Information Circular 9272 

Summary of Combustion Products 

From Mine Materials: Their 

Relevance to Mine Fire Detection 

- By Margaret R. Egan 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 

T S Ary, Director 
Library of Congress Cataloging in PubIication Data: 

. 

Egan, Margaret R 

Summary of combustion products from mine materials : their relevance to mine 

fire detection / by Margaret R Egan. 

p. em. - (Bureau of Mines information circular; 9272) 

Includes bibliographical references @. 11). 

Supt. of Docs. no.: I 28.27:9272. 

1. Mine fires. ,2. Combustion gases. I. Title. 11. Series: Information circular 

(United States. Bureau of Mines); 9272. 

TN295.U4 [TN315] 622 ~--dc20 1622'81 90-2488 CIP 
CONTENTS 

Page 

Abstract ........................................................................... 1 

Introduction ........................................................................ 2 

Experimental methods and materials ...................................................... 2 

Intermediate-scale fire tunnel ........................................................... 4 

Calculations ........................................................................ Production parameters ............................................................... Heat-release rates ................................................................. Smoke intensity parameters .......................................................... .Smoke particle diameters ............................................................ combustion hazards .................................................................. Firedetection ....................................................................... Conclusions ........................................................................ References ........................................................................... Appendix.-Symbols used in this report .................................................... 

ILLUSTRATIONS 

1 . Wood crib configurations ........................................................... 2 . Schematic of intermediate-scale fire tunnel and data-acquisition system ......................... 

TABLES 

Materials. ignition sources. ventilation rates. mass-loss rates. major elemental constituents. ash. and 

heatingvalues ................................................................... Heat-release equation variables ...................................................... Gas concentrations. gas ratios. heat-release rates. and heats of combustion ...................... Smoke characteristics .............................................................. Relative gas and smoke values from flaming combustion .................................... Production constants from flaming combustion ........................................... Production yields from flaming combustion .............................................. Sensor alarm ratios and fire intensity at sensor alarm for flaming combustion .................... Relative levels of CO and smoke at respective alarm thresholds for smoldering combustion .......... Detect ability ranking of smoldering mine combustibles ..................................... 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

B tu/lb British thermal unit per pound m meter 

"C degree Celsius m" reciprocal meter 

cm centimeter m2/g square meter per gram 

cm3 cubic centimeter mg/m3 milligram per cubic meter 

g gram mi. minute 

g/cm3 gram per cubic centimeter mm millimet er 

g/g gram Per gram ,Frm micrometer 

g/kJ gram per kilojoule m3/s cubic meter per second 

g/(m3 ppm) gram per cubic meter times p/cm3 particle per cubic centimeter 

part per million 

PC~ percent 

g/s gram per second 

p/g particle per gram 

kg kilogram 

P/W particle per kilojoule 

H/g kilojoule per gram 

P/S particle per second 

kJ/m3 kilojoule per cubic meter 

PPm part per million 

kW kilowatt 
SUMMARY OF COMBUSTION PRODUCTS FROM MINE MATERIALS: 

THEIR RELEVANCE TO MINE FIRE DETECTION 

By Margaret R. ~gan' 

ABSTRACT 

The U.S. Bureau of Mkies investigated the product-of-combustion (POC) characteristics of 

combustible materials used in typical coal mining operations in a series of experiments conducted in an 

intermediate-scale fire tunnel. The materials examined include wood cribs, transformer fluid, coal, 

conveyor belting, brattice cloth, and ventilation ducting. 

Smoke and toxic gases evolved from burning materials contribute to panic conditions and hinder 

escape. Smoke irritates and obscures vision, while toxic gases physically debilitate and disorient the 

victims. However, POC emissions may be used for early warning fire detection. POC levels will vary 

not only between materials but also between stages of combustion and the conditions in which they are 

burning. This report summarizes the POC characteristics of each material and evaluates their 

effectiveness for early warning mine fire detection. Results show that smoke was the POC most readily 

detected from the smoldering materials tested. 

'~esearch chemist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

These studies were undertaken by the U.S. Bureau of 

Mines to determine the levels and detectability of the POC 

from various mine combustibles. Ventilated mine conditions were simulated in an intermediate-scale fire tunnel. 

This report includes and expands upon data from previous 

studies (1-q2 in which the POC of these materials were 

examined separately. 

The goals of this research are to develop more reliable 

and sensitive mine fire sensors using the most efficient 

and effective methods available and to determine the levels 

of smoke and toxic gases produced from different types 

of combustibles in fires. To achieve these goals, the 

POC levels of the potential fuels must be evaluated 

experimentally. 

Toxic gas can incapacitate victims far removed from the 

actual fire. Smoke, when liberated in any quantity, 

presents serious problems of obscuration delaying 

evacuation and rescue. However, smoke and gas provide 

2~talic numbers in parentheses refer to items in the list of references 

preceding the appendix at the end of this report. 

measurable products that can be detected when the fire is 

smoldering or flaming. The POC levels are related to 

fundamental differences in the materials, such as physical 

state (solid or liquid), origin (natural or synthetic), 

chemical composition (which may vary according to source 

or manufacturer), and the fire conditions (oxygen supply). 

