, depending on 

temperatures and flow patterns developed within an enclosure. The previous effort [5] was 

meant to overlap some of the conditions explored by Bryner et al. and to repeat and fill gaps in 

the data. Pitts expanded the work to full-scale and other fuels such as heptane and wood. It was 

established that wood pyrolysis in the upper layer of an enclosure fire can produce high 

concentrations of CO directly without further oxidation to CO2 [10]. A subsequent study by 

Lattimer confirmed and expanded on this research [11]. 

Researchers at Virginia Tech investigated fires in a reduced-scale enclosure that directed the air 

inflow through slots in the floor connected to a duct where instrumentation was used to quantify 

air entrainment [12]. Several fuels were studied, and this configuration produced results 

consistent with GER predictions due to the more distinct, less dynamic nature of the gas layer 

structure. Later work used a more typical enclosure design and focused on transport of gas 

species outside the doorway and how it was affected by doorway geometry, soffit design, and 

hallway configuration [13]. More recently, Gann et al [14] conducted research on transport of 

toxic species in a full-scale enclosure with a corridor. These data were analyzed by Hirschler 

[15]. Researchers in Sweden conducted a study [16] of under-ventilated fires in an ISO 9705 

room with a window vent of varying height. Several polymer fuel types were included in this 

study and measurements of local equivalence ratio and toxic gas species were performed. 

Pitts [17] provides a comprehensive review of the application of the GER concept to predict CO 

concentration in building fires, using data from the Harvard and Cal Tech hood experiments [3, 

9], the Virginia Tech enclosure studies [11], and the NIST reduced-scale enclosure experiments 

[10, 19]. Several CO formation mechanisms were identified, which were substantiated by 

detailed chemical kinetic modeling. While the GER concept is of limited utility for predicting the 

local CO concentration, important aspects of enclosure fire dynamics and chemistry are 

highlighted in this paper. 

Several recent experimental studies [18-20] have used very small scale enclosures (0.21 m3

, 

0.06 m3

, and 0.05 m3, respectively) while investigating under-ventilated burning of propane and 

heptane fires. These bench-scale studies described the structure and dynamics of under-ventilated 

burning including extinction, flame projection and flame stability. Another recent study [21, 22] 

has used an intermediate-scale enclosure similar to that used for this paper, but a roof vent was 

added as well. 

Most recently a previous component of this research project focused on similar experimental 

measurements of a Reduced Scale Enclosure (RSE1)[5]. The RSE was a 2/5 scale ISO 9705 

room designed based on the previous studies of Bryner [9]. Similar to Bryner’s experiments, 

natural gas served as a fuel; the burning of heptane, toluene, methanol, ethanol, and polystyrene 

 

1

 The data from this set of experiments is currently available online at http://www.fire.nist.gov/testdata/RSE/ 
4 

was also investigated. In most experiments, the fuel was controlled and metered by flow valves 

or pumped into a pool burner or spray nozzle. Experiments were run to near-steady conditions. 

Multiple fire sizes were run consecutively to decrease the time required to approach steady-state. 

Ventilation was varied during some experiments by modifying the door opening. Two types of 

enclosure lining materials were investigated and compared. 

Recently, NIST has conducted a number of high-profile case studies in which realistic-scale 

mock-ups of actual fire scenarios were recreated with the ultimate goal of improving building 

codes and standards. These studies included the World Trade Center disaster investigation [23] , 

the Rhode Island Station nightclub fire [24], and the Chicago Cook County Administration 

Building fire investigation [25]. The compartment fires in all of these studies burned real 

furnishings and became under-ventilated as the fire evolved. In addition, a series of large-scale 

compartment fire experiments were conducted to simulate an over-ventilated fire in a nuclear 

power plant cable room [26] to provide data for fire model validation. 

1.3 Experimental Scope

While some previous studies have considered the mixture fraction to analyze experimental 

compartment fire data, few have considered minor hydrocarbon species and with the exception 

of Ref. [5] none have considered soot. In tandem, accurate measurements of temperature at these 

same locations allowed analysis of thermal effects on species concentrations. A wide range of 

fuel types were considered, including aliphatic hydrocarbons (natural gas and heptane), aromatic 

hydrocarbons (toluene, polystyrene) and an alcohol (isopropanol). 

The series of experiments reported on here was conducted in a full scale (ISO 9705 room) 

enclosure (FSE). The enclosure defined in the international standard ISO 9705 “Full-scale room 

test for surface products” [1] is an important structure in which to conduct fire research. The 

experiments repeated and extended a part of the work of Bryner and coworkers [9] as well as the 

authors previous work with a reduced scale enclosure [5]. Similar to Bryner’s experiments, 

natural gas served as a fuel; the burning of heptane, toluene, iso-propanol, polypropylene, nylon, 

and polystyrene were also investigated. The fuel was either allowed to burn freely in a pan or 

controlled and metered by flow valves or pumped into a pool burner or spray nozzle. 

Experiments were either run as free burns or at near-steady conditions. Multiple fire sizes were 

run consecutively to decrease the time required to approach steady-state. Ventilation was varied 

during some experiments by modifying the door opening. 

Temperature and species composition measurements in the current experiment were made at 

many of the same nominal locations (scaled where appropriate) as studied previously by Bryner 

et al,[9] and Bundy et al [5]. Measurements included O2, CO, CO2, total hydrocarbons, 

temperature, and heat fluxes. One emphasis of this series was to further develop techniques for 

the measurement of hydrocarbons and soot. Hydrocarbons were measured with FID analyzers 

(total hydrocarbons) and gas chromatography (GC). The GC measurements were used to 

independently validate the total hydrocarbon measurements and to allow accurate determination 

of species mass distribution. The quantification of hydrocarbon species was needed to describe 

the chemical structure of under-ventilated fires. Soot samples were extracted from within the 

enclosure and measured gravimetrically. Optical soot measurements were also performed. 
5 

The fuels included in this test series were selected to cover a wide range of combustion 

properties and to simulate fuels encountered in actual building fires. Gases, liquids, and solids 

were selected for testing to cover a wide range of physical properties. Realistic materials 

represent complex multi-component fuels. In this study, all of the fuels selected were 

homogeneous single component fuels to simplify the analysis and to attempt to find 

generalizable trends in the results. Real materials are often oxygenated. This includes many 

types of commodity materials including nylon (e.g., carpet), cellulose (e.g. paper and building 

products), polyester (e.g., fabric), epoxy (e.g., adhesives), polymethylmethacrylate (PMMA), and 

polyoxometalate (POM ). In this study, iso-propanol was selected as a surrogate to represent 

the compartment fire chemistry in the burning of oxygenated fuels. 

In a real compartment fire, fuel sources are physically distributed throughout the compartment. 

In this study, a multiple locations for the fuel were used to simulate this effect for the purpose of 

model validation. Multiple fuel locations allow for comparison with single fuel sources and add 

value to the overall research product. 

Heat feedback and natural ventilation give rise to important aspects of the structure and 

dynamics of the fire, such as the temperature field and the spatial distribution of combustion 

products. This study deliberately set out to investigate representative fire conditions at two key 

locations in the upper layer of the compartment, which were selected based on the geometrically 

scaled locations used previously [5]. The upper layer locations were selected to provide two 

distinct conditions in the upper layer, one relatively close to the natural ventilation flow of fresh 

air through the doorway and the other relatively far from the doorway, on the far side of the fire 

source. Combined gas species and temperature measurement probe was situated in the room 

and moved along a vertical line to provide additional data. The vertically moving probe allowed 

for sampling in the upper layer, lower layer or within the transition as deemed useful by the 

researchers. Two thermocouple trees were also situated in the room in order to evaluate the 

vertical thermal profile within the room. To enhance the range of conditions investigated and in 

an attempt to seek information on the relationship between the combustion products and local 

fire conditions, a broad range of fire heat release rates and a number of very different fuel types 

were selected for study. At the same time, the effect of compartment ventilation was changed to 

induce a range of mixing and compartment fire conditions. 
6 

2 EXPERIMENTAL DESIGN

2.1 Design of the room

The dimensions of the ISO 9705 room were used in this experiment due to its wide utilization in 

other works and to build upon the previous experiments with the reduced scale enclosure (RSE) 

which was purposefully scaled to 2/5 of the ISO 9705 dimensions. The RSE investigation looked 

at a variety of room construction materials and helped to guide the development of the final 

design of the ISO 9705 room which was used here. 

2.1.1 Dimensions

The experiments discussed in this report are based on the dimensions of the ISO 9705 room [1]. 

The full scale enclosure (FSE) is illustrated in Figure 2.1. The design internal dimensions of the 

room were set to the ISO 9705 standard to be 240 cm x 240 cm x 360 cm with a doorway of 80 

cm x 200 cm. The floor of the enclosure was raised 35 cm above the ground. Fractional 

doorways were also utilized with a Doorway Fraction, DF, defined as the fractional width (and 

therefore area) of the 80 cm door. The height of the door was not varied. Due to the nature of the 

lining material and the fasteners used to hold it in place there is some variability in the actual 

dimensions of the room. However, the as built dimensions were measured extensively and all 

uncertainty was found to be within ± 2 cm, well within the tolerance of the ISO 9705 standard of 

± 5 cm. Additional measurements were taken periodically within the room during the 

experimental tests and never exceeded an uncertainty of ± 2 cm. 

2.1.2 Materials

The support structure of the room was built using 20 gauge (0.89 mm) steel structural studding 

and 20 gauge (0.89 mm) sheet steel. The floor of the structure was constructed of 0.48 cm thick 

steel sheet metal. The actual room used in the experiments can be seen in Figure 2.2. The studs 

and sheet metal were built such that their internal dimensions were 10 cm greater than the ISO 

9705 standard. On top of the sheet metal (on the interior surfaces) were installed two layers of 

2.5 cm thick, 128 kg/m3

 density, ceramic fiber blanket, K-litetm HTZ. The blanket was composed 

of 30 % AL2O3, 54 % SiO2, 16 % ZrO2, and trace amounts of other components. The uncertainty 

in the composition of the primary four components is ± 1 %. The ceramic fiber blanket was held 

in place by alumina ceramic (99 % Al2O3) insulation retainers (Refractory Anchors Inc. model 

RA38) with a depth of 5 cm. These anchors are shown in Figure 2.3. The ceramic anchors were 

secured to the sheet steel wall with self-tapping sheet metal screws and washers. Insulation 

retainers were installed in the ceiling studs, spaced 40.5 cm, at 30.5 cm intervals along each stud. 

On the walls the insulation retainers were also installed with an arrangement of 40.5 cm by 

30.5 cm near the top of the wall with the spacing increasing to 40.5 cm by 70 cm as the retainer 

placement approached the floor. Extra retainers were placed as necessary to hold edges and 

corners securely in place. 

This structure design proved to be quite robust. Through a series of 24 tests only minor repairs to 

the blanket and ceramic retainers were necessary. The steel skin and steel studs held up well with 

the exception of the portions of the structure framing the doorway. Figure 2.2 shows that in the 

vicinity of door way the ceramic fiber insulation was wrapped around the doorway to protect it 

from the heat and radiation from the room. This additional insulation was not sufficient to protect 

the studs from excessive heat causing them to soften and deform over time. This situation was 
7 

further exacerbated by the convective heat transfer from the hot, fast moving gasses leaving the 

enclosure. 

Figure 2.1 Internal dimensions of ISO 9705 enclosure used in these experiments including multiple door widths and gas 

sample and temperature probe locations. All dimensions have an uncertainty of ± 2 cm. 
8 

Figure 2.2 Photograph of the actual ISO 9705 room used for experiments. The structural construction of sheet steal on 

steel studs can be seen along with the internal surface covering of ceramic fiber blanket. 

 

Figure 2.3 Ceramic insulation retainers used to secure the ceramic fiber blanket to the sheet steel walls. The actual 

retainer is shown (left) as well as its installed configuration (right). 
9 

2.1.3 Doorway Dimensions

A 20 cm doorway (1/4th of the ISO 9705 standard) was used for the majority of the experiments 

in order to force the room to reach under-ventilated conditions with a smaller fire size and 

therefore limiting the temperatures and thermal radiation within the room. Several other doorway 

widths were also utilized in order to evaluate the effect of the vent area. In addition to the 1/4 

width (20 cm) door, a full ISO 9705 door (80 cm) width, a 1/2 width (40 cm), and a 1/8 width 

(10 cm) doorway were considered. The height of each doorway was held constant at 200 cm. The 

ISO 9705 structure was not modified in order to create the different door widths, instead inserts 

were constructed from steel studding and ceramic fiber blanket. The doorway inserts allowed for 

a quick change of the door size as well as keeping the doorway accessible for work inside the 

room. Unfortunately, repeated heating and cooling of the door inserts resulted in deformations. 

Every attempt was made to ensure that proper door sizing was maintained, however due to 

variations there is an uncertainty of ± 10 % in the doorway widths. 

The specific door dimensions for each test are included in the description of test conditions (refer 

to Table 3.1). In some places in the document the doorway fraction (DF) was used to indicate the 

width of the doorway utilized. 

2.1.4 The Burners

Two primary types of burners were utilized, free-burn fuel pans and a spray burner. Additionally, 

a pump-fed, water cooled liquid burner and a gravel filled natural gas burner were also utilized 

for a limited number of tests. 

The free-burn pan type burners were constructed from welded sheet steel 0.635 cm thick. Two 

each of burners with internal dimensions sized at 50 cm x 50 cm (0.25 m2

), 70.7 cm x 70.7 cm 

(0.5 m2

), and 100 cm x 100 cm (1 m2) each with a 10 cm lip were constructed as illustrated in 

Figure 2.4. The uncertainty in the burner dimensions was ± 0.5 cm, not taking into account 

warping that occurred during the experiments. The burners were used individually and in 

matched pairs to simulate single and distributed fuel loads. The burners were positioned in the 

geometric center of the floor (position 1) and/or along the centerline of the room next to the rear 

wall (position 2) as illustrated in Figure 2.5. The single burner cases were also moved between 

the two discrete positions (1 and 2) to simulate various fuel package locations. 

Each of the free-burn fuel pans was mounted through the floor to one of two load cells, Mettler 

Toledo, Jaguar KCC150 or KCC300, each with a measurement accuracy of ± 1 g. In this way the 

fuel loss rate could be measured to calculate the ideal heat release rate and combustion efficiency 

of the free burn cases. Additionally this configuration allowed for a measurement of fuel being 

collected in the pan beneath the spray burner for those cases. 

One 0.5 m2 (70.7 cm x 70.7 cm) pan in position 1 (cf. Figure 2.5) was also used with the spray 

burner configuration as well. Different spray nozzles were utilized depending on the desired fuel 

flow rate. All spray nozzles were BETE Low Flow/Full Cone Whirl nozzles. WL 1 and 

WL 1-1/2 were both utilized, both were constructed from stainless steel and featured a 90 degree 

cone angle. The pump flow rate was varied in order to provide different flow rates at the nozzle 

to produce different fire sizes. A load cell was utilized in the spray burner configuration in 

addition to the pump flow-rate monitoring to determine if any fuel collected in the pan. In this 
10 

way all of the fuel from the spray burner could be accounted for and measured to calculate the 

overall combustion efficiency. 

Figure 2.4: Free-burn and spray burner pan construction and dimensions. The dimensions of 50 cm, 70.7 cm, and 100 cm 

are all internal burner dimensions. All burners had a lip height of 10 cm. 

Figure 2.5: Positioning of free-burn pan burners. The burners of different size were placed at the geometric center of the 

floor and/or along the centerline against the back wall. Pans in either position were mounted on load cells to measure the 

mass loss (or gain in the case of the spray burner) to determine fuel loss rate. For the spray burner cases only a single 70.7 

cm x 70.7 cm pan was used in the center of the floor to catch the fuel spray. Both the pump fed pool burner and the gravel 

filled natural gas burner were located at position 1 inside the room. 
11 

2.2 Overview of equipment

2.2.1 Heat Release Rate Measurement

Heat Release Rate (HRR) measurements were conducted using the 6 m × 6 m calorimeter at the 

NIST Large Fire Research Laboratory (LFRL). The HRR measurement was based on the 

oxygen consumption calorimetry principle first proposed by Huggett [27]. This method assumes 

that a known amount of heat is released for each gram of oxygen consumed by a fire. The 

measurement of exhaust flow velocity and gas volume fractions (O2, CO2 and CO) were used to 

determine the HRR based on the formulation derived by Parker [28]. A detailed description of 

the methodology used for this measurement can be found in a previous report [29]. In 2001, the 

6 m × 6 m square hood was installed in the LFRL. A schematic drawing of the 6 m square hood 

is shown in Figure 2.6. The exhaust flow rate and extractive gas measurements were performed 

in a horizontal straight section of the 152 cm diameter duct on the roof of the large fire lab. Six 

bi-directional probes, located on the vertical centerline, were used to measure the exhaust flow 

velocity. Because of the non-uniform shape of the velocity profile, a flow calibration coefficient 

was used in the HRR calculation. The flow coefficient was determined using a natural gas 

burner to conduct a five point calibration before and after the test series. The flow calibration 

coefficients ± 2σ for these tests ranged from 0.906 ± 0.04 to 0.933 ± 0.05. The calibrations were 

performed over a range of fire sizes from 500 kW to 3000 kW. The exhaust mass flow rate for 

the experiments described here varied from 12 kg/s to 17 kg/s. 

Exhaust gases was sampled through a perforated tube cross in a horizontal section of the duct 

downstream of the velocity probes. Figure 2.7 shows the exhaust gas sampling system. The 

main difference between this system and the one previously reported [29] was the method for 

removing water from the gas sample. The current system uses a Nafion® dryer instead of a dry 

ice cold trap. Nafion is a copolymer of tetrafluoroethylene (Teflon®) and perfluoro-3,6-dioxa-4-

methyl-7-octene-sulfonic acid. A dew point meter was added to monitor the efficiency of the gas 

dryer. The dew point temperature meter measures the change in electrical impedance of a 

hygroscopic conductive polymer in the range of -80 °C to 20 °C. The delay time from the gas 

sample tube to the analyzers was 25 s. Measurements of exhaust soot and total hydrocarbons 

were not performed, because in most cases they have negligible effect on the HRR measurement. 

The combined expanded relative uncertainty of the HRR measurements reported here was 14 %, 

based on a propagation of uncertainty analysis [29]. The exhaust mass flow rate was the largest 

component of uncertainty in the HRR measurement. A list of commercial equipment used for 

all of the measurements described in this report can be found in Appendix B. 

 
12 

Figure 2.6: Schematic drawing of 6 m square hood and exhaust stack instrumented for calorimetry measurements. Taken 

from Ref. [29] 
13 

Figure 2.7: Exhaust gas sampling system used for heat release rate measurement. 

2.2.2 Gas analyzers

Gas species were continuously measured at two locations (front and rear) inside the FSE during 

each of the tests and sometimes at a third location (vertically moving probe near rear on 

centerline). Oxygen was measured using paramagnetic analyzers. The 10 % to 90 % response 

time (t10-90) of the oxygen analyzer was less than 12 s. Carbon monoxide and carbon dioxide 

were measured using non-dispersive infrared (NDIR) analyzers. The t10-90 response time for the 

CO2/CO analyzers was less than 5 s. Total hydrocarbons were measured using two flame 

ionization detectors (FID) having a t10-90 response time of less than 1 s. A gas chromatograph 

(GC) was used intermittently during some of the tests at the front and rear gas sampling location. 

The cycle time on the GC measurements was 2 min. The dried sample gas dew point 

temperature was measured using a thin polymer sensor. Soot and temperature were also 

measured at these two locations. The total delay times for each of the analyzers were measured 

by initiating a small flame at the gas sample probe inlet and timing how long until a response 

was recorded by the gas analyzers. A summary of the delay times for each of the three sample 

probes discussed above is presented in Table 2.1. 

The three total hydrocarbon analyzers used in these experiments were designed to measure high 

volume fractions of hydrocarbons. The analyzers were factory calibrated for up to 50 % volume 

(43 L/min)

Disposable

desiccant

tube

CO2=1.0 L/min

CO=1.0 L/min

O2=0.2 L/min

O2, bypass=2.8 L/min

Excess Sample Flow Enclosure:

Pump, Filter 

and 

Blow Back Air Heated teflon line (93 °C)

Dry purge 

air (or N2) in Wet purge 

air (or N2) out

Nafion tube dryer (2 m)

(5 L/min)

Dry flow 

to analyzers

Beaded

cold trap

(0 °C to 10 °C)

(~ 10 L/min)

3m X 3m hood

Exhaust stack

(D = 0.48 m)

Ball valve

3-way valve

Dew point meter 

Filter

Flow meter

Mass flow controller 

Pressure gauge

Pump

Ball valve

3-way valve

Dew point meter 

Filter

Flow meter

Mass flow controller 

Pressure gauge

Pump

Gas sampling

Calibration gases

N2(100%)

O

CO(0.28%)

2(20.95%)

CO2(2.80%)

CH4(0.0093%)

Calibration gases

N2(100%)

O

CO(0.28%)

2(20.95%)

CO2(2.80%)

CH4(0.0093%)

6 m x 6 m hood

D1.52 m
14 

fraction of hydrocarbons as methane and were capable of measuring even higher concentrations. 

The primary span gas used for these tests was 20 % volume fractions of methane with a balance 

of nitrogen. A span gas of 1 % methane was also used to periodically check the linearity of the 

detector. The FID burner fuel used was 40 % hydrogen and 60 % nitrogen on a volumetric basis. 

The expanded (k = 2) relative uncertainty of each of the span gas volume fractions, including 

CH4, CO, CO2, and O2 was ± 1 %. 

Each hydrocarbon analyzer had an internal filter to prevent soot from accumulating in the 

plumbing and internal sample pump which could lead to less sensitivity due to hydrocarbon 

contamination and also deterioration of some components of the instrument. It was later 

determined that additional external filtration of soot was necessary to protect the analyzer and 

enable a sufficient time period for sampling soot-laden flows. The external filter could be 

replaced much more frequently and easily than the internal filter. 

Two liquid cooled probes were used to sample gas inside the enclosure at the front and rear 

locations. The 1 m long probes were constructed of 3 concentric stainless steel (type 304) tubes. 

Liquid coolant (water) was forced through the inner shell and returned through the outer shell. 

This design allowed the cooling fluid to condition the entire length of the probe. The inner 

diameter of the sample probe was 4.0 mm. The front and rear gas sample systems were identical, 

except the GC measurement was conducted continuously only at the front sample location and a 

gas sample storage system was used at the rear location. The moving sample probe did not 

include GC analysis. 

The third, moving sample probe was constructed from an aspirated thermocouple. The aspirated 

thermocouple flow rate was set at 50 SLM and the gas sample was split off from that stream and 

pumped at 1 LPM to the gas analyzers. 

The sample probes shown in Figure 2.8 were cooled using house water heated to 55 °C at a flow 

rate of 1 L/min. The total hydrocarbon analyzers were placed in the gas racks with the other 

analyzers. The gas sample stream water was removed with membrane dryers consisting of a 

bundle of Nafion tubes purged with dry air to selectively remove moisture from the sample 

stream. The Nafion conditioner has no effect on most of the gas species of interest, however, 

polar organic compounds (i.e. ketones and alcohols) are trapped by the dryer. A large area filter 

was added between the heated line and gas dryer to collect soot. Because the external filters and 

transfer lines after the gas dryer were not heated, there was a potential loss of high molecular 

weight hydrocarbons due to condensation. Due to limitations in the flow capacity of the dryer, 

the gas analyzers were connected in series. A mass flow controller set to 1 L/min was used to 

control the flow through the O2/CO2/CO analyzers. The flow to the hydrocarbon analyzer was 

split prior to the mass flow controller. A 5 way ball valve was connected to each analyzer to 

switch between the gas sample, zero calibration gas and span calibration gas. A dew point 

transducer was connected to the sample gas line prior to the oxygen analyzer. The oxygen 

analyzer had separate inlet ports for zero and span gases. A needle valve was used to set the total 

flow to 3 L/min (only a small fraction of this passed through the FID). The bypass flow from the 

hydrocarbon analyzer was connected to the injection port of the GC (front sample location) or 

the gas sample storage system (rear sample location). 
15 

Figure 2.8: Schematic drawing of gas sampling system. 

Table 2.1: Total delay times for the three gas sample probes used in the experiment. All delay times have an expanded 

uncertainty of ±2 s. 

Channel Delay time (s)

O2Rear 25 

CO2Rear 21 

CORear 21 

UHRear 20 

O2Front 23 

CO2Front 19 

COFront 18 

UHFront 12 

O2Move 19 

CO2Move 15 

COMove 14 

UHMove 10 

Heated SS line (11.8 m)

 liquid-cooled probe (4.7 m)

Gas rack

RSE

enclosure

FSE

Sample conditioning system Blow back air

CO2

O2

CO

Vent from FID

to GC

Total Hydrocarbon Analyzer

(1 L/min)

(3 L/min)

Calibration gases

Water

(T = 30°C)

Drain Wet sample

Wet purge 

gas

(15 L/min)

Membrane 

dryer

Dry purge 

gas (air)

Electric temperature

controller (T = 65°C) Heated 

enclosure

Heater Dry sample 

to gas rack

Ball valve

3-way valve

5-way valve

Dew point meter

Filter

Filter

Flow meter

Mass flow controller

Pump

Ball valve

3-way valve

5-way valve

Dew point meter

Filter

Filter

Flow meter

Mass flow controller

Pump

Vent

Vent

FID

Bypass

N

2

O

CO2

CH4

To total 

hydrocarbon

analyzer

Metering

valve

O2 (20.85 %) 

CO (3.99 %) 

CO2 (9.00 %) 

N2 (100.0 %) 

CH4 (20.00 %) 
16 

2.2.3 Gas Chromatography

A micro gas chromatograph (GC) was used periodically during the FSE tests. The GC was able 

to quantify a number of stable fuel, intermediate, and combustion product species extracted from 

the FSE during each test. An Agilent 300A micro-GC was used to quantify the species. 

Chromatographic separation of species was achieved by four columns working in parallel. A 

molecular sieve 5A, Plot-U, OV-1, and Stabilewax columns were used. Thermal conductivity 

detectors (TCD) were used on each column. A carrier gas of Helium was used on most of the 

columns while Argon was used on the mole-sieve column. Due to the similar thermal 

conductivity of Helium and Hydrogen it is difficult to distinguish between the two of them with 

the TCD, Argon, with a significantly different thermal conductivity, being different from any of 

the species we were expecting to find allowed for the quantification of a larger number of gas 

species. A summary of the different columns, their physical specifications, and the GC 

parameters used during analysis are listed in Table 2.2. Due to the nature of this particular GC, it 

allows for very fast methods to identify species, a method lasting only 2 minutes was utilized to 

provide a large number of data samples from each experimental run. The tradeoff to the high 

speed of the analysis was reduced sensitivity compared to conventional GCs. This means that the 

detail and separation of individual heavy hydrocarbons was sacrificed in order to provide a larger 

number of measurements of gas species such as hydrogen, methane, and nitrogen which are very 

important but not available from any other analysis utilized here. 

Identification and quantification of gaseous species was accomplished by the use of gas phase 

calibration standards. Due to the wide variety of columns used and the large number of species 

and varying quantities that can be potentially identified, several different gas standards, listed in 

Table 2.3, as well as locally made calibrations for high concentrations of CO2, H2O, and CH3OH 

were utilized to create the calibration for the GC. 

 
17 

Table 2.2. List of micro-GC columns, specifications, and GC parameters used during FSE experiments. 

Mole-Sieve PlotU OV-1 Stabilwax 

Inlet Backflush Backflush Variable Variable 

PreColumn PlotU PlotQ None None 

 Film 30.00 μm 10 μm N/A N/A 

 Diameter 320.33 μm 320.00 μm N/A N/A 

 Length 3 m 1 m N/A N/A 

Film 12.00 μm 30.00 μm 2.00 μm 0.50 μm 

Diameter 320.00 μm 320.00 μm 150.00 μm 250.00 μm 

Length 10 m 8 m 8 m 10 m 

Detector TCD TCD TCD TCD 

Carrier Gas Argon Helium Helium Helium 

Table 2.3. List of calibration standards and precision analyzed gases that were utilized for GC calibration. 

