Table 6.—Steady-state generation rates from smoldering Table 8.—Initial smoke characteristics from smoldering

brattice cloth and conveyor belting brattice cloth and conveyor belting
Sample Geo, Gcoy Scythe comms Ne Mo dye Gap Obscura: 0,
10% 9/8 _10°g/s_107g/s_g/tm?s)_g/(m*s) me pment
BRATTICE CLOTH BRATTICE CLOTH

oe fe bed 0.01 00s 127 «2470.29 ND 3003
23 os % ay 1490 «677040089 181.5
3 “3 z t 6 189° 9090 BT.

‘ 0 7 0 ‘ 1530 55003749 10.1.2

7 135 65 02 14 12300 «6840S 285 1201.8

3 Ww 7 or oO 157 168 = 25) ND 45 5

3 1 20 ot 05 92 516 = 432 80 2

2 o 20 <.01 ed 1.01 34.1 37ND 23 2

4 3.0 24 0 05 145 303030. sND 73 8

13 20.4 ND o7 ND 36 69 29 ND 26 3

CONVEYOR BELTING CONVEYOR BELTING

6.6 18.7 28 0.33 0.14 052 1565 075 0.58 15.8 15
77 21.0 26 38 13 87 164.5 77 54 157 17
60 © 15.2 37 30 18 52. 166 2=6 68ST TA
38 84 36 19 18 135 14970 55h ( HT
43 103 1.9 22 .09 30 749 «4585213800 1.4
84 74 29 42 AS 78 107.9 Bt 58 19.9 2.2
18 41 7 09 04 63 51.3 AT 50 10.4 a
23 89 34 12 45 149476 36 99 10

Not determined. Not determined.

Table 7.-A,-V,A, ratios for TLV and IDLH from initial Table 9.—Steady-state smoke characteristics from smoldering
and steady-state stages of smoldering brattice brattice cloth and conveyor belting
cloth and conveyor belting
Ny My dq dy, Obscura- OD,
Ratio, Ratio, Sample 10° mg/m? ym am tion, m?
Sample AVA AV Adour B/om? pet
Initial Steady-state Initial Steady-state BRATTICE CLOTH
BRATTICE CLOTH a. 0.82 27 0.15 ND 30 (03
B. 1.07 35.14 ND 1881.5
.( 147 ). 2s
ed ow on a c.. 1.32 49 17) ND 1121.2
‘009 ‘047 7 ‘96 D 1.16 8.2 21 ND 10.4 1.2
‘008 ‘055 ‘V7 410 E. 1.24 85 21 (0.33 12.0 13
, ‘ . F 1.55 32 14 ND 45 5
032 056 66 1
G. 74 31 16 38 80 2
058 537 1.17 10.10
H 1 52 19 ND 23 2
019 77 38 3.55
1 88 47° 20 ND 73 38
055 181 1.10 3.63 af 30 4 14ND a ood
ar abus zs oad CONVEYOR BELTING : :
CONVEYOR BELTING
Pre. 074 680 049 048 193 14
0.029 0.043 0.60 0.95 » 60 709 55 446 122 12
033 044 a 99 70 21 34 46 127 14
-039 036 at 78 187 69439 (1213
024 039 50 83 320 557) 84116316
046 _ 7 1.46 69 180 «3154173128
—_ 040 56 89 49 34400 427 86 9
112 172 2.38 3.80 1.54407 33ND 7.0 8
036 048 73 1.00

ND Not determined,


Page

16. Relative levels of CO and smoke at respective alarm thresholds of steady-state stage from smoldering

fires

17. Detectability ranking of steady-state stage from smoldering mine combustibles .

2
12

°C degree Celsius m?
cm centimeter m/s
g/cm? gram per cubic centimeter mg/m?

g/(m*ppm) gram per cubic meter times part per million min

g/s gram per second pm
g/(m*s) gram per square meter times second p/em?
h hour pet

m meter ppm

mt reciprocal meter v

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

square meter
cubic meter per second
milligram per cubic meter
minute

micrometer

particle per cubic centimeter
percent

part per million

volt



CONCLUSIONS

In a mine fire, all the burning materials combine to
produce a wide varicty of toxic or irritating gases and
particles that can be transported by the ventilating system.
Previous studies have identified and measured the products
of PVC combustion (16). These toxic emissions may over-
come their victims far removed from the actual fire. More
effective sensing devices and smoke alarms would alert
miners of dangerous situations while there is adequate
time to take appropriate action.

Smoldering jute brattice will alarm a 5 ppm CO sensor
before a smoke sensor. At the other end of the spectrum,
a smoke sensor is the more efficient method of detecting
smoldering PVC brattice. PVC brattice also had the
highest CO,-CO and HCI-CO ratios. The combustion of
these small samples has demonstrated the potential for
smoldering PVC brattices to produce toxic smoke levels
before detection by most CO sensors, Smoldering con-
veyor belts are, by comparison, more detectable. How-
ever, smoke detectors are still more effective than CO
sensors. The irony of the toxicity-detectability dilemma is
that the materials producing low toxic emissions may be

less detectable. Fires involving these materials may
smolder for a long period before emissions reach alarm
thresholds levels. Therefore, emissions containing low
smoke and CO concentrations could be considered less
toxic, but still hazardous because they are more difficult to
detect.

It was not the intent of these experiments to judge
which material is the most hazardous. Each generates
unique and dangerous combustion products. The pyrol-
ysis of synthetic materials adds small, volatile, organic
compounds which are highly flammable to the toxic CO,
increasing the hazards of their emission products. In any
fire, as fresh materials are engulfed the composition of
the emissions changes. To determine the total toxicity of
the mixture, the possible synergistic effect of the thermal
decomposition and combustion products must be consid-
ered. In this series of experiments, each material was
studied independently to compare their combustion prod-
uct emission rates, relative toxicities, and the detectability
of their toxic products.