The objectives of this report are (1) to explore the 

hazardous POC generated from selected mine materials, 

(2) to examine the relative detectabilities of these 

products, (3) to provide data on the performance of 

materials in a fire, and (4) to provide data which could be 

used to develop reliable and sensitive early warning fire 

detectors. The measurements include: ventilation rate 

(VA), mass-loss rate (Am/At), gas concentrations, 

smoke particulate mass (M,) and number (No) 

concentrations, and light transmission (T) through smoke. 

From these results, the following parameters can be 

calculated: heat-release rate (~a, generation rates (GJ, 

production yields (Ya, production constants (PJ, particle 

diameters (d,J and (d32), and optical density (OD). 

EXPERIMENTAL METHODS AND MATERIALS 

Two important factors influencing mine fire environ- The following materials were examined in this study: 

ments are heat and air velocity. The selection of the 

ignition source d6pended upon the fire response char- (1) Wood cribs: Four configurations of wood cribs 

acteristics of the material. Smoldering materials (those were tested in duplicate. The height and spacing of the 

from which flames did not erupt Or propagate) were PY- sticks were chosen to study the growth and the propaga- rolyzed using three electric strip heaters. Materials that tion of the fire. The cribs approhately 2 kg and 

flame were ifited with a natural gas flame* were constructed of Douglas fir using a small amount of 

lists the sources, VAO, Am/At, carpenter's glue for joining. The configurations and their elemental constituents, ash, and heating values for the dimensions are shown in figure mine combustibles tested. 

Table 1 .-Materials, ignition sources, ventilation rates, mass-loss rates, 

major elemental constituents, ash, and heating values 

Material Ignition v&,, Am/& cJ H, Ash, CI, Heating value, 

solirce m3/s g/s pct pct PCt PCt Btu/lb 

Wood ....:......... 

Transformer fluid ..... Coal ............... SBR belts ........... NP belts ............ PVC belts ........... PVC brattice ......... Jute brattice ......... Ventilation ducting .... 

Gas jet .......... .. do. .......,. Strip heaters .... Gas jet ......... .. do. ......... .. do. ......... Strip heaters .... .. do. ......... .. do .......... ND not determined. 

'~esults from thermal degradation, not flaming combustion. 

2~romine content = 7.0 pct. 
Standard high Quadratic 

Standard low Linear 

Figure 1.-Wood crib configurations. Air flows in direction of arrows. 

(2) Transformer fluid: Ten experiments were completed using three commercially available brands of transformer fluid-four with brand A and three with brands B 

and C. A 25-cm-dim pan filled with transformer fluid to 

a depth of 2.5 cm was used for each experiment. The 

natural gas jet flame was turned off once the transformer 

fluid had ignited. The flames spread quickly, engulfing the 

entire fuel surface within 1 min and remained visible for 

approximately 30 min. 

(3) Coal: Bituminous coal from the Pittsburgh Seam 

was used for all six experiments. Approximately 18 kg of 

coal was broken into pieces measuring 125 cm3 or less and 

placed in a 59- by 68-cm stainless steel pan. Three strip 

heaters were equidistantly imbedded approximately 2.5 cm 

beneath the surface of the coal. In this configuration, the 

coal smoldered for 9 rnin before flames erupted. The 

smoldering data were compiled during this preflaming 

period. 

(4) Conveyor belts: A 23- by 30-cm section of each 

belt was tested in duplicate. The belts were classified according to covering. They included four different styrene 

butadiene rubber (SBR) belts, two neoprene (NP) belts, 

and four polyvinyl chloride (PVC) belts. Once the gas 

burner was extinguished, the SBR belts sustained flaming 

combustion from 26 to 52 min, the NP belts from 15 to 

18 min, and the PVC belts from 3 to 15 min. The high 

chlorine content of the PVC belts accounts for their selfextinguishing tendency. However, none of the belts were 

totally consumed. 

(5) Brattice cloth: Fourteen different PVC brattice 

cloths from several manufacturers and one sample of 

treated jute were tested in duplicate. A double thickness 

of brattice measuring 20- by 40-cm was placed on a wire 

mesh, which rested on three strip heaters. The thermal 

decomposition of PVC brattice cloth did not result in 

flaming combustion. The results listed under smoldering 
combustion were actually the peak emission levels. This glass fibers contributed to the physical integrity by assuring 

occurred from the 15th through the 19th min after the certain minimum levels of solid residue. The polyester 

strip heaters were l~rned on. After this period, the t~&- components of these ducts are combustible and even with 

sion levels gradually dmxxised- The jute experiments fire-prevention additives, they can still erupt into flames 

were conducted under the same conditions as the PVC the proper condit.ons, The samples ranged in 

brattice experiments. Although jute is a woody fiber and thielmess from to mm. but one was cylindrical 

can burn, the was not enough to bite with a diameter of either 41 or 46 cm. A sample 20- by it. The jute smoldered and reached its peak emissions 

from the 15th through the 20th min. 40-cm rested on three strip heaters. The ducting 

(6) ventilation ducting: ~igh~ types of fiberglass smoldered for 5 min. Flaming combustion lasted about 

reinforced polyester resin from several manu- 10 min. The polyester resin coating charred or completely 

facturers were tested in triplicate. The reinforcing burned leaving only strands of fiberglassINTERMEDIATE-SCALE FIRE TUNNEL 

The Bureau's ventilated intermediate-scale fire tunnel equipment, and procedures are presented in full detail in 

was used to simulate a ventilated mine entry. Figure 2 previous reports (1-5). Smoke and effluent gases were 

shows a schematic view of the tunnel with its data continuously sampled at the same location in the tunnel. 

acquisition system. The tunnel specifications, test The instrument readings were recorded every minute. 