Gas Standard 

Identification Species Quantity Uncertainty 

Restek 

Refinery Gas #2 

SN: 480885 

H2, Ar, N2, CO, CO2, 

CH4, C2H6, C2H4, 

C2H2, C3H8, Æ C6H14

0.10% -- 37.287% ±1 % 

Scotty 

Lot No. 612201B 

Mix: 01-04-235--14 

1-Butene, Ethylene, 

1-Hexane, 1-Pentene, 

Propylene 

1000 ppm ±5 % 

Scotty 

Lot No. 612203B 

Mix: 01-04-224--14 

N-Butane, Ethane, 

N-Hexane, Methane, 

N-Pentane, Propane 

1000 ppm ±5 % 

 
18 

Analysis of variance (ANOVA) and regression analysis were employed in an effort to determine 

the uncertainty associated with the quantification of the gas species. The result of this analysis 

was the uncertainty of a single value, Sy, calculated from the calibration curve. This value was 

combined with the uncertainty of calibration gases and additional type B uncertainty and is 

presented as expanded uncertainty with a coverage factor of k=2 in the data set and the 

appropriate plots. The equations utilized for the analysis to determine Sy are show below: 

( )

xx

i regression

S

y y

m N

s

y s 2

2

1 1

β β

− = + + (1) 

where, 

( ) ( )

( )

2

2

−

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

= N

S

S

S

regression

xx

xy

yy

s (2) 

( )

N

y

s y yy

2

2 ∑ = ∑ + (3) 

( )

N

x y

s xy xy

∑ ∑ = ∑ + (4) 

( )

N

x

s x xx

2

2 ∑ = ∑ + (5) 

m = number of measurements of the unknown sample 

N = number of calibration curve points (typically, 3) 

y = TCD area count of calibration species 

x = volume fractions of calibration species 

yi = TCD area count of unknown species 

β = slope of linear least squares fit to calibration points 

The results of this analysis are included in all of the quantification graphs for each of the fuels 

examined in this program. This value was combined with the uncertainty of calibration gases 
19 

and additional type B uncertainty and is presented as expanded uncertainty with a coverage 

factor of k = 2 in the data set and the appropriate figures in this report. 

2.2.3.1 Gas Sample Storage System

The GC described above is a powerful and fast tool for analyzing gas samples. However, it only 

measures a single sample at a time. As described above data was taken primarily at two separate 

locations for this investigation and it is desirable to sample both locations simultaneously. To 

this end a gas sample storage system was designed to collect and store gas samples from the 

other discreet spatial point in the FSE for later analysis. The system in question is schematically 

illustrated in Figure 2.9. 

The three primary valves are the Vici 6-Port switching valve, model number ED46UWE, the 

Vici 4-Port switching valve, model number ED44UWE, and the Vici 16 position switching 

valve, model number EMT4ST16MWE. These valves were sequentially switched in a particular 

order depending on the operation being conducted. The switching sequences was generically 

divided into two categories: Sample Acquisition and Sample Analysis. 

A diagram of the sample storage system is presented in Figure 2.9, and the operation of the 4port 

and 6-port switching valves is illustrated in Figure 2.10. In sample acquisition the gas sample 

entered the sample port and flowed through the 4-port valve into a long coil of tubing, with a 

volume of ~100 mL.The sample then flowed through a 6-port valve and into the 16 position 

valve and 10 mL sample storage loop. After flowing through the sample storage loop the sample 

flowed through the 6-port valve again and out through the vent of the 6-port valve. Once a 

sufficient quantity of sample had flowed so that the sample storage loop was full of the sample, 

generally 2 minutes for this particular apparatus, the 6-port valve vent was closed and the 4-port 

valve switched to pressurize the sample still stored in the tubing coil and the sample storage 

loop. This step ensured that each sample was stored at the same pressure, placing the apparatus 

in an oven ensured each sample was stored at the same temperature. A summary of the control 

settings for capturing and analyzing gas samples from this system is provided in Table 2.4. 

To retrieve the samples for acquisition the coil was first flushed with helium. The 16-position 

valve switched to the loop which was to be analyzed and the pressurized helium pushed the 

sample out of the loop and into the 6-port switching valve which fed the sample directly to the 

GC. At this point there was no flow and the sample was pressurized in the line upstream of the 

GC. The internal GC sample pump was used to draw the sample into the GC for analysis. The 

timing of the internal GC pump was critical because there was helium pressurized both upstream 

and downstream of the sample and the GC pump must act just long enough to ensure that only 

the sample gas was injected into the various columns of the GC. For the specific equipment used 

here there were two sample pumps with a capacity of 250 ml/min in the GC and it was found that 

running them for 15 s ensured that only the sample gas was injected into the columns. This time 

can vary based on the GC being used, the length and diameter of tubing and the pressure of the 

helium. After the sample was analyzed the 6-port valve switched to vent the remaining sample 

and purge the sample loop with helium. Then the 6-port valve switched back to the GC, the 16-

position valve advanced to the next loop and the procedure was repeated until all of the samples 

had been analyzed. A summary of the control settings for capturing and analyzing gas samples 

from this system is provided in Table 2.4. 
20 

Figure 2.9: Schematic diagram of gas sample storage system in position B-A. 

Figure 2.10: Positions of the control valves for the gas sample storage system. 

Position A 

Position B 

4 Port Valve 6 Port Valve 

He 

He

Vent

Vent

GC 

Sample 

In 

Coil

Coil

Into Storage 

Loops

He 

Vent

Coil

Sample 

In 

From 

Storage 

Loops 

He 

Vent

GC 

Coil

Into Storage 

Loops

From 

Storage 

Loops 

Sample 

In 

Vent 

He 

@ 20psi 

GC 

Vent 

Sample Storage 

Loops 

16-Pos. 

Valve 

4-Port 

Valve

6-Port 

Valve

Oven @ 90 °C 

Exhaust Vent 

Solenoid

Inlet Vent 

Solenoid 
21 

Table 2.4: Sequence of controls for storing and then analyzing gas samples in the gas sample storage system. 

Operation Δt 4 

Port 

6 

Port 

16 

Position 

Exhaust 

Vent 

Solenoid 

Inlet 

Vent 

Solenoid 

Sample Collection (sample number N) 

Flow Sample 120s A A N closed open 

Pressurize Sample Loop 10s B A N open closed 

Close Loop, Flush Coil 10s B A N+1 open open 

Analyze Sample (sample number N) 

Send Sample 240s B B N closed closed 

Flush Sample Loop 10s B A N closed open 

2.2.4 Soot Samples

2.2.4.1 Gravimetric

A gravimetric sampling system (shown in Figure 2.11) was used to measure soot mass fractions 

at the two sample locations within the enclosure. The design of the soot probe was similar to the 

gas sampling probes except the inner diameter of the sample tube was 6.4 mm. The soot 

sampling probes were conditioned with 65 °C water flowing at 1.0 L/min. A three way solenoid 

valve was used to rapidly switch from the bypass to sample flow. A sample gas mass flow rate of 

2.75 standard L/min (N2 @ 0 °C, 101.3 kPa) was drawn through the collection filter for a period 

of 60 s to 300 s. The collection filter was a 47 mm round Zeflour membrane filter with an aerosol 

retention efficiency of 99.99 % for 2 μm sized particles. A gas correction factor was applied to 

the mass flow rate measurement to account for the gas composition in the enclosure. The amount 

of time for sampling was determined by monitoring the pressure drop across the filter to ensure 

an optimal amount of filter loading. 

The collection filters (shown at the base of the probes in Figure 2.11 below) and probe cleaning 

pads were conditioned in a desiccant drier before and after the tests. The conditioned filters were 

weighed using an analytic mass balance with an expanded uncertainty of 0.12 mg. After each 

soot sampling period, the probe was cleaned twice with gun cleaning pads. The total soot mass 

collected on both the filter and 2 cleaning pads was used in determining the soot mass fraction. 

Both the soot mass and sample mass flow rates were measured on a dry basis. For most of the 

tests conducted in this series between 10 mg and 200 mg of soot was collected during the 1 min 

to 5 min sample time. The extracted gas volume was corrected for the water removed by the 

method described in Sec. 0. The combined expanded relative uncertainty of the soot mass 

fraction measurement (for mass fraction measurements greater than 0.001 g/g) was in the range 

of 2 % to 5 % based on a propagation of uncertainty analysis. 
22 

Figure 2.11: Schematic drawing of gravimetric soot sampling system. 

RSE

enclosure

FSE

Temperature 

Controlled 

Water bath 

(T=65 °C)

Water-cooled

sample probe

HEPA filter

(T=70 °C)

Bypass

intake

Standby probe

vent

LFL rack

( 2.75 L/min N2)

Beaded 

dry ice trap

Coiled wet 

ice trap

3-way valve

Filter

Mass flow controller

Pressure gauge

Pump

3-way valve

Filter

Mass flow controller

Pressure gauge

Pump
23 

2.2.4.2 Real time extractive

The real-time extractive soot probe was designed to measure the local soot concentration at a 

single location inside the enclosure using a light extinction method [30]. The probe continuously 

extracted a sample through an optical path; the measured attenuation of a laser passing through 

the sample was used to determine the soot mass concentration. Sample extraction was 

performed using a rack identical to the one shown schematically in Figure 2.11 by the dashed 

box labeled “LFL rack”. A schematic of the probe is shown in Figure 2.12. The main section of 

the probe was constructed from two coaxial stainless steel tubes with a cap welded to each end, 

forming a seal around the annulus between the tubes. The sample was drawn through the inner 

tube, past the measurement section and out through a particulate filter. The inner tube had an 

outer diameter of 2.5 cm (1 in), a wall thickness of 3.2 mm (0.125 in) and was constructed from 

porous 316 stainless steel. The outer tube had an outer diameter of 5.1 cm (2 in), a wall 

thickness of 3.0 mm (0.120 in) and was constructed using 316 stainless steel. The sample gas 

flow rate was controlled by a mass flow controller (MFC) calibrated for N2. The set point of the 

MFC was held fixed at 4 standard L/min (N2 @ 0 °C, 101.3 kPa) for all tests. The actual flow 

rate was then obtained by correcting for the time-dependent local gas concentrations at the probe 

inlet based on the gas species analysis presented in Section 3.5. 

Thermophoretic soot deposition was avoided by a nitrogen purge which flowed into the annular 

region between the tubes and was forced through the porous inner tube. The porous steel tube 

had a fine pore size (99.9 % collection efficiency for 0.2 μm particles) to maximize the pressure 

drop of the purge gas and distribute the flow as evenly as possible through the tube wall. The 

pressure drop associated with a typical 3.2 L/min N2 purge flow was calculated to be 

approximately 1 kPa. The corresponding velocity at the inner tube surface was 0.7 mm/sec. The 

section of probe that was exposed to the heated environment inside the enclosure was protected 

by water cooling consisting of 6.4 mm (0.25 in) copper tubing wrapped around the exterior of the 

probe and a layer of the same ceramic fiber blanket used to cover the walls. House water (15 °C) 

flowed through the copper tubing at a rate of 0.95 L/min during the tests. The overall probe 

length was 1.22 m; the probe was inserted 61 cm (24 in) into the enclosure. The probe was 

positioned near the rear gas sampling probe (location specified in Table 2.5) so that sample 

conditions (temperature, species concentrations) could be determined. 

The measurement section was located 1.12 m (44 in) from the sample inlet point. Two 1.9 cm 

(0.75 in.) O.D. tubes were welded to the probe to provide access for the laser and detector. Each 

of these tubes was connected to commercially available stackable lens tubes that were used to 

align the laser and detector and to shield the detector from stray light. A low-flowing nitrogen 

purge was used to prevent combustion products, including soot, from entering the tubes. The 

optical path was defined by the spacing of the optical tubes, which were flush with the inner 

diameter (1.9 cm) of the porous sample tube. The beam from a 780 nm diode laser was passed 

through a beam splitter to two identical high-speed silicon photodiodes. The detectors were 

sensitive to the range between 350 nm – 1100 nm. One detector was utilized to detect the 

attenuated signal that passed through the sample, the other compensated for the laser drift. 

Several optical components were placed in front of each detector. A narrow bandpass filter, 

centered at 780 ± 2 nm with FWHM of 10 ± 2 nm, acted to attenuate radiation other than that 

from the laser. A ground glass diffuser was used to expand the laser beam. Each detector was 

water cooled by coiled 3.2 mm (0.125 in) copper tubing (flowing 15 °C house water) wrapped in 

a layer of ceramic fiber blanket. 
24 

The determination of soot density (ms) from an optical extinction measurement is based on 

Bouguer’s law, in which the light extinction coefficient (K) is defined in terms of the attenuated 

intensity (I), and the reference intensity (Io) of monochromatic light passing through a 

homogeneous smoke path of distance (L ) [31]: 

ܭൌെ ௟௡ሺூ ூ ⁄ ሻబ

௅

 1 

݉௦ ൌ ௄

ఙೞ

 2 

where σs is the mass specific extinction coefficient. The recommended value of σs for flame 

generated smoke in over-ventilated fires is 8.7 m2/g ± 5.4 % (standard relative uncertainty) [31]. 

This value is based on measurement at 632 nm. It has been shown that the mass specific 

extinction coefficient is approximately inversely proportional to wavelength [32]. For this 

reason, the present analysis uses a value of σs = 6.96 m2/g. 

The expanded combined uncertainty of the soot mass concentration was computed as the sum of 

the individual standard uncertainties [u(xi)] associated with each of the terms that influence the 

soot mass measurement. Drift in the laser baseline, as measured by pre- and post-test values of 

I/Io, was the dominant contributor to the overall uncertainty. In some cases this term was small, 

on the order of 1 – 3%, however it ranged as high as 19%. The average was approximately 8%. 

The combined uncertainty of the optical soot density measurement was calculated as follows: 

ܷ௠ೞ ൌ 2ටቀ డ௠ೞ

డ୪୬ሺூ ூ ⁄ ሻబ

ቁ

ଶ

൯଴ ሻ ⁄ ܫ ܫ൫lnሺݑ

ଶ ൅ ቀడ௠ೞ

డ௅ ቁ

ଶ

ݑሺܮሻଶ ൅ ቀడ௠ೞ

డఙೞ

ቁ

ଶ

 3 ௦ሻଶߪሺݑ

The estimate of the combined relative expanded uncertainty was 30%. 
25 

Figure 2.12: Schematic of real time extractive soot measurement probe. 

2.2.5 Thermocouples

2.2.5.1 Aspirated Thermocouples

A bare-bead thermocouple situated in a compartment fire typically experiences radiative 

exchange with walls, hot smoke, flames, and the surrounding environment with the effect that 

the measured temperature is not the true gas temperature. Accurate correction for these effects is 

complex, due to temporally and spatially varying local temperatures, velocities, and species. To 

reduce the effect of energy exchange on temperature measurement accuracy, aspirated 

thermocouple probes were used in addition to bare-bead thermocouples in this study. 

An aspirated thermocouple probe is a bare-bead thermocouple contained within a small 

cylindrical metal tube through which the sample gas flows. If the flow over the bead is at least 

5 m/s, a more accurate gas temperature measurement may be obtained [33]. According to 

Blevins [34], higher flows may be required depending on the thermal environment. Aspirated 

thermocouple probes may be shielded by a single cylindrical tube or by two or more concentric 

cylindrical tubes. In either case, the flow and thermal conditions and the detailed design of the 

assembly can impact measurement accuracy. Double-shielded aspirated thermocouple probes 

based on a design from NACA, the predecessor agency to NASA, were used in this study [35]. 

Figure 2.13 shows a drawing of an end-hole type NACA design aspirated thermocouple probe. 

Models with the entrance hole perpendicular to the probe axis were also used. 
26 

Each aspirated thermocouple was connected directly to a venturi pump using 9.5 mm (3/8 in) OD 

copper tubing. A schematic of venturi pump setup is shown in Figure 2.14. Filtering and drying 

of the flow was not necessary due to the design of the venturi pump which merely blows the flow 

out into the hood. Flows were set at 24 L/min for each aspirated probe. While the volumetric 

flows were set with flow meters at room temperature to be the same for all probes, high 

temperature compartment gases produced much higher velocities at the bead compared to those 

produced by low temperature gases. The uniform setting of the cold volumetric flows kept the 

mass flows consistent across the probes. This velocity difference effect was not completely 

proportionate to the gas temperature differences since a higher flow would experience a greater 

pressure drop and flow resistance through the probe and tubing. Due to the large flows pumped 

through the aspirated thermocouple probes, the resulting temperature represents a volumetric 

average over a several centimeter diameter region at the end of the probe. For further discussion 

of the probe and gas interaction have been previously reported [5]. 

Each aspirated thermocouple probe was attached to the data acquisition system using K-type 

thermocouple wire and connectors. During each experiment, the flow meters and measured 

temperatures were monitored. These checks were performed in order to determine if any probe 

system became clogged so it could be unclogged with high pressure air. The difference in 

temperature signal between an inoperative probe and a properly flowing probe was obvious. A 

functioning aspirated thermocouple showed higher frequency temperature fluctuations due to the 

transient thermal environment and effective convective heat transfer while a non-functioning 

probe would not show rapidly fluctuating temperatures since the large mass of hot metal of the 

probe radiating to the bead and lack of convection would dampen any short fluctuations. A 

probe typically required about 1 min when activated to overcome accumulated heat and reach the 

true gas temperature. 

To evaluate measurement uncertainty and instrument time response, a series of detailed flow and 

heat transfer calculations, focusing on double-shielded aspirated thermocouples and bare-bead 

thermocouples were performed for a previous study. A detailed description of the calculations 

and results can be found in Ref. [5]. It was determined that in a worst case scenario, with a gas 

temperature of 1200 K and an ambient temperature of 300 K, the uncertainty of the aspirated 

thermocouple measurement was 25 %. However, since the aspirated thermocouples did not ‘see’ 

a large temperature difference, the uncertainty of the aspirated thermocouple temperatures were 

much less than that, typically less than 10 %. The aspirated thermocouples do however have a 

larger temporal uncertainty and tend to average temperatures over time and may miss fast gas 

temperature fluctuations due to the thermal mass of the radiation shields. 
27 

Figure 2.13: Detailed drawing of aspirated thermocouple using NACA design [34]. 
28 

Figure 2.14: Schematic drawing of aspirated thermocouple measurement hardware. 

2.2.5.2 Radiation Effects on Bare Beads

Because bare bead thermocouples were used for some measurements inside the room it is 

important to discuss the effect of radiative losses on the value of this measurement. Unlike the 

aspirated thermocouples which are specifically designed to eliminate radiative losses from the 

measurement [34] the bare bead thermocouples are subject to radiative losses. This occurs for 

example when you have an optically thin flame, e.g. premixed methane, in which the 

temperature is being measured by a thermocouple and the surrounding ambient conditions are 

much colder than the flame, e.g. 2000 K flame in a 300 K room. In some of our tests, the 

thermocouple environment is optically thick due to heavy soot loading, and the thermocouple 

does not radiatively ‘see’ a cool surface, such as the vent of the FSE. However there are some 

cases where the thermocouples may be reading very high temperatures in a optically thin 

environment with significant radiative exchange through the door with the ambient room 

conditions. 

Consider the example where there is a thermocouple located on the center of the front 

thermocouple tree. That thermocouple would be located at a position of 120 cm x 72 cm x 120 

cm in room coordinates. That places it 72 cm from the center of a door that is nominally 40 cm 

wide by 200 cm tall. Now consider that the thermocouple reads 1200 °C, the temperature outside 

the room is 20 °C and the environment within the room is optically thin. The temperature being 

Aspirated 

(end hole type)

Aspirated 

(side hole type)

Data acquisition

system

Outer shield

Inner shield

TC bead

TC

Outer shield

Inner shield

TC bead

TC High Pressure 

Air

Venturi Pump
29 

read by the thermocouple is not the actual temperature, but rather a steady state balance between 

heat entering the thermocouple by convection and heat leaving the thermocouple by radiation. 

The general expressions of heat transfer in this case, for convection and radiation, respectively, 

are: 

( ) conv conv gas bead q A hT T = − 4 

4 4 ( ) rad rad bead cold qA TT = − σε 5 

The temperature that is desired is the actual temperature of the gas, Tgas, the thermocouple bead 

temperature, Tbead, and the cold surrounding temperature, Tcold, are presumably known. One can 

then solve for the actual temperature of the gas: 

( ) 4 4

rad bead cold

gas bead

conv

A TT

T T

A h

σε − = + 6 

Since updating the temperature of the gas can change the convective heat transfer coefficient, h, 

and the emissivity, ε, so that the equation should be solved iteratively until a correct gas 

temperature is obtained. One additional complication here is that the area subject to radiation is 

not the same as the area subject to convection, Aconv ≠ Arad. If the rest of the room should be 

approximately the same temperature as the gas at the bead then the thermocouple in this situation 

only sees a small angle of the cold environment due to the size and location of the doorway. An 

analysis of this problem with the given geometry showed that the temperature change for this 

worst-case scenario of a thermocouple bead inside an enclosure was only 2 % at 1200 °C. By 

contrast, in a worst case scenario, if the bare bead thermocouple were at 30 °C, seeing an 

environment at 1200 °C, the uncertainty in the bare bead temperature reading could be on the 

order of 200 % [5]. Taking into account the other components of uncertainty including random 

variations and the inherent accuracy of the thermocouple a combined expanded uncertainty of -

20 % to +6 % with a coverage factor of 2 is reported in Table 2.6. 

2.2.6 Heat flux gauges

Total heat flux was measured at six locations during each experiment. The heat flux gauges 

were 6.4 mm diameter Schmidt-Boelter type, water cooled gauges with embedded type-K 

thermocouples. The particular model information is contained in Appendix D. The nominal 

range for the gauges was 150 kW/m2

. Schmidt-Boelter gauges measure a temperature difference 

across a thin insulating material using a thermopile to generate a voltage from the small 

temperature difference. These gauges typically generate voltages much less than 100 mV even 

for heat fluxes near their maximum range. 

Each gauge was inserted in the floor flush with the upper surface and facing vertically upward. 

The floor heat flux gauges were located in three places, just outside the doorway on the 

centerline of the floor and straddling the burner at y = 90 cm and y = 270 cm. The exact location 

coordinates for the gauges are listed in Table 2.5. The condition of the installed gauges was 

checked periodically. If significant soot accumulated on a gauge, it was brushed off. If a gauge 

was no longer flush with the surface of the floor, a note was made, but there was no attempt to 

move the gauge since the gauges were very difficult to access. 
30 

Heat fluxes as high as 300 kW/m2

 were observed. These heat fluxes are beyond the stated range 

of the gauges. According to the manufacturer, the calibrations remain linear and valid beyond 

the stated range as long as the materials do not degrade and change the sensitivity of the gauge. 

Previously the calibration of the gauges has been checked after experiencing these large heat 

fluxes [5]. Each gauge’s responsivity was found to remain within 3 % of the factory calibration. 

The main sources of uncertainty related to the total heat flux measurements are: the calibration, 

soot and dust deposition, and shifting of the gauge surface below the floor. These sources will 

be described and the total uncertainty estimated for the reported measurements. A model of 

uncertainty for heat flux gauge measurements in fire environments can be found in the study by 

Bryant et al. [36]. 

The total heat flux gauge calibration from the manufacturer was used to convert millivolt 

readings to kW/m2

. This calibration was performed using cooling water at 23 °C ± 3 °C. The 

cooling water in the Large Fire Laboratory was found to be within the same range. The 

manufacturer reported a ±3 % expanded uncertainty in the responsivity (the slope in 

kW/m2

/mV). Calibrations at the NIST facility have varied within the 3 % range of the nominal 

manufacturer’s calibration. A recent round-robin study of heat flux gauge calibration 

consistency [38] sent the same heat flux gauges to multiple laboratories around the world and 

found that while several calibrations fell within the 3 % range, if some outlier data were 

included, then the uncertainty rose to around 8 %. For this current project, an uncertainty of 

±6 % for gauge calibration was chosen as fairly conservative since the NIST calibration was 

within the 3 % range in the round-robin study. 

While the cooling water was supplied at approximately 23 °C, the fire heated the water such that 

the gauge temperature typically rose to between 40 °C and 60 °C, and less frequently to 100 °C. 

For the fires where the water temperatures increased to between 40 °C and 100 °C, the heat 

fluxes were on the order of 100 kW/m2 to 300 kW/m2 which represent blackbody temperatures in 

the 950 °C to 1300 °C range. The most extreme combination (affecting uncertainty) of cooling 

water and environment temperature would be a 75 °C increase in cooling water in a 950 °C 

environment. This combination would only have about a 0.5 % effect on the measured heat flux. 

The effect was determined by calculating the ratio of the T4

 difference between 950 °C and the 

25 °C cooling water with 950 °C and the 100 °C cooling water. This is a simplified comparison 

which assumes everything else is equal, but generates an approximation of the magnitude of the 

cooling water effect under specified conditions. 

Heat flux uncertainty due to soot and dust deposition is difficult to quantify. For many tests, 

such as those burning methanol, ethanol, and natural gas, there was little to no contact with soot 

or combustion products. Also, even for the sootier fuels at low HRRs, the lower layer remained 

as air with little opportunity for soot-laden gases to contact the gauges. For those experiments 

with sooty fuels and under-ventilated conditions, combustion products including soot sometimes 

impinged on the gauges. For these periods of time, it was estimated that the soot coating on the 

gauge would add an additional uncertainty of ±10 % due to variations in surface emissivity, and 

soot agglomerates shadowing the surface of the gauge. 

The physical shifting of the gauge surface below the floor could have impact on a heat flux 

measurement if the solid angle viewable by the gauge was significantly diminished. Since the 
31 

gauge is not sensitive either in calibration or application to radiation at angles close to the plane 

of the gauge surface due to reflection, and the radiation approaching from the lowest angles is 

generally from the coolest regions of the enclosure, the gauge would have to be below the 

surface of the floor by a few millimeters or more for there to be a significant impact on its 

measurement. Neither gauge was ever observed to be shifted by that amount in the course of 

testing. 

2.3 Sampling locations

The gas species, temperatures, heat fluxes, and soot data were taken at various discrete places in 

the room. Table 2.5 lists the various data that was acquired in the room and where each probe 

was located. In the case of the movable probe, the vertical location (z – direction) was variable 

between z=100 cm and z=240 cm. In the data files published online as a part of this report the 

position of the movable probe is noted, in centimeters, for each of the cases where the movable 

probe was used. In some of the cases the relative location of a particular probe is indicated by it’s 

data label. As an example, TFSampA refers to the temperature measurement at the front of the 

room; TF30 refers to the temperature measurement at the front thermocouple tree, located 30 cm 

from the floor. 

 
32 

Table 2.5. Location of measurement probes inside of the enclosure. 

Probe Description Data Label x (cm) y (cm) z (cm)

O2 at Rear Sampling location (Rack #1) O2Rear 189 286 208

CO2 at Rear Sampling location ( CO signal) overrange CO2Rear 189 286 208

CO at Rear Sampling location CORear 189 286 208

UH at Rear Sampling location (before GC) UHRear 189 286 208

Rear Temperature at Sampling Location PtRh TRSampPtRh 169 286 208

O2 at Front Sampling location (Rack #2) O2Front 189 25 208

CO2 at Front Sampling location CO2Front 189 25 208

CO at Front Sampling location COFront 189 25 208

UH at Front Sampling location (before auto sample storage) UHFront 189 25 208

Front Temperature at Sampling Location PtRh TFSampPtRh 169 25 208

O2 at Moving Sampling location (Rack #3) O2Move 120 290 z

CO2 at Moving Sampling location CO2Move 120 290 z

CO at Moving Sampling location COMove 120 290 z

Moving Sample in room Aspirated TC TRMoveSamp 120 290 z

Total Heat Flux Gauge Rear Floor A (SN=131835) HFRFL 119.5 266 0

Total Heat Flux Gauge Front Floor B (SN=131836) HFFFL 119.5 90 0

Total Heat Flux Gauge Outside Floor C (SN=131833) HFOFL 119.5 -20 0

Total Heat Flux Gauge Rear Ceiling D (SN=131837) HFRCE 119.5 266 233

Total Heat Flux Gauge Center Ceiling E (SN=131838) HFCCE 119.5 178 233

Total Heat Flux Gauge Front Ceiling F (SN=131834) HFFCE 119.5 90 233

Temperature of Total Heat Flux Gauge Rear Floor A THFRFL 119.5 266 0

Temperature of Total Heat Flux Gauge Front Floor B THFFFL 119.5 90 0

Temperature of Total Heat Flux Gauge Outside Floor C THFOFL 119.5 -20 0

Temperature of Total Heat Flux Gauge Rear Ceiling D THFRCE 119.5 266 233

Temperature of Total Heat Flux Gauge Center Ceiling E THFCCE 119.5 178 233

Temperature of Total Heat Flux Gauge Front Ceiling F THFFCE 119.5 90 233

Interior Enclosure Surface Temp Near Total HF Gauge Rear Floor A TSHFRFL 119.5 266 0

Interior Enclosure Surface Temp Near Total HF Gauge Front Floor B TSHFFFL 119.5 90 0

Interior Enclosure Surface Temp Near Total HF Gauge Outside Floor C TSHFOFL 119.5 -20 0

Interior Enclosure Surface Temp Near Total HF Gauge Rear Ceiling D TSHFRCE 119.5 266 233

Interior Enclosure Surface Temp Near Total HF Gauge Center Ceiling E TSHFCCE 119.5 178 233

Interior Enclosure Surface Temp Near Total HF Gauge Front Ceiling F TSHFFCE 119.5 90 233

Exterior Enclosure Surface Temp Near Total HF Gauge Rear Floor A TSXHFRFL 119.5 266 0

Exterior Enclosure Surface Temp Near Total HF Gauge Front Floor B TSXHFFFL 119.5 90 0

Exterior Enclosure Surface Temp Near Total HF Gauge Rear Ceiling C TSXHFRCE 119.5 -20 0

Exterior Enclosure Surface Temp Near Total HF Gauge Center Ceiling D TSXHFCCE 119.5 266 233

Exterior Enclosure Surface Temp Near Total HF Gauge Front Ceiling E TSXHFFCE 119.5 178 233

TC Tree Rear TC 1 in up TR3 120 288 2.5

TC Tree Rear TC 1 ft up TR30 120 288 30

TC Tree Rear TC 2 ft up TR60 120 288 60

TC Tree Rear TC 3 ft up TR90 120 288 90

TC Tree Rear TC 3.5 ft up TR105 120 288 105

TC Tree Rear TC 4 ft up TR120 120 288 120

TC Tree Rear TC 4.5 ft up TR135 120 288 135

TC Tree Rear TC 5 ft up TR150 120 288 150

TC Tree Rear TC 6 ft up TR180 120 288 180

TC Tree Rear TC 7 ft up TR210 120 288 210

TC Tree Rear TC 7 ft 11 in up TR237 120 288 237.5

TC Tree Front TC 1 in up TF3 120 72 2.5

TC Tree Front TC 1 ft up TF30 120 72 30

TC Tree Front TC 2 ft up TF60 120 72 60

TC Tree Front TC 3 ft up TF90 120 72 90

TC Tree Front TC 3.5 ft up TF105 120 72 105

TC Tree Front TC 4 ft up TF120 120 72 120

TC Tree Front TC 4.5 ft up TF135 120 72 135

TC Tree Front TC 5 ft up TF150 120 72 150

TC Tree Front TC 6 ft up TF180 120 72 180

TC Tree Front TC 7 ft up TF210 120 72 210

TC Tree Front TC 7 ft 11 in up TF237 120 72 237.5

Interior Surface Temperature Back Wall Centerline Top TSBWCTop 125 356 180

Interior Surface Temperature Back Wall Centerline Middle TSBWCMid 125 356 120

Interior Surface Temperature Back Wall Centerline Bottom TSBWCBot 125 356 60

Exterior Surface Temperature Back Wall Centerline Top TSXBWCTop 125 360 180

Exterior Surface Temperature Back Wall Centerline Middle TSXBWCMid 125 360 120

Exterior Surface Temperature Back Wall Centerline Bottom TSXBWCBot 125 360 60
33 

2.4 Data acquisition

Data acquisition (DAQ) for this series of experiments was divided into two systems. One DAQ 

system was dedicated to fuel flows, oxygen depletion calorimetry, and the constituent 

measurements required to calculate heat release rate using that method. The other DAQ system 

was used to record signals from all other measurements (refer to previous report). Each DAQ 

system used National Instruments hardware and was controlled with LabVIEW software. The 

calorimetry DAQ system has been previously described in detail [29]. 