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.
—— Coal Combustion in a Ventilated Tunnel.
Ic 0 1987, 13 pp.
Emission Products from the Combustion of Conveyor
bat BuMines IC 9205, 1988, 12 pp.
. Thermal Decomposition of Ventilation Ducting. BuMines
Ic 08, 7990, 12 pp.

6. McCaffrey, B. J., and G. Heskestad. A Robust Bidirectional
Low-Velocity Probe for Flame and Fire Application. Combust. and
Flame, v. 26, No. 1, 1976, pp. 125-127.

7. Patashnick, H., and G. Rupprecht. Microweighing Goes On-Line
in Real Time. Res. and Dev., v. 28, No. 6, 1986, pp. 74-78.

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. Hilado, C. J. (ed.). Flammability Handbook for Plastics. Tech-
nomic Publ,, 3d ed., 1982, pp. 56-59.

10. Parmeggiani, L. (ed.). Encyclopedia of Occupational Health and
Safety. Int. Labour Organ., v. 1, 3d ed., 1983, p. 395.

BuMines

11, Parmeggiani, L. (ed.). Encyclopedia of Occupational Health and
Safety. Int. Labour Organ., v. 1, 3d ed., 1983, p. 1084.

12, Hartzell, G. E., A. F. Grand, and W. G. Switzer. Modeling of
Toxicological Effects of Fire Gases: VI. Further Studies on the Toxicity
of Smoke Containing Hydrogen Chloride. J. Fire Sci., v. 5, No. 6, 1987,
Pp. 368-391.

13. American Conference of Governmental Industrial Hygienists.
‘Threshold Limit Values for Chemical Substances and Physical Agents in
the Workroom Environment with Changes. 1980, pp. 1-93.

14, Tewarson, A., and J. S. Newman. An Experimental Investigation
of the Fire Hazards Associated With Timber Sets in Mines. Paper in
Underground Metal and Nonmetal Fire Protection. BuMines IC 8865,
1981, pp. 86-103.

15. Egan, M. R. Summary of Combustion Products from Mine Ma-
terials: Their Relevance to Mine Fire Detection. BuMines IC 9272,
1990, 12 pp.

16. Ultrasystems, Inc. Coal Mine Combustion Products Identifica-
tion and Analysis Procedures and Summary (contract H0133004),
1978, 130 pp.



To estimate the toxicity of the CO and HCl emissions,
two established levels will be considered. The first level is
the threshold limit value (TLV), which represents the max-
imum average exposure that can be tolerated for an 8-h
period without suffering any adverse effects, The TLV for
CO is 50 ppm and for HCl is 5 ppm (9). The second level
is the immediately dangerous to life and health (IDLH),
which represents the level at which severe health effects
and possibly death could occur. The IDLH for CO is
1,500 ppm (10) and for HCl is 100 ppm (17). Assuming
that the toxicities of combined CO and HCl are addi-
tive (12), then if the sum of the following fractions

aco , AHCI - 1

AHCI < @
30ppm | Sppm

the TLV of the mixture has not been exceeded (13).
Similarly, when

ACO
1,500 ppm

AHCI
100 ppm

<1, ©)

the IDLH level has not been exceeded, and the toxicity is
not life-threatening. Then, when the following expression

As
VoAo

©

Cra
SMua

Sco
50Mco

is satisfied, the combined toxicity is within the TLV.
Similarly, when the following expression is satisfied, the
combined toxicity exceeds or is equal to the IDLH level.

=: 10)
Sco Cra
T300Mco | 100Muq

VoAo

Early fire detection can minimize the toxic and irritat-
ing effects of combustion emissions and maximize the
chances of escape or rescue. However, a balance must be
reached between an alarm threshold that is low enough to
be effective and still reliable. The minimum requirements
for CO sensor alarm thresholds, CO,, can be calculated by
using the As-V,A, ratio for TLV from equation 6 in the
following expression,

a = vx 8)
Mco | Voto
An evaluation of combustion toxicity and detectability

would not be complete without considering the smoke
intensity and particle size.

co, = Seo |_As }

SMOKE PARTICLE DIAMETERS

Measurements of both M, and N, of the smoke can be
used to calculate the average size of the smoke particles,
using the expression

3

(69) No =1x10°M,, 0)

where dy, = diameter of a particle of average mass,
um,

Pp = individual particle density, g/cm,
N, = number concentration, p/cm?,
and M, = mass concentration, mg/m*,

If the value of p, = 1.4 g/cm’, then the d,, can be cal-
culated in micrometers from

1/3
dj, = 11.09 [F ] . (10)

lo

When the three-wavelength smoke detector is used, 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, 2,
from the following log-transmission ratios:

InT, -1.00 InT, 20.63

oor te
InT, .0.45 Ink, .0.45

When these extinction coefficients and the curve in
figure 11 of reference 8 are used, the surface mean
particle size, d,,, can be determined. (Calculation of the
extinction-coefficient curves assumes spherical particles
with an estimated refractive index.) The T must be less
than 85 pct before reliable particle sizes can be calculated
using this technique.

SMOKE INTENSITY PARAMETERS

Another important factor of the particulate phase of
smoke is visual obscuration. Smoke concentration is most
often expressed in terms of optical density (OD) in
reciprocal meters. This characteristic provides a measure
of fire hazard, in that escape and rescue depend on
visibility. It is related to T by the following expression:

op-

(nT), (4)

zg

where 2 = path length, m.