0.61-m -diam duct 

IOm I - 12 m, I - 

38+ Air 

0.8 -m-square duct I I f exhaust 

Manually Ventilation 

L0.305-m-diam 

entrance duct 

( hinged and movable) 

Pressure transducers 

u I channel I 

i11.1 

CO meter 

sition +Digital input 

C02 meter 

'ystern for CNM 

- . range 

TEOM 

CALCOMP -4 pbtter I 

KEY 

A Pressure transducer (flow probe) CALCOMP California computer products 

Differential pressure transducer CNM Condensation nuclei monitor 

* 3 X detector DECNET Digital equipment networking 

Thermocouples PDP Programmed data processor 

Sampling ports TEOM Tapered-element oscillating microbalance 

VA X Virtual address extension 

C 

Figure 2.--Schematic of Intermediate-scale fire tunnel (top) and data-acquisition system (bottom). 

48- 

3X 

%detector 
CALCULATIONS 

For the evaluation of detectability, the following When the fire size of a certain combustible and its 

determinations were considered to be important: GX, Yx, VA are known, the resultant gas and smoke levels from 

Px, relative values, QA, d, and G2, and smoke obscuration that material may be calculated from 

and OD. 

PRODUCTION PARAMETERS 

where Px = the value for a specific material. 

_The of a product is related to its measured concentration and V&, by the general expression For example, if Q JVA for a wood fire is known, this 

equation could be used to calculate the relative gas or 

~x = Mx (vOA0) (Ax) ('1 smoke concentrations to be expected for wood by using 

where Mcoz = 1.97 x los3 g/(m3*ppm), 

VoAo = ventilation rate, m3/s, 

, and AX = measured change in a given quantity. 

the appropriate value for ,BX when AX is gas or smoke 

from wood. I 

Alternately, one can calculate the Q JVB, at specified 

levels of gas or smoke from 

Once the G~ ;,e known and the mass-loss rate of the This last equation is ~Sef~l for assessing fire intensity at 

fuel (MJ is calculated using the load-cell assembly, the fire Sensor alarm thresholds* For example, if a carbon 

fractional yield of each combustion product (Ya can be monoxide (CO) Sensor has an alarm level of 15 PPm (m) 

calculated by the expression and the emissions are from coal (8, = 4.8 x 109 g/kJ), 

then the Q~VJI, is 3.9 at the fire intensity sufficient to 

Yx = G~/M, (2) produce 15 ppm of CO. 

The Yx for Mo and No of smoke are calculated in a HEAT-RELEASE RATES 

similar manner by the expression 

where C, = appropriate units conversion factor: 1.00 x 

10" when Mo is in milligram per cubic meter or 1.00 x 106 

when No is in particle per cubic centimeter; and AX = 

smoke concentration above ambient (when Mo is measured 

in milligram per cubic meter and No is measured in 

particle per cubic centimeter). 

In an actual mine fire, it is often dZfmdt, if not 

impossible, to calculate the actual heat of combustion. For 

flaming fires, the relative hazards tend to increase with the . QA. An indication of the hazard potential can be calculated from the ratio of generation rate to fire size as in the 

following equation 

All combustion reactions are exothermic. The energy 

release rate and amount given off is highly variable and 

depends upon many factors. It has been shown (6) that 

the & rate realized during a fire can be calculated from 

the expression 

where t)A = actual heat release, kW, 

Hc = net heat of complete combustion, 

kJ/g, 

Hco = heat of combustion of CO, 

10.1 M/g, 

Using the rate of formation of gas or smoke as a function Kcoz A = theoretical yield of C02, g/g, 

of the fre size is also beneficial in comparing the combustion hazards of different materials. and Kco = theoretical yield of CO, g/g. 
Because each material is unique and has a different carbon A typical fire rarely realizes the state of complete 

content and British thermal unit per pound rating, the combustion. For this reason, the actual heat of corntheoretical yields of CO and carbon dioxide (COJ will bustion (HA) during a fire is usually less than the total 

vary. The actual values listed in table12 were derived from heat of combustion (Elc)). By measuring both the QA, 

an independent testing laboratory. The Q* for each com- equations 8-15, and the M,, the HA can be calculated from 

bustible can be calculated by substituting the experimental the expression 

data for V&, ACO,, and ACO, and the values from 

table 2 in equations 1 and 7, which yields: HA = Q~/M~ (16) 

for wood and jute: SMOKE INTENSITY PARAMETERS 

QA = VoAo [(0.O216)(ACO2) + 8.9 x loe3 (ACO)], (8) Smoke evolution is most often expressed in terms of 

OD, in reciprocal meters. This characteristic provides a 

transformer fluid: measure of fire hazard, in that escape and rescue depend 

on visibility. It is related to T by the following expression 

QA = V,A, [(o.o251)(~Co~) + 7.1 x lom3 (ACO)], (9) 

coal: 

-1 OD = - (ln T), e 

QA = Vo& [(0*0214)(Aco2) + 8.5 x lo3 (ACO)], (10) where e = path length in m. 