For this series of experiments, the channel list contained in Appendix C was used to program the 

DAQ system. The types of measurements included: gas analyzers, dew point readers, heat flux 

gauges, pressure transducers, and thermocouples. These measurements were recorded on the 

DAQ hardware as voltages with 200 samples recorded every second. Each second, the average 

value for each channel was then converted to meaningful physical units. Two event marking 

channels were used to note the time of important events such as ignition, fuel flow change, or 

extinguishment. These event marker channels, which are in both DAQ programs, were 

especially useful in synchronization of the two data sets. 

The data acquisition hardware had 16 bit precision, with stated accuracies of the data acquisition 

board and multiplexing module equal to 0.014 % and 0.015 % of the reading. These 

uncertainties were orders of magnitude lower than those from other sources in all of the 

measurements reported here. 

2.5 Data post­processing

A Matlab script file was created for post-processing all data files generated during the test series. 

This program was used to make corrections to the data, generate plots, and save results to ASCII 

text files for archival purposes. The program was also used to compute time averaged values and 

uncertainties for examining trends in the data. An input file was used to allow batch processing 

of the raw data files. The input file contained the parameters needed for the heat release 

calculation (this file was also read by the DAQ program during the data collection process). 

Additional parameters were added to the end of the standard HRR input file to account for the 

gravimetric soot measurements and to record the time windows when channels had known 

missing or corrupted data. 

The first step in data reduction was to inspect the data files and lab notebooks for erroneous data 

resulting from open channels, loss of sample flow, or some other instrument or data acquisition 

malfunction. Because data were collected on two separate computers, the series were 

synchronized to a common reference time. The ignition time was marked using a virtual event 

channel on each computer and defined as time zero for the reduced data. The gas analyzer 

measurements from inside the FSE and exhaust hood measurements were shifted in time to 

account for the sample flow transfer (delay) time as discussed in section 2.2.2. 

Corrections to the heat release rate measurements were applied to account for the exhaust flow 

calibration factor and drift in the oxygen analyzer. 

Since the gases sampled from the FSE were dried before entering the detectors, an estimate of 

the water removed can be made in order to correct the measurements to the in situ wet volume 

fraction. In this report the wet volume fraction of gases is only used to determine the mixture 
34 

fraction values, see section 4.1. Other gas species measurements are reported on a dry basis. This 

is done because converting the dry gas sample volume fractions to a wet basis introduces an 

additional source of uncertainty. The general combustion reaction assuming all the fuel is reacted 

and that the soot can be represented as pure carbon is: 

CxH yOz + aO2 → bCO 2 + cCO + dCH 4 + eC + fH2O 7 

The molecular yield of water can be related to the combustion product yields using the known 

hydrogen/carbon (y/x) ratio of the fuel: 

( ) b c d e 2d

2x

y f = + + + − 8 

If the yield of soot is small compared to the other products, the water volume fraction, XH2O, can 

be estimated from Eq.11. 

( ) H O XCO ,wet XCO,wet 2x

y X 2 2 = + 9 

The relationships for wet CO2 and CO are given by the following: 

( ) CO ,dry CO,dry

CO,dry

CO,wet

X X

2x

y 1

X

X

2 + +

= 10 

( ) CO ,dry CO,dry

CO ,dry

CO ,wet

X X

2x

y 1

X

X

2

2

2

+ +

= 11 

Other gas volume fraction measurements performed on a dry basis were corrected using the 

following relationship: 

( ) spec,wet spec,dry XH2O X = X 1− 12 

The total hydrocarbons can contribute to the formation of water, however the gas composition 

measurements confirmed that when total hydrocarbons were present in significant quantities, 

they were in the form of unburned fuel (methane in the natural gas tests). Unburned fuel does not 

contribute to the formation of water. Therefore, the resulting relative error in the water volume 

fraction estimation due to neglecting hydrocarbons was always less than 3 %. The error in the 

water volume fraction estimate due to neglecting soot was as much as 10 % for the highly 

sooting fuels. However, since the soot measurements were sparse, we chose to report the results 

on a consistent basis. In some cases the volume fraction of hydrogen measured by GC was as 

high as 0.10 which may result in an additional uncertainty of the water volume fraction by as 

much as 10 %. A more accurate estimate of water volume fraction can be made for the short time 

windows where soot and hydrogen volume fractions were both collected. 
35 

2.6 Uncertainty  

There are different components of uncertainty in the temperatures, total heat flux, soot mass 

fraction, chemical species, and heat release rate reported here. Uncertainties are grouped into two 

categories according to the method used to estimate them. Type A uncertainties are evaluated by 

statistical methods and type B are evaluated by other means [37]. Type B analysis of systematic 

uncertainties involves estimating the upper (+a) and lower (-a) limits for the quantity in question 

such that the probability that the value would be in the interval (±a) is 95 percent. After 

estimating uncertainties by either Type A or B analysis, the uncertainties are combined in 

quadrature to yield the combined standard uncertainty. Multiplying the combined standard 

uncertainty by a coverage factor of two results in the total expanded uncertainty that corresponds 

to a 95 percent confidence interval (2σ). 

Components of uncertainty are tabulated in Table 2.6. Some of these components, such as the 

zero calibration elements, are derived from instrument specifications. Other components, such as 

radiation loss and thermophoretic soot deposition include past experience with these 

measurements. The uncertainty in the air temperature measurements does include radiative 

cooling which is likely to result in a measured temperature lower than the actual gas temperature. 

Smoke measurements were primarily conducted gravimetrically. Part of the uncertainty was 

attributed to the accuracy of the mass scale used to weigh the soot filters, see section 2.2.4.1, and 

part of the uncertainty was due to the flow rate which is measured after the gases have been 

cooled and is therefore highly depended on the temperature at the entrance to the soot probe. 

Additional uncertainty is introduced by the water correction discussed in section 2.5. 

Uncertainties in the heat release rate measurement can be traced to variations in the hood duct 

flow profile, soot and total hydrocarbons which are not accounted for, and a small instrument 

uncertainty. The general function of the heat release rate measurement is discussed in section 

2.2.1 and the uncertainty of the measurement in this hood has been well documented [29, 38]. 

The associated uncertainty in the ideal heat release rate, used to calculate combustion efficiency 

is related primarily to the purity of the fuel and the uncertainty in the fuel flowrate measurement 

device, both of which are small. The gas analyzers, CO/CO2/O2/THC, use precision mixed zero 

and span gases and have a small uncertainty reported by the manufacturer. For these devices the 

random and mixing/averaging due to long sample lines are a larger source of uncertainty. The 

gas chromatograph was calibrated with a variety of different gas standards and some mixtures 

that were made in-house. The calibration of the GC for all of the species that it detects is a long 

procedure and was only conducted at the beginning and end of the test series which introduces 

significant uncertainty beyond the gas standard mixture uncertainty. Additionally the ANOVA 

analysis presented in section 2.2.3 provides information on the statistical uncertainty associated 

with using the GC. Because of the large amount of sample tubing and the sparse timing of GC 

data there is also an uncertainty in the GC sample timing. Generally the GC sample time can be 

considered to be ±30 s. The heat flux gauges used here were generally very precise devices and 

despite being used beyond their calibrated range have been shown to be quite linear and 

repeatable, cf. section 2.2.6. The larger sources of uncertainty came as a result of the cooling 

water being unable to remove heat from the heat flux gauge fast enough and because of 

thermophoretic soot deposition on the heat flux gauge window surface. The uncertainties are 

reported as a range in Table 2.6 and are represented by error bars in the associated figures. 

Table 2.6: Uncertainty of measurements 
36 

 Component 

Standard 

 Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

Temperature 

 Calibration 

 Radiative Cooling 

 Random 

±1 % 

-10 % to 0 % 

±3 % 

-10 % to +3% -20 % to +6 % 

Heat Flux 

 Soot Deposition 

 Cooling Water Temp 

 Calibration 

 Random 

-5 % to 0 % 

±5 % 

±1 % 

±3 % 

-8 % to +6 % -16 % to +12 % 

Gas Analyzers 

 Zero and Span Gas 

 Equiptment Uncertainty 

 Mixing and Averaging 

 Random 

±1 % 

±1 % 

±5 % 

±3 % 

±6 % ±12 % 

Gas Chromatography 

 Anova 

 Calibration 

 Mixing and Averaging 

 Random 

±1 % 

±5 % 

±5 % 

±3 % 

±8 % ±16 % 

Soot Mass Fraction 

 Mass Measurement 

 Volume Flow Rate 

 Water Estimation 

 Random 

±1 % 

±1 % 

±2 % 

±3 % 

±3 % ±5 % 

Measured Heat Release Rate 

 Exhaust Flow Rate 

 Soot and THC 

 Instruments Uncertainty 

 Random 

±5 % 

±3 % 

±1 % 

±3 % 

±7 % ±14 % 

Ideal Heat Release Rate 

 Fuel Purity 

 Equiptment Uncertainty 

 Random 

±1 % 

±1 % 

±3 % 

±3 % ±6 % 
37 

3 RESULTS

3.1 List of Test Conditions

Thirty experiments were conducted in the full scale enclosure and are listed in Table 3.1. The 

first column is the Test ID used to identify each test in this report; the second column is the date 

at which the test was completed followed by the fuel consumed. Next the quantity of fuel 

consumed, when a fixed quantity of fuel was used, is listed followed by the number of burners, 

the size of each burner and the doorway size, in terms of fractions of a standard 80 cm doorway. 

Whether the room flashed over or not (determined by oxygen depletion in the upper layer), the 

duration of the test and the actual ignition time are also listed. A general discussion of the test 

conditions for each test follows. 

In tests ISONG1, ISONG2, ISONG3, ISOHept4, and ISOHept5 a slightly different room 

configuration to that described above in section 2.1 was used. The same ceramic fiber blanket 

insulation was used with similar ceramic anchors except that only one 2.5 cm layer of insulation 

was used instead of 5 cm. Also, the exterior skin of the room was constructed of gypsum board 

instead of steel. The internal dimensions of the room were slightly smaller as well. The internal 

dimensions for these tests were 239 cm x 239 cm x 360 cm with the same uncertainty of ± 2 cm 

in each direction. From Table 3.1 it can be seen that these tests were conducted almost 5 months 

earlier than the subsequent tests. These were the first under-ventilated FSE tests in this test series 

and therefore they were conducted primarily to evaluate the robustness of the structure, the 

instrumentation, and the burner. For these tests a special burner was also tested, the water cooled, 

pump fed, variable surface area burner described in section 2.1.4 was used. It was hoped that this 

burner could be used to control the heat release rate in the room while maintaining a pool fire 

type scenario by utilizing the variable surface area feature of the burner. For the natural gas cases 

the burner was filled with gravel and the flow of natural gas was metered to the burner. 

This burner worked well for natural gas, however no better than other simpler gravel burners 

which are already used in the lab. Figure 3.1 shows the measured and ideal heat release rate for 

test ISONG3. Here we can see that the measured heat release rate increases at nearly the same 

time as the change in flow and both the measured and metered heat release rates remain fairly 

steady at the same time. For heptanes, the gravel was removed and the flow rate of heptanes was 

also metered along with a measurement of the pool height and therefore surface area by means of 

the pressure transducer discussed previously. The success of controlling the heat release rate for 

the heptanes fuels with this burner was significantly more limited. Figure 3.2 presents the 

measured and metered heat release rates for test ISOHept5. The metered fuel flow rate was 

controlled very carefully and several steps of steady pump flow rate were tested. However, as 

Figure 3.2 illustrates the measured heat release rate from the fire was not steady at any point 

during the test despite the steady flow rates. This instability was assumed to be a result of a 

competition between the burning rate (a function surface area, and net heat flux) and manually 

controlled fuel delivery rate. The process could not be well controlled and it was decided that 

this burner was not adequate for the tests that needed to be done. Additionally, the gypsum walls 

of the structure failed and the structure was unusable after test ISOHept5. Thus testing was 

halted and the structure discussed above in section 2.1 was constructed and used for the 

subsequent experiments. Tests 6 and 7 do not exist and were skipped because of a numbering 

error. The numbering was not corrected here in order to maintain the persistence of the test 
38 

names that are recorded permanently in various places including laboratory notebooks, 

experimental logs, and computer data files. 

Table 3.1: List of test conditions considered in this report. 

Test ID Date Fuel 

Fuel 

Mass 

(kg) 

# of 

Burners

Burner 

Size (m2)

Doorway 

(fraction 

of 80cm)

Flashover Duration 

(min) 

Ignition 

Time of 

Day 

(hr:min)

ISONG1 9/7/2007 Natural Gas Pool 

Fed 1 1 1 N 37 12:41 

ISONG2 9/10/2007 Natural Gas Pool 

Fed 1 1 1 N 33 15:38 

ISONG3 9/11/2007 Natural Gas 104 1 1 1 N 70 14:31 

ISOHept4 9/12/2007 Heptane Pool 

Fed 1 1 1 N 65 14:39 

ISOHept5 9/13/2007 Heptane Pool 

Fed 1 1 1 N 75 14:16 

ISOHept8 2/27/2008 Heptane 10 1 0.5 0.25 Y 6 11:13 

ISOHept9 2/28/2008 Heptane 20 1 0.5 0.25 Y 10 14:32 

ISONylon10 2/29/2008 Nylon 10 1 0.5 0.25 N 30 10:35 

ISOPP11 2/29/2008 PolyProp 10 1 0.5 0.25 N 35 14:22 

ISOHeptD12 3/3/2008 Heptane 20 2 0.25 0.25 Y 10 11:32 

ISOHeptD13 3/4/2008 Heptane 20 2 0.25 0.25 Y 10 10:15 

ISOPropD14 3/4/2008 Propanol 24 2 0.25 0.25 Y 12 2:09 

ISOProp15 3/5/2008 Propanol 24 1 0.5 0.25 Y 10 10:55 

ISOStyrene16 3/5/2008 PolyStyrene 10 1 0.5 0.25 N 35 14:32 

ISOStyrene17 3/7/2008 PolyStyrene 30 1 1 0.25 Y 37 11:53 

ISOPP18 3/10/2008 PolyProp 20 2 0.5 0.25 Y 40 10:37 

ISOHept19 3/10/2008 Heptane 20 1 0.5 0.25 Y 10 14:07 

ISOToluene20 3/11/2008 Toluene 17 1 0.5 0.25 Y 10 10:56 

ISOStyrene21 3/11/2008 PolyStyrene 15 1 0.5 0.25 N 35 14:47 

ISOHept22 3/12/2008 Heptane spray 1 0.5 0.25 Y 45 10:43 

ISOHept23 3/12/2008 Heptane spray 1 0.5 0.25 Y 40 3:10 

ISOHept24 3/13/2008 Heptane spray 1 0.5 0.125 Y 40 10:43 

ISOHept25 3/13/2008 Heptane spray 1 0.5 0.5 Y 20 14:23 

ISOHept26 3/14/2008 Heptane spray 1 0.5 0.5 Y 20 10:27 

ISOHept27 3/17/2008 Heptane spray 1 0.5 0.125 Y 40 10:48 

ISOHept28 3/17/2008 Heptane spray 1 0.5 0.25 Y 20 14:48 

ISOToluene29 3/19/2008 Toluene spray 1 0.5 0.25 Y 35 10:50 

ISOPropanol30 3/19/2008 Propanol spray 1 0.5 0.25 Y 35 1:40 

ISOPUF31 3/20/2008 Polyurathane 

Foam 2.5 1 0.5 0.25 N 10 10:11 

ISONG32 3/20/2008 Natural Gas 1 0.28 0.25 Y 25 12:01 

 
39 

Figure 3.1: Heat release rate for test ISONG3 comparing the ideal heat release rate, as imposed by gas flow rate, by the 

red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Figure 3.2: Heat release rate for test ISOHept5 comparing the ideal heat release rate, as imposed by pump flow rate, by 

the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Time from Ignition (s)

Heat Release Rate (kW)

0 2000 4000 0

500

1000

1500

2000

2500

3000

Time from Ignition (s)

Heat Release Rate (kW)

0 2000 4000 0

500

1000

1500

2000

2500
40 

3.2 Heat Release Rate

The heat release rate (HRR) measurement was used to characterize the size of the fire and also to 

help determine (along with heat flux data, temperatures, and gas species concentration trends) 

when the fire conditions had reached steady state. As the fire becomes under-ventilated burning 

can take place outside of the enclosure. The HRR measurement represents the total burning 

inside and outside of the enclosure. Table 3.2 shows a description of the measurement labels 

used in the table column headings and figure legends in this section. These labels are identical to 

the column headings in the reduced data files. 

Table 3.2: Description of calorimetry measurement labels. 

Measurement Label Description 

HRR Heat Release Rate from Calorimeter, kW

IHRR Ideal Heat Release Rate from Burner (gas, pool or spray), kW

The heat release rate of a natural gas fueled fire is shown in Figure 3.1. The flow of natural gas 

was precisely metered with a gas flow valve, and the surface area in this test was controlled by 

the surface are of the gravel in the burner which did not change. The gaseous fed burner was 

much easier to control in the fire than the liquid fuel burners because there was no thermal 

induced time lag between fuel delivery rate and the burning rate. In contrast, the heat release rate 

results for a heptanes fueled fire test are shown in Figure 3.2. In that case the fire was never 

steady due to instability in the burning rate process control variables. Maintaining a constant 

burning rate was difficult because of the coupled effects of fuel cooling, due to the water cooled 

burner, natural burning quickly changing the surface area of the fuel and a manually controlled 

fuel delivery system. 

Figure 3.3 shows the heat release rate from a free burn of heptanes in test ISOHept9. In this test, 

a fixed quantity of fuel, 30 L, was placed in a constant surface area, 0.5 m2

 pan burner, c.f. 

Figure 2.4, located in the center of the floor, Position 1, c.f. Figure 2.5. A 20 cm (1/4 width) 

doorway was used. The fuel was ignited and the mass loss from the pan was measured 

simultaneously to the oxygen calorimetry, both are shown in Figure 3.3. The difference between 

the measured mass loss, ideal HRR (IHRR), and the measured calorimetry is related to the 

combustion efficiency of the fire. The ideal HRR leads the dynamic behavior of the measured 

HRR and there is a proportional response of the two values. The HRR values from this type of 

free burn are not extremely steady; they fluctuate due to the dynamic and highly turbulent nature 

of the fire. However, the fire was steadier than ISOHept5, described in Figure 3.2, and more 

accurately simulated a real situation than ISONG3, presented in Figure 3.1. Generally speaking, 

the fire was ignited and then the HRR ramps up over a period of about 70 s to approach a 

pseudo-stead state burning of the fuel in the pan which was maintained until the fuel evaporated 

from the pan. The ideal heat release rate preceded the measured heat release rate because the fuel 

vaporized and ignited before any oxygen depletion was measured. Likewise, near the end of the 

test all of the fuel is gone from the pan, but still in vapor form for a short time leading to the 

ideal HRR dropping off sooner than the measured HRR. 
41 

Figure 3.4 presents the ideal and measured HRR of an iso-propanol fire in an identical 

configuration to that illustrated above for a heptanes fire, ISOHept9. In this case 30 L of 

propanol was used again with a 20 cm (1/4 width) doorway. Again, the fire was ignited and then 

approached a pseudo-steady burning rate. The differences in this case are that: 1) the isopropanol fire took nearly 160 s to reach pseudo-steady state as compared to 70 s for the heptanes 

fire, 2) the test lasted nearly 700 s for iso-propanol while it only lasted 600 s for heptanes, and 3) 

the steady state heat release rate for iso-propanol was approximately 1200 kW while it was 2000 

kW for the heptanes case. These differences can be partly attributed to the lower heat of 

combustion of iso-propanol when compared with heptanes. (Iso-propanol has a net heat of 

combustion of 30.45 MJ/kg and heptane has a neat heat of combustion of 44.4 MJ/kg [3].) 

Figure 3.5 and Figure 3.6 present ISOHeptD12 and ISOHeptD13, two identical distributed 

heptanes fueled fire cases. Both cases were conducted with two 0.25 m2

 burners located in the 

center of the floor and against the back wall centered in the x-direction, positions 1 and 2, cf. 

Figure 2.5. Both tests were conducted with a 20 cm (1/4 width) doorway. There are two things to 

note here. First, these tests were conducted in an identical manner so that the repeatability of the 

experiment was established. Comparing Figure 3.5 and Figure 3.6 there were only minor 

differences in the dynamic behavior of the fires, and the global behavior of the two experiments 

was almost exactly the same. Second, the behavior of the distributed fuel sources relative to that 

of the single fuel source was examined. Both the quantity of the fuel and the surface area of the 

fuel in ISOHept9 were maintained globally. The fire was ignited and slightly overshot the steady 

state HRR before reaching the steady burning condition. The steady burning condition of the 

distributed fuel case had a similar heat release rate to that observed for the single burner case 

presented in Figure 3.3. Near the end of the test there was a sharp drop off in both the ideal and 

measured heat release rates prior to the fuel burn out. A second steady burning rate was 

established for approximately 100 s. This drop off in HRR was due to the fuel in the rear burner 

being consumed faster than the fuel in the front burner. This was confirmed by observing that the 

mass of fuel measured in the rear burner reached zero while the middle burner still showed some 

fuel mass prior to the fire going out. An attempt was made to verify this visually, however due to 

the intense nature of the fire and the narrow door opening it was not possible, cf. Figure 3.7. 

Figure 3.8 presents the heat release measurements from test ISOStyrene17, a burn with 30 kg of 

polystyrene on a 1 m2

 burner situated in the center of the room, position 1 cf. Figure 2.5, and a 

20 cm (1/4 width) doorway. The global intent of this study was to investigate under-ventilated 

fires and previous tests, e.g. ISOStyrene16, with a smaller surface area of polystyrene failed to 

provide under-ventilated conditions. This was the only test done with the 1 m2

 pan burner 

because the size of the burner caused it to warp significantly during the test. Figure 3.9 shows 

images of the pan warping and the front edge of the pan lifting off of the enclosure floor by as 

much as 20 cm during the test. This resulted in a failure of the mass loss measurement, Figure 

3.8, because the burner was in contact with the enclosure floor. A similar failure can be seen in 

Figure 3.10, ISOPPD18, where polypropylene was burned in two 0.5 m2 pans at the center and 

center rear of the enclosure, positions 1 and 2 cf. Figure 2.5. In both cases the ideal HRR follows 

the measured HRR near the beginning and end of the test, however in the middle of the test, 

specifically during flashover the burners were warped due to excessive temperature. Excessive 

burner temperatures are more likely to occur with solid fuels because vaporization of the fuel 

happens at a much higher temperature than it does for liquid fuels, thus the burner will likely 

experience a higher temperature even if more heat is absorbed by the fuel. 
42 

Figure 3.11 presents the heat release rate results for the heptanes spray burner case, ISOHept22. 

The spray nozzle was positioned 25 cm above the floor in the center of the room. The 0.5 m2

 pan 

burner was used in position 1, cf. Figure 2.5 and allowed for measurement of any fuel collecting 

in the pan. The spray burner allowed for much better control over the heat release rate in the 

room than either the fed pool or the natural burning. Utilizing a spray burner was not as realistic 

as freely burning fuel, however there was a strong advantage to having a very steady HRR for a 

period of minutes for validation of numerical simulations. The spray burner experiments allow 

for steady state comparisons of other features of the enclosure, such as scaling of the doorway. 

An extensive discussion of scaling of the doorway is presented in section 6.3. 

Figure 3.12 presents the test, ISOHept27, where a HRR ramp created by linearly increasing the 

fuel delivery rate to the spray burner over a period of time. The room configuration was identical 

to that discussed above for ISOHept22. The ideal HRR in Figure 3.12 increased faster than the 

measured HRR, as expected. As more fuel was pumped into the room there was, relatively 

speaking, less oxygen present for the fuel to consume. A combination of the HRR data with the 

oxygen species in the room allows determination of when the under-ventilated conditions were 

achieved. A thorough discussion of the HRR ramp test is presented in section 6.4. 

A summary of steady state heat release rates for many of the fuels investigated here is presented 

in Figure 3.13. The dashed line indicates ideal or complete burning of the fuel in each case. The 

ideal burning rate was determined from either the mass loss rate (derived from load cell mass 

data), the liquid fuel flowrate, or the gaseous fuel flow rate as appropriate for each test. As 

expected and in agreement with Ref. [5] the combustion efficiency of the cleaner burning fuels 

(e.g. natural gas) was closer to ideal than the highly sooting fuels (e.g. toluene). For most fuels, 

the global combustion efficiency decreased as the fire became more under-ventilated. A more 

thorough discussion of combustion efficiency can be found later in section 4.3. A tabulated 

summary of the averaged steady-state results used to produce Figure 3.13 are presented in Table 

3.3. 

 
43 

Figure 3.3: Heat release rate for test ISOHept9 (Heptane) comparing the ideal heat release rate, as measured by the 

burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Figure 3.4: Heat release rate for test ISOProp15 (Iso-Propanol) comparing the ideal heat release rate, as measured by the 

burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Time from Ignition (s)

Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500

2000

2500

3000

Time from Ignition (s)

Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500
44 

Figure 3.5: Heat release rate for test ISOHeptD12 (Heptane) comparing the ideal heat release rate, as measured by the 

burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Figure 3.6: Heat release rate for test ISOHeptD13 (Heptane) comparing the ideal heat release rate, as measured by the 

burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Time from Ignition (s)

Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500

2000

2500

Time from Ignition (s)

Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500

2000

2500
45 

Figure 3.7: Fire leaving the door of the ISO 9705 room during test ISOHeptD12. It was not possible to view the inside of 

the room during this test. 

Figure 3.8: Heat release rate for test ISOStyrene17 (Polystyrene) comparing the ideal heat release rate, as measured by 

the burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. The mass 

loss reading was lost during the experiment due to warping of the burner pan. The ideal HRR values were smoothed 

because of excessive signal noise. 

Time from Ignition (s)

Heat Release Rate (kW)

0 500 1000 1500 2000 0

500

1000

1500

Ideal HRR data

smoothed with

Tecplot
46 

 

Figure 3.9: Images of the burner warping and moving during test ISOStyrene17. The burner was observed to be as much 

as 20 cm off of the floor in one corner. The burner warped because of its large size, 1m2

, and the excessive heat transfer to 

the burner in the room. This caused a loss of the mass loss measurement in this experiment. 

Figure 3.10: Heat release rate for test ISOPPD18 (Polypropylene) comparing the ideal heat release rate, as measured by 

the burner mass loss rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. The mass 

loss reading was lost during the experiment due to warping of the burner pan. The ideal HRR values were smoothed 

because of excessive signal noise. 

Time from Ignition (s)

Heat Release Rate (kW)

0 500 1000 1500 2000 0

500

1000

1500

Ideal HRR data

smoothed with

Tecplot

20 cm
47 

Figure 3.11: Heat release rate for test ISOHept22 (heptane) comparing the ideal heat release rate, as measured by the 

spray burner pump flow rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. 