INTRODUCTION

In a fire, smoke is the most important factor affecting
life and property. It may be defined as the airborne
products evolved when organic materials smolder or burn.
It can obscure the route to safety by irritating the eyes and
respiratory tract and can cause injury or death by inhala-
tion. Smoke is not only the first sign of an impending dis-
aster but also it can trigger an alarm saving lives and
property. Developing sensitive and effective smoke detec-
tors has been a challenge accepted by the U.S. Bureau of
Mines.

Brattice cloth is used as a space divider or temporary
partition installed to direct the airflow. Brattices were
formerly made of untreated jute, but nylon-reinforced plas-
tics or similar materials are more commonly used today.
Most conveyor belts used in mines today contain a halo-
genated base polymer or are treated with a halogenated
fire retardant.

Since the introduction of synthetic components, the fire
problem has taken on yet another dimension—that of the
possible production of additional toxic gases. In ventilated

passageways, the risks from fires are compounded because
the toxic gases and smoke can be transported throughout
the mine endangering people far removed from the actual
flames. The Bureau uses an intermediate-scale fire tun-
nel at the Pittsburgh Research Center to simulate a mine
environment.

This report focuses on the smoldering combustion, its
detection, and relative toxicity. Once the emission prod-
ucts of combustible materials are known, more efficient
detection, fire-suppression, and rescue equipment can be
designed to improve health and safety conditions in under-
ground mines.

The objectives of this study were to analyze the gas
concentrations and particulate characteristics of smoldering
brattice cloths and conveyor belting. The thermal decom-
position results presented in this report, together with pre-
vious analyses of data for wood, transformer fluid, coal,
conveyor belting, and ventilation ducting (1-5)? form a data
base by which future findings of other mine combustibles
can be compared.

EXPERIMENTAL EQUIPMENT

INTERMEDIATE-SCALE FIRE TUNNEL

A schematic of the Bureau’s intermediate-scale fire
tunnel with its data-acquisition system is shown in figure 1.
A bidirectional flow probe (6) with a pressure transducer
was used to determine velocity. The airflow was produced
by the exterior exhaust fan and was detected by the flow
probe centered in the air-intake cylinder.

Before each experiment, background readings were ob-
tained after the material was positioned and the exhaust
fan was started. Every minute throughout the experiment,
the readings from each channel are scanned, stored, and
displayed. After the experiment was completed, the data
were plotted.

GAS ANALYZERS .
The CO analyzer measures accurately within 1 pct
of the range or +1 ppm. The carbon dioxide (CO,) ana-
lyzer measures accurately within 1 pct of the range or
+25 ppm. The HCI analyzer has a sensitivity of 0.2 ppm.
These analyzers were calibrated at the beginning of each
experiment.

SMOKE MONITORS

The particle number concentration (N,) was obtained
with a condensation nuclei monitor (CNM), manufactured

by Environment One Corp.,3 Schenectady, NY. This moni-
tor uses a cloud chamber to measure the concentration of
submicrometer airborne particles (p). The particulate
cloud attenuates a light beam which ultimately produces a
measurable electrical signal. The accuracy is stated as
+20 pet of a point above 30 pct of scale within the linear
range from 3,000 to 300,000 p/em?. Therefore, in these
experiments, the calculated error could have been as great
as +18,000 p/cm?.

The particle mass concentration (M,) was obtained by
a tapered-element oscillating microbalance (TEOM) devel-
oped by Ruprecht & Patashnick Co., Inc., Voorheesville,
NY (7). It measures the mass directly by depositing the
particles on a filter attached to an oscillating tapered
element. The oscillating frequency of the tapered element
decreases as the deposited mass increases. The apparatus
is capable of measuring the particulate concentration with
a better than 5 pet accuracy at the level used. According
to the manufacturer, the filter collects at least 50 pet of all
particles with a volume mean diameter of 0.05 um, with
increasing collection efficiency as the diameter increases.
Actual data obtained by the Bureau using particles of vol-
ume mean diameter equal to 0.048 um indicated a collec-
tion efficiency closer to 90 pet.

“Italic numbers in parentheses refer to items in the list of references
preceding the appendix at the end of this report.

3Reference to specific products does not imply endorsement by the
US. Bureau of Mines.


SMOKE, CARBON MONOXIDE, AND HYDROGEN CHLORIDE
PRODUCTION FROM THE PYROLYSIS OF CONVEYOR
BELTING AND BRATTICE CLOTH

By Margaret R. Egan’

ABSTRACT

In an underground mine fire, a toxic mixture of combustion product gases and particulate matter is
transported by the ventilating system endangering everyone downstream. To determine the magnitude
of the problem that these toxic combustion products pose, the U.S. Bureau of Mines is investigating the
combustion products of typical materials found in underground mines. The total toxicity of the com-
bustion products depends upon the evolving gas species and particulate matter, the amount of material
involved, and the ventilation rate. In a simulated mine environment, the products from smoldering poly-
vinyl chloride (PVC) brattice and conveyor belting were analyzed for gas concentrations and smoke
characteristics. The primary toxic gases are hydrogen chloride (HCI) and carbon monoxide (CO).
Smoldering conveyor belts are more detectable than smoldering PVC brattice cloths. These results,
combined with previous analyses, are used to estimate relative toxicities, product levels, and detect-
ability of smoldering mine combustibles.

1Research chemist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.


Ax

CO,

dy

Gx

APPENDIX.—SYMBOLS USED IN THIS REPORT

area of a given material, m?

minimum requirement for CO sensor alarm
threshold, ppm

diameter of a particle of average mass, pm
surface mean particle size, pm

generation rate of a given combustion product,
g/s

generation rate of a given combustion product
from a given arca of sample, g/(m*s)

path length, m
logarithm, natural
particle mass concentration, mg/cm?

density of a given gas, g/(m*ppm)

No

oD

OD,

VAo

dm

Pp

particle number concentration, p/em?
optical density, m*

minimum requirement for smoke sensor alarm
threshold, nx?

particle

transmission of light

ventilation rate, m?/s

measured change in mass, g
measured quantity of a given gas, ppm
wavelength of light source, um

individual particle density, g/cm?


neoprene (NP) belt. Three electric strip heaters were
clamped on top of each belt sample. The power was set
at 150 V for the 30 min duration of the experiment.