SBR belts: Most smoke detectors are triggered at an OD of 0.1 m-l. 

The probability of escape and rescue is reduced si6- 

QA = VoAo [(0*0245)(AC02) + 1.18 X loe2 (Ace)], (11) cantly once the critical level of smoke (OD = 0.5 m-l) has 

NP belts: 

accumulated (7) .3 

Another measure of smoke hazard is the smoke particle . 

optical density as specific extinction coefficient, E. It 

QA = VoAo [(0.0238)(AC02) + 1-67 x (ACO)], (12) considers the influence that VA, and M~ have on OD. . The relationship between f and OD is expressed as 

PVC belts: 

QA = VoAo [(0.0258)(AC02) + 1.83 x (ACO)], (13) 

PVC brattice: 

QA = VoAo [(0.0268)(AC02) + 1.41 x (ACO)], (14) 

and ducting: 

Q* = V,-,Ao [(0.0216)(AC02) + 8.8 x 10" (ACO)]. (15) 

Table 2.4eat-release equation variables 

- pppp - - - --- - 

Material Ha Kc01 ko21 

kJlg g/g 919 

Wood ............. 16.4 1 .I0 1.72 

Transformer fluid .... 40.7 2.03 3.19 

Coal .............. 31 .O 1.82 2.86 

SBR belts .......... 31 .O 1.59 2.49 

NP belts ........... 23.4 1.23 1.94 

PVC belts .......... 24.8 1.21 1.89 

PVC brattice ........ 23.5 1.11 1.74 

Jute brattice ........ 13.6 .79 1 -24 

Ventilation ducting ... 9.0 .52 .82 

A convenient measurement of smoke density is to examine the obscurant effect of smoke. Some factors influencing obscuration are the number and size of the particles, refractive index, light scattering, ventilation, and 

distance through which the light must travel. The smoke 

obscuration is the percentage of light absorbed by the 

smoke or 100 pct of the light minus the percent T. It is 

calculated using the following equation: 

Obscuration = 100(1 - T). (19) 

The obscuration values presented in this report are an 

average of the attenuation of the beam of light at the two 

wavelengths in the visible range, 0.45 and 0.63 pm. 

3~eference 7 quotes a value of OD = 0.218 me' for the critical value 

determined from the expression OD =-111 log T. When the natural 

logarithm is used, as in equation 17, then OD = 2.303 x 0.218 = 0.5 me', 

the value used in the text. 
7 

SMOKE PARTICLE DIAMETERS Using the three-wavelength smoke detector developed 

Measurements of both Mo and No of the smoke can be 

used to calculate the average size of the smoke particles, 

using the expression m 

by the Bureau (8), the transmission of the light (T) 

through the smoke can be calculated for each wavelength. 

The extinction-coefficient ratio can be calculated for each 

pair of wavelengths (A) from the following logtransmission ratios: 

(20) 

where dm = diameter of a particle of average mass, 

Pm, InT,=l.oo, 

_ 

pp = individual particle density, g/cm3, 

M, = particle mass concentration, mg/m3, Using these extinction coefficients and the curve in referand No = particle number concentration, p/cm3. ence 8, figure 11, the volume-to-surface mean particle 

diameter (4J can be determined: (Calculation of the 

Assuming a value of Pp = 1.4 g/cm3, then the dm can be extinction-coefficient curves assumes spherical particles 

calculated in micrometers from with an estimated refractive index.) The T must be less 

1/3 than 85 pct before reliable particle sizes can be calculated 

dm = 11.09 [?] . (21) using this technique. 

COMBUSTION HA2ARDS 

The principal hazards encountered in smoldering in which strip heaters were used to keep plywood and 

combustion involve toxic gas and smoke production. conveyor belting in a nonflaming stage. 

Flaming combustion introduces additional dangers of heat 

release and flame spread. Tables 3 and 4 give a summary Table 8--Gas concentrations, gas ratios, heat-release 

of the fire characteristics for both flaming and smoldering rates, and heats of combustion 

combustion. The gas concentrations and smoke levels 

have all been obtained during the steady state, when fairly Material CO, CO, Ratio, QA, HA 

constant values were noted. 

ppm ppm COJCO kW kJ/g Flaming combustion was observed during the wood, FLAMING coal, transformer fluid, SBR belt, and NP belt experi- Wood ........... 145 6,759 46.6 110.2 10.6 

ments. The materials that tended to smolder were jute, Transformer fluid , , 113 1,769 15.7 21.1 24.3 

PVC brattice, and PVC belts. Four of the eight ventilation Coal . . . . . . . . . . . . 89 i ,095 12.3 5.9 15.1 

ducts resulted in flaming combustion. Their results are 

listed as ignitable ducting. Two ducts just smoldered. 