Figure 3.12: Heat release rate for test ISOHept27 (heptane) comparing the ideal heat release rate, as measured by the 

spray burner pump flow rate, by the red dashed line and the measured, by oxygen loss calorimetry, solid blue line. This 

test featured a linear increase in the fuel delivery rate to observe the effects of a HRR ramp. 

Time from Ignition (s)

Heat Release Rate (kW)

0 500 1000 1500 2000 2500 0

500

1000

1500

2000

Time from Ignition (s)

Heat Release Rate (kW)

0 500 1000 1500 2000 2500 0

500

1000

1500

2000
48 

Figure 3.13: steady state heat release results. The dashed line indicates ideal or complete burning. 

 

Ideal HRR (kW)

Measured HRR (kW)

0 500 1000 1500 2000 2500 3000 0

500

1000

1500

2000

2500

3000

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas

Heptane
49 

Table 3.3: Summary of averaged steady-state results of HRR and exhaust stack species measurements. U indicates the 

standard deviation in each steady state measurement. 

Test No. Fuel Steady State Window HRR cal HRR ideal 

start (s) stop (s) Mean U Mean U 

1 Natural Gas 

350 800 295.38 6.0 287.7 2.8 

1300 1550 761.02 18.5 752.1 5.6 

1800 2100 1052.78 26.8 1034.8 2.7 

2 Natural Gas 200 600 781.76 18.3 759.1 0.9 

800 1300 1063.78 26.4 1042.4 4.0 

3 Natural Gas 

700 1350 1074.84 27.5 1050.9 3.0 

1500 1900 1866.63 51.0 1789.6 5.5 

3650 4050 2382.37 76.6 2390.3 8.1 

4 Heptane 3300 3700 2069.25 184.8 2403.1 1.13

5 Heptane 3100 3800 1490.86 98.0 1850.2 88.24

8 Heptane 170 230 1183.0 29.0 1164.6 354.9 

9 Heptane 150 500 1460.2.4 251.1 1816.8 315.6 

10 Nylon 650 1100 70.6 6.1 18.1 423.2 

11 PolyPropylene 1100 1900 312.1 24.0 323.6 283.9 

12 Heptane 125 450 1401.0 78.2 1794.0 237.0 

13 Heptane 125 450 1448.4 81.7 1861.9 309.7 

14 Iso-Propanol 280 460 1239.6 68.4 1500.3 149.9 

16 Polystyrene 800 1600 204.5 17.7 267.4 196.7 

15 Iso-Propanol 250 600 1107.2 75.8 1268.7 174.0 

17 Polystyrene 800 1175 0.0 0.0 0.0 38.7 

19 Heptane 125 425 1510.0 99.7 N/A N/A 

18 PolyPropylene 1100 1425 1181.4 53.3 N/A N/A 

21 Polystyrene 950 1400 696.7 36.2 N/A N/A 

20 Toluene 150 450 1207.4 59.0 1566.9 311.9 

22 Heptane 

350 1050 600.1 22.3 603.6 3.3 

1250 1700 1085.5 34.4 1209.2 38.4 

1775 2000 1297.1 41.7 1506.0 1.4 

23 Heptane 

125 500 270.9 10.9 284.4 1.9 

725 975 538.4 36.1 629.6 42.3 

1050 1350 719.0 40.8 1001.1 1.1 

1475 1725 980.7 38.1 1400.8 1.9 

24 Heptane 

200 360 414.0 26.2 321.8 55.8 

450 850 581.6 27.3 601.0 1.0 

950 1450 923.4 41.5 1202.7 1.5 

1650 1950 1092.7 59.4 1404.4 1.2 

25 Heptane 

350 575 991.0 61.5 1003.3 0.9 

650 1000 1380.9 57.6 1403.4 18.3 

1050 1350 1762.2 84.4 1993.5 3.6 

26 Heptane 325 575 1795.6 41.6 1998.8 0.9 

640 800 2048.5 76.3 2527.6 129.3 

28 Heptane 250 650 1396.6 50.9 1997.9 2.7 

750 1100 1756.0 70.6 2500.1 1.5 

30 Iso-Propanol 

400 800 875.3 46.2 937.4 0.6 

1350 1600 1204.7 55.3 1563.2 1.0 

1650 1850 1411.2 84.8 1948.9 55.8 

29 Toluene 

180 320 564.1 46.0 623.7 104.5 

400 700 1020.2 73.2 1383.7 1.3 

800 1150 1323.3 113.0 2309.0 1.6 

1600 1760 1591.2 96.6 2890.0 32.4 

32 Natural Gas 200 300 507.4 10.7 494.4 0.4 

500 1000 1086.6 42.9 1192.3 6.8 
50 

3.3 Temperatures

When a bare bead thermocouple is measuring a high temperature but is exposed to a relatively 

cool ambient the thermocouple looses heat to that ambient due to thermal radiation and reports 

an incorrect, lower, temperature. This is a problem when trying to instrument experiments which 

incorporate high temperature gases such as jet engines or fires. To combat this problem an 

aspirated thermocouple was developed [34] which includes a double radiation shield and pulls 

hot gases over the shields and thermocouple bead at a high rate, as described in section 2.2.5.1. 

However, the utilization of aspirated thermocouple requires the sacrifices of temporal and spatial 

resolution. In addition, this is constraining when many thermocouples are used simultaneously in 

a compartment fire since a vacuum flow for each aspirated TC is needed. Thus, in this study, 

bare bead thermocouples were primarily used to measure temperature. In order to validate the 

results aspirated and bare bead thermocouples were compared side by side in tests ISONG1, 

ISONG2, ISONG3, ISOHept4, and ISOHept5. 

Figure 3.14 shows a comparison between temperatures measured using bare bead and aspirated 

thermocouples at front sampling location as a function of time for natural gas test ISONG3. The 

heat release rate measured from calorimeter was also plotted to show fire conditions. Refer to 

Table 2.5 and Figure 2.1 for exact locations of the temperature probes. The measurement labels 

used in the table column heading and figure legends in this section are described in Table 3.4. 

For all locations, bare bead thermocouples provide lower temperatures compared to those of 

aspirated thermocouples due to the effect of radiative losses. At the front sample location, bare 

bead (TFSampPtRh) and aspirated thermocouples (TFSampA) show similar time histories of 

temperature qualitatively. However, the difference between these thermocouples decreases for 

heat release rates greater than approximately 1200 kW. At the rear sample location, the 

difference between bare bead and aspirated thermocouple temperatures is smaller compared to 

those at the front sample location. 

Figure 3.15 presents a comparison of the averaged bare bead and aspirated thermocouple 

temperatures for the same natural gas test, ISONG3, shown in Figure 3.14. Averaged 

temperatures were calculated over pseudo-steady periods and averaged periods are described in 

the figure. The difference between the two thermocouples decreases as the heat release rate 

increases. For example, at the front sample location, the relative difference of bear bead and 

aspirated thermocouple measurements decreases from 4.06 % to 0.83 % when heat release rate 

increases from 1203 kW to 2667 kW. These variations correspond to the temperature 

differentials of 37 °C and 10 °C, respectively. The decrease in the difference between the 

aspirated and bare bead temperatures at larger fire size is likely due to larger amounts of soot 

being produced in the room and blocking radiative losses from the bare bead thermocouple. In 

addition, the rear sample location, better agreement between bear bead and aspirated 

thermocouple measurements is observed compared to the measurements at the front sample 

location. This may be expected because the front thermocouple location is likely to have greater 

radiative heat exchange with a cool ambient via the doorway. These results illustrate the 

performance of bare bead thermocouples in this experimental configuration and provide 

confidence that the bare bead thermocouples are providing accurate results. 

To demonstrate the reproducibility of the measurements over a number of different tests, Figure 

3.16 shows averaged temperatures measured at the front and rear thermocouple trees as a 

function of the height above the floor for ISOHetpD12 and ISOHeptD13. These tests were two 
51 

identical distributed heptanes fueled fire cases and conducted one day apart so that the 

reproducibility of the experiment could be established. As mentioned earlier, there were only 

minor differences in the dynamic behavior of the fires in terms of heat release rate. In this figure, 

the vertical profiles of temperature at the front location for the two cases are nearly identical. The 

temperature profiles at the rear location also show only minor differences between the two cases 

except for the measurements below 0.9 m. From this figure it is clear that temperature 

measurements are reproduced well between ISOHeptD12 and ISOHeptD13. 

 
52 

Table 3.4. Description of interior gas temperature measurement labels.

Measurement 

Label Description 

TFSampPtRh Bear bead thermocouple at front sample location (208 cm above floor) 

TRSampPtRh Bear bead thermocouple at rear sample location (208 cm above floor) 

TFSampA Aspirated thermocouple at front sample location (208 cm above floor) 

TRSampA Aspirated thermocouple at rear sample location (208 cm above floor) 

TF3 Bear bead thermocouple at front location(2.5 cm above floor) 

TF30 Bear bead thermocouple at front location (30 cm above floor) 

TF60 Bear bead thermocouple at front location (60 cm above floor) 

TF180 Bear bead thermocouple at front location (180 cm above floor) 

TF210 Bear bead thermocouple at front location (210 cm above floor) 

TF237 Bear bead thermocouple at front location (237.5 cm above floor) 

TR3 Bear bead thermocouple at rear location (2.5 cm above floor) 

TR30 Bear bead thermocouple at rear location (30 cm above floor) 

TR60 Bear bead thermocouple at rear location (60 cm above floor) 

TR180 Bear bead thermocouple at rear location (180 cm above floor) 

TR210 Bear bead thermocouple at rear location (210 cm above floor) 

TR237 Bear bead thermocouple at rear location (237.5 cm above floor) 

Figure 3.14: Comparison between temperatures measured from bare bead and aspirated thermocouples at front sampling 

location as a function of time for test ISONG3. 

Time from ignition (s)

Temperature (oC)

Heat release rate (kW)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 600

800

1000

1200

1400

0

500

1000

1500

2000

2500

3000

TFSampPtRh

TFSampA

TRSampPtRh

TRSampA

HRRcal
53 

600

800

1000

1200

1400

Temperature (

oC)

TFSampPtRh

TFSampA

TRSampPtRh

TRSampA

1203 2089 2667

Heat release rate (kW)

800 ≤ time(s) ≤ 1450

1600 ≤

time(s) ≤ 2000

3750 ≤ time(s) ≤ 4150

Figure 3.15: Comparison of averaged temperatures measured from bare bead and aspirated thermocouples at front 

sample location for test ISONG3. 

Figure 3.16: Comparisons of averaged temperature measured at front and rear thermocouple trees for test ISOHeptD12 

and ISOHeptD13.

Height (m)

Temperature (oC)

0.0 0.5 1.0 1.5 2.0 2.5 200

400

600

800

1000

1200

1400

ISOHeptD12 - Front TC

ISOHeptD12 - Rear TC

ISOHeptD13 - Front TC

ISOHeptD13 - Rear TC
54 

To understand the temperature characteristics as a function of time at front and rear locations of 

the upper and lower layer, Figure 3.17 presents the histories of temperature at 4 locations for the 

heptanes spray burner case, ISOHept22. In the upper layer, the front and rear temperatures 

(TFSampPtRh and TRSampPtRh) show similar behaviors compared to the change of heat release 

rate plotted in the same figure. However, the general trend for almost all tests is higher 

temperatures at the rear location in the room than at the front. The temperature differences 

between front and rear location are attributed to ventilation effects in the fire. It was observed 

here and previously [5] that as the area of the vent is reduced in an enclosure the temperature in 

the front of the room becomes lower relative to the temperature at the rear of the room. In the 

lower layer the rear temperature is higher than the front temperature. In particular, the rear 

temperature in the lower layer approaches the upper layer temperature. This result may be 

explained by the fire’s dynamic flow inside the room. As cool air enters the under-ventilated 

compartment fire the lower level of the front of the room is cooled. As the air moves along the 

floor from the front of the room to the rear it is heated by the floor and hot gases in the room and 

begins to react with the fuel source in the room. Rear thermocouples also have smaller view 

angles of the cool external environment outside the door so they are more effectively heated by 

the thermal radiation from the upper layer and interior room surfaces, especially when high soot 

levels make the room gases optically thick. 

Figure 3.18 and Figure 3.19 show the histories of temperature at front and rear thermocouple 

trees, respectively, from a free burn of heptanes in test ISOHept9. The front temperatures as a 

function of height show that temperatures increase gradually with height and then decrease again 

above 180 cm. There is a difference in temperature of 900 °C between 2.5 cm and and the 

maximum temperature at 180 cm. At the rear location as presented in Figure 3.19, temperatures 

located above 60 cm show a similar qualitative behavior to that observed in the front of the 

room. This indicates that the top of the upper layer in the room (180 cm and higher) is very 

uniform thermally. The temperatures at 2.5 cm and 30 cm decrease with time while the higher 

locations increase in temperature with time. This is part of the initial transient of the room where 

the initial fire, prior to becoming under-ventilated, would have been burning closer to the burner 

thus producing more heat near the floor. Another contribution to this effect is that as the fire 

becomes under-ventilated, most of the burning (and heat release) occurs near the front. The rear 

is deprived of oxygen and the actual flame sheet is confined to the front of the enclosure. The 

hot products are still convected upward and heat the whole upper layer, but rear surfaces, 

including the floor, receive less radiation from the flame sheet. Similar results are observed in 

other tests, such as ISOPropD14, ISOProp15, ISOStyrrene17, ISOHept23 and ISOHept25. Note 

that the rear thermocouple at 60 cm was about 100 °C to 150 °C higher than the front 

thermocouple at the same height. This indicates a very hot region closer to the floor in the rear 

possibly near the layer interface where the flame sheet is located. 

Figure 3.20 and Figure 3.21 present steady temperatures at the front and rear sample locations 

for all fuels tested in this study. In general, the soot producing fires (heptane, polypropylene, 

polystyrene, toluene) produce hotter gas temperature inside the enclosure than the cleaner fires 

(natural gas) at the same measured heat release rate. These results also found in the previous 

experiments with the reduced-scale ventilation-limited compartment fires [5]. A summary of the 

averaged front and rear temperature measurements with combined expanded uncertainty (U) are 

listed in Table 3.5 and Table 3.6. 
55 

Figure 3.17: Histories of temperature at front and rear sampling locations for test ISOHept22 (heat release rate measured 

from calorimeter was included to show fire condition). 

Figure 3.18: Histories of temperature at front thermocouple trees for test ISOHept9. 

Time from ignition (s)

Temperature (oC)

Heat release rate (kW)

0 500 1000 1500 2000 2500 0

200

400

600

800

1000

1200

1400

0

250

500

750

1000

1250

1500

1750

2000

TFSampPtRh

TRSampPtRh

TF3

TR3

HRRcal

Time from ignition (s)

Temperature (oC)

-100 0 100 200 300 400 500 600 700 800 0

200

400

600

800

1000

1200

1400

TF3

TF30

TF60

TF180

TF210

TF237
56 

Figure 3.19: Histories of temperature at rear thermocouple trees for test ISOHept9. 

Time from ignition (s)

Temperature (oC)

-100 0 100 200 300 400 500 600 700 800 0

200

400

600

800

1000

1200

1400

TR3

TR30

TR60

TR180

TR210

TR237
57 

Figure 3.20: Averaged temperatures as a function of heat release rate at front sample location for all fuels tested. 

Figure 3.21: Averaged temperatures as a function of heat release rate at rear sample location for all fuels tested. 

Heat release rate (kW)

Temperature (oC)

0 500 1000 1500 2000 2500 3000 0

250

500

750

1000

1250

1500

Natural gas

Heptane

Iso-Propanol

PolyPropylene

Polystyrene

Toluene

Nylon

Heat release rate (kW)

Temperature (oC)

0 500 1000 1500 2000 2500 3000 0

250

500

750

1000

1250

1500

Natural gas

Heptane

Iso-Propanol

PolyPropylene

Polystyrene

Toluene

Nylon
58 

Table 3.5: Summary of averaged steady-state results of temperatures at front locations. 

Test No. Fuel Steady State Window TFSampA (°C) TF3 (°C) 

start (s) stop (s) Mean U Mean U 

1 Natural Gas 

350 800 

1300 1550 

1800 2100 

2 Natural Gas 200 600 668 17.7 

800 1300 854 18.4 

3 Natural Gas 

700 1350 867 15.8 

1500 1900 1087 14.1 

3650 4050 1204 27.7 

4 Heptane 3300 3700 1164 32.9 

5 Heptane 3100 3800 1278.4 16.4 

8 Heptane 170 230 830 21.6 610.7 134.0 

9 Heptane 150 500 1061 43.2 261.4 51.2 

10 Nylon 650 1100 154 14.9 41.5 4.0 

11 PolyPropylene 1100 1900 569 10.3 170.2 9.7 

12 Heptane 125 450 999 53.6 317.9 41.3 

13 Heptane 125 450 1000 51.0 376.0 42.3 

14 Iso-Propanol 280 460 1005 20.9 350.9 35.4 

16 Polystyrene 800 1600 446 19.8 79.9 3.7 

15 Iso-Propanol 250 600 1056 43.3 326.4 43.5 

17 Polystyrene 800 1175 1142 32.9 563.5 56.8 

19 Heptane 125 425 1056 46.2 392.3 64.5 

18 PolyPropylene 1100 1425 1151 29.4 472.6 106.4 

21 Polystyrene 950 1400 929 23.3 404.5 29.8 

20 Toluene 150 450 1107 61.7 483.9 76.2 

22 Heptane 

350 1050 806 48.9 295.8 55.5 

1250 1700 1235 19.0 662.5 35.6 

1775 2000 1283 13.1 725.3 50.7 

23 Heptane 

125 500 574 42.3 107.9 14.4 

725 975 989 24.6 360.5 32.5 

1050 1350 1001 8.0 453.0 42.8 

1475 1725 976 10.9 591.7 14.9 

24 Heptane 

200 360 736 25.9 236.7 23.2 

450 850 980 40.1 358.7 36.7 

950 1450 978 20.0 579.2 37.2 

1650 1950 942 11.9 711.5 28.5 

25 Heptane 

350 575 873 26.0 332.7 29.1 

650 1000 1158 31.6 645.8 21.3 

1050 1350 1336 11.6 904.5 55.1 

26 Heptane 325 575 1207 45.2 613.8 88.8 

640 800 1360 11.5 847.0 39.6 

28 Heptane 250 650 1037 34.4 444.0 60.4 

750 1100 1041 27.6 547.3 18.8 

30 Iso-Propanol 

400 800 1059 46.1 452.6 66.5 

1350 1600 1054 9.8 431.6 18.6 

1650 1850 1018 20.5 485.3 12.8 

29 Toluene 

180 320 733 24.0 171.6 21.0 

400 700 1135 41.3 426.0 76.3 

800 1150 1242 16.5 554.2 19.4 

1600 1760 1164 55.9 481.6 23.3 

32 Natural Gas 200 300 759 25.6 176.2 14.8 

500 1000 974 32.5 646.2 69.2 
59 

Table 3.6: Summary of averaged steady-state results of temperatures at rear locations. 

Test No. Fuel Steady State Window TRSampA (°C) TR3 (°C) 

start (s) stop (s) Mean U Mean U 

1 Natural Gas 

350 800 340 4.6 

1300 1550 663 6.7 

1800 2100 807 20.9 

2 Natural Gas 200 600 660 15.5 

800 1300 823 20.1 

3 Natural Gas 

700 1350 830 16.8 

1500 1900 1028 21.5 

3650 4050 1144 25.3 

4 Heptane 3300 3700 1309 53.3 

5 Heptane 3100 3800 1407.0 24.0 

8 Heptane 170 230 909 27.1 926.9 12.7 

9 Heptane 150 500 1120 45.7 820.6 29.9 

10 Nylon 650 1100 150 13.9 115.6 11.0 

11 PolyPropylene 1100 1900 546 13.5 487.6 14.5 

12 Heptane 125 450 1095 64.3 783.2 21.8 

13 Heptane 125 450 1093 54.2 878.8 51.9 

14 Iso-Propanol 280 460 1117 27.3 831.6 14.7 

16 Polystyrene 800 1600 433 18.7 340.6 13.1 

15 Iso-Propanol 250 600 1169 46.4 1047.8 126.0 

17 Polystyrene 800 1175 1240 42.4 907.9 56.0 

19 Heptane 125 425 1198 48.0 866.2 37.8 

18 PolyPropylene 1100 1425 1239 25.2 980.8 96.8 

21 Polystyrene 950 1400 943 19.5 954.9 28.9 

20 Toluene 150 450 1234 67.3 1331.8 139.9 

22 Heptane 

350 1050 812 48.4 706.5 69.2 

1250 1700 1230 32.3 1180.8 41.5 

1775 2000 1294 10.3 1238.9 32.5 

23 Heptane 

125 500 553 41.9 450.7 57.5 

725 975 1063 28.9 1081.9 24.0 

1050 1350 1046 14.0 903.3 41.2 

1475 1725 1010 13.6 670.0 33.8 

24 Heptane 

200 360 727 25.8 659.2 31.8 

450 850 1066 42.1 931.2 51.5 

950 1450 1040 8.4 698.0 65.6 

1650 1950 936 6.7 582.7 6.3 

25 Heptane 

350 575 911 39.1 795.6 28.6 

650 1000 1185 29.5 1111.1 29.5 

1050 1350 1346 17.6 1266.1 58.3 

26 Heptane 325 575 1333 43.0 1963.8 620.0 

640 800 1357 24.5 1381.9 1025.3 

28 Heptane 250 650 1053 27.1 951.9 21.5 

750 1100 1068 21.6 923.2 10.9 

30 Iso-Propanol 

400 800 1175 52.6 1230.9 53.5 

1350 1600 1149 13.6 1015.1 19.8 

1650 1850 1117 5.7 954.3 13.7 

29 Toluene 

180 320 769 30.4 801.8 75.4 

400 700 1244 47.5 1186.5 36.5 

800 1150 1248 9.9 928.6 26.7 

1600 1760 1233 12.4 843.5 16.1 

32 Natural Gas 200 300 694 19.6 507.5 26.5 

500 1000 1044 28.7 949.6 32.1 
60 

3.4 Heat Flux

Schmidt-Boelter type thermopile heat flux gauges were used to continuously measure heat fluxes 

at five locations in the room, and one location outside the doorway of the room, cf. Table 2.5. In 

the interest of brevity only the heat flux measurements from a single 1/4 doorway heptanes fuel 

test, ISOHept9, will be analyzed. It is however important to note that these heat flux 

measurements only represent test ISOHept9 and that significantly different qualitative behavior 

in heat fluxes was observed for different fuels, different fuel distributions, and different 

ventilation conditions. An example of how the different fuel types affected the heat flux 

measurements is discussed later in section 6.1.1. 

Figure 3.22 and Figure 3.23 present the heat flux measurements made in the ceiling and floor, 

respectively, of the enclosure for test ISOHept9. For this test the maximum peak heat flux 

recorded was ~300 kW/m2. Nominally the heat flux measurements inside the room were in the 

range of 50 – 150 kW/m2. As an example of how different fuels behave, the toluene fueled test 

ISOToluene20 had a maximum sustained heat flux of 250 kW/m2

. Initially the center ceiling heat 

flux measurement had a larger magnitude than the front ceiling heat flux measurement. 

However, halfway through the test the front ceiling heat flux measurement surpassed the center 

ceiling heat flux measurement. Similarly, on the floor, the rear floor heat flux measurement is 

initially much higher than the front floor heat flux measurement and then midway through the 

experiment the front floor heat flux measurement magnitude surpassed the rear floor heat flux 

measurement. Since both phenomena happened at approximately the same time it is reasonable 

to assume that the two instances are related. Considering the temperature plots presented in 

Figure 3.18 and Figure 3.19 it is evident that there is a development in the thermal environment 

of the room with the temperatures and heat fluxes in the rear half of the room tending to decrease 

and the temperature and heat fluxes in the front of the room tending to increase. These different 

trends manifest themselves immediately once the room becomes under-ventilated, cf. Figure 

3.27. The likely cause for the variation in thermal behavior is therefore the under-ventilated 

environment of the room. Prior to becoming under-ventilated the fire has sufficient air to burn 

and burns more in the rear of the room as the incoming air flows over the fuel source and brings 

the fire to the back. As the room becomes under-ventilated there is insufficient air in the room, 

the fire in the rear of the room becomes very rich, and its temperature is decreased as it is diluted 

by excess fuel. By contrast the front of the room then contains more unburned and partially 

burned hydrocarbons which begin to burn in the air just as the air is entering the room. 

Therefore, as this situation develops the rear of the room is producing less heat at a lower 

temperature and the front of the room produces more heat and consequently a higher 

temperature. 

Additionally, high heat fluxes can result in a faster vaporization of fuel. This may be evident in 

the heat flux measurements taken from ISOPropD14. In this test the fuel is located in two 

burners, one in the center of the room and the second in the rear of the room, cf. Figure 2.5. In 

this test the load cells attached to the burner pans revealed that the rear burner, in position 2, lost 

its fuel faster than the center burner, at position1. Additionally, as shown in Figure 3.24, the heat 

being transferred to the rear burner is so much more than the center burner that it is visibly 

hotter, glowing red immediately after the test, while the center burner is not. This observation is 

supported by the heat flux measurements presented in Figure 3.25 and Figure 3.26. The rear floor 

is receiving by far the greatest amount of heat flux up until the point where the fire starts to burn 

out. At this point the fuel in the rear burner is exhausted so burning in the front of the room is 
61 

likely to produce more heat flux, however the heat flux in the rear of the room still remains quite 

high. 

 
62 

Figure 3.22: Comparison of heat flux measurements made in the ceiling for 1/4 width (20 cm) doorway heptanes fuel test 

ISOHept9. 

Figure 3.23: Comparison of the heat flux gauges positioned in the floor for 1/4 doorway (20 cm) heptanes fuel case 

ISOHept9. 

Time

Heat Flux (kW/m2

)

0 200 400 600 800 0

50

100

150

200

250

300

Rear Ceiling

Center Ceiling

Front Ceiling

Time

Heat Flux (kW/m2

)

0 200 400 600 800 0

50

100

150

200

250

300

Rear Floor

Front Floor

Outside Floor
63 

Figure 3.24: Photograph of the center (front) and rear burners immediately after fire test ISOPropD14. 

Figure 3.25: Comparison of heat flux gauge measurements for heat flux gauges positioned in the floor for 1/4 doorway (20 

cm) distributed fuel isopropanol case ISOProp14. 

Time

Heat Flux (kW/m2

)

0 200 400 600 800

50

100

150

200

250 Rear Floor

Front Floor

Outside Floor
64 

Figure 3.26: Comparison of heat flux gauge measurements for heat flux gauges positioned in the floor for 1/4 doorway 

(20 cm) distributed fuel isopropanol case ISOProp14. 

Time

Heat Flux (kW/m2

)

0 200 400 600 800 0

50

100

150

200

250 Rear Ceiling

Center Ceiling

Front Ceiling
65 

3.5 Interior Compartment Gas Species

All gas species measurements are reported on a dry basis unless otherwise stated. Gas species 

O2, CO, CO2, and total hydrocarbons (THC) were all monitored continuously by the gas 

analyzers discussed in section 2.2.2. Additionally, gas chromatography (GC) measurements of 

H2, O2, CO, CO2, N2, CH4, C3H8, heptanes, hexanes, and other higher hydrocarbons were made 

as well. The GC measurements were generally made with a frequency of every 2 minutes at the 

front sample location, and a variable frequency at the rear location due to the limited capacity of 

the sample storage system. 

Figure 3.27 presents the transient gas species profile for the rear sample location of ISOHept9. 

The lines indicate gas analyzer data and the symbols indicate GC data. The agreement between 

the GC and gas analyzers is very good for O2, CO, and CO2, the three species the two systems 

both detect. Methane is slightly lower than the value reported by the THC analyzer, however the 

THC may be measuring species besides methane to report its volume fraction. The GC data also 

provides an additional piece of valuable information in that the volume of H2 in the room is 

increasing substantially during the test indicating there is a significant amount of potential fuel in 

the room that was not otherwise accounted for. When H2 is not accounted for, it also contributes 

to errors in the water correction. 

Figure 3.28 presents measurements of gas analyzers and GC for an under-ventilated 

polypropylene fire, ISOPP18. Similarly to test ISOHept9, there is good agreement between gas 

analyzer and GC measurements for O2, CO, and CO2. Coincidentally the volume fractions of 

THC and CH4 match for this test as well; however, they are both zero which was common to 

many of the solid fuels tested here. 

Figure 3.29 presents the gas analyzer and GC measurements for test ISOHept27, burning 

heptanes fuel with a 20 cm doorway. This test is discussed in detail later in section 6.4 and is 

used here to illustrate some of the behaviors of the gas analyzers and GC. Considering CO, CO2, 

and O2 the gas analyzers and GC again show good agreement throughout the experiment. 