Brattice cloth: Nine different PVC brattice cloths and
one sample of jute brattice (treated with fire retardant)
were tested in duplicate. A double thickness of brattice
measuring 23- by 30-cm was placed on a wire mesh which
rested on three strip heaters. The power was set at 100 V
for 5 min and increased to 175 V for the remaining 25 min
of the experiment.

The pyrolysis of the conveyor belting and brattice cloth
did not result in flaming combustion. The combustion

emissions were designated initial and steady state. After
the strip heaters were turned on, the initial production
occurred on average between the 9th and 19th min for the
conveyor belting and the 13th and 16th min for brattice
cloth. These results were usually the peak emission levels.
After this period, the steady-state production occurred
between the 2ist and 30th min for conveyor belting and
the 22nd and 30th min for brattice cloth. The ventilation
rate (V,A,) throughout all the experiments averaged
0.16 m3/s.

Table 1.—Materlals analyzed

Material Description Chlorine, pet |] Material Description Chlorine, pet

BRATTICE CLOTH CONVEYOR BELTING
x Polymer component is PVC resin 2299 ||P1.... Polymer component is PVC resin, . 23.00
B. + do. 29.29 «(|| PIA. + do. : 21.00
c. ..do. 37.99 P2 ..do. 11.13
D. +do 40.39 || P3 +. do. 18.34
E. + do. 3459 || Pa + do. 4.40
FB. +.do. 37.59 || Pa ..do . 15.20
a. +do . 2659 |/SBR... Polystyrene. 5.38
H. + .do . 28.99 chlorinated additi
le +.do. 27.53 ||NP.... Polymer component is neoprene 12.86
Jute Jute burlap with chlorinated additi 7.27 tuber.

CALCULATIONS

It is necessary to measure certain parameters to com-
pare the combustion products, hazard potential, and de-
tectability of various fuels. The measurements include gas
concentrations, smoke particle M, and N,, and V,A,.
Other combustion properties can be calculated once these
values are known.

PRODUCT GENERATION RATES

The generation rate, Gx, of a product is related to
its measured concentration and V,A, by the general
expression

Gx = Mx (VA,) (4X), @

where, for gases Meo, = 1.97% 10° g/(m*ppm),

Mco = 1.25 x 10% g/(m*ppm),
Myc) = 1.63 x 10° g/(m*-ppm),
VA = ventilation rate, m?/s,

and AX = measured quantity of a given

gas.

To determine the amount of toxic gas generated from
the combustion of a specific area of a sample, the follow-
ing expression can be used

Gx = Gx/Ay, ®
where Aj, is area of the strip heaters, 0.02 m*, The de-
composition of the conveyor belts occurred only where the
belt came into direct contact with the strip heaters. By
contrast, the entire sample of PVC brattice cloth was
destroyed. At any one time, this area measured between
0.02 m? (the area of the strip heaters) and 0.07 m? (the
entire sample area). For the steady-state stage calcula-
tions, an average area of 0.045 m? was chosen to represent
the involved area of the brattice sample.

The concentrations of toxic gas can be predicted for a
certain area and V,A, by the following expression

Cx [As

Mx | VoAo
where Ag is heated area of the sample, and My is density
ofa given gas,

1}


BUREAU OF MINES
IC} 9304 |i INFORMATION CIRCULAR/1992

Smoke, Carbon Monoxide, and
Hydrogen Chloride Production
| From the Pyrolysis of Conveyor

Belting and Brattice Cloth

By Margaret R. Egan

UNITED STATES DEPARTMENT OF THE INTERIOR



Table 3.—Initial gas concentrations and ratios from
‘smoldering brattice cloth and conveyor belting

‘Sample CO, CO, Ratio, HCl, Ratio,
ppm ppm _CO,CO ppm __HCICO
BRATTICE CLOTH

BK 4 19 44 at 7.0
B 12 86 60 36 29
c 7 18 14 69 45
D 5 34 65 70 14.4
E 13 70 5.3 18 14
F 2 34 13.8 10 43
G 4 23 5.1 37 76
H 2 32 15.4 W 5.2
. 7 23 3.4 16 22

32 149 47 __ND ND

CONVEYOR BELTING

Pr. 32 44 73 19 06
PIA 42 49 1.2 15 4
Pe. 32 39 1.2 13 4
P3.... 17 24 1.4 24 14
Pa... 20 13 6 12 6
PEL... 44 15 4 20 5
SBR... 10 20 5 5 5
NP. 12 24 1.4 7 14

ND Not determined.

Table 4.—Steady-state gas concentrations and ratios
from smoldering brattice cloth and conveyor belting

Sample CO, CO, “Ratio, HCl, __—Ratio,
ppm ppm _CO,CO ppm ___HCI-CO.

BRATTICE CLOTH
A 1 0) 0.0 e 82
B 15 70 47 35 23
c 12 26 24 28 23
D 2 3 18 25 15.4
E 4 46 127 26 74
F 1 5 4.0 3 23
G 1 5 38 8 67
H 1 3 3.4 8 10.0
1. 2 10 46 10 45
J 7 69 9.9 ND ND
CONVEYOR BELTING
Pr. 34 61 18 1 03
PIA 37 62 17 10 3
P2 30 48 16 14 5
P3 19 2 14 14 ae
P4 22 33 15 7 3
Ps. 44 24 6 12 3
SBR... 10 14 15 3 3
NP... 12 30 25 12 1.0

ND Not determined.