Their results are listed as nonignitable ducting. The 

thermal decomposition of the remaining two of the ducts 

sometimes resulted in flaming combustion. Their results 

are listed in the appropriate combustion designation. 

Included in the smoldering data are preflaming coal and 

smoldering plywood and conveyor belts. These smoldering 

results were obtained from another series of experiments 

SBR belts . . . . . . . . 902 13,771 15,3 38.4 16.2 

NP belts . . . . . . . . . 112 826 7.4 2.3 2.6 

Ignitable ducting . . 700 13,239 18.9 42.5 96.6 

SMOLDERING 

Wood ........... 43 ND ND ND ND 

Coal . . . . . . . . . . . . 15 19 1.3 0.1 ND 

Jute brattice . . . . . . 32 149 4.6 .6 ND 

PVC brattice . . . . . . 25 22 .9 .1 ND 

Nonignitable ducting 28 139 5.0 .5 ND 

ND Not determined. 
Table 4.4moke characteristics 

Material NO, M~, dm, d32* Obscur- OD, C , 

lo6 p/cm3 mg/m3 CL~ pm- ation, pct m" m2/g 

FLAMING 

Wood ................... 6.0 49.1 0.22 ND 9 1.39 0.13 

Transformer fluid .......... 1.1 35.3 -39 0.39 46 7.31 3.95 

Coal .................... 1.5 11.4 .21 .23 20 2.77 1.70 

SBR belts ................ .2 43.7 .62 .33 75 15.93 .74 

NP belts ................. .2 4.7 .30 .30 15 1.63 .20 

Ignitable ducting .......... 1.8 224.3 .56 .48 5 1 7.52 2.56 

SMOLDERING 

Wood ................... ND 50.8 ND ND 12 1.36 ND 

Coal .................... 1 .O 3.2 0.16 ND 9 .91 ND 

Jute brattice .............. 0.4 6.9 .29 ND 3 .30 ND 

PVC brattice .............. 3.0 72.3 .32 0.47 11 1.23 ND 

Nonignitable ducts ......... 1.3 32.2 .28 .36 11 1 -20 ND 

ND Not determined. 

The most important narcotic fire gas is CO (9). It is 

highly toxic because of its affinity to combine with hemoglobin which blocks the uptake of oxygen. Conditions in 

most fires are normally such that complete oxidation to 

CO, does not occur, thus, some amount of CO is formed. 

In these experiments, SBR belts and ignitable ducting 

generated the highest concentrations of CO. 

CO, is not considered a toxic agent. However, 

inhalation of CO, will stimulate respiration which in turn 

will lead to increased inhalation of the toxic POC. SBR 

belts and ignitable ducting lead in the production of CO, 

also. A better indication of combustion efficiency is the 

C0,-CO ratio. Most flaming combustion generates 

predominantly CO, with a relatively small amount of CO 

resulting in a high C0,-CO ratio. Lower ratios may 

indicate less efficient combustion such as that resulting 

from smoldering fires. The flaming combustion of wood 

produced the highest C0,-CO ratio. 

Other toxic gas products measured in these experiments 

were hydrogen cyanide (HCN) and hydrogen chloride 

(HCl). HCN is the most dangerous of the toxic POC after 

CO because it can interfere with the body's use of oxygen. 

It is liberated only during the burning of nitrogencontaining materials such as coal. The steady-state 

production of HCN during these coal experiments 

averaged 6.5fl.5 ppm. HCL irritates the eyes and upper 

respiratory tract. It is liberated during the thermal 

degradation of chlorine-containing materials such as PVC. 

The average peak production of HCl during the rapid 

degradation of the PVC brattices was 38 ppm at an 

average temperature of 283" C. This occurred 3 min after 

the peak CO production. However, measurable levels of 

smoke were recorded 3 min prior to measurable concentrations of either HC1 or CO. During the smoldering 

stage, the steady-state HCl-CO ratio was approximately 

4 to 1. 

Another hazard occurring in flaming combustion is 

rapid heat transfer to unburned materials, which promotes 

flame spread. Its effects can be demonstrated by the 

combustion of different configurations of wood cribs. The 

arrangement of the sticks influenced heat transfer. 

Lowering the crib profde decreased the efficiency of the 

heat transfer, which produced longer burning times and 

reduced the mass loss. Lowering the ventilation rate also 

reduced the heat transfer and mass loss. With less oxygen 

available, the wood was consumed at a slower rate. In 

underground fires, it may be beneficial to decrease or stop 

the airflow, whenever possible. This would slow the progress of the fire by reducing the available oxygen and by 

lowering the heat released and slow its transfer. An 

increase in the ventilation once a fue has developed serves 

only to reoxidize the flames. 