However, as the heat release rate increased there was an increase of total hydrocarbons in the 

room. Qualitatively a similar trend was observed in the volume fraction of CH4 as it increased 

with heat release rate. However, the disparity between the THC and CH4 volume fractions 

increased heat release rate. Therefore, early in the burn when the heat release rate was low most 

of the hydrocarbon species in the room were simple hydrocarbons such as CH4. Then as the 

room becomes more under-ventilated larger hydrocarbons were produced. Also, large quantities 

of H2 were produced in the fire, which if not accounted for can contribute to erroneous 

interpretation and calculations of derived quantities such as mixture fraction and water. Other 

than CH4 the GC detects other higher hydrocarbons as well. Figure 3.30 presents example 

concentrations taken from test ISOHept27, illustrated in Figure 3.29, at a time step of 1375 

seconds. Here the large concentration of H2 is evident as well as CH4. Additionally, small 

amounts of ethylene, C2H4, and acetylene, C2H2, are present which can contribute to the larger 

detected total hydrocarbon volume fraction reported by the analyzer. Overall it is important to 

note the trends in the gas species volume fractions as a function of heat release rate. 

Figure 3.31 and Figure 3.32 present the steady state averages of oxygen volume fraction from the 

front and rear sample positions, respectively, plotted as a function of heat release rate. As the 

heat release rate increased there was a linear relationship with the volume fraction of O2. 
66 

Measurements from several different fuels, including heptanes, polystyrene, toluene, 

polypropylene, and natural gas all exhibited nearly identical trends. This figure includes all of 

the experiments done in this series and nearly all of the experiments have an identical ventilation 

condition, 1/4 (20 cm) doorway. The exception to this is the heptanes fires where various 

doorway widths were compared in order to evaluate their effect, as discussed later in section 6.3. 

This accounts for the small amount of scatter present in the heptanes data. 

Figure 3.33 and Figure 3.34 present the steady state CO2 volume fraction measurements as a 

function of heat release rate for the front and rear sample locations, respectively. Initially, for 

heat release rates generally less than 1000 kW, the same linear trend observed in Figure 3.31 and 

Figure 3.32 for oxygen was observed. The variation from this linear behavior is again primarily 

represented by heptanes and is a result of the various ventilation conditions that were tested with 

heptanes. However, while the O2 volume fraction drops linearly to zero and stays there, the CO2

volume fraction appears to exhibit a maximum in almost all of the fuels in nearly the same place. 

This is similar to the maximum observed in Figure 3.29 for ISOHept27, the heat release rate 

ramp and correlates with the point at which most of the O2 volume fractions in Figure 3.31 and 

Figure 3.32 reach zero. At this point the combustion is becoming less efficient as there is 

insufficient O2 to provide complete combustion products and it is likely that other intermediate 

combustion products become more prevalent. 

Figure 3.35 and Figure 3.36 present the steady state CO volume fraction measurements as a 

function of heat release rate for the front and rear sample locations, respectively. Again, similar 

to the CO2 and O2 measurements, nearly all of the measurements report the same trend as a 

function of heat release rate. The production of CO in the fires tends to begin to pick up at 

approximately 1000 kW, the same place that the O2 volume fraction drops off and the CO2

volume fraction reaches a maximum. For all of these plots, once all of the O2 is consumed there 

is a larger variation in the results so it is not readily evident from these plots if the CO volume 

fraction reaches a maximum or will continue to rise. Referring back to Figure 3.29 again, the 

heat release rate ramp test tends to indicate that there may be a maximum in CO volume fraction 

after which the CO volume fraction would become lower again. This concept is expanded upon 

later in section 6.4. 

Figure 3.37 and Figure 3.38 present the steady state total hydrocarbon (THC) volume fraction 

measurements as a function of heat release rate for the front and rear sample locations, 

respectively. The only trend evident from these plots is that once total hydrocarbons begin to be 

detected they continue to be produced in larger quantities as the heat release rate is increased. 

Generally, the THC volume fraction begins to be measureable at the same time that oxygen is 

being consumed and CO starts to be produced. This is the case for the liquid and gaseous fuels, 

however the solid fuels do not appear to produce measureable hydrocarbons at these sample 

locations. 
67 

Figure 3.27: Transient gas volume fraction s and soot mass fraction of test ISOHept9 (Heptane). 

Figure 3.28: Transient gas volume fraction s and soot mass fraction of test ISOPP18 (Polypropylene). 

Time (s)

Xi

HRR (kW), T (oC)

0 200 400 600 0

0.05

0.1

0.15

0.2

0

200

400

600

800

1000

1200

1400

1600 O2 Rear

CO2 Rear

CORear

THC Rear

Temp Rear

H2 (GC)

O2 (GC)

CO (GC)

CH4 (GC)

CO2 (GC)

HRR

Time (s)

Xi

HRR (kW), T (oC)

0 500 1000 1500 2000 0

0.05

0.1

0.15

0.2

0

200

400

600

800

1000

1200

1400

O2 Front

CO2 Front

COFront

THC Front

Temp Front

HRR

H2 (GC)

O2 (GC)

CO (GC)

CO2 (GC)

CH4 (GC)
68 

Figure 3.29: Transient gas volume fractions and heat release rate of test ISOPP18 (Polypropylene). 

Figure 3.30: Gas species volume fractions from GC analysis of front sample location in ISOHept27 at t=1375 s. 

Time (s)

Xi

HRR (kW), T (oC)

0 500 1000 1500 2000 2500 3000 0

0.05

0.1

0.15

0.2

0.25

0

200

400

600

800

1000

1200

1400

1600

O2 Front

CO2 Front

COFront

THC Front

HRR

H2 (GC)

O2 (GC)

CO (GC)

CO2 (GC)

CH4 (GC)

Gas sample probe

blocked.

12.33

0

2.19

5.64

7.27

5.16E‐02

0

0.22

00000

0

2

4

6

8

10

12

14

Volume Percent

t = 1375 s
69 

Figure 3.31: Steady state average oxygen volume fraction measurements at front sample probe location. 

Figure 3.32: Steady state average oxygen volume fraction measurements at rear sample probe location. 

Measured HRR (kW)

Front Sample O2 Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas

Measured HRR (kW)

Rear Sample O2 Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas
70 

Figure 3.33: Steady state average CO2 volume fraction measurements at front sample probe location. 

Figure 3.34: Steady state average CO2 volume fraction measurements at rear sample probe location. 

Measured HRR (kW)

Front Sample CO2 Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas

Measured HRR (kW)

Rear Sample CO2 Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas
71 

Figure 3.35: Steady state average CO volume fraction measurements at front sample probe location. 

Figure 3.36: Steady state average CO volume fraction measurements at rear sample probe location. 

Measured HRR (kW)

Front Sample CO Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas

Measured HRR (kW)

Rear Sample CO Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas
72 

Figure 3.37: Steady state average THC volume fraction measurements at front sample probe location. 

Figure 3.38: Steady state average THC volume fraction measurements at rear sample probe location. 

Measured HRR (kW)

Front Sample THC Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas

Measured HRR (kW)

Rear Sample THC Volume Fraction

0 500 1000 1500 2000 0.00

0.05

0.10

0.15

0.20 Heptane

PolyPropylene

Toluene

Iso-Propanol

Nylon

Polystyrene

Natural Gas
73 

3.6 Soot

3.6.1 Gravimetric

Soot samples were collected during 1 min to 5 min sample time after the heat release rate was 

quasi-steady. Measurements at the front location were conducted by the gravimetric soot probe 

seen in Sec. 2.2.4.1 at the front locations, while soot samples at the rear location were collected 

from the filter mounted at the real time extractive soot probe seen in Sec. 0. 

Figure 3.39 and Figure 3.40 present the steady state gravimetric soot mass fraction 

measurements as a function of heat release rate for the front and rear sample locations, 

respectively. Overall trend shows that the soot mass fraction increases with the heat release rate, 

except for heptane fires that larger values are shown from 500 to 1000 kW than those over 1000 

kW. This is because the heptane fire experiments were conducted under various conditions, such 

as burner types and door configurations (see Table 3.1). The maximum soot fractions reach to 7 

% for the heptane and the toluene fires, while those do not exceed 2 % for natural gas fires. More 

detail on the species mass fraction results are examined further in Sec. 4.1 of this report. 
74 

 

Figure 3.39: Steady state gravimetric soot mass fraction measurements at front sample probe location. 

Figure 3.40: Steady state gravimetric soot mass fraction measurements at rear sample probe location. 

Measured HRR (kW)

Front Sample Soot Mass Fraction (g/g,wet)

0 500 1000 1500 2000 0

0.02

0.04

0.06

0.08

0.1

Heptane

Polypropylent

Toluene

Iso-Propanol

Polystyrene

Natural Gas

Measured HRR (kW)

Rear Sample Soot Mass Fraction (g/g,wet)

0 500 1000 1500 2000 0

0.02

0.04

0.06

0.08

0.1

Heptane

Polypropylent

Toluene

Iso-Propanol

Polystyrene

Natural Gas
75 

3.6.2 Real time extractive

Results are available for Tests 21, 26, and 28 only, mainly because the measurement proved to 

be very challenging. Changes were made to the experimental setup throughout the test series, 

however due to the difficult nature of conditions inherent in this measurement, meaningful data 

is available only for a limited set of tests. Therefore, this data is presented as illustrative of a 

promising new technique that still needs further refinement. 

Figure 3.41 shows a chart of the optically measured soot mass concentration plotted as a function 

of time for test #21, for which the fuel was polystyrene. The chart also shows the heat release 

rate, which had a peak value below 800 kW. The increase in soot concentration lagged behind 

the heat release rate; the rise in soot concentration began as the HRR approached 300 kW. 

Overall, the soot concentration does not appear to correlate well with the HRR. Figure 3.42 

shows a comparison between the optical and gravimetric soot mass fraction in the rear of the 

compartment during test #21. The average optical measurement during the three minute 

gravimetric sampling period was 8.8 x 10-4 g/g. This was nearly seven times higher than the 

gravimetric average of 7.2 x 10-5 g/g. 

Figure 3.41: Soot mass concentration and heat release rate during polystyrene fire test 21. 

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Time (s)

Soot Mass Concentration (g/m3

)

0

100

200

300

400

500

600

700

800

900

1000

Heat Release Rate (kW)

Soot Concentration

HRR
76 

Figure 3.42: Comparison of the optical and gravimetric soot mass fraction at the rear of the compartment in test #21. 

Figure 3.43 and Figure 3.44 show charts of the optically measured soot mass concentration and 

heat release rate for test #26 and test #28, respectively. The fuel in each of these tests was 

heptane. The soot mass concentration appears to track better with the heat release rate during 

these tests that in the polystyrene fueled test. In both tests the heat release rate was ramped 

initially to approximately 500 kW. At this level, the soot concentration rose steadily, but 

remained low. Following this period, the fire was ramped up - to approximately 1800 kW in test 

#26 and 1400 kW in test #28. 

In test #26 the lag between the increase in HRR and the increase in soot concentration was 

approximately 60 seconds. After the HRR was leveled off, the soot concentration fluctuated 

around an average value of approximately 25 g/m3

. After the HRR was ramped down to 500 

kW, the drop in soot concentration lagged by 30 seconds. After this time, the soot concentration 

returned to the level it had stabilized during the initial 500 kW fire. 

In test #28, when the fire size was increased from 500 kW to 1400 kW, the increase in soot 

concentration lagged by 30 seconds. In this test, with the HRR stabilized, the soot concentration 

was not as consistent. It climbed to 27.5 g/m3

 at 300 seconds, then dropped to 8.3 g/m3 at 580 

seconds. This was followed by a rapid increase to 48.7 g/m3 at 590 seconds. The concentration 

then dropped off for the remainder of the test, despite relatively stable heat release rate levels. 

Figure 3.45 shows a comparison between the optical and gravimetric soot mass fraction in the 

rear of the compartment during test #28. The average optical measurement during the two 

minute gravimetric sampling period was 0.0138 g/g. This was nearly seven times higher than the 

gravimetric average of 0.002 g/g. 

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Time (s)

Soot Mass Fraction (g/g)

Optical

Gravimetric
77 

Figure 3.43: Soot mass concentration and heat release rate during heptane fire test 26. 

Figure 3.44: Soot mass concentration and heat release rate during heptane fire test 28. 

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200

Time (sec)

Soot Mass Concentration (g/m3

)

0

500

1000

1500

2000

2500

3000

Heat Release Rate (kW)

Soot Concentration

HRR

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800

Time (s)

Soot Mass Concentration (g/m3

)

0

500

1000

1500

2000

2500

Heat Release Rate (kW)

Soot Concentration

HRR
78 

Figure 3.45: Comparison of the optical and gravimetric soot mass fraction at the rear of the compartment in test #28. 

4 COMPARTMENT CHEMISTRY ANALYSIS

4.1 Mixture Fraction Analysis

It is useful to consider the compartment fire composition measurements in terms of the mixture 

fraction. The use of mixture fraction to analyze flame data was first used by Bilger [39] and later 

modified by Peters [40] and others. The mixture fraction approach has been widely used to 

represent the chemistry in turbulent flame models and fire field models, and has been used to 

analyze the structure of laminar counterflowing and coflowing hydrocarbon and alcohol flames 

[41, 42] 

Pool fires and compartment fires differ from simple laminar flames, as they are typically 

transient and turbulent by nature. Yet, application of the mixture fraction concept to these 

complex combustion situations can provide additional insight into the structure of the fire. The 

mixture fraction approach allows evaluation of a set of species measurements in terms of selfconsistency, and at the same time facilitates rapid assessment of the overall behavior of a 

combustion system. Floyd et al [43] applied the mixture fraction approach to evaluate the species 

composition at various locations in compartment fires. Pitts [44] measured the local equivalence 

ratio at various locations in compartment fires, investigating the possibility of a correlation for 

CO. Since there is a one-to-one correspondence between mixture fraction and equivalence ratio, 

the approach used here is similar to that used previously by Pitts [44] and other experimentalists, 

with the difference that soot is considered in the analysis of mixture fraction and local 

equivalence ratio. 

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0 200 400 600 800 1000 1200 1400 1600

Time

Soot Mass Fraction (g/g)

Optical

Gravimetric
79 

Sivathanu and Faeth [45] considered the relationship between soot and mixture fraction in an 

effort to improve the understanding associated with radiative emissions from fires. Their 

measurements [45] clearly showed that soot did not correlate well with mixture fraction in 

laminar hydrocarbon diffusion flames. Their data suggest, however, a relationship between soot 

volume fraction and temperature in the fuel rich regions of turbulent hydrocarbon diffusion 

flames. 

Recently, a mixture fraction analysis was performed to investigate the characteristics of chemical 

species production in the upper layer of the 2/5 scale compartment based on the ISO-9705 

room [5]. The analysis showed that plotting the local composition as a function of the mixture 

fraction collapsed hundreds of species measurements from an assortment of compartment 

conditions, with varying heat release rates, burner types and spatial locations, into a few coherent 

lines or bands. Also, inclusion of soot into mixture fraction analysis allowed identification of fuel 

rich or under-ventilated conditions for the compartment fires of smoky fuels, such as heptane, 

toluene, and polystyrene. The analysis performed here for full scale experimental data is the 

extension of our previous study [5] for the reduced scale compartment fires. 

In this section, the mixture fraction was used to evaluate the species composition in the hot upper 

layer of the compartment fires. The analysis provides a check on the quality of the data and 

provides insight into the chemistry of compartment fires. Also, the significance of the inclusion 

of soot as part of the mixture fraction analysis was investigated. The importance of measurement 

uncertainty is highlighted, and its value is quantified as part of the mixture fraction analysis. 

4.1.1 Definition of Mixture Fraction  

The mixture fraction is a non-dimensional quantity representing the mass fraction of a species, at 

a particular location, that was originally part of the fuel stream. The mixture fraction based on 

carbon containing species is defined as follows: 

Soot

F

Soot

co

F

co

co

F

F co x MW

MW Y

x MW

MW Y

x MW

MW Z = Y + Y + +

2

2 13 

or 

 

Soot

F

Soot

co

F

co

co

F

co

UH

F

UH

x MW

MW Y

x MW

MW Y

x MW

MW Y

xMW

MW Z = Y + + +

2

2 14 

where MWi is the molecular weight of chemical species i, Yi is the mass fraction of that species, x

is the number of carbon atoms in the parent fuel molecule (CxH yOz ), MWF is the molecular 

weight of the parent fuel, MWCO is 28 g/mol, MWSoot is taken as 12 g/mol (assuming that soot can 

be approximated as pure carbon), and MWCO2

 is 44 g/mol. Alternative definitions of mixture 

fraction yield results similar to those shown below. 
80 

In the experiments reported here, the measurement of unburned hydrocarbon (UH) was made 

using the total hydrocarbon analyzer, reported on an equivalent methane (CH4) basis. Thus, Eq. 

14 is used to calculate mixture fraction from experimental data instead of Eq.13. 

In the fire literature, soot is typically not considered in Eq. 13. Here, it is included formally. In 

the analysis given below, the results with and without soot in Eq. 13 and 14 are compared with 

each other. Its inclusion is especially important for highly sooting conditions, as will be shown in 

the results section below. 

The mass fraction, Yi, of each species i is determined from the measured volume fraction, Xi, by 

the following expression: 

Yi X iMWi MWtot = / 15 

MWtot represents the average molecular weight of all gas species and is a function of the local 

composition. 

i

i

MWtot = ∑XiMW 16 

The state relations can be derived by considering the idealized reaction of a hydrocarbon fuel, 

rewritten here in an expanded form of Eq. 7(in Sec. 2.5): 

2 2 2

2 2 2

min(1, )( / 2)H O max(0, 1)( / 4 / 2)O ( / 4)3.76N

C H O ( / 4 / 2)(O 3.76N ) max(0,1 )C H O min(1, ) CO

y x y z x y

x y z x x y z x y z

+ + − + − + +

+ + − + → − +

η η η

η η η 17 

where the function max(α,β) returns the larger of the two parameters, α or β, and the function 

min(α,β) returns the smaller of the two parameters, α or β. Here, η is a parameter ranging from 

zero (all fuel and zero oxygen) to infinity (all oxygen and zero fuel) and becomes unity for 

stoichiometric conditions. The definition of η shows that it is the reciprocal of the local fuel 

equivalence ratio, φ . 

η

η φ 1

/( / 4 / 2)( 3.76 )

/ ( / 4 / 2)( 3.76 )

( / )

( / )

2 2

2 2 = + − +

+ − + = =

F O N

F O N

st MW x y z MW MW

MW x y z MW MW

F A

F A

 18 

where F/A is the fuel-air ratio and the subscript ‘st’ refers to stoichiometric conditions. The 

idealized mass fractions of products are obtained from the right side of the Eq. 17. At the flame 

sheet where both the fuel and oxygen concentrations go to zero, 0 YF = YCO = Ysoot , and Eq. 14

leads to: 

2

2

CO

F

st CO

x MW

MW Z = Y 19 

The value of the stoichiometric mixture fraction for the fuels considered in this report is shown 

in Table 4.1. Its value varied from about 0.0554 for natural gas to 0.1346 for methanol. 
81 

Table 4.1. Stoichiometric Value of the Mixture Fraction (Zst) for different fuels.

Fuel Chemical Formula Zst

Methane CH4 0.0552 

Natural Gas 0.93 CH4 + 0.04 C2H6 + 0.01 C3H8 + 0.01 CO2 +..* 0.0554 ± 0.0002**

n-Heptane C7H16 0.0622 

Toluene C7H8 0.0694 

Polystyrene (C8H8) n 0.0705 

Polypropylene (C3H6)n 0.0637 

Iso-Propanol C3H7OH 0.0885 

* typical composition; actual composition varies day to day. 

** average value based on measured natural gas composition. 

A mixture fraction calculation for a methane-air flame is presented here as an example. For 

methane, Eq. 17 becomes: 

2 2

4 2 2 4 2 2

2max(0, 1)O 7.52 N

CH 2 (O 3.76N ) max(0,1 )CH min(1, )CO 2min(1, )H O

η η

η η η η

+ − +

+ + → − + +

 20 

The traditional mixture fraction model holds that the mass fraction, Yi, of products can be 

determined through the right side of Eq. 20 as follows: 

N N tot

O O tot

H O H O tot

CO CO tot

CH CH tot

Y MW MW

Y MW MW

Y MW MW

Y MW MW

Y MW MW

2 2

2 2

2 2

2 2

4 4

7.52

2max(0, 1)

2min(1, )

min(1, )

max(0,1 )

η

η

η

η

η

=

= −

=

=

= −

 21 

where YCO and YSoot in Eq. 14 were taken as zero for this mixture fraction model calculation. The 

molecular weight of the mixture is a function of the local composition and can be calculated 

from the reactant concentrations: 

2 ( 3.76 ) MWtot MWCH 4 MWO2 MWN2 = + η + . 22 

SinceYCO and YSoot are assumed to be equal to zero and F CH 4 Y = Y the mixture fraction defined in 

Eq. 14 can be rewritten as: 

2

4

4 2

CO

CH

CH CO

xMW

MW

Z = Y +Y 23 

Using Eqs. 21 and 22 , Eq. 23 can be rewritten as: 
82 

2 ( 3.76 ) 4 2 2

4 4

CH O N

CH

tot

CH

MW MW MW

MW

MW

MW

Z

+ + = = η

 , 24 

and 

st

O N

CH F A

Z

Z

MW MW

MW

Z

Z ( ) (1 )

2( 3.76 )

(1 )

2 2

4 − = +

− η = . 25 

Figure 4.1 presents the relationship between the mixture fraction and the equivalence ratio (1/η) 

as delineated in Eq. 5.12 for the methane-air system. Under stoichiometric conditions (η = 1), the 

mixture fraction is 0.0552 for a methane-air flame as listed in Table 4.1. In Figure 4.1, natural 

gas is treated as if it were methane. The figure shows that the mixture fraction compresses a 

large range of equivalence ratio values. Figure 4.2 shows the relationship between the mass 

fraction and the mixture fraction for most of the major species in the methane-air system, when 

YCO is taken as zero. 

4.1.2 Mixture Fraction Uncertainty

The uncertainty in the mixture fraction is propagated through Eq. 14 and is based on the 

measurement uncertainty of the species concentrations. The positive square root of the estimated 

variance, ( ) UZ Yi , is obtained from 

2

1

2

2

( ) Yi

N

i i

Z i U

Y

Z U Y ∑=

⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂ = 26 

where Yi U is an estimate of the combined expanded measurement uncertainty of the measured 

mass fraction, Yi, of species i. 
83 

Figure 4.1: The equivalence ratio as a function of mixture fraction for nonpremixed flames burning methane and nheptane.

Figure 4.2: The mass fraction vs. the mixture fraction calculated by the single-parameter mixture fraction model.

mixture fraction

fuel equivalence ratio

0 0.25 0.5 0.75 1 10-1

100

101

102

103

methane

heptane

0.0552 for methane

0.0622 for heptane

mixture fraction

mass fraction

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

CH4

CO2

O2

H2O

N2 /2
84 

4.1.3 Species Composition Results in terms of Mixture Fraction

In this section, the time-varying species measurements are presented as a function of the mixture 

fraction. The results are organized in terms of fuel type, since the fuel type establishes the basis 

for the correlation (see Eqs. 7 (in Sec.2.5) and 17). 

The species data are considered in terms of the species mass fraction (Yi), which is plotted as a 

function of the local mixture fraction (Z), based on the fuel mass. Measurements from the front 

and rear of the compartment, for all fire conditions (i.e., heat release rate, burner type) and all 

times during the experiment are plotted on a single graph in terms of mixture fraction. The mass 

fractions of H2O and N2 were not measured in the experiments; the values of these species in this 

report (and shown in Figure 4.3 through Figure 4.8) are estimated from the stoichiometric 

relation (Eqs. 7-12 in Sec. 2.5). The mass fractions of the unburned hydrocarbons (UH) in each 

plot were taken from the hydrocarbon analyzer measurements. The total hydrocarbons (UH) 

results were normalized in terms of the equivalent fuel molecule for each fuel type. 

The lines in Figure 4.3 through Figure 4.8 represent complete stoichiometric combustion and the 

hypothetical case when only CO2 is produced (no CO or soot; see Figure 4.2). In some cases, 

because of the number of data points, the theoretical lines are somewhat obscured. The lines on 

the average steady-state measurement plots labeled as “(b)” and “(c)” are easier to distinguish as 

the plots are less crowded. In those plots, the propagated uncertainty is also presented. Soot was 

not measured at all times, but only during the periods when the fire heat release rate was quasisteady. Soot is shown only on the plots labeled “(c)” and is presented with the time-averaged gas 

species as a function of mixture fraction including soot. 

Figure 4.3 presents all of the gas species measurements taken during the natural gas experiments 

(tests #2 - #3, and #32) in both the front and rear of the compartment as a function of mixture 

fraction. Figure 3a shows all of the transient measurements for all of the natural gas tests with the 

full- and quarter- door configuration (tests #2-#3, and #32, respectively). Figure 4.3b and c show 

the time-averaged steady-state measurements as a function of mixture fraction without and with 

soot, respectively. At any single location, the mixture fraction can vary from lean to rich, due to 

the dynamics of the fire. The stoichiometric mixture fraction (Zst) is a useful reference point for 

consideration of fire chemistry (see Table 4.1; Zst = 0.0544). For fuel lean conditions (Z < Zst), 

the measured mass fractions of methane and carbon monoxide are near zero. As the mixture 

fraction increases, the mass fraction of oxygen decreases, and the carbon dioxide and water 

vapor mass fractions increase. For mixture fraction values greater than stoichiometric, the 

oxygen mass fraction approaches zero, whereas the fraction of unburned fuel increases 

approximately linearly. Under these conditions, the generation of carbon monoxide is observed 

and YCO attains a maximum value of about 0.04 g/g. 

As seen in the figure, the hypothetical lines show reasonable agreement with the measurements 

for fuel lean and near-stoichiometric conditions. As the mixture fraction increases beyond 

stoichiometric, however, the difference between the hypothetical lines and the measurements 

becomes considerable. In Figure 4.3a, there are some data that does not follow the theoretical 

lines. Contrarily, the deviated points connected to these data are not shown in the time-averaged 

measurement plots (Figure 4.3b and c). It indicates that these data were measured when the fire 

has been developing and ceasing, not when the HRR was quasi-steady. The value of YCO is not 

negligible for fuel rich conditions. As a result, the hypothetical lines over-predict the CO2 mass 
85 

fraction by about 10 % for mixture fraction values for Zst < Z < 0.12. As expected, the plots 

show that the simple traditional mixture faction approach does not correlate the experimental 

results for CO. This behavior is also observed in laminar flames, which is attributed to finite rate 

chemistry effects associated with slow CO chemistry [42]. Other approaches to predict CO, 

possibly using variables that are functions of mixture fraction, will need to be considered to 

improve predictions of its concentration. 

The vertical and horizontal error bars in Figure 4.3b represent the combined expanded 

uncertainty of the mass fractions of gas species and the mixture fraction, respectively. The 

uncertainties in the mixture fraction increase with the mixture fraction, and the values of relative 

errors are under 10% except one point showing 22% relative error. Figure 4.3c shows the mass 

fractions of gas species as a function of mixture fraction calculated with soot mass fraction (Eq. 

14). For fuel lean and stoichiometric conditions, the mixture fractions calculated with soot are 

almost same as those without soot because amounts of soot are very small. However, the gas 

species of Z=0.09 in Figure 4.3b move to Z=0.11 in Figure 4.3c. The soot mass fraction of this 

point is about 0.01 g/g. By this move of data, the deviation of unburned hydrocarbon from 

theoretical line increases, but the sum of unburned hydrocarbon and soot mass fraction follows 

the line instead. 
86 

(a) 

(b) (c) 

Figure 4.3: Mass fractions of front and rear compartment gas species for the natural gas fire tests #1-#3, and #32: (a) 

transient measurements, (b) time-averaged measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

CH4

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

CH4

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
87 

4.1.4 Condensed­Phase Hydrocarbon Fuels

Figure 4.4 to Figure 4.7 show the mass fraction as a function of mixture fraction for the fires 

burning heptane (tests #5, #9, #12, #13, #19, #22-#26, #28), toluene (tests #20, #29), 

polypropylene (tests #11, #18) and polystyrene (tests #16, #17, #21), respectively. These contain 

the species concentrations measured under various configurations, such as different burner types, 

numbers, sizes, and door sizes (see Table 3.1). For small values of mixture fraction (Z << Zst), 

the overall trends of species mass fractions follow to the mixture fraction model for toluene, 

polypropylene, and polystyrene fires. Even for the heptane fires, the steady-state data agree with 

the theoretical lines. The deviated data in Figure 4.4a, especially for oxygen mass fraction, are 

measured during fire developing periods. Figure 4.4 to Figure 4.7 shows, for near-stoichiometric 

conditions, YCO is non-zero, which leads to CO2 Y lower than predicted by the mixture fraction 

model. The values of YCO reach to 6 %, 9 %, 0.2 % and 0.1 % for heptane, toluene, 

polypropylene, and polystyrene, respectively. 

Figure 4.4b, Figure 4.5b, Figure 4.6b and Figure 4.7b show that the measurement uncertainty 

was relatively small for lean mixture fractions. For large values of the mixture fraction, the 

variance of the species mass fraction results was relatively broad. This is particularly true for the 

transient results, but also for the time-averaged results. By Figure 4.5b, Figure 4.6b and Figure 

4.7b, the local conditions are not fuel-rich for any of the conditions investigated during the 

toluene, polypropylene and the polystyrene tests. It is interesting because at least one case for 

each fuel has reached the flashover condition (see Table 3.1) and under-ventilation condition. 