The CO, concentrations for the PVC and NP belts in-
creased slightly from the initial stage to the steady-state
stage. The SBR belt showed a slight decrease in CO, pro-
duction, For PVC and jute brattice, the CO, concentra-
tions decreased. However, jute brattice produced the

highest concentration of CO, of all the materials. The
CO,-CO ratios in both stages were higher for brattices
than for belts. During the steady state, incomplete oxida-
tion produces less CO, lowering the CO,-CO ratios of
both belts and brattices.

The main toxic risk from the pyrolysis of PVC is HCl
production. As little as 5 to 10 ppm can cause irritation to
the mucous membranes (9). Some correlation between
chlorine content and HCI production was found. For
example, brattices with high chlorine content tend to emit
high concentrations of HCl and conveyor belts with low
chlorine content tend to emit low concentrations of HCl.
For both brattice and belting, the HCl emissions are
higher in the initial stage than the steady-state stage
(fig. 4). The belts, at temperatures averaging less than
100° C, release HCI slowly showing an initial peak fol-
lowed by a gently decreasing steady-state production of
HCI. Most of the HCI is emitted as the polymeric mate-
tial is being consumed in the initial stage. At this stage,
the temperatures averaged 300° C.

The greatest ratio variation between the belts and
brattices is seen in HCI-CO ratios. The brattices have
high ratios averaging 6.5 in the initial stage and 5.5 in the
steady-state stage. The PVC belts have much lower ratios
averaging 0.6 in the initial stage and 0.4 in the steady-state

stage.

30

T T T T

KEY
~ — Brattice
\\ ~7 Belting

Neots. 4
N.

a)

\
\
\
\
1
\
iy
\
\
\

Detection y
threshold \

I
1
1
1
!
1
!
'
f
1
'
!
1
1
1
I

/

4
5

L 1 L n
lo 15 20 25 30 35
TIME, min

Figure 3.—Results of typical CO concentrations for PVC
brattice and conveyor belting.


Most smoke detectors are triggered at an OD of
0.1 m" or less. The probability of escape and rescue is
reduced significantly once the critical level of smoke
(OD = 0.5 m*) has accumulated (14).4 The minimum
requirements for smoke sensor alarm thresholds, OD,, can
be determined in a similar manner to CO, (equation 6) by
the following expression

_ Geo OD\ / As
op, = G22 (98)/8, ay

Smoke density may be defined as the degree of light
obscuration produced by the smoke from the burning

material under given conditions of combustion. Some
other factors influencing obscuration include the number,
size, and refractive index of the particles and light fre-
quency. 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). (13)
The obscuration values presented in this report are an

average of the attenuation of the beam of light at two
wavelengths in the visible range, 0.45 and 0.63 um.

RESULTS AND DISCUSSION

Figure 2 shows the charred remnant of a PVC brattice
after pyrolysis. At least two thirds of the brattice was
consumed in the typical experiment. By contrast, the
exterior of the conveyor belting was only scorched by the
strip heaters with little damage to the interior fibers. The
average PVC belt lost 14 pct of its mass while the NP
belt lost 7 pet and the SBR belt lost only 3 pct. Table 2
lists the mass loss and steady-state temperature for cach
belt and brattice. A probe located above, but not touching
the test sample was used to determine temperature. All
the reported results are an average from all experiments
for each belt and brattice. Figures 3, 4, and S illustrate
the typical gas and smoke production as a function of time
for PVC belt, P1, and PVC brattice, I.

GAS CONCENTRATIONS

These hydrocarbons were found in grab samples of
the steady-state emissions of PVC brattices. They includ-
ed: 8 ppm methane, <2 ppm ethane and ethylene, and
<1 ppm propane and propylene. However, the concentra-
tions of CO, CO,, and HCI were continuously measured.
These initial gas concentrations and ratios for each belt
and brattice are listed in table 3. The same determina-
tions for the steady-state stage are listed in table 4.
For all belts, the CO production remains fairly con-
stant throughout the experiments. However, for brattice,
the CO production decreases as the cloth is consumed.
Figure 3 compares the production of CO for a typical PVC
belt and brattice. The amount of material consumed must
be considered when comparing the relative concentrations
of CO produced. Initially, all brattices but A, F, G, and H
produced CO above the detection level of 5 ppm.

‘Reference 14 quotes a value of OD = 0.218 m for the critical
value determined from the expression OD = -1/2 log T. When the nat-
ural logarithm is used, as in equation 11, then OD = 2.303 x 0.218
= 0.5 m', the value used in the text.

Table 2.Mass loss and steady-state

temperature
Material Am, g Am, pet___Temp, “©

BRATTICE CLOTH
255 43.1 330
57.8 44.9 407
427 48.4 344
375 45.2 296
46.2 470 281
97 40.9 220
29.1 39.8 266
18.2 36.4 289
26.6 427 219
ND ND ND

CONVEYOR BELTING

125.0 142 94
122.2 13.7 93
142.2 128 7
119.4 13.3 7
118.3 13.0 127
162.2 17.3 82
43.5 32 113
613 69 214

ND Not determined.

Figure 2.—Appe:

nce of PVC brattice after pyrolysis.


Air

intake 7

/0.6|-m-diam duct

0.305-m-diam
entrance duct
(hinged and movable)

—Diffusing grid

- 10m f l2 my 4 «
ir
|.22m Sample of
+-—+/ combustible /0.8-m-square duct __# exhaust
Fire zone q material [ Manually — Ventilation
z = adjustable fan
iad! eae: orifice plate { 2-speed)

CALCOMP,
Pressure transducers plotter
bid VAX
L 3d N/78
TEOM a OF detector ° VAX
channel terminal
data-
CNM acqui-
sition Digital input
CO meter system for CNM Control, Printer
COe2 meter range terminal

« Pressure transducer (flow probe)
* Differential pressure transducer
* 3) detector

* Thermocouples
= Sampling ports

KEY
CALCOMP California computer products
CNM Condensation nuclei monitor
TEOM Tapered-element oscillating microbalance
VAX Virtual address extension

Figure 1.Schematic of intermediate-scale tunnel (top) and data-acquisition system (bottom).