Heat of combustion may be defined as the heat produced by the combustion of a given weight or volume of 

material. This characteristic provides a measure of fire 

hazard in that a material which burns with the evolution 

of little heat per unit quantity burned will contribute appreciably less to a conflagration than a material which generates large amounts of heat per unit quantity burned (10). 

As an example, a fire involving a small amount of ignitable 

ducting may result in a high actual heat of combustion. 

Steady-state data in terms of QA and HA are listed in table 3. Since wood burned with the greatest QA, of all the 

materials tested, as measured by the heat release, the 
flaming POC of the other materials were scaled to this fue 

intensity. These values may be found in table 5. Ignitable 

ducting produced the highest values, except for No which 

was produced by coal. If ignitable ducting burned at that 

fire intensity, the most toxic emissions would theoretically 

result. 

Table 5.--Relative1 gas and smoke values 

from flaming combustion 

Material CO, CO,, NO, Mo, 

PPm ppm lo6 p/cm3 mg/rn3 

WO"~ ......... 145 6,759 6.04 49.1 

Transformer fluid. 284 4,992 2.79 85.2 

Coal .......... 441 5,762 7.12 50.6 

SBR belts ...... 294 5,017 .01 13.5 

NP belts. ...... 602 5,009 1.00 22.3 

Ignitable ducting. 956 12,393 1.89 294.9 

'scaled to the fire intensity of wood. 

Smoke density provides a measure of fue hazard as well 

as detectability. The chances of escape and rescue are 

inversely proportional to the OD. However, the OD of 

smoke can also be used to alert personnel of potential 

danger. The thick smoke emitted from burning SBR belts 

can be compared with the clean burning wood cribs with 

the resulting escape and detection ramifications. NP belts 

may be the least hazardous of the flaming combustibles 

not only because of the low gas and smoke concentrations 

but also because of the tendency of these belts to selfextinguish. 

The average size of the particles is a major factor in 

smoke obscuration. Two methods of calculating particle 

size are possible from these determinations. The d, and 

d3 usually show good agreement. Ignitable ducting and 

smoldering PVC brattice produced smoke particles with 

the largest diameter. Wood and coal combustion produced the smallest particles. The smoke characteristics 

varied slightly between the brands of transformer fluid. 

One brand produced 52 pct fewer particles than the other 

brands. Another brand produced particles with an 82 pct 

lower Mo. Because of these differences, the dm ranged 

from 0.21 to 0.5 pm. The d3, had a narrower range from 

0.35 to 0.44 pm. However, the average of both diameter 

determinations was the same, 0.39 pm. The obscuration 

ranged from 40 to 60 pct. The brand with the largest 

particle diameters had the highest OD and obscuration. 

The POC can also be scaled according to fire size 

(&) or the yield per mass-loss rate (Yd. Only those 

materials with significant mass-loss rates and fire sizes 

were calculated. The Bx values can be found in table 6, 

and the Y, values can be found in table 7. These are 

convenient determinations for assessing the hazardous 

nature of the emissions. As might be expected, ignitable 

ducting produced the most toxic emissions per gram of 

material consumed with wood producing the least. Coal 

and ignitable ducting produced the most hazardous 

emissions per kilowatt of heat released. 

Table 6.4roduction constants from flaming combustion 

Material P~~, BCO~, P~O1 @M,, 

10" g/kJ 1u2 g/kJ lo1' p/kJ 10' g/kJ 

Wood ......... 1.6 10.4 5.79 4.9 

Transformer fluid. 3.1 7.7 2.48 7.8 

Coal .......... 4.8 8.9 6.83 4.7 

SBR belts ...... 3.2 7.8 .05 1.2 

NP belts ....... 6.6 7.7 .96 2.2 

Ignitable ducting. 4.3 8.9 -69 10.7 

Table 7.4koduction yields from flaming combustion 

Material Y~~, Y~~21 Y No, Y 

Mo, 

lo-, g/g lul g/g loll p/g 10-~ g/g 

Wood ......... 1.7 1.3 5.78 4.7 

Transformer fluid. 7.6 1.9 5.94 19.1 

Coal ........,. 6.8 1.3 9.23 7.0 

SBR belts ...... 14.4 3.5 .26 5.6 

NP belts ....... 1.8 2.1 .26 .6 

Ignitable ducting. 29.8 8.9 6.14 76.5 

FIRE DETECTION 

Reliable fue detection is an essential aspect of fue light. POC sensors use chemical changes based on ionprotection, both for safe evacuation and fire control or ization, photoelectric sensing, or gas detection (11). These 

extinguishment. Detection is based on the environmental . various types of sensors can be used separately or in 

changes occurring during the combustion process such as combination for a more effective system. The appropriate 

the production of heat, light, gases, and smoke. Thermal choice depends on the environmental changes most easily 

sensors may be fixed-temperature or rate-of-rise sensors. detected. For flaming fues, the speed of detection is 

Optical sensors measure ultraviolet, infrared, or visible another consideration. Transformer fluid fires propagate 
immediately, but the dense smoke can be quickly detected. 

By comparison, the flaming combustion of the wood cribs 

yielded a clean burning fire with low obscuration rate and 

OD. Therefore, an optical smoke sensor would not be as 

effective for detecting fires in areas heavily loaded with 

wood. However, wood crib fires burn with great intensity 

which might be expected from the high combustion ratio. 