Although there was a high concentration of mass fraction results about near-stoichiometric 

conditions, the negligible amounts of hydrocarbons measured during these tests led to mixture 

fraction values which were less than stoichiometric in value. 

Species concentration results in the fire literature, such as those presented in Figure 4.4b, Figure 

4.5b, Figure 4.6b and Figure 4.7b, are typically reported without consideration of soot in the 

definition of mixture fraction. It is correct to include soot in Eq. 23 as the conserved scalar 

approach is based on the idea that elemental mass is neither created nor destroyed in a fire. The 

appearance of the plots qualitatively changes when soot is considered. Figure 4.4c, Figure 4.5c, 

Figure 4.6c and Figure 4.7c show that the inclusion of soot reduces the scatter in the mass 

fractions for large values of Z, while otherwise leaving the plots unchanged. Inclusion of soot 

stretches the value of Z proportional to the measured soot mass fraction in a non-linear manner as 

illustrated in Figure 4.8. This is because YSoot is negligible for lean conditions, whereas it is 

significant for large values of Z, taking on values as large as 0.1. Neglecting soot for the fires 

burning natural gas may be reasonable, whereas considering it for heavily sooting fires is 

necessary. The scatter in the mass fractions was reduced for these fuels when soot was 

considered in the definition of Z (see Eq. 14). In Figure 4.4c, Figure 4.5c, Figure 4.6c and Figure 

4.7c, the sum of the soot and unburned hydrocarbons (UH) appears to closely follow the mixture 

fraction model results. The results plotted in this way are particularly convincing in Figure 4.4c, 

Figure 4.5c, where the independent results for soot and THC do not follow the state relationship 

model, but their sum does. Interestingly, Figure 4.5b, Figure 4.6b and Figure 4.7b show that 

there was no significant amount of UH measured in the upper layer of the compartment in the 

toluene, polypropylene or polystyrene fires. The carbon in the upper layer of these fires is 

primarily in the form of CO, CO2 or soot. Examination of Figure 3.23 and Figure 3.24 present 

the same data, which reaffirms that the total HC measurements were relatively small in the 
88 

toluene, polypropylene and polystyrene fires, and that the unburned hydrocarbons did not 

represent a significant fraction of the carbon in the upper layer. 

Figure 4.9 shows the gas species mass fractions at the front and rear of the compartment as a 

function of mixture fraction for the iso-propanol fire tests #14, #15 and #30. Figure 4.9a shows 

all of the transient measurements, and Figure 4.9b and c show the averaged quasi-steady 

measurements as a function of mixture fraction with and without soot, respectively. From nearstoichiometric conditions (Z > 0.8), YCO increases rapidly, which leads to CO2 Y lower than 

predicted by the mixture fraction model. The value of YCO is as high as 7 %. In Figure 4.9b, the 

measured data are distributed over the range of 0.09 < Z < 0.13, while those in Figure 4.9c are 

over the range of 0.12 < Z < 0.15. Different from above results for other fuels, even the sum of 

UH and soot does not reach the UH line by the mixture fraction model. 
89 

(a) 

 

(b) (c) 

Figure 4.4. Mass fractions of front and rear compartment gas species for the heptane fire tests #5, #9, #12, #13, #19, #22-

#26 and #28: (a) transient measurements, (b) time-averaged measurements as a function of mixture fraction without soot, 

and (c) time-averaged measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C7H16

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C7H16

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
90 

(a) 

 

(b) (c) 

Figure 4.5: Mass fractions of front and rear compartment gas species for the toluene fire tests #20 and #29: (a) transient 

measurements, (b) time-averaged measurements as a function of mixture fraction without soot, and (c) time-averaged 

measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C7H8

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C7H8

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
91 

(a) 

 

(b) (c) 

Figure 4.6: Mass fractions of front and rear compartment gas species for the polypropylene fire tests #11 and #18: (a) 

transient measurements, (b) time-averaged measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

(C3H6)n

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

(C3H6)n

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
92 

(a) 

 

(b) (c) 

Figure 4.7: Mass fractions of front and rear compartment gas species for the polystyrene fire tests #16, #17 and #21: (a) 

transient measurements, (b) time-averaged measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

(C8H8)n

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

(C8H8)n

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
93 

Figure 4.8: Comparison of mixture fraction calculated with and without soot using the time-averaged species 

measurements when the HRR was quasi-steady. 

mixture fraction without soot

mixture fraction with soot

0 0.05 0.1 0.15 0.2 0

0.05

0.1

0.15

0.2

Heptane

Natural Gas

Polypropyrene

Iso-Propanol

Polystyrene

toluene
94 

(a) 

 

(b) (c) 

Figure 4.9: Mass fractions of front and rear compartment gas species for the iso-propanol fire tests #14, #15 and #30: (a) 

transient measurements, (b) time-averaged measurements as a function of mixture fraction without soot, and (c) timeaveraged measurements as a function of mixture fraction including soot. 

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C3H7OH

CO2

CO2

O2

O2

H2O

H2O

CO

mixture fraction

mass fraction [g/g]

0 0.05 0.1 0.15 0.2

0

0.1

0.2

0.3

0.4

UH

C3H7OH

CO2

CO2

O2

O2

H2O

H2O

CO

soot

CO+soot
95 

4.2 Post­Compartment Product Yields

The behavior of under-ventilated compartment fires may be divided into burning inside and 

burning outside of the compartment. Therefore, to investigate the overall fire characteristics of 

the compartment fire, it is important to consider the product emissions in the exhaust stack 

including those inside the compartment which flow out. The information in the exhaust stack can 

be used to estimate the overall combustion efficiency and estimate the fraction of burning 

occurring within the compartment for complete combustion. 

Figure 4.10 presents the pseudo-steady state averages of CO2 volume fraction, CO2 X , determined 

from the measurements made in the exhaust stack during the quasi-steady burning periods 

(indicated in Table 3.3), plotted as a function of heat release rate. Because overall fire behaviors 

may be affected by doorway size indicating the ventilation condition, only two ventilation 

conditions, i.e. full doorway (80 cm) and 1/4 doorway (20 cm), are plotted in the figure. In the 

figure, DF is defined as the Doorway Fraction, that is, the fraction of a full scale ISO 9705, 80 

cm doorway. As the heat release rate is increased there is an essentially linear increase of CO2 X

for all fuels including natural gas, heptane, iso-propanol, polypropylene, polystyrene, and 

toluene. Comparing the value of CO2 X between DF=1.00 and 0.25 as a function of heat release 

rate, there only difference is that the value of CO2 X at DF=0.25 is somewhat larger than at 

DF=1.0. On the other hand, there are clear differences among the different fuel tested. For 

example, consider the value of CO2 X as a function of heat release rate, while polypropylene, 

polystyrene, toluene and iso-propanol show a large CO2 X , natural gas has the smallest value. As 

the heat release rate is increased, the difference in CO2 emission among the different fuels 

increases. Therefore, it can be observed that overall CO2 emission is affected more by heat 

release rate and fuel type rather than vent size. 

Figure 4.11 presents the pseudo-steady state CO volume fraction, XCO , measurements from the 

exhaust stack as a function of heat release rate for the same fuels and ventilation conditions as 

shown in Figure 4.10. For DF=1.00, XCO increases continuously as heat release rate increases, 

even though XCO is very low compared to that observed in the DF=0.25 case. This may be 

explained as CO emission rate increasing as heat release rate increases due to insufficient O2

within the room. However, in the case of DF=0.25, XCO exhibits different behavior compared to 

the case of DF=1.00. The maximum values of CO emission occur near the heat release rate of 

1250kW and then drop off at higher heat release rates. This may be an indication of a transition 

from burning inside the room to burning outside the room. That is, as the heat release rate 

continues to increase more CO is produced within the room that is not consumed after it exits the 

room. However, beyond some critical point there is sufficient unburnt fuel and intermediate 

combustion products coming out of the room that they are able to support a fire outside of the 

room which then consumes the remaining CO. This observation may not be conclusive though, 

since there were relatively few DF=0.25 cases with a heat release rate greater than 1500 kW. 

 
96 

Figure 4.10: The CO2 volume fraction, CO2 X 2, in the exhaust stack as a function of the fire heat release rate during the 

periods when the HRR was quasi-steady for each of the fuels tested (DF indicates the doorway fraction of 80 cm). 

Figure 4.11: The CO volume fraction, XCO 2, in the exhaust stack as a function of the fire heat release rate during the 

periods when the HRR was quasi-steady for each of the fuels tested. 

 

2

 CO and CO2 volume fractions are measured as absolute values and not adjusted for various hood flow rates that 

may vary between data points. Adjusting for hood flow rate would shift the slope of the volume fractions but would 

not affect the qualitative behavior illustrated here. 

Heat release rate (kW)

CO2 volume fraction

0 500 1000 1500 2000 2500 0.0x10+00

2.0x10-03

4.0x10-03

6.0x10-03

8.0x10-03

Natural gas

Heptane

Natural gas

Heptane

Iso-Propanol

PolyPropylene

Polystyrene

Toluene

Nylon

DF=1.00

DF=0.25

Heat release rate (kW)

CO volume fraction

0 500 1000 1500 2000 2500 0.0x10+00

5.0x10-05

1.0x10-04

1.5x10-04

2.0x10-04

2.5x10-04

3.0x10-04

Natural gas

Heptane

Natural gas

Heptane

Iso-Propanol

PolyPropylene

Polystyrene

Toluene

Nylon

DF=1.00

DF=0.25
97 

4.3 Carbon Balance

Compartment measurements show that elemental carbon was primarily distributed among soot 

and three principal gaseous species (CO2, CO, and CH4) in the upper layer of the compartment. 

Other hydrocarbons were measured in only trace quantities compared to methane. In our 

previous study [5], the fractional mass-based amount of carbon was newly used to analyze the 

species compositions. This new parameter has an advantage that the values are bounded from 0 

to 1, contrary to the production yields or generation factor (defined below) which has been 

typically used to present the composition results. Our previous study [5] showed the trends of the 

fractional mass-based amount of carbon were very similar in appearance to those of the 

production yields or generation factor, indicating the new parameter is a reasonable way to 

represent the composition results. 

This fractional mass-based amount of carbon that existed in the form of carbon monoxide (FCO) 

or carbonaceous soot (Fsoot) is related to the mass fractions of carbon containing species at each 

measurement location as: 

CH CO CO soot

soot

soot

Y Y Y Y

Y F

+ + +

=

28

12

44

12

16

12

4 2

; 

CH CO CO soot

CO

CO

Y Y Y Y

Y

F

+ + +

=

28

12

44

12

16

12

28

12

4 2

 27 

In the results presented for the compartment data, the value of Xs, which is a representation of the 

amount of carbonaceous soot is defined as: 

= ∑ i

i

C

soot

s MW

Y

MW

Y X 28 

which comes directly from algebraic manipulation of Eqs. 15 and 16 (in Sec 4.1.1), and the facts 

that ∑ XiMWi is a constant, and ∑ Xi =1. 

Table 4.2 lists Fsoot and FCO based on averages of the quasi-steady species measurements at the 

front and rear locations during each of the fires (heptane, natural gas, polypropylene, 

polystyrene, iso-propanol and toluene). For convenience, the fire heat release rate (HRR), the 

local equivalence ratio (φ) and the ratio (FCO/Fsoot) are also included in the table. Also, Figure 

4.12a and Figure 4.12b show the FCO and Fsoot as a function of the local equivalence ratio for all 

fuels. The value of Fsoot was different for the different fuels, tending to increase with the local 

equivalence ratio (or mixture faction). The Fsoot was largest for the toluene fires and the heptane 

fires (see Table 4.2), reaching a value of over 0.50. This means that in those cases, about half of 

the carbon exists in the form of soot. The Fsoot in the other fires was also large, taking on values 

as large as 0.31 in one of the natural gas fires, 0.23 in one of the polypropylene fires, 0.41 in one 

of the iso-propanol fires, and 0.26 in one of the polystyrene fires. The value of FCO was as large 

as 0.003 to 0.30 for the heptane fires, 0.0 to 0.18 for the natural gas fires, 0.02 to 0.13 for the 

polypropylene fires, 0.05 to 0.2 for the iso-propanol fires, 0.002 to 0.06 for the polystyrene fires, 

and 0.05 to 0.2 for the toluene fires. In the richest toluene fire (φ=1.93), the sum of Fco and Fsoot
98 

reached to 0.72, indicating that over 70 % of the carbon exists in the form of CO or soot, with 

relatively little carbon in the form of CO2 or unburned fuel. The maximum values of the sum of 

FCO and Fsoot were 0.67, 0.31, 0.35, 0.49, and 0.29 for the heptane, natural gas, polypropylene, 

iso-propanol, and polystyrene, respectively. Table 4.2 lists value of FCO /Fsoot, which depends on 

fuel type, and physical location. Its value was less than 1.0, except in a few cases of the heptane 

fires and natural gas fires. 

Measurements by Koylu et al [46] and Puri and Santoro [47] showed that there is a linear 

relation in the emission of soot and CO from buoyant turbulent diffusion flames burning various 

hydrocarbon fuels (acetylene, propene, etc.). Measurements in the fuel lean (overfire) plume 

region of hydrocarbon fires showed that the soot and CO generation factors (ηS and ηCO) tended 

to increase with flame residence time, until a near-constant value was reached after long times 

(compared to the smoke point). Koylu et al [46] reported that the ratio of the CO and soot 

generation factors for a range of fuel types was such that, ηCO /ηS = 0.34 ± 0.09. The generation 

rate was defined as the mass of soot (or gas species) produced per unit mass of fuel carbon 

consumed. This is slightly different than the soot (or gas species) yield (yCO and y S), which is 

based on the mass of all elements (not just carbon) in the fuel stream. The ratios of the yields and 

the generation rates, however, are equal, and their value can be determined at any location from 

the ratio of the mass fractions of CO and soot: 

CO soot CO soot YCO Ysoot FCO Fsoot η η = y y = = (7 / 3) 29 

The constant value (7/3) in Eq. 29 is the ratio of the total CO mass to the mass of carbon. 

Table 4.3 lists yco, ysoot, and the ratio yco/ysoot based on the time-averaged species measurements at 

the front and rear compartment locations when the heat release rate was quasi-steady during each 

of the fires (heptane, natural gas, polypropylene, iso-propanol, polystyrene and toluene). The fire 

heat release rate (HRR) and the local equivalence ratio are also listed. Much of the same data 

was used as in Table 4.2. Figure 4.13a and Figure 4.13b also show the yield of CO and soot as a 

function of the local equivalence ratio for all fuels (heptane, natural gas, polypropylene, 

polystyrene, iso-propanol and toluene). Figure 4.13 is analogous to Figure 4.12, with the 

parameters yCO and ysoot considered in lieu of FCO and Fsoot. The trends and values of the data 

shown in the graphs are very similar in appearance, consistent with the data presented in Table 

4.2, and this shows that FCO and Fsoot is a reasonable way to represent the composition results. 

Figure 4.14 shows the ratio of the CO yield to the soot yield as a function of the local 

equivalence ratio for the same quasi-steady data shown in Figure 4.13 for the heptane, natural 

gas, polypropylene, iso-propanol, and toluene fires. Figure 4.15 shows the CO yield as a function 

of the soot yield for the same quasi-steady data for the heptane, natural gas, polypropylene, isopropanol, and toluene fires. Shown is a line representing the results of Koylu et al [46]. Koylu 

reported about 30 % scatter in the ratio of the yields of CO to soot, which is considerably smaller 

than that seen in the figure. Nevertheless, more data are needed to examine this relationship in 

the upper layer of compartment fires. It is interesting to note that Tewarson et al [48] reported 

that the ratio of the CO and soot generation efficiencies from small fires burning polymers 

varied, depending on the exact fuel type and the amount of ventilation. 
99 

Table 4.2: Average fractional soot, CO and CO/soot ratio at the front and rear compartment measurement locations. 

Fuel HRR 

[kW] 

Rear Front 

φlocal FCO Fsoot FCO Fsoot φlocal FCO Fsoot FCO Fsoot

Heptane 271 - - - - 0.473 0.003 0.033 0.088 

 414 - - - - 0.895 0.003 0.240 0.013 

 538 0.968 0.030 0.033 0.906 1.729 0.026 0.453 0.057 

 582 1.208 0.053 0.201 0.265 1.954 0.044 0.500 0.087 

 600 - - - - 0.111 0.011 0.149 0.072 

 719 - - - - 1.905 0.149 0.424 0.351 

 923 - - - - 2.557 0.135 0.480 0.282 

 991 - - - - 0.558 0.006 0.036 0.159 

 1086 0.926 0.017 0.088 0.189 1.356 0.121 0.323 0.376 

 1093 - - - - 3.380 0.100 0.432 0.231 

 1297 - - - - 1.599 0.254 0.420 0.604 

 1381 0.710 0.010 0.019 0.526 0.839 0.005 0.030 0.178 

 1397 1.367 0.295 0.144 2.053 1.860 0.187 0.377 0.496 

 1397 1.475 0.135 0.310 0.436 1.792 0.140 0.282 0.498 

 1435 1.951 0.121 0.478 0.254 1.977 0.130 0.321 0.405 

 1460 1.421 0.249 0.266 0.939 1.589 0.186 0.306 0.608 

 1503 - - - - 1.892 0.152 0.401 0.378 

 1594 1.056 0.105 0.141 0.743 1.137 0.094 0.148 0.638 

 1756 - - - - 2.295 0.210 0.430 0.488 

 1762 - - - - 1.427 0.157 0.363 0.433 

 1796 - - - - 1.538 0.067 0.422 0.158 

 2218 0.908 0.041 0.110 0.370 0.891 0.014 0.087 0.162 

Natural Gas 507 0.572 0.000 0.110 0.000 0.732 0.000 0.309 0.000 

 1087 - - - - 1.901 0.176 0.111 1.584 

 1140 0.786 0.001 0.005 0.133 0.612 0.004 0.022 0.175 

 1203 0.508 0.001 0.006 0.160 0.584 0.004 0.013 0.307 

 2089 0.776 0.006 0.050 0.113 0.924 0.030 0.057 0.527 

Polypropylene 311 0.288 0.018 0.083 0.213 0.298 0.018 0.125 0.142 

 1174 - - - - 1.216 0.126 0.227 0.555 

Iso-Propanol 875 1.527 0.052 0.384 0.136 1.592 0.045 0.408 0.110 

 1111 1.312 0.089 0.255 0.348 1.473 0.118 0.147 0.797 

 1205 - - - - 1.664 0.200 0.294 0.680 

 1254 1.414 0.091 0.280 0.324 1.665 0.133 0.192 0.691 

Polystyrene 203 - - - - 0.267 0.032 0.257 0.124 

 690 0.542 0.002 0.010 0.231 0.601 0.003 0.037 0.076 

 939 1.177 0.058 0.250 0.230 1.127 0.031 0.207 0.151 

Toluene 1020 - - - - 1.212 0.053 0.223 0.235 

 1209 - - - - 1.299 0.053 0.281 0.189 

 1323 - - - - 1.931 0.196 0.519 0.377 
100 

(a) 

(b) 

Figure 4.12: The values of FCO and Fsoot as a function of the local equivalence ratio for the time averaged measurements 

during the period when the HRR was quasi-steady. 

 

local equivalence ratio

FCO

01234 0

0.1

0.2

0.3

0.4

0.5

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene

local equivalence ratio

Fsoot

01234 0

0.1

0.2

0.3

0.4

0.5

0.6

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene
101 

Table 4.3: Average yields of soot, CO and CO/soot ratio at the front and rear compartment measurement locations.

Fuel HRR 

[kW] 

Rear Front 

φlocal CO y soot y CO soot y y φlocal CO y soot y CO soot y y

Heptane 271 - - - - 0.473 0.006 0.028 0.206 

 414 - - - - 0.895 0.006 0.202 0.029 

 538 0.968 0.058 0.027 2.113 1.729 0.050 0.381 0.132 

 582 1.208 0.105 0.169 0.618 1.954 0.086 0.421 0.204 

 600 - - - - 0.111 0.022 0.129 0.168 

 719 - - - - 1.905 0.293 0.357 0.820 

 923 - - - - 2.557 0.266 0.404 0.659 

 991 - - - - 0.558 0.011 0.031 0.371 

 1086 0.926 0.033 0.074 0.442 1.356 0.239 0.272 0.877 

 1093 - - - - 3.380 0.196 0.364 0.539 

 1297 - - - - 1.599 0.498 0.354 1.408 

 1381 0.710 0.020 0.016 1.228 0.839 0.011 0.026 0.416 

 1397 1.367 0.580 0.121 4.788 1.860 0.367 0.317 1.157 

 1397 1.475 0.266 0.261 1.017 1.792 0.276 0.237 1.162 

 1435 1.951 0.239 0.403 0.592 1.977 0.256 0.270 0.945 

 1460 1.421 0.490 0.224 2.190 1.589 0.366 0.258 1.419 

 1503 - - - - 1.892 0.298 0.338 0.883 

 1594 1.056 0.205 0.119 1.732 1.137 0.186 0.125 1.487 

 1756 - - - - 2.295 0.412 0.362 1.137 

 1762 - - - - 1.427 0.309 0.306 1.010 

 1796 - - - - 1.538 0.131 0.356 0.368 

 2218 0.908 0.080 0.093 0.862 0.891 0.028 0.073 0.379 

Natural Gas 507 0.572 0.000 0.083 0.000 0.732 0.000 0.233 0.000 

 1087 - - - - 1.901 0.308 0.083 3.695 

 1140 0.786 0.001 0.003 0.311 0.612 0.007 0.017 0.407 

 1203 0.508 0.002 0.004 0.374 0.584 0.007 0.010 0.715 

 2089 0.776 0.010 0.038 0.264 0.924 0.053 0.043 1.229 

Polypropylene 311 0.288 0.036 0.072 0.496 0.298 0.036 0.108 0.331 

 1174 - - - - 1.216 0.253 0.195 1.294 

Iso-Propanol 875 1.527 0.100 0.315 0.317 1.592 0.086 0.334 0.258 

 1111 1.312 0.170 0.209 0.812 1.473 0.225 0.121 1.860 

 1205 - - - - 1.664 0.382 0.241 1.586 

 1254 1.414 0.174 0.230 0.757 1.665 0.255 0.158 1.612 

Polystyrene 203 - - - - 0.267 0.069 0.240 0.289 

 690 0.542 0.005 0.009 0.539 0.601 0.006 0.034 0.178 

 939 1.177 0.124 0.232 0.536 1.127 0.067 0.192 0.352 

Toluene 1020 - - - - 1.212 0.112 0.204 0.549 

 1209 - - - - 1.299 0.114 0.257 0.442 

 1323 - - - - 1.931 0.417 0.475 0.879 
102 

(a) 

(b) 

Figure 4.13: The CO and soot yields as a function of the local equivalence ratio for the time averaged measurements 

during the period when the HRR was quasi-steady. 

local equivalence ratio

yCO

01234 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene

local equivalence ratio

ysoot

01234 0

0.1

0.2

0.3

0.4

0.5

0.6

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene
103 

Figure 4.14: The ratio of the CO to soot yield as a function of the local equivalence ratio during the period when the HRR 

was quasi-steady. 

Figure 4.15: The CO yield as a function of the soot yield during the period when the HRR was quasi-steady. Also shown is 

a line representing the results of Koylu [2]. 

 

local equivalence ratio

yCO/ysoot

01234 0

1

2

3

4

5

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene

ysoot

yCO

10-3 10-2 10-1 100 10 10 1

-4

10-3

10-2

10-1

100

101

Heptane

Natural Gas

Polypropylene

Iso-Propanol

Polystyrene

Toluene

= 0.34 ± 0.09 CO soot y y
104 

4.4 Combustion Efficiency

To better understand the compartment chemistry, it is of interest to determine the combustion 

efficiency both in the exhaust stack and at various locations in the upper layer of the 

compartment. Moreover, the accurate prediction of burning fraction inside compartment may 

provide useful information to understand the formations of CO and soot including detailed fire 

dynamics. The combustion efficiency ( χ a ) is a global representation of the fractional amount of 

heat released by the fire as compared to complete combustion. It is defined as: 

,

c

a

c ideal

H

H χ

Δ = Δ

 30 

where ΔHc ideal , is the net heat of complete combustion based on the conversion of all carbon and 

hydrogen in the fuel to CO2 and H2O (assumed to remain in the vapor phase) and ΔHc is the net 

heat of combustion, which is the actual heat released in a chemical reaction. The value of χ a is 

bounded by 0 % to 100 %. 

The local combustion efficiency at the front and rear locations in the upper layer of the 

compartment was calculated based on the difference in the heat of formation of species measured 

using gas analyzer. The combustion efficiency at the exhaust stack was determined as the ratio of 

the measured heat release rate to the measured mass delivery rate. A summary of averaged 

steady-state results of combustion efficiency in the exhaust stack is shown in Table 4.4. 

Figure 4.16 and Figure 4.17 show the combustion efficiency in the exhaust stack using 

measurements made during the steady state burning periods (indicated in Table 3.5) as a function 

of the ideal heat release rate for the condition of full doorway (DF=1.00) and 1/4 doorway size 

(DF=0.25), respectively. Figure 4.16 presents the results for natural gas and heptane fuels 

corresponding to ISONG1~3 and ISOHept4~5. Ideal heat release rate was calculated based on 

the measured mass delivery rate and ideal heat of combustion. Some natural gas cases have 

average combustion efficiencies above 100 % but still within the uncertainty of the hood, 

heptane has a maximum combustion efficiency of approximately 90 %. The combustion 

efficiencies above 100 % are a result of the uncertainty associated with the heat release rate 

measurement. As mentioned in section 2.2 heat release rate measurements have the combined 

expanded relative uncertainty of 14 %. For the DF=0.25 (1/4 door) case the combustion 

efficiency decreases as the ideal heat release rate increases and there is similar behavior among 

all the fuels tested. 

Figure 4.18 presents the combustion efficiency in the exhaust stack as a function of the ideal heat 

release rate for several doorway sizes in heptane spray burner fires. The tests plotted are 

ISOHept22~25. In this figure, all ventilation conditions show that the combustion efficiency 

decreases as ideal heat release rate increases as illustrated in Figure 4.17. The combustion 

efficiency significantly decreases as the doorway width changes from DF=0.500 (1/2 doorway) 

to DF=0.125 (1/8 doorway). 

Figure 4.19 presents the local combustion efficiency at the front and rear sample locations as a 

function of the ideal heat release rate for the same heptane spray tests with various doorway sizes 
105 

plotted in Figure 4.18. Comparing Figure 4.18 and Figure 4.19, the combustion efficiency inside 

compartment of DF=0.500 and 0.250 is higher than that of exhaust stack. It may be attributed to 

absence of soot yield in the process of calculating the heat of combustion. In the DF=0.125 case, 

the local combustion efficiency sharply decreases as ideal heat release rate increases while the 

global combustion efficiency increases. For this situation more of the fuel is burning outside of 

the compartment while less is burning inside. As a result, the combustion efficiency in the 

exhaust stack is somewhat larger than that inside the compartment. 

Figure 4.20 compares the burning rates inside and outside of the compartment by showing the 

burning fraction inside compartment and the ratio of combustion efficiency between inside and 

outside the compartment as a function of ideal heat release rate for the condition of DF=0.125 in 

heptane spray fires. Averaged combustion efficiency of front and rear sample location was used 

to represent the combustion efficiency inner compartment. In this figure, for heat release rate less 

than 750 kW, most of the burning occurs inside the compartment. As the ideal heat release 

increases from 750 kW to 1500 kW, the portion of burning outside the compartment significantly 

increases from 0 % to 60 % of the total. 

 
106 

Figure 4.16: The combustion efficiency in the exhaust stack as a function of the ideal heat release rate for natural gas and 

heptane fuels under the condition of full doorway size (DF=1.0). The indicated uncertainty includes the 14% uncertainty 

of the calorimetry used to make the measurements. 

Figure 4.17: The combustion efficiency in the exhaust stack as a function of the ideal heat release rate for various fuels 

under the condition of DF=0.25. The indicated uncertainty includes the 14% uncertainty of the calorimetry used to make 

the measurements. 

Ideal heat release rate (kW)

Combustoin efficiency (%)

0 500 1000 1500 2000 2500 50

60

70

80

90

100

110

120

Natural gas

Heptane

Ideal heat release rate (kW)

Combustion efficiency (%)

0 500 1000 1500 2000 2500 50

60

70

80

90

100

110

120

Natural gas

Heptane

Iso-Propanol

Toluene
107 

Figure 4.18: The combustion efficiency in the exhaust stack as a function of the ideal heat release rate for various 

doorway sizes in heptane fires. The curve fit lines are for illustrative purposes only. 

Figure 4.19: The local combustion efficiency at the front and rear sample locations as a function of the ideal heat release 

rate for various doorway sizes in heptane fires. The curve fit lines are for illustrative purposes only. 