Since the diameter of average mass is calculated from
the mass and number concentrations, its accuracy was
dependent upon the precision of the TEOM and CNM.
Considering the error estimates of the mass and number
concentrations, the diameter of average mass could vary
by £0.05 pm.

A three-wavelength light-transmission technique (8)
developed by the Bureau was used to measure particle

size and smoke obscuration, White light was transmitted
through the smoke cloud to the detector. The beam was
split into three parts, and each passed through an inter-
ference filter centered at wavelengths of either 0.45, 0.63,
or 1.00 um. Each photodiode output was amplified and
recorded.

MATERIALS AND TEST PROCEDURES

Table 1 lists the materials studied with their chlorine
content, Flaming combustion emissions of some of the
same conveyor belts were studied using a natural gas
burner as the ignition source. The results of these studies
have been reported in reference 4.

Conveyor belts: A 23- by 30-cm section of each belt
was tested in duplicate or triplicate depending on the
amount of belting available. The belts were classified
according to covering. They included six different PVC
belts, one styrene-butadiene rubber (SBR) belt, and one


CONTENTS

Page
Abstract 1
Introduction . . 2
Experimental equipment . 2

Intermediate-scale fire tunnel 2
Gas analyzers 2
Smoke monitors .. . 2
Materials and test procedures 3
Calculations .......... 4
Product generation rates 4
Smoke particle diameters . . 5
Smoke intensity parameters ..... 5
Results and discussion ... 6
Gas concentrations . 6
Smoke characteristics . . 8
Detection limits ...... 10
Comparison of materials tested cel
Smoldering emissions . co
Detectability n
Conclusions 13
References . tee 13
Appendix.—Symbols used in this report 14
ILLUSTRATIONS
1, Schematic of intermediate-scale tunnel and data-acquisition system . 3
2. Appearance of PVC brattice after pyrolysis 6
3. Results of typical CO concentrations for PVC brattice and conveyor “belting 7
4, Results of typical HCI concentrations for PVC brattice and conveyor belting 8
5. Results of typical OD levels for PVC brattice and conveyor belting . 10
6. Detection limits for smoldering brattice cloths for initial stage . u
7. Detection limits for smoldering conveyor belts for initial stage . 11
TABLES
1. Materials analyzed ........... seeeeee 4
2. Mass loss and steady-state temperature .. 6
3. Initial gas concentrations and ratios from smoldering brattice cloth and conveyor belting .. 7
4, Steady-state gas concentrations and ratios from smoldering brattice cloth and conveyor belting - 7
5. Initial generation rates from smoldering brattice gloth and conveyor belting 8
6. Steady-state generation rates from smoldering brattice cloth and conveyor belting . : 9
7. Ag-V,A, ratios for TLV and IDLH from initial and steady-state stages of smoldering brattice cloth ‘and
conveyor belting .. . . 9
8. Initial smoke characteristics from smoldering brattice cloth and conveyor belting . 9
9. Steady-state smoke characteristics from smoldering brattice cloth and conveyor belting 9
10. Minimum requirements for sensor alarm thresholds from initial stage . . 10
11. Minimum requirements for sensor alarm thresholds from steady-state stage . 10
12. Gas concentrations and CO,-CO ratios from initial stage of smoldering combustion . M1
13. Smoke characteristics from initial stage of smoldering combustion . 12

14. Relative levels of CO and smoke at respective alarm thresholds from initial stage of smoldering fires .. . 2
15. Detectability ranking of initial stage from smoldering mine combustibles .



DETECTION LIMITS

Smoldering materials that do not produce much smoke
or toxic gas are less hazardous, but are also more difficult
to detect. This can be demonstrated by calculating the
CO, (equation 8) and OD, (equation 12) for smoldering
brattice cloths and conveyor belts. Tables 10 and 11 list
these values for the initial stage and steady-state stage.
The lowest set point for a CO sensor to safely detect
smoldering brattice cloths is below the alarm threshold of
most CO sensors (5 ppm). Smoldering conveyor belts are
easier to detect and require slightly higher thresholds.

In a similar manner, the CO, and OD, at the IDLH
level would be required to warn of extremely unsafe
conditions. Figures 6 and 7 illustrate the effectiveness of
sensors with specific threshold alarm levels. The nontoxic
region would have a relative hazard level below the TLV.
In this area, smoke detection for all belts and most
brattices is effective. The potentially toxic region would
have a relative hazard between the TLV and IDLH level.
CO detection for some belts and all brattices lie in this
area. Only smoldering brattices A, C, and D could not be
detected in the nontoxic region by a 0.1-m" smoke sensor.
Only smoldering belts P3 and NP could not be detected in
the nontoxic region by a 5 ppm CO sensor. The combus-
tion emissions from these belts may be less toxic, but more
difficult to detect. Figures 6 and 7 confirm that smoke
detection is more effective than CO detection. It is also
clear that smoldering conveyor belts are more detectable
than smoldering PVC brattice cloths.