Therefore, in areas with large amounts of wood, thermal 

sensors might be the appropriate choice. In a smoldering 

wood fire where little heat is generated, smoke sensors 

would reach their alarm threshold before CO sensors. 

The unique fire characteristics of each material present 

distinct detection dilemmas. The following are examples 

of different fire scenarios. Coal fires may be preceded by 

prolonged periods of smoldering such as when spontaneous combustion or self-heating occurs. Fire detection 

under these circumstances may not be as critical, but must 

still be reliable. This type of fire, if left undetected, can 

become a dangerous and life-threatening situation. The 

smoke of coal fires seems to be most easily detected POC. 

SBR is a very flammable copolymer with high mechanical strength when reinforced with carbon black. 

Since conveyor belts are subject to friction ignition, 

flammability can be reduced by the incorporation of a 

combination of flame retarding additives which, unfortunately, tend to increase the formation of smoke and 

toxic products. The high obscuration rate and OD observed are evidence of this smoke-producing characteristic 

which can be readily detected. 

Although ri*d PVC is not very flammable because of 

its high chlorine content, significant amounts of flammable 

plasticizers can be added to increase flexibility. Consequently, flame retardants are incorporated into the polymer to reduce flammability. Unfortunately, in some cases, 

the addition of fire retardants results in a decreased 

tendency to ignite, but an increasing tendency to smoke 

when ignition finally takes place (12). In the manufacturing process, a compromise formulation must be 

reached to achieve either reduced smoke formation or low 

flammability depending upon the intended application. 

Smoldering PVC brattice produced smoke with rather 

large particle diameters and relatively high OD. For 

either PVC belts or brattice, smoke detection would be the 

appropriate choice. 

As demonstrated, the selection of a CO sensor verses 

smoke detector can be simplified when the relative 

quantities of the POC are measured. If one assumes 

that a typical CO fire sensor has a maximum alarm 

threshold level of 15 ppm above ambient, and a typical 

smoke fire sensor has a maximum alarm threshold level 

of 0.1 m-l OD, then the data in tables 1, 3, and 4 can 

be used to estimate fire sizes at which these levels of 

CO and smoke are expelled into the ventilation airflow. 

Table 8 makes this comparison for flaming combustion as 

a function of Q JV& using equation 19 and the average 

ratio of smoke OD to ppm CO for the materials tested 

(column 2 of table 8). 

Table 8.--Sensor alarm ratios and fire intensity 

at sensor alarm for flaming combustion 

Material OD, Q,/VA, k~/m~ at- 

(m-')/ppm CO 15 ppm CO 0.1 m" OD 

Wood . . . . . . . . . 0.0096 11.7 8.15 

Transformer fluid. ,0647 6.0 .62 

Coal . . . . . . . . . . ,031 1 3.9 .84 

SBR belts . . . . . . ,0255 5.9 1.53 

NP belts . . . . . . . ,0146 2.8 1.29 

Ignitable ducting. .0107 4.4 2.71 

From table 8, at a constant VA,, CO fire sensors 

would detect a smaller NP belt fire than any of the other 

flaming combustibles. Smoke fire sensors would detect a 

transformer fluid fire with a low fire intensity better than 

any other flaming combustible. Detectable fire intensities 

for wood are significantly greater than for the other materials, indicating that this type of fire is more =cult to 

detect. Smoke sensor alarm thresholds are reached at 

smaller ratios than CO alarm thresholds. 

To assist in determining which type of fire sensor 

(smoke or CO) is more effective for smoldering materials, 

a comparison can be found in table 9. A smoke sensor is 

the obvious choice because the OD of the smoke is well 

above the alarm threshold of 0.1 m-I by the time the CO 

threshold of 15 ppm is reached. Jute brattice is the only 

exception, with smoke detection only slightly ahead of CO 

detection. However, for all materials tested, the CO concentration had not reached alarm levels by the time the 

OD had more than surpassed its alarm threshold. Table 10 ranks mine combustibles for ease of fire detection. 

The combustion emissions detected by a CO sensor are in 

the reverse order of smoke detection and that all the 

combustibles tested are more readily detected by smoke 

(OD) than by CO concentration. 
Table 9.--Relative levels of CO and smoke 

at respective alarm thresholds 

for smoldering combustion 

Material OD, co, 

15 ppm CO 0.1 m'l OD 

PVC'belts ........ 1.52 0.99 

SBR belts ........ 1.42 1.05 

NP belts ......... 1.05 1.44 

Coal ............ .91 1.65 

PVC brattice ...... .72 2.10 

Nonignitable ducting. -64 2.33 

Wood ........... .47 3.16 

Jute brattice ...... .I4 10.67 

 able 10.-Detectability ranking 

of smoldering mine 

combustibles 

Material CO sensor Smoke sensor 

Jute brattice ...... 1 8 

Wood ........... 2 7 

Nonignitable ducting. 3 6 

PVC brattice ...... 4 5 

Coal ............ 5 4 

NP belts ......... 6 3 

SBR belts ........ 7 2 

PVC belts ........ 8 1 

CONCLUSIONS 

Burning materials generate unique and dangerous POC. 