Ideal heat release rate (kW)

Combustion efficiency (%)

0 500 1000 1500 2000 2500 50

60

70

80

90

100

110

120

DF=1.000

DF=0.500

DF=0.250

DF=0.125

Ideal heat release rate (kW)

Combustion efficiency (%)

0 500 1000 1500 2000 2500 20

40

60

80

100

120

1.000 at front

1.000 at rear

0.500 at front

0.500 at rear

0.250 at front

0.250 at rear

0.125 at front

0.125 at rear

DF
108 

Figure 4.20: The burning fraction inside compartment as a function of ideal heat release rate under the condition of 

DF=0.125 in heptane fires. The curve fit line is for illustrative purposes only. 

Ideal heat release rate (kW)

Bu

rning fraction inside compartment (%)

0 250 500 750 1000 1250 1500 20

40

60

80

100

120
109 

Table 4.4: Summary of averaged steady-state results of combustion efficiency in the exhaust stack. The steady state 

periods here are the same used for all steady state measurements and are listed in Table 3.5. The uncertainty, U, indicated 

here only reflects the statistical variation 

Test No. Fuel HRR ideal (Kw) Combustion Efficiency (%) 

Mean U Mean U 

1 Natural Gas 

287.7 2.8 110.05 2.37 

752.1 5.6 108.46 2.78 

1034.8 2.7 109.05 2.79 

2 Natural Gas 759.1 0.9 110.38 1.22 

1042.4 4.0 109.38 1.27 

3 Natural Gas 

1050.9 3.0 114.45 2.94 

1789.6 5.5 116.73 3.25 

2390.3 8.1 111.52 3.62 

4 Heptane 2243.5 590.6 92.29 8.24 

5 Heptane 1526.5 716.0 86.52 6.44 

8 Heptane 1164.6 354.9 114.11 45.49 

9 Heptane 1816.8 315.6 82.83 14.93 

12 Heptane 1794.0 237.0 79.20 11.34 

13 Heptane 1861.9 309.7 78.99 12.63 

14 Iso-Propanol 1500.3 149.9 84.40 10.19 

15 Iso-Propanol 1268.7 174.0 88.94 11.58 

20 Toluene 1566.9 311.9 79.96 15.03 

22 Heptane 

603.6 3.3 99.44 3.59 

1209.2 38.4 90.00 2.85 

1506.0 1.4 86.13 2.78 

23 Heptane 

284.4 1.9 95.25 3.83 

629.6 42.3 86.34 6.32 

1001.1 1.1 71.80 4.07 

1400.8 1.9 70.00 2.71 

24 Heptane 

321.8 55.8 133.15 13.40 

601.0 1.0 96.78 4.54 

1202.7 1.5 76.79 3.43 

1404.4 1.2 77.79 4.24 

25 Heptane 

1003.3 0.9 98.80 6.16 

1403.4 18.3 98.56 4.10 

1993.5 3.6 88.42 4.23 

26 Heptane 1998.8 0.9 88.28 2.59 

2527.6 129.3 82.11 5.12 

28 Heptane 1997.9 2.7 69.91 2.57 

2500.1 1.5 70.23 2.14 

30 Iso-Propanol 

937.4 0.6 93.30 4.89 

1563.2 1.0 77.11 3.55 

1948.9 55.8 72.39 4.61 

29 Toluene 

623.7 104.5 93.07 9.84 

1383.7 1.3 73.74 5.28 

2309.0 1.6 57.29 4.89 

2890.0 32.4 54.99 3.40 

32 Natural Gas 494.4 0.4 102.64 2.18 

1192.3 6.8 91.15 3.49 
110 

5 SCALING FROM RSE TO FSE

The applicability of the experimental results reported here to other compartment fire scenarios, 

including the reduced scale enclosure (RSE) experiments [5],can be considered in terms of a 

number of normalized parameters traditionally used in fire modeling applications. Use of 

normalized parameters facilitates comparison of results from scenarios of different scales by 

normalizing key physical characteristics of the scenario. A number of different forms of scaling 

may be considered, depending on the fire phenomena of interest [3, 49, 50]. Table 5.1 lists three 

normalized parameters that may be used to compare fire scenarios with the experiments reported 

here. The ranges of values for the normalized parameters examined in this study are listed in the 

table. The table is intended to provide guidance when evaluating the applicability of the data set 

reported here. For any given fire scenario, more than one normalized parameter may be 

necessary for determining applicability of the validation results, depending on the parameters of 

interest, as will be shown here. In this sense, the Table should be considered illustrative, not 

exhaustive. 

The most important parameter of any fire experiment is the heat release rate, as its magnitude 

drives changes in the thermal environment of the compartment or space of interest. A Froude 

number expression which normalizes heat release rate to the diameter of the fire, D, is the first 

entry in Table 5.1, commonly known as , where Q is the heat release rate (kW), ρ ∞ is the 

ambient air density (kg/m3), T∞ is the ambient air temperature (K), cp is the specific heat of air 

(kJ/kg-K), and g is the acceleration of gravity (m/s2

). A large value of * Qd represents a fire with 

a relatively large value of energy output power compared to its physical diameter or a large fire 

plume relative to the burner diameter, like an oil well blowout fire. A low value of * Qd represents 

a fire with a relatively small value of energy output compared to its diameter or a small plume 

relative to the burner diameter, like a smoldering fire. Many typical accidental fire scenarios 

have * Qd values on the order of 1 which indicates the flow is buoyancy driven as in the case of a 

pool fire, rather than momentum driven as in the case of a jet flame. The physical diameter of a 

realistic fire may not be well-defined and may not actually matter when assessing the “size” of a 

fire. Instead, a characteristic diameter, D* is considered in the definition of * Qd as noted in the 

table. The range of values of * Qd varied as a function of fuel type. In this study, * Qd took on 

values as small as 0.17 and as large as 12.74, varying by 2 orders of magnitude, as seen in Table 

5.1. In the context of these experiments the larger values of * Qd indicate that the room is likely 

under-ventilated, having a very large fire within the room, and the smaller values of * Qd indicate 

that the room is likely well ventilated, having a small fire within the room. Figure 5.1 illustrates 

the two extremes of this parameter contrasting the ISONylon10 fire with a * Qd = 0.17 where you 

can see into the room through the door and the ISOPropD14 fire with a * Qd of 12.74 where much 

of the fire is burning outside of the room because the heat release rate is so large relative to the 

burner sizes. 

* Qd
111 

Table 5.1: List of Normalized Scaling Parameters for Compartment Fires and the Range of Values Examined in this 

Study.

Parameter Normalized Representation Range of Values Fuel Type 

Heat Release 

Rate [3, 49] 

*

d 2

p

Q Q

ρ ∞ ∞ c T gDD = 

0.36 

0.85 

2.12 

2.12 

0.71 

1.07 

0.17 

to 

to 

to 

to 

to 

to 

to 

12.74 

10.19 

12.74 

12.74 

3.93 

4.29 

0.68 

Natural Gas 

Heptane 

Toluene 

Iso-Propanol 

Polystyrene 

Polypropylene 

Nylon 

Ventilation 

[9, 17, 51] O o o

F O where m A h

r

m m

2

0.23 , /

2

2 =  =   φ

0.13 

0.13 

1.27 

1.26 

1.02 

1.57 

0.10 

to 

to 

to 

to 

to 

to 

to 

7.90 

12.48 

7.63 

7.53 

5.61 

6.27 

0.41 

Natural Gas 

Heptane 

Toluene 

Iso-Propanol 

Polystyrene 

Polypropylene 

Nylon

Compartment 

height [3, 49] 

2/5

*

* , where 

p

H Q D

D ρ cT g ∞ ∞

⎛ ⎞

= ⎜ ⎟

⎝ ⎠



2.17 

2.38 

2.17 

2.17 

2.46 

2.38 

7.02 

to 

to 

to 

to 

to 

to 

to 

6.42 

6.42 

4.45 

4.45 

4.87 

4.14 

12.23 

Natural Gas 

Heptane 

Toluene 

Iso-Propanol 

Polystyrene 

Polypropylene 

Nylon 

The second entry in the table is the global equivalence ratio (φ), which is associated with the 

overall fire-induced ventilation and compartment stoichiometry. An estimate of the maximum 

achievable steady-state oxygen supply is given by: mO Ao ho 2

0.23

2

 = , where O2 m is an empirical 

correlation for the mass flow rate of oxygen (kg/s), Ao and ho are the area and height of the 

doorway opening (m2

), 0.23 is the mass fraction of oxygen in air. The parameter r in the table is 

the mass-based stoichiometric ratio of fuel to air required for complete combustion. The value of 

φ is useful in characterizing whether a given compartment fire is limited in size by its fuel supply 

or by its oxygen supply. The correlation for oxygen entrainment is valid for flashover conditions 

only, that is for values of φ >1. 

In all of the experiments performed as part of this study, the fuel mass flow rate was either 

controlled (for the gaseous and liquid fuels) or measured (for the liquid and solid fuels), whereas 

the oxygen supply was naturally controlled by the size of the compartment doorway and the fire 

heat release rate. The range of values of φ varied as a function of fuel type, taking on values as 

small as φ = 0.1 and as large as φ = 12.38 as seen in Table 5.1. The value of φ was greater than 

1.0 for almost all of the experimental conditions. This implies that conditions inside of the 

compartment were under-ventilated for the majority of the cases presented here. For each of the 

fuels listed in the table, except Nylon, flames were observed outside of the doorway, oxygen 

volume fractions were near zero and increased CO production was measured in the upper layer 

for the largest fires sizes. These are all strong indicators of under-ventilated burning. Pitts [52] 

proposed that a large fraction of the incoming air may be entrained into the out-flowing gases 

and never reach the reaction zone which indicates that the application of this relationship alone 
112 

for scaling inadequate. A recent paper comparing results from the reduced scale enclosure [5] 

and experiments ISONG3 and ISOHept4, full door cases, also showed that this scaling factor 

does not always work [53]. According to the simple Ah0.5 scaling relationship, the intermediate 

species observed at 250 kW in the reduced-scale enclosure, should be present at 1600 kW in the 

full-scale enclosure (FSE), however they were not present until approximately 2700 kW. 

The third entry in the table is the compartment height, H, normalized by D*, an effective 

characteristic burner dimension. The parameter H/D* relates Q to its physical dimensions and

indicates the relative importance of the fire plume to other features of the fire-driven flow, such 

as the ceiling jet or doorway flow. This value is related to * Qd and similarities can be seen in the 

expressions for * Qd and H/D*

 in Table 5.1. In contrast to the relative magnitude of * Qd , where 

larger values indicate a larger fire, larger values of H/D*

 indicate a smaller fire in that the room is 

much larger than the fire size. * Qd only relates the fire size to the burner size while H/D*

 relates 

the fire size to the dimension of the room. For this reason, the H/D*

 parameter should give a 

better indication of the relationship of the fire size to the room size and be more effective for 

scaling predictions. Considering the case taken above for Ah0.5 scaling [53], if the H/D*

 scaling 

is used for the same cases, RSE: Q = 250 kW, H = 0.98 m; FSE: Q =2700 kW, H = 2.4 m, and 

the RSE and FSE return values of H/D*

 = 1.82 and H/D* = 1.72, respectively. This indicates 

H/D*

 is a better scaling relationship for these specific two tests than Ah0.5 scaling. The range of 

values of H/D*

 varied as a function of fuel type, taking on values as small as 2.17 and as large as 

12.23 for conditions examined in this study, as seen in Table 5.1. For the reduced scale enclosure 

H/D*

 had values in the range of 1.4 to 5.2. 

Table 5.2 presents a comparison of scaling factors for three different heptanes fires including one 

fire from the RSE [5] and two heptane fires with different doorway openings in the FSE. Each 

case is compared at the heat release rate, Q, at which CO began to be detected at the front 

location in the room, indicating that the room was becoming under-ventilated and thus that there 

should be applicable under-ventilated scaling relationship coming into play. Previously a study 

that only considered the Ah0.5 scaling was considered, and it was observed that for the full door 

FSE case the scaling relationship did not hold [53]. However if the 1/4 doorway (20 cm) case 

presented in Table 5.2 (ISOHept23) is considered with Ah0.5 scaling the relationship is more 

applicable with the RSE and FSE where Ah0.5 = 0.35 and Ah0.5 = 0.57, respectively, predicting a 

heat release rate of 407 kW for the FSE, only a 40% error rather than the 60% error observed for 

the full door FSE case. The Ah0.5 scaling works even better between the two FSE tests having 

values of Ah0.5 = 2.26 for the full door case and Ah0.5 = 0.57 for the quarter door case, resulting 

in only a 20% error in the predicted heat release rate between the two cases. Considering the 

other scaling factors the full doorway FSE case (ISOHept4) relates much better to the RSE case 

when H/D*

 scaling is considered, the RSE and FSE having H/D* = 1.82 and H/D* = 1.72, 

respectively. However, when considering this scaling factor, the 1/4 doorway case no longer 

shows a scaling relationship to the RSE case, having H/D*

 = 3.27. This indicates that the scaling 

factor that is used must be chosen judiciously in order to find accurate scaling of experiments. It 

also shows that it may be necessary to utilize multiple scaling factors to convert between one 

type of geometry and another, e.g. the full door RSE and the 1⁄4 door FSE.
113 

Table 5.2: Scaling comparison between the reduced scale enclosure (RSE) and the full scale enclosure (FSE) for heptane 

fires. The heat release rate values (Q) are taken as the heat release measured when CO began to be measured in the room. 

Enclosure Test ID Q (kW) H (m) Doorway 

(h × w) 

* Qd Ah0.5 φ H/D*

RSE #15 250 0.89 0.81 × 0.48 2.11 0.35 0.49 1.81 

FSE ISOHept4 2700 2.4 2.0 × 0.8 9.82 2.26 0.83 1.71 

FSE ISOHept23 540 2.4 2.0 × 0.1 7.04 0.28 1.32 3.27 

Figure 5.1: Example normalized scaling quantities with * Qd = 0.17, φ = 0.1, and H/D* = 12.23, on the left (ISONylon10) 

and a * Qd = 12.74, φ = 7.53, and H/D*

 = 2.17, on the right (ISOPropD14). 
114 

6 DISCUSSION

6.1 Behavior of different fuels

A variety of different fuels in three different phases were investigated here. Each fuel and each 

phase had its own unique challenges and behavior. This section endeavors to summarize some of 

the differences between individual fuels as well as between different fuel phases. 

6.1.1 Liquid Fuels

In this investigation three liquid fuels were used. Heptane was used for many cases because it is 

a relatively well understood fuel that has been investigated extensively at NIST and by others. 

Heptane produces a moderate level of sooting and has a heat of combustion similar to gasoline. 

Iso-propanol was used because it is a different fuel, containing oxygen, and thus is expected to 

produce different results from heptane. Iso-propanol also produces a moderate level of soot but 

has a lower heat of combustion than heptane. Toluene was used as the third liquid fuel. Toluene 

generally produces copious amounts of soot and has a heat of combustion between that of 

heptane and iso-propanol. 

ISOHept9, ISOProp15, and ISOToluene20 were three tests conducted under nearly identical 

conditions for the three fuels. For each case the 20 cm (1/4 width) door was used with a 0.5 m2

pan burner situate in the center of the room at position 1, cf. Figure 2.5. For the heptane and isopropanol tests 30 L of fuel was used and 20 L of fuel was used for the toluene test. In each case 

the fuel was ignited and allowed to burn freely until all the fuel was consumed. Figure 6.1, and 

Figure 6.3--Figure 6.6 present the heat release rate, temperatures, O2, CO, and CO2 time profiles 

respectively for the three liquid fuels considered here. Figure 6.1 presents the heat release rates 

of the three fuels as a function of time. The first observation that can be made is that the peak 

and average hat release rates of each fuel are qualitatively related to their heat of combustion. 

The heats of combustion, measured and ideal heat release rates of heptanes, toluene, and isopropanol are listed in Table 6.1. There is a nearly linear relationship between the heat of 

combustion and the heat release rate for each of these fuels in the free burn. Figure 6.2 shows 

how the measured and ideal heat release rates vary with the net heat of combustion. Besides the 

nearly linear relationship it is also apparent from this plot that the combustion efficiencies of the 

different fuels may play a role here as well. However, despite heptanes having the largest heat 

release rate and heat of combustion and toluene having the lowest combustion efficiency the 

temperatures in the toluene fire were larger than those observed in either the heptane or isopropanol fires, cf. Figure 6.3. The significantly higher temperature of toluene may be related to 

the chemistry happening within the enclosure. Considering Figure 6.4--Figure 6.6 the toluene 

fire has higher oxygen concentrations than either heptanes or iso-propanol, cf. Figure 6.4, along 

with less CO, cf. Figure 6.5, and more CO2, cf. Figure 6.6. This indicates that the fire is not 

becoming as under-ventilated with toluene as it is with either heptane or iso-propanol. The 

increased temperature of the toluene fire can then be explained as the global equivalence ratio of 

the room being closer to stoichiometric conditions where fire temperatures are higher. The 

decrease of flame temperatures as the fuel/air mixture moves far beyond stoichiometric is a well 

understood fundamental phenomenon due to the increased quantity of unburnt fuel that absorbs 

energy from the reaction. A similar observation was made for the RSE experiments [5] and will 

be noted here in section 6.4 when the time varying heat release rate is discussed. Therefore, the 

reduced combustion efficiency indicates that much less than the ideal amount of fuel is being 

consumed and there is sufficient extra oxygen to achieve more complete combustion (more CO2
115 

and less CO) of the fuel that does burn. However, Figure 6.6 indicates that the toluene fire also 

has a very low volume fraction of hydrocarbons being sampled from the fire, however there is 

significant loss of fuel that is neither burned nor turned to detectable hydrocarbons. It is 

theorized that the majority of the unburnt toluene was converted to soot and was caught on the 

soot filters which were used to condition the gas sample flow. 

Figure 6.8 and Figure 6.9 present a comparison of the heat flux being measured from three 

different liquid fuels: heptanes, isopropanol, and toluene. For each of the three heat flux gauges 

located in the ceiling the highest heat flux was realized from heptanes, cf. Figure 6.8. At the 

same time, for each of the two heat flux gauges located on the floor inside the room, toluene 

produced the largest heat flux, cf. Figure 6.9. One reason for this may be the chemical 

composition of the combustion products in the room. Figure 6.6 presents the comparison of the 

CO2 volume fraction measured for each of these three fuels and shows that the CO2 volume 

fraction for toluene is significantly higher than that for either heptanes or isopropanol. Therefore, 

one explanation for toluene having a higher heat flux to the floor than the other fuels is that its 

product gases are more heavily laden with CO2. CO2, being heavier than most of the other 

expected product gas constituents, is more likely to move the product gasses closer to the floor 

and increase the heat flux there. 

Table 6.1: Heat of combustion and measured and ideal heat release rates for liquid fuels. 

Net Δh 

(MJ/kg) [3] 

Measured 

HRR (kW) 

Uncertainty 

of HRR 

Ideal HRR 

(kW) 

Uncertainty 

of Ideal HRR 

Heptane 44.56 1460 105 1816 134 

Toluene 40.52 1209 59.1 1567 155 

Iso-Propanol 30.45 1111 75.9 1268 47 

 
116 

Figure 6.1: Comparison of measured heat release rate for three different liquid fuels, Heptane, Iso-Propanol, and 

Toluene. 

Figure 6.2: Plot of heat of combustion of each fuel verses measured and ideal heat release rate for three liquid fuels. 

Time from Ignition (s)

Measured Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500

2000

Heptane

Iso-Propanol

Toluene

Δh (MJ/kg)

HRR (kW)

26 28 30 32 34 36 38 40 42 44 46 48 50 1000

1200

1400

1600

1800

2000

Measured HRR

Ideal HRR

Linear Fit

iso-propanol

toluene

heptane
117 

Figure 6.3: Comparison of measured front (solid lines) and rear (dashed lines) temperatures for three different liquid 

fuels, Heptane, Iso-Propanol, and Toluene. 

Figure 6.4: Comparison of measured front (solid lines) and rear (dashed lines) oxygen volume fraction as a function of 

time for three different liquid fuels, Heptane, Iso-Propanol, and Toluene. 

Time from Ignition (s)

Temperature (oC)

0 200 400 600 0

500

1000

1500

Heptane

Iso-Propanol

Toluene

Time from Ignition (s)

XO2

0 200 400 600 0

0.05

0.1

0.15

0.2

Heptane

Iso-Propanol

Toluene
118 

Figure 6.5: Comparison of measured front (solid lines) and rear (dashed lines) CO volume fraction as a function of time 

for three different liquid fuels, Heptane, Iso-Propanol, and Toluene. 

Figure 6.6: Comparison of measured front (solid lines) and rear (dashed lines) CO2 volume fraction as a function of time 

for three different liquid fuels, Heptane, Iso-Propanol, and Toluene. 

Time from Ignition (s)

XCO

0 200 400 600 0

0.02

0.04

0.06

0.08

0.1

Heptane

Iso-Propanol

Toluene

Time from Ignition (s)

XCO2

0 200 400 600 0

0.05

0.1

0.15

0.2

Heptane

Iso-Propanol

Toluene
119 

Figure 6.7: Comparison of measured front (solid lines) and rear (dashed lines) total hydrocarbon (THC, on a CH4 basis) 

volume fraction as a function of time for three different liquid fuels, Heptane, Iso-Propanol, and Toluene. (Note: Front 

Iso-propanol results are not shown as the analyzer failed during this test. 

Figure 6.8: Comparison of the measured radiative heat flux at the front ceiling location, channel ID:HFFCE, for 

heptanes, toluene, and isopropanol. 

Time from Ignition (s)

XTHC

0 200 400 600 0

0.01

0.02

0.03

0.04

0.05

Heptane

Iso-Propanol

Toluene

Time

Heat Flux Front Ceiling (kW/m2

)

0 200 400 600 800 0

50

100

150

200

250

300

Heptane 9

Propanol 15

Toluene 20
120 

Figure 6.9: Comparison of the measured radiative heat flux at the front floor location, channel ID:HFFFL, for heptanes, 

toluene, and isopropanol. 

6.1.2 Solid Fuels

In the configuration described in this report, creating under-ventilated fires with solid fuels while 

still being able to measure ideal heat release rate as the mass loss rate of the fuels was 

problematic. For this reason only two under-ventilated solid fuel fires were successfully created. 

ISOStyrene17 and ISOPP18 using 30 kg polystyrene and 20 kg polypropylene, respectively, are 

those two cases. The cases are similar in that they each used the same door opening (20 cm) and 

utilized the same surface area of solid fuel, and similar masses of fuel. However, the two tests 

differ in that the polystyrene fire utilized a single 1 m2

 burner positioned in the center of the 

room at position 1, cf. Figure 2.5, and the polystyrene fire utilized two 0.5 m2

 pans at positions 1 

and 2. Despite these differences in configuration there are some interesting comparisons that can 

be made between the two solid fuels. 

Figure 6.10 presents the measured heat release rate for the polystyrene and polypropylene fuels. 

The polystyrene fire heat release rate initially increases very quickly compared to the 

polypropylene fire. Later the polystyrene heat release rate peaks earlier than the polypropylene 

heat release rate. The earlier maximum in heat release rate for polystyrene can be attributed to 

the pan configuration. All of the polystyrene fuel is contiguous while the polypropylene fuel was 

in two separate locations that initially did not interact much. The initially faster rise in heat 

release rate for polystyrene however is more likely to occur because of a smaller heat capacity of 

polystyrene. Additionally, it is observed that the maximum heat release rate of the polypropylene 

Time

Heat Flux Front Floor (kW/m2

)

0 200 400 600 800 0

50

100

150

200

250

300

Heptane 9

Propanol 15

Toluene 20
121 

fire is higher than that of the polystyrene fire. This is likely because the net heat release rate for 

polypropylene is larger than polystyrene. 

Figure 6.11 compares the temperatures of polypropylene and polystyrene as a function of time. 

Analogous to the heat release rate the temperature of the polystyrene fire initially increases faster 

than that of the polypropylene fire. The maximum temperature of the polystyrene fire occurs 

earlier than the polypropylene fire as well, however the maximum temperature of the polystyrene 

fire is identical to that of the polypropylene fire within the experimental uncertainty. This can 

again be related to the heat capacity of the two materials. The polypropylene has a larger heat 

capacity than the polystyrene which negatively influences the temperature of the fire. So that 

even though polypropylene has a higher heat release rate than polystyrene the temperatures are 

nearly equal. 

Figure 6.12 -- Figure 6.15 illustrate the chemistry of the two fires. These plots illustrate the 

expected behavior. Specifically, O2 decreases while CO2 and CO increase earlier for polystyrene. 

Then the polypropylene fire has a lower O2 and CO2 volume fractions with a larger CO and THC 

volume fractions than the polystyrene flame. This corresponds to the larger heat release rate 

shown in Figure 6.10. When the heat release rate is higher more oxygen is necessary for 

complete combustion, however the same ventilation is provided for both the polystyrene and 

polypropylene fires. Therefore, the polystyrene fire has more oxygen than the polypropylene fire. 

Less oxygen for the polypropylene fire results in lower O2 volume fraction, lower CO2 volume 

fraction, and higher CO and THC fractions because there is not enough oxygen to convert CO to 

CO2 or even consume the extra fuel. 

 
122 

Figure 6.10: Comparison of the measured heat release rate for polystyrene and poly propylene solid fuels. 

Figure 6.11: Comparison of measured front (solid lines) and rear (dashed lines) temperature as a function of time for two 

different solid fuels, polystyrene and polypropylene. 

Time from Ignition (s)

Measured Heat Release Rate (kW)

0 500 1000 1500 2000 0

500

1000

1500

polystyrene

polypropylene

Time from Ignition (s)

Temperature (oC)

0 500 1000 1500 2000 0

500

1000

1500

polystyrene

polypropylene
123 

Figure 6.12: Comparison of measured front (solid lines) and rear (dashed lines) oxygen volume fraction as a function of 

time for two different solid fuels, polystyrene and polypropylene. 

Figure 6.13: Comparison of measured front (solid lines) and rear (dashed lines) CO2 volume fraction as a function of time 

for two different solid fuels, polystyrene and polypropylene. 

Time from Ignition (s)

XO2

0 500 1000 1500 2000 0

0.05

0.1

0.15

0.2 polystyrene

polypropylene

Time from Ignition (s)

XCO2

0 500 1000 1500 2000 0

0.05

0.1

0.15

0.2 polystyrene

polypropylene
124 

Figure 6.14: Comparison of measured front (solid lines) and rear (dashed lines) CO volume fraction as a function of time 

for two different solid fuels, polystyrene and polypropylene. 

Figure 6.15: Comparison of measured front (solid lines) and rear (dashed lines) total hydrocarbon volume fraction (on a 

CH4 basis) as a function of time for two different solid fuels, polystyrene and polypropylene. 

Time from Ignition (s)

XCO

0 500 1000 1500 2000 0

0.01

0.02

0.03

0.04

0.05

polystyrene

polypropylene

Time from Ignition (s)

XTHC

0 500 1000 1500 2000 0

0.002

0.004

0.006

0.008

0.01

0.012

0.014 polystyrene

polypropylene
125 

6.1.3 Comparison

There are several significant differences between the combustion of solid and liquid fuels that are 

worth noting here. First the liquid fuels always start burning faster. This is because the liquid 

fuels have a much smaller effective heat capacity than the solid fuels. The liquid fuels must only 

vaporize to burn, while the solid polymer fuels first melt then vaporize and burn. Overcoming 

this initial heat capacity takes more time for the solid fuels. Secondly, the radiative feedback to 

the fuel source is important. All of the liquid fuels became under-ventilated easily with a 0.5 m2

pan while a total area of 1 m2

 was necessary to cause the solid fuels to consume all of the oxygen 

in the room. This again is because of the significantly larger heat needed to actually burn the 

solid fuels. In effect the solid fuels need to recycle some of their heat of combustion to the fuel 

surface to sustain combustion. Convection and conduction are insufficient in this case because 

the cool air is entering the room from the doorway and cooling the pan burner so that the 

additional heat needed to melt and vaporize the solid polymer fuels must come from radiative 

feedback from the high temperature upper layer of the room. A list of some general fuel 

properties is provided in Table 6.2. 

Table 6.2: Fuel Properties (r is the stoichiometric ratio of fuel to air). 

Formula ρ (g/cm3) Cp (J/g°C) Δhnet (kJ/g) r 

Natrual Gas ~CH4 7ൈ10-4-9ൈ10-4 2.23 50.03 0.058 

Heptane ~C7H16 0.684 2.2 44.56 0.066 

Toluene C7H8 0.866 1.67 40.52 0.075 

Iso-propanol C3H8O 0.786 2.42 30.45 0.101 

Polystyrene C8H8 1.05 1.4 39.75 0.076 

Polypropylene C3H6 0.855 2.1 43.23 0.068 

Nylon C6H11NO 1.15 1.5 29.3 0.102 

6.2 Effect of fuel distributions

In this report fuel distribution refers to having the fuel sources, or burners located at more than 

one position inside the room. Most often the fuel distributions that were studied here were a 

comparison of a single 0.5 m2

 burner located at position 1, cf. Figure 2.5, and two 0.25 m2

burners located at positions 1 and 2, cf. Figure 2.5. Figure 6.16 -- Figure 6.22 compare several 

quantities from heptane fires in a single burner (ISOHept9) and in two, distributed, burners 

(ISOHept12) as described above. 