Table 10.—Minimum requirements for sensor alarm
thresholds from initial stage

Sample CO,, ppm OD,, m?
atTLV atIDLH at TLV_at IDLH
BRATTICE CLOTH
0.70 1417 0.049 ~—~«0.97
1.66 33.75 200 4.06
1.18 23.69 0841.70
38 7.29 086 1,72
3.31 67.77 328 671
1.14 23.00 254-512
70 14.16 1460-293.
cx) 18.79 107 (2.15
2.02 40.93 232471
CONVEYOR BELTING
732 16395 0345 7.26
1160 251.23 461 9.98
10.04 215.30 580 12.45
3.41 69.70 3326.79
7.45 156.51 504 10.59
846 179.55 445 (9.44
878 186.51 912 19.37
3.28 66.95 277 5.66

Table 11.—Minimum requirements for sensor alarm
thresholds from steady-state stage

Sample CO,, ppm OD,, mt
at TLV at IDLH atTLV at IDLH
BRATTICE CLOTH
A 0.62 12.53 0.160 3.21
B 2.02 51.06 .203 5.13
c 2.07 41.99 200 4.06
D 33 6.53 247 4.96
E 68 13.61 nu 4.25
F 2.60 49.00 1.044 19.64
G 92 18.45 590 11.86
H 53 10.71 150 3.00
1. 1,09 21.86 393 7.91
CONVEYOR BELTING
11.41 250.79 0.478 10.51
13.64 (305.45 456 10.21
8.68 186.38 407 8.74
5.93 124.29 AIG 872
11.36 249.60 824 18.11
13.31 297.39 560 12,52
12.29 272.17 1.198 26.53
5.32 92.20 336 5.82
2.0 tt ot
KEY
— Brattice
Let , ~—— Belting _|
Non awa
mV Ty PMNS
IT Vi] \
owe NA
— Lee ! VA 4
7, 1 Via
iS i \
8
set 4
\
! 1
| \
4 | \
! ! 1
\
| 7 detection threshold \

a
os 10 15

1 1 14
20 25 30 35

TIME, min

Figure 5.—Results of typical OD levels for PVC brattice and

conveyor belting.


brattice and belts, compare figures 3 and 5 for onset of
detectable smoke (OD = 0.1 m*) and CO (5 ppm). The
smoke from smoldering PVC conveyor belts reaches the
alarm threshold at the 5th min while the smoke from PVC
brattice reaches the alarm threshold at the 7th min. The
same comparison for CO detection is even more striking.
Most brattices did not produce enough CO to reach the
alarm threshold, but the PVC belting exceeded the alarm
threshold at the 7th min. A comparison of the relative
levels of CO and smoke at respective alarm thresholds for
initial stage emissions of all the combustibles tested can be
found in table 14. A smoke sensor is the obvious choice
because the OD of the smoke is well above the alarm
threshold by the time the CO threshold is reached. Jute
brattice is the only exception with CO detection only
slightly ahead of smoke detection. Table 15 ranks mine
combustibles for ease of fire detection. The combustion
emissions detected by a CO sensor are in reverse order of
smoke detection, and that all the combustibles tested are
more readily detected by smoke (OD) than by CO
production,

Table 13.—Smoke characteristics from initial stage
‘of smoldering combustion

Mate dd, Obscuration, OD,
um am pet m?
PVC brattice.. 0.35 0.41 8 0.89
Jute brattice . . 29 ND 3 30
PVC belts 64 54 16 1.94
‘SBR belts. AT 50 10 1,06
NP belts . 36 21 10 1.02
ND ND 12 1.36
. 16 ND 9 ot
Nonignitable
ducts . 28 36 W 1.20

ND Not determined.

le 14,—Relative levels of CO and smoke
at respective alarm thresholds from initial
stage of smoldering fires

Material ‘OD, 5
15 ppm CO_0.1m70D

PVC brattice .. 06 08 .
Jute brattice <1 10.6 .
PVC belts 3 16
SBR belts 5 1.0
NP belts . 4 1.2

2 32

3 17

2 23

Table 15.—Detectability ranking of initial
stage from smoldering mine

combustibles
Material CO sensor Smoke sensor
Jute brattice .... 1 8
: 2 7
3 6
4 5
5 4
NP belts . 6 3
‘SBR belts . 7 2
PVC bratti 8 1

During the steady-state stage, the levels change slight-
ly as seen in table 16, Jute brattice has surpassed the
alarm threshold of CO, but remains just below the smoke
alarm threshold. The detectability ranking also changes
(table 17) and is not quite in the reverse order for smoke
sensors.

16.—Relative levels of CO and smoke
spective alarm thresholds of steady-
state stage from smoldering fires

Material , 0,
15 ppm CO_0.1m70D

PVC brattice . 10 05
Jute brattice . <1 16.0
PVC belts . 4 7
SBR belts . 9 1.0
NP belts . 3 16
Wood . 3 3.2
Coal 6 17
Nonignitable

ducting ........ 4 23

Table 17.—Detectabllity ranking of steady-
state stage from smoldering mine
combustibles

Material ‘CO sensor Smoke sensor

Jute brattioe .... 7 8
. 2 7
3 4

Nonignitable
ducting . 4 6
PVC belts . 5 2
Coal... 6 5
SBR belts . 7 3
PVC bratti 8 1



Library of Congress Cataloging in Publication Data:

Egan, Margaret R.
Smoke, carbon monoxide, and hydrogen chloride production from the pyrolysis of
conveyor belting and brattice cloth / by Margaret R. Egan.
p. cm. — (Information circular; 9304)
Includes bibliographical references (p. 13).
Supt. of Docs. no.: I 28.27:9304.
1. Conveyor belts—Fire-testing. 2. Plastic brattices (Mining)—Fire-testing.

3. Combustion gases—Analysis. 4.‘ Smoke—Analysis. I. Title. II. Series: Infor-
mation circular (United States. Bureau of Mines); 9304.