These experiments were conducted to measure the smoke 

and gas generated and to compare their potential detectability. The following combustion characteristics were 

derived from this series of experiments. Burning wood 

cribs liberated the most heat as was expected from the 

high M~ Transformer fluid fires can quickly produce 

critical smoke and propagation levels which make them 

readily detectable, but limit escape and rescue efforts. 

SBR belts produced dense smoke evidenced by the high 

obscuration rate and OD. NP belts may support flame 

propagation (given the proper conditions) even though 

considered self-extinguishing. Ignitable ventilation ducting 

produced the largest M, resulting in large d, and on a 

relative scale produced the highest amounts of CO and 

CO,. Burning PVC belt and brattice emissions have 

increased toxicity because of the release of HCl. 

Smoldering jute brattice releases small amounts of CO and 

smoke and could, therefore, go undetected. Smoke 

detection proved only slightly more effective than CO 

detection. Nonignitable ventilation ducting may be one of 

the safest materials underground because it is difficult to 

ignite and does not support flame propagation. However, 

if consumed in a fire, it could add toxic components to the 

combustion product mixture. In a mine fire, these 

products combine to produce a wide variety of smoke 

particles and volatile gases that are transported by the 

ventilation system. Because of the unique nature of 

underground mining, fire detection is of utmost 

importance. For the materials tested, smoke sensors are 

more effective for frre detection because their alarm 

thresholds are reached before that of the CO sensors. 

REFERENCES 

1. Egan, M. R, and C. D. Litton. Wood Crib Fires in a Ventilated 

Tunnel. BuMines RI 9045,1986, 18 pp. 

2. Egan, M. R Transformer Fluid Fires in a Ventilated Tunnel. 

BuMines IC 9117,1986, 13 pp. 

3. - .Coal Combustion in a Ventilated Tunnel. BuMines 

IC 9169, 1987,13 pp. 

4. - .Emission Products From Combustion of Conveyor Belts. 

BuMines IC 9205, 1988, 12 pp. 

5. - .Thermal Decomposition of Ventilation Ducting. BuMines 

IC 9263, 1990, 11 pp. 

6. Tewarson, A. Generation of Heat and Chemical Compounds in 

Fires. Ch. in The SF'PE Handbook of Fire Protection Engineering, ed. 

by P. E. DiNenno. Natl. Fire Prot. Assoc., 1st ed., 1988, pp. 1-179 to 

1-199. 

7. Tewarson, A., and J. S. Newman. An Experimental Investigation 

of the Fire Hazards Associated With Timber Sets In Mines. Paper in 

Proceedings: Bureau of Mines Technology Transfer Seminars, Denver, 

CO, Nov. 3, 1981, and St. Louis, MO, Nov. 6, 1981. BuMines IC 8865, 

1981, pp. 86-103. 

8. Cashdollar, K L., C. K Lee, and J. M. Singer. Three-Wavelength 

Light Transmission Technique To Measure Smoke Particle Size and 

Concentration. Appl. Optics, v. 18, No. 11, 1979, pp. 1763-1769. 

9. Purser, D. A. How Toxic Smoke Products Affect the Ability of 

Victims to %ape From Fires. Fire Prev., No. 179, 1985, pp. 28-32. 

10. Hilado, C. J. (ed.). Flammability Handbook for Plastics. Technomic Publ., 3d ed., 1982, p. 118. 

11. Pomroy, W. H. Fire Detection Systems for Noncoal Underground Mines. Paper in Recent Developments in Metal and Nonmetal 

Fire Protection. BuMines IC 9206, 1988, p. 21. 

12. Landrock, A. H. Handbook of Plastics Flammability and Combustion Toxicology. Noyes Publ., 1983, p. 95. 
APPENDIX.-SYMBOLS USED IN THIS REPORT 

d, diameter of a particle of average mass, pm p particle 

4, v'olume-to-surface mean size, pm Q actual heat-release rate, kW 

G generation rate of a given combustion product, g/s Q heat-release rate of the fuel, kW 

or p/s 

T transmission of light, pct 

HA actual heat of combustion, kJ/g 

Vd)i, ventilation rate, m3/s 

Hc net heat of combustion of the material, kJ/g 

Hco heat of combustion of CO, kJ/g 

Kx theoretical yield of a given gas, g/g 

4 optical path length, m 

In logarithm, natural 

M, mass loss, g 

Yx yield of a given combustion product, g/g or p/g 

Px production constant of a given combustion product, 

g/kJ or p/kJ 

Am measured change in mass, g 

At measured change in time, s 

AX measured change in a given quantity 

Mo particle mass concentration, mg/m3 X wavelength of light source, pm 

Mx conversion unit for generation rates f specific extinction coefficient or particle optical 

No particle number concentration, p/cm3 density, m2/g 

OD optical density per unit path length, m-l p, individual particle density, g/cm3 

'U.S. Government Printing Office: 1990 - 511010J400M