Figure 6.16 compares the heat release rates of the one and two burner configurations. The 

average heat release rate from each configuration is nearly the same, which is to be expected 

since an identical quantity of fuel with identical surface area was used for each configuration. 

The differences between the two configuration is in their transient behavior. The one burner case 

heat release rate is initially smaller than the two burner case and gradually increases to a 

maximum near the end of the experiment. The two burner case initially peaks in heat release rate 

early and then proceeds to gradually decrease before dropping off rapidly after the fire burns out. 

Figure 6.17 presents a comparison of the front and rear temperatures for the one and two burner 

cases. The front temperatures show a small difference (~50 °C) however the rear temperatures 
126 

are nearly identical which indicates that the thermal environment of the two tests was nearly 

identical. 

Figure 6.18 presents a comparison of the front and rear O2 volume fractions for the one and two 

burner tests. Similarly to the temperature results presented in Figure 6.17, the one and two burner 

cases are nearly identical in their O2 volume fraction profiles. The only difference in O2 volume 

fraction of note is the small increase in the rear O2 volume fraction prior to the fire going out for 

the two burner case. In this case the rear burner exhausted its fuel prior to the center burner. This 

may have allowed more oxygen to move and be present in the rear of the enclosure. 

Figure 6.19 and Figure 6.20 present comparisons of the CO2 and CO volume fraction profiles 

respectively. A more pronounced difference between the one and two burner cases can now be 

seen. More CO2 and less CO are present for the two burner case. This could indicate that the two 

burner case is more well ventilated than the one burner case causing it to produce more CO2 and 

less CO. However when Figure 6.21 is considered the total hydrocarbons in the front of the 

enclosure are much higher for the two burner case than the one burner case. These results seem 

to counter indicate each other, however the higher total hydrocarbons in the front of the 

enclosure may be the result of vaporized fuel (from the center burner) being pushed out of the 

enclosure so quickly that it does not have time to burn completely. Another indication of this is 

the heat flux measured directly over the center burner. Figure 6.22 presents a comparison of the 

front floor (between the center burner and the doorway) and the center ceiling (directly above the 

center burner) heat flux gauges for the one and two burner cases. The front floor heat flux is 

largely similar for the two cases. The center ceiling heat flux shows a dramatically different 

behavior. For the one burner case the center ceiling heat flux is much larger than the front floor 

heat flux while for the two burner case the center ceiling heat flux is much smaller than the front 

floor heat flux. This is in agreement with the previously presented theory of blowing vaporized 

fuel out of the enclosure before it can burn. As the combustion products from the rear burner 

move over the center burner they heat the fuel and vaporize it, however all of the oxygen has 

already been consumed. Therefore the heat present in the room above the center burner is much 

smaller due to its being absorbed by the fuel which is not burning. It is likely that the excess fuel 

burns once it exits the enclosure as evidenced by the nearly equal heat release rates from the two 

cases. 

 
127 

Figure 6.16: Comparison of heat release rate for heptane fires with a single burner and two distributed burners. 

Figure 6.17: Comparison of front (solid line) and rear (dashed line) temperatures for heptane fires with a single burner 

and with two distributed burners. 

Time from Ignition (s)

Measured Heat Release Rate (kW)

0 200 400 600 0

500

1000

1500

2000

Single Burner

Two Burners

Time from Ignition (s)

Temperature (oC)

0 200 400 600 0

500

1000

Single Burner

Two Burners
128 

Figure 6.18: Comparison of front (solid line) and rear (dashed line) O2 volume fraction for heptane fires with a single 

burner and with two distributed burners. 

Figure 6.19: Comparison of front (solid line) and rear (dashed line) CO2 volume fraction for heptane fires with a single 

burner and with two distributed burners. 

Time from Ignition (s)

XO2

0 200 400 600 0

0.05

0.1

0.15

0.2 Single Burner

Two Burners

Time from Ignition (s)

XCO2

0 200 400 600 0

0.05

0.1

0.15

0.2 Single Burner

Two Burners
129 

Figure 6.20: Comparison of front (solid line) and rear (dashed line) CO volume fractions for heptane fires with a single 

burner and with two distributed burners. 

Figure 6.21: Comparison of front (solid line) and rear (dashed line) total hydrocarbon volume fraction for heptane fires 

with a single burner and with two distributed burners. 

Time from Ignition (s)

XCO

0 200 400 600 0

0.02

0.04

0.06

0.08

0.1

Single Burner

Two Burners

Time from Ignition (s)

XTHC

0 200 400 600 0

0.02

0.04

0.06

0.08

0.1

Single Burner

Two Burners
130 

Figure 6.22: Comparison of front floor (solid line) and center ceiling (dashed line) heat fluxes for heptane fires with a 

single burner and with two distributed burners. 

6.3 Ventilation effects

Figure 6.23 -- Figure 6.28 present comparisons of several key variables for three heptane fires 

with various door widths to vary the ventilation of the enclosure. ISOHept25, ISOHept22, and 

ISOHept24 represent heptanes fires where a spray burner was used; the door width was varied in 

fractions of the full scale (80 cm) ISO 9705 room. ISOHept25 utilized a 1/2 width (40 cm) 

doorway. ISOHept22 utilized a 1/4 width (20 cm) doorway, which was also used for the majority 

of the other experiments in this test series. ISOHept24 utilized a 1/8 width (10 cm) doorway. 

Each test used the full doorway height (2 m) dimension of the ISO 9705 enclosure. Each test 

stepped through a series of steady state heat release rates, the heat release rate of 1000 kW was 

common to each test and the pseudo-steady period when that heat release rate was measured is 

presented in Figure 6.23 -- Figure 6.28. 

Figure 6.23 presents a comparison of the measured heat release rate for each of the three 

ventilation cases. The measured heat release rate was very similar for each of the cases over the 

duration of the pseudo-steady state region that is presented. This is by design and provides 

confidence for the ensuing discussion that the heat release rate is actually the same for each case 

and only the vent dimensions of the enclosure are changing. 

Figure 6.24 presents a comparison of the temperatures in the three different ventilation 

conditions. A slight transient is evident for the 40 cm door case, however the temperatures in 

both the front and rear of the room are similar between the three ventilation cases. This may be 

explained by the fact that the heat release rate is being maintained for each case so that the total 

heat being produced in the room is similar and the same thermal environment should be present. 

Time from Ignition (s)

Heat Flux (kW/m2

)

0 200 400 600 0

20

40

60

80

100

120

140

160

180

200

220

Single Burner

Two Burners
131 

However, as will be seen later the chemical environment of the room was much different among 

the cases. 

Figure 6.25 presents a comparison of the oxygen measurements at the front and rear of the room 

for each of the three cases. Approximately 10 % oxygen is present in the 40 cm door case while 

there was approximately 3 % oxygen in the rear of the 20 cm door and no measured oxygen for 

the other cases. This indicates that even though the same heat release rate was present and 

similar temperatures were observed the 40 cm case was not ventilation limited while the 20 cm 

and 10 cm cases were sequentially more ventilation limited with decreasing vent size. 

Figure 6.26, Figure 6.27, and Figure 6.28 present the CO2, CO, and total hydrocarbon (THC) 

volume fractions respectively for each ventilation condition. The 10 cm and 40 cm doorway 

cases have similar volume fractions of CO2 while the 20 cm doorway has significantly more 

CO2. This seems contradictory in comparison to the heat release rate and oxygen data where it 

might be expected to produce more CO2 in the 10 cm doorway case as more O2 is consumed. 

However, considering Figure 6.27 and Figure 6.28 it is evident that the carbon that would have 

been going to CO2 production is instead being used to produce CO and is resulting in a larger 

volume fraction of THC because all of the oxygen has been used. Thus, the 10 cm doorway case 

can have less CO2 than the 20 cm doorway case and the same CO2 volume fraction as the 40 cm 

doorway case when there is significantly less oxygen present in the room. 

This brief investigation into the effects of varying the ventilation of a free burning fire in a room 

provides insight into how the enclosure fire behaves. Reducing the vent size with the same size 

fire is equivalent to increasing the fire size in a room with a larger vent size. Both of these 

scenarios contribute to producing an under-ventilated condition within the enclosure. This idea is 

expanded upon in the next section (section 6.4) where an enclosure with a fixed vent size has the 

heat release rate increased linearly with time so that the evolution of a room from well ventilated 

to under-ventilated can be observed. 

A correlation such as the ventilation scaling relationships discussed in section 5 may be used to 

correlate effective ventilation conditions. As an example consider the oxygen volume fractions 

presented in Figure 6.25. The O2 volume fraction being measured in the rear of the 40 cm 

doorway case is approximately twice the value measured in the rear of the 20 cm doorway case. 

The ventilation scaling relationship says that the ventilation of the room is proportional to the 

factor Ah0.5. Since this investigation considers only varying the width of the doorway the factor 

of proportionality is simply wh1.5 or the width multiplied by a constant, for constant doorway 

height. In this context, reducing the width of the vent (doorway) by a factor of 2 results in a 

reduction in the ventilation of the room by 1/2 which is reflected in the 1/2 factor difference in 

the O2 volume fraction between the 40 cm doorway case and the 20 cm doorway case. Similarly, 

consider Figure 6.27 where the CO volume fractions are presented. The CO volume fraction 

scales with the width of the vent. The 10 cm doorway has twice the CO volume fraction of the 20 

cm doorway case, proportional the variation in ventilation, proportional here only to doorway 

width. 

 
132 

Figure 6.23: Comparison of heat release rates for three different ventilation conditions of a heptane spray burner fire 

operating at a nearly steady state of 1000 kW. 

Figure 6.24: Comparison of front (solid likes) and rear (dashed lines) temperatures for three different ventilation 

conditions of a heptane spray burner fire operating at a nearly steady state of 1000 kW. 

Steady State Time (s)

HRR (kW)

0 50 100 150 200 250 0

500

1000

1500

2000

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)

Steady State Time (s)

Temperature (oC)

0 50 100 150 200 250 0

500

1000

1500

2000

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)
133 

Figure 6.25: Comparison of front (solid likes) and rear (dashed lines) O2 volume fraction for three different ventilation 

conditions of a heptane spray burner fire operating at a nearly steady state of 1000 kW. 

Figure 6.26: Comparison of front (solid likes) and rear (dashed lines) CO2 volume fraction for three different ventilation 

conditions of a heptane spray burner fire operating at a nearly steady state of 1000 kW. 

Steady State Time (s)

XO2

0 50 100 150 200 250 0

0.05

0.1

0.15

0.2

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)

S teady S tate Tim e (s)

XCO2

0 50 100 150 200 250 0

0.05

0.1

0.15

0.2

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)
134 

Figure 6.27: Comparison of front (solid likes) and rear (dashed lines) CO volume fraction for three different ventilation 

conditions of a heptane spray burner fire operating at a nearly steady state of 1000 kW. 

Figure 6.28: Comparison of front (solid likes) and rear (dashed lines) total hydrocarbon volume fraction for three 

different ventilation conditions of a heptane spray burner fire operating at a nearly steady state of 1000 kW. 

Steady State Time (s)

XCO

0 50 100 150 200 250 0

0.05

0.1

0.15

0.2

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)

Steady State Time (s)

XTHC

0 50 100 150 200 250 0

0.05

0.1

0.15

0.2

40 cm (Half Door)

20 cm (Quarter Door)

10 cm (Eighth Door)
135 

6.4 Heat release rate ramp

Figure 6.29 and Figure 6.30 present the heat release rate, temperature, and species volume 

fractions for test ISOHept27 where heat release rate was ramped linearly with time with a 10 cm 

(1/8 width) door. This test is illustrative of how the environment inside the room is changing as 

a function of heat release rate. Figure 6.29 compares the ideal heat release rate controlled as the 

fuel pump flow rate and the actual heat release rate as measured by oxygen loss calorimetry. 

Initially at 500 kW the ideal and actual heat release rate are very close indicating that there is a 

very high combustion efficiency for the room with this relatively small heat release rate. As the 

heat release rate increases we see that the combustion efficiency decreases as less of the fuel 

being pumped into the room is actually burning which suggests that there should be large 

concentrations of hydrocarbons as well as intermediate species within the room. Figure 6.30 

presents the temperature and species volume fractions inside the room and confirms that indeed 

there is a large quantity of hydrocarbons and other intermediate species in the room when the 

combustion efficiency is poor. Comparing the temperature plot with the heat release rate a 

maximum in temperature is observed at a measured heat release rate of ~600 kW with an ideal 

heat release rate of 750 kW. As the heat release rate is increased beyond this point the 

temperature in the room drops indicating that the fuel is acting as a diluent and cooling the room 

since there is no oxygen to consume it. Indeed at nearly the same time as the temperature peak in 

the heat release rate ramp the oxygen volume fraction drops to zero and the total hydrocarbons in 

the room begin to accumulate and larger volume fractions are measured. As the heat release rate 

is increased there is proportionately more hydrocarbons in the room. 

Initially the CO volume fraction is increasing in the room with heat release rate. However the 

CO volume fraction also reaches a peak around 1400 s (~800 kW), this is a phenomenon that has 

been noticed by other researchers [54]. At the same time the CO2 volume fraction is leveling off 

in the room. This indicates several things, first the volume fraction of CO in the room does not 

continue to rise indefinitely as the heat release rate rises. Also, the leveling off of CO2 volume 

fraction indicates that beyond a certain point only a fixed volume of fuel is being consumed, 

likely related to a relatively steady state supply rate of O2. The drop in CO production is likely 

related to the drop in temperature in the room as the lower temperature favors CO2 production. In 

fact the water gas shift reaction indicates that CO would be consumed and more hydrogen would 

be produced as a byproduct. Figure 6.31 presents the GC measurements for the heat release rate 

test, ISOHept27. The data set is limited, however there does seem to be a slight increase in H2

volume fraction corresponding to the decrease in CO volume fraction as predicted by the water 

gas shift reaction. 

 
136 

Figure 6.29: Comparison of ideal heat release rate, determined from fuel flow rate, and measured heat release rate 

measured from oxygen loss calorimetry for test ISOHept27, where the heat release rate was ramped linearly with time.. 

Figure 6.30: Comparison of temperature and various species mole fractions for ISOHept27 test with a linear heat release 

rate ramp. 

Time from Ignition (s)

Heat Release Rate (kW)

0 500 1000 1500 2000 2500 0

500

1000

1500

2000 Ideal HRR (kW)

Measured HRR (kW)

Time from Ignition (s)

Xi

Temperature (oC)

0 500 1000 1500 2000 2500 0

0.05

0.1

0.15

0.2

0.25

0

200

400

600

800

1000

1200

O2Rear 1400

TRSampPtRh

CO2Rear

CORear

UHRear
137 

Figure 6.31: Comparison of various gas species from both gas analyzers and GC analysis with heat release rate for heat 

release rate ram test ISOHept27. 

7 SUMMARY

This report documents a set of 30 full scale ISO 9705 room under-ventilated fire experiments 

looking at the effects of different fuels, different fuel distribution, ventilation effects, and how 

the fire changes as a function of heat release rate. The data for all of these experiments is 

collected and published in parallel with this report as a digital online resource that can be 

accessed at http://www.fire.nist.gov/testdata/FSE. Analysis was conducted on each case in order 

to verify the validity of results and to begin to explain some of the phenomena observed in the 

tests. 

Gaseous, liquid, and solid fuels were all considered in order to provide a range of different fuels 

for numerical model validation but also to highlight the different behaviors of each fuel 

considered in an identical environment. Methane was the only gaseous fuel considered here with 

under-ventilated conditions reached for full door and quarter door experiments. A metered gravel 

burner was used to accurately measure the fuel supply rate. Heptane, iso-propanol, and toluene 

were the three liquid fuels considered here. For each liquid fuel a free burn pan burner was used 

in a variety of pan configurations in addition to a spray burner. Under-ventilated conditions were 

achieved for each fuel in each type of burner configuration. Nylon, polystyrene, and 

polypropylene are the solid fuels which were considered. Both single and distributed solid fuel 

sources were used. Each solid fuel was consumed in a free burn pan. Under-ventilated fires were 

achieved for both polystyrene and polypropylene when a total surface area of 1 m2

 was available 

for the fuel. Under-ventilated conditions were not achieved for nylon in this test series. 

There were three forms of fuel delivery that were used in this investigation. First, and somewhat 

unsuccessfully, a water cooled pan burner that was pump fed was used for some of the early 

Time (s)

Xi

HRR (kW), T (oC)

0 500 1000 1500 2000 2500 3000 0

0.05

0.1

0.15

0.2

0.25

0

200

400

600

800

1000

1200

1400

1600

O2 Front

CO2 Front

COFront

THC Front

HRR

H2 (GC)

O2 (GC)

CO (GC)

CO2 (GC)

CH4 (GC)

Gas sample probe

blocked.
138 

heptane fires. Second, and more predominately, free burn pans placed on digital mass load cells 

were used for both liquid and solid fuels. Thirdly a pump fed spray burner was used with the 

liquid fuels to provide longer duration steady state fire conditions than were achievable with the 

free burn pans. For the pump fed pan and the spray burners only one fuel distribution was 

utilized. Specifically, each burner was placed at the geometric center of the room. All of the 

pump fed pan experiments used a 1 m2

 pan with inclined walls so that it had a variable surface 

area which was difficult to measure. All of the spray burner experiments utilized a 0.5 m2

 pan 

attached to a load cell to catch the fuel spray and provide some indication if fuel was 

accumulating inside the room. A variety of different fuel distributions were utilized with the free 

burn pans. Three pan sizes with internal dimensions of 1 m2

 (100 cm by 100 cm), 0.5 m2 (71c m 

by 71 cm), and 0.25 m2

 (50 cm by 50 cm) were used, each with a lip height of 0.1 m. Two load 

cells were used with the free burn pans to allow for either a single burner or two burners to be 

utilized. Distributed fuel source cases were investigated, comparing a fuel pan in the center of 

the room versus a fuel pan at the rear of the room versus two fuel pans, one located at the center 

of the room and one located at the rear of the room. 

Enclosure ventilation was investigated with a heptanes spray burner. The doorway of the room 

was varied in width, and consequently area. Half (40 cm), quarter (20 cm), and eighth (10 cm) 

doorways were investigated. For the same heat release rate, similar temperatures were observed 

for each case, however dramatically different chemical compositions were observed. 

Specifically, as the doorway width was decreased the room became more under-ventilated. These 

results are helpful in testing and designing scaling relationships for enclosure fires. 

The changes within the room as a function of heat release rate were illustrated using an enclosure 

with a one eighth width (10 cm) doorway and a heptanes spray burner. The heptanes fuel flow 

rate was incremented linearly with time to provide a linear increase in ideal heat release rate 

within the room. This allowed for an observation of how the thermal environment and the 

chemical environment of the room changes as a continuous function of heat release rate. This 

experiment allowed for the observation of maxima of both temperature and CO volume fraction 

in the room in the middle of the heat release rate ramp. Considering all of the fuels in this report 

a global peak in CO concentration was also observed in the hood after the combustion gases had 

left the room. The CO volume fraction peaked at approximately 1250 kW for all fuels. 

A new real time extractive optical soot measurement probe was developed and tested with this 

set of experiments as well. The design of this probe is still in its infancy. However, a proof of 

concept was developed which illustrated that it is indeed possible to make a real time soot mass 

fraction measurement at an interior point within an enclosure during an under-ventilated 

compartment fire. Gravimetric soot data was also collected which features a lower uncertainty 

and provided the data for the optical soot probe calibration as well as a total carbon balance in 

the room. 

Highly under-ventilated fire conditions were achieved for a number of fuels. The capture and 

measurement of carbon in all of its forms allowed for a detailed analysis of the compartment 

chemistry at discrete points within the room. This analysis was done in the form of mixture 

fraction state relationships. It was found that for Z < Zst the mixture fraction model does a good 

job of predicting the chemical composition within the room. For Z > Zst the agreement is not as 

good and in some cases really poor. This has been previously illustrated by other researchers. 
139 

However, by collecting real data that accounts for all carbon in the system at discrete points in a 

real fire, the foundation has been laid to develop better combustion models for fire researchers 

that still maintain the speed and simplicity of the mixture fraction model. 

Scaling relationships allow for the comparison of data from this full scale ISO 9705 room with 

that obtained in the 2/5 scale compartment. Care must be taken when selecting scaling laws to 

compare compartments of different geometry even if they are only geometrically scaled. For 

example, the dimentionless compartment height showed a good agreement between the full and 

reduced scale experiments when the doorway width (ventilation) was scaled with the rest of the 

room. However, if the doorway width (ventilation) is not scaled with the volume of the room it 

may be necessary to apply two or more scaling relationships to understand the differences in the 

room. This was noted by the ventilation scaling factor which showed good agreement for change 

in vent size given a room of equal size, but needs to be used secondarily if both the room size 

and vent size are independently scaled. 

As a whole this data provides a significant amount of information for modelers to use to 

validated their models for steady state conditions and to determine how well their models are 

able to recreate the effects of specific changes to the geometry, reactant supply, and fuel type. So 

far only fairly simple geometries, fuels, and fuel distributions have been utilized. Therefore it is 

important to note that this set of experiments and this report are only one step in a larger process. 

These results build on the reduced scale enclosure results [5] and will be expanded upon in the 

proposed investigations presented in section 8. 

8 FUTURE WORK

These results build on the work conduced in the reduced scale enclosure [5] and provide a wealth 

of information on scaling of the enclosure, ventilation, and fuel heat release rate. However, these 

are generally global effects measured at a few discrete points that are generally well understood 

and may be relatively easy to model but may not be an adequate basis of validation for real and 

much more complicated scenarios that fire models are used to simulate. Therefore, in order to 

build on these results and expand the applicability and usefulness of this data, these simplistic 

experiments are going to be expanded to include more complicated and realistic fuel sources 

such as furniture. 

It in planned that in the Spring of 2009 and 2010 another series of experiments will be conducted 

in which real fuel packages such as furniture will be burned and investigated. This will provide 

more realistic and complete validation data that is more convincing when you are trying to 

simulate a real fire situation. Adding real fuels to the existing suite of data will provide a robust 

set of conditions for modelers to validate against. This will allow, for example, an investigator 

who is having difficulty modeling a specific real fire scene to go back and look at the more 

global fire conditions and determine the specific source of the problem in a systematic way 

rather than randomly changing variables until the system works as desired. 

The diagnostics used in this test will be expanded upon for the next set of experiments. It is 

planned to provide more detailed mapping of the interior of the ISO 9705 enclosure as well as 

some mapping of the doorway. This implementation will require the implementation of linear 

stages to move probes within the room and in the doorway. 
140 

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143 

10 ACKNOWLEDGEMENTS

The authors wish to acknowledge the contributions of several people without whom this work 

would not be possible. The large fire lab staff, Lauren Delauder, Doris Reinhart, Tony Chakalis, 

and Greg Masenheimer did an excellent job of preparing and running the experiments as well as 

providing technical services to facilitate this test matrix. Kevin McGrattan and Jason Floyd 

provided invaluable insight and guidance into the design of the test matrix used here. Kelly Opert 

was a SURF student who provided help with developing plots and contributed to the post 

processing of data. 
144 

APPENDICES
145 

A. CHANNEL LISTS

 
146 
147 

B. EQUIPMENT LIST

Description Manufacturer Model Serial# NIST# 

Oxygen analyzer for HRR Servomex 540A 549709 

CO2/CO analyzer for HRR Seimens Ultramat 6 615207 

Total HC analyzer for HRR Rosemount 400A 569041 

Mass flow controller for HRR MKS 1179A53C 000346712 

Dew Point Transmitter for HRR Vaisala DMT242 A4850006 

Sample dryer for HRR PermaPure PD-200T-72SS 973-0905-6 

Micro GC for natural gas Agilent 3000A 623489 

Sample pump for HRR Gast MOA-P122-AA 4Z026 

Liquid fuel turbine flow meter Exact Flow 

Natural gas flow meter Instromet IRMA 15M-125 319396 605032 

Total heat flux gauge (HF Front) Medtherm 16-0.75-10-4-12-36-

20679k 131836 

Total heat flux gauge (HF Rear) Medtherm 16-0.75-10-4-12-36-

20679k 131835 

Oxygen Analyzer (O2Rear) Servomex 4100 393063 623487 

Oxygen Analyzer (O2Front) Servomex 4100 393064 623488 

CO2/CO Analyzer (Rear) Seimens Ultramat 6E NI-L00197 600671 

CO2/CO Analyzer (Front) Seimens Ultramat 6E 609425 

Total HC analyzer (Rear, Front, and 

Movable) Baseline-Mocon 8800 H 625764, 

623892 

Dew point meter (Rear, and Front) Vaisala DMT242 B074008, 

B074009 

Mass flow controller (Rear&Front) MKS M100B53C 

MFC power supply MKS 247D 

Gas Chromatograph (Front) Agilent 3000A US10713004 

Pressure Transducer for Velocity MKS 220DD 

Flow meter (spot check flows) Bios Dry Cal DCLT 20K 

Sample pump for aspirated TCs and 

gas sample tests #1-6 Gast DOA-P703-FB 

Gas conditioning system 

(Rear&Front) PermaPure MG-2812 rental 

Glass-lined stainless steel tubing Grace Davison 3149 

Soot sample MFC MKS M100B53CCS1BV 021407828 

Soot sample MFC MKS M100B53CCS1BV 021407829 

MFC power supply MKS 247D 000763015 

Soot sample filter Pall P5PJ047 

Soot sample cleaning pad Hoppe’s 1203 

Soot sample filter holder Gelman Sciences 2220 

Soot sample 3-way solenoid valves Parker 04F30C2208AAF4

C05 

Soot sample pumps Gast MOA-P122-AA 
148 

C. MICRO­GC METHOD REPORT

 
149 

 
150 

 
151 

 
152 

INDEX

Burners ........................................................ 9 

Locations ............................................... 10 

Calorimetery ............................................. 11 

Ceramic Insulation Retainers ...................... 8 

Delay Times .................................. 13, 15, 33 

Doorway ...................................................... 9 

Enclosure 

Full Scale Enclosure (FSE) ..................... 4 

Reduced Scale Enclosure (RSE) ......... 2, 3 

equivalence ratio ..................................... 111 

FDS ............................................................. 1

Fuel Distribution ..................................... 125 

Fuel Properties ........................................ 125 

fuel types ................................................. 4, 5 

Fuel Types 

Liquid Fuels ........................................ 114 

Solid Fuels .......................................... 120 

Gas Analyzers ........................................... 13 

Gas Chromatography 

Calibration Standards ............................ 17 

Columns ................................................ 17 

Gas Sample Storage System ..................... 19 

Gas Species Measurements 

GC vs. Gas Analyzer............................. 65 

Wet/Dry Basis ....................................... 65 

Global equivalence ratio (GER) .................. 2 

Gravimetric Soot Sampling ....................... 21 

Heat flux.................................................... 29 

Heat Release Rate 

normalized........................................... 110 

Hood .......................................................... 11 

HRR 

Distributed Fuels ................................... 41 

Gaseous Fuels ....................................... 40 

Liquid Fuels .......................................... 41 

Ramp ..................................................... 42 

Solid Fuels ............................................ 41 

Spray Burner ......................................... 42 

Steady States ......................................... 42 

ISO 9705 ................................................. 4, 6 

Labview..................................................... 33 

Load cell...................................................... 9 

Matlab ....................................................... 33 

NIST Large Fire Research Laboratory 

(LFRL) .................................................. 11 

Real Time Extractive Soot Measurement . 23 

Reduced Scale Enclosure (RSE) ................. 3 

Response Time .......................................... 13 

Sample Probe Locations ............................. 7 

Sample probes 

Gas Drying ............................................ 14 

Locations ............................................... 32 

Sample Probes ........................................... 14 

Scaling..................................................... 110 

Doorway .............................................. 131 

Ventilation........................................... 112 

Soot 

Filtering ................................................. 14 

Spray Nozzle ............................................... 9 

stoichiometric ratio ......................... 111, 125 

Test Conditions ......................................... 38 

Thermocouples .......................................... 25 

Aspirated Thermocouples ..................... 25 

Compare Bare Bead and Aspirated ....... 50 

Radiation Effects ................................... 28 

Repeatablility ........................................ 50 

Total Hydrocarbon Analyzer .................... 13 

Uncertainty ................................................ 35

Burner Dimensions ................................. 9 

Ceramic Fiber Blanket Composition ...... 6 

Data Acquisition (DAQ) ....................... 33 

Doorway Width ....................................... 9 

Gas Chromatography ............................ 18 

Heat Flux ............................................... 30 

Listing ................................................... 35 

Load Cell ................................................. 9 

Mass Balance ........................................ 21 

Room Dimensions ................................... 6 

Soot Measurements ............................... 21 

Span gas ................................................ 14 

Thermocouple, Aspirated ...................... 26 

Thermocouple, Bare Bead .............. 29, 50 

Water Correction ................................... 34 

Validation 
153 

RSE ......................................................... 2 

Ventilation............................................... 130 

Venturi Pump ...................................... 26, 28 

Water correction ........................................ 33