TN295.U4 [TH9446.5.B44] 622 s—dc20 [621.8'675] 91-25937 CIP



Information Circular 9304

Smoke, Carbon Monoxide, and
Hydrogen Chloride Production
From the Pyrolysis of Conveyor
Belting and Brattice Cloth

By Margaret R. Egan

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
TS Ary, Director


30 T T T T T T

20-

HCI, ppm

oS 10 15 20 25 30 35

TIME, min _

Figure 4.—Results of typical HCI concentrations for PVC
brattice and conveyor belting.

Using the data in tables 5 and 6, equations 6 can be
used to calculate the maximum A,-V,A, ratio at which a
safe-working environment exists. For example, brattice F
with low CO and HCI production has an A,-V,A, ratio
of 8, whereas, belt P8 with high CO and HCI production
has a ratio of 0.4. Low ratios would indicate a greater
potential for dangerous conditions to exist because smaller
amounts of sample or higher V,A, would be needed to
keep the toxic levels below the TLV and IDLH levels. In
these experiments, the actual A,-V,A, ratio is 0.125 for
conveyor belts (both stages) and brattices (initial stage
only) and 0.281 for brattices (steady-state stage). Using
these actual ratios, only brattice F and the SBR belt are in
the safe region. Table 3 confirms that these samples have
low combined CO and HCI emissions. Table 7 lists the
maximum A,-V,A, ratios to achieve the upper limit for the
TLV and IDLH levels. When the calculated ratios exceed
the actual ratios, a safe environment exits. Low ratios
indicate potentially toxic levels as demonstrated by brat-
tices C and D and belts P1A and P8 in the initial stage.

SMOKE CHARACTERISTICS

The smoke characteristics including N,, M,, particle
size, obscuration, and OD for the initial stage of belts and
brattices are listed in table 8. The same values for the
steady-state stage are listed in table 9.

Many differences can be found between the smoke
emissions of brattice and belting. The difference in M, is
the most noticeable property. It influences both the par-
ticle size and smoke obscuration. PVC belts with larger
particles had higher M, and obscured more light than the
other belts and brattices. This occurred in both stages of
combustion. Good agreement can be seen between the d,,
and dy, that are measured independently, All the ma-
terials produced smoke above the OD detection level of
0.1 m7 and all but jute produced smoke above the OD
critical level of 0.5 m1, The profile of the OD curve
(fig. 5) resembles the CO curve (fig. 3). The PVC belt
produces steady smoke throughout the experiment while
the PVC brattice produced more smoke in the initial
stage.

Table 5.—Initial generation rates from smoldering brattice
cloth and conveyor belting

Sample Geo Goo — Gucn cos Gc
10% g/s_10%9/s_10%g/s_g/(m*s)__g/(m*s)
BRATTICE CLOTH
A. 09 63 8.2 0.04 0.41
B. 25 27.0 9.3 12 AT
c. 3.4 5.7 18.5 7 93
D. Wd Wd 19.3 05 96
Ee. 26 21.4 47 13 24
F. 5 10.8 28 02 14
G. 2 73 85 05 43
H. 4 10.4 29 02 15
1 13 72 4.2 07 21
Jute . 6.3 46.3 ND 32 ND
CONVEYOR BELTING
64 13.6 49 0.32 0.24
88 16.8 38 4 19
64 12.4 3.3 32 WW
35 75 63 18 31
4.0 4.0 3.0 20 15
8.0 48 51 40 26
2.0 62 2 10 06
23 7.2 43 12 21

ND Not determined.


KEY
KEY © 5.0 ppm CO sensor
‘* 5.0 ppm CO sensor 4 0.1 m! smoke sensor
‘4 0.1 mt smoke sensor Toxic
Toxie a
2 < COp, ppm or ODa, mm!
< COg, ppm or ODa, m”! eI ‘at IDLH
y ot IDLH =
@ . 2 Potentialt
2 x otentially
x Potentially 3 toxic
S|. oxic °
r . woe w
wl. . : : vm
2 aoe COp, ppm or OD,, ml = COq, ppm of OD mv
& « at TLV & at
a al. .
@ ‘ @ on
= “ a Nontoxic oe Nontoxic
a* rn a “
a, a
‘oa 4
ABCDEFGH I PI PIA P2 P3_P4 PS SBR NP

BRATTICE CLOTHS CONVEYOR BELTS

Figure 6.—Detection limits for smoldering brattice cloths for

Figure 7.—Detection limits for smoldering conveyor belts for
Initial stage.

initial stage.

COMPARISON OF MATERIALS TESTED

SMOLDERING EMISSIONS produced from smoldering PVC belts resulted in dense
smoke as measured by the obscuration and OD.

A comparison of the gas concentrations and smoke
characteristics of other smoldering combustible mine ma-
terials was reported previously (15). This report updates
and expands those results. The tests were all conducted
in the intermediate-scale fire tunnel and all materials

Table 12.—Gas concentrations and COCO
ratios from initial stage of
‘smoldering combustion

at s i Material CO, CO, Ratio,
were pyrolyzed using strip heaters. The tables combine ppm ppm _CO,CO.
the initial stage results from this report with the earlier PVC bratiice 7 W 5
smoldering data. Jute brattice 32 149 46
A summary of the updated gas concentrations can be a1 31 10
found in table 12, Those materials with high gas produc- % 3 30
tion, jute brattice, and nonignitable ducting, have higher 4 OND ND
CO,-CO ratios indicating more complete combustion. 15 19 13
Lower ratios, indicative of less efficient combustion, are
usually produced from smoldering fires. PVC brattice, duoting ......- 28130 5.0
although it has low gas production, has a high CO,-CO NO Not determined.

ratio.
A summary of the smoke characteristics is in table 13.
The particle size is a major factor in smoke density.
Those materials with large particle size tend to produce

thick smoke.

For example, the particles, d,, and dy

DETECTABILITY

To determine which type of fire sensor (smoke or CO)
might be more effective for detection of smoldering PVC