RI 9626 REPORT OF INVESTIGATIONS/1996

A 20-Liter Furnace Test Method

To Determine the Combustion

Gas Toxicity of Conveyor Belts

By Maria I. De Rosa

lJNITED STATES DEPARTMENT OF ENERGY

PITTSBURGH RESEARCH CENTER
Report of Investigations 9626

A 20-Liter Furnace Test Method

To Determine the Combustion

Gas Toxicity of Conveyor Belts

By Maria I. De Rosa

UNITED STATES DEPARTMENT OF ENERGY

PITTSBURGH RESEARCH CENTER
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract '" , . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . .. .. . . . .. . . . . . . . .. . 1

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

20-liter furnace experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Procedures and data reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Laboratory fire tunnel experimental system 5

Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Procedures and data reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Discussion and treatment of experimental results 5

Toxicity index parameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Toxicity hazard parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 10

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

ILLUSTRATIONS

1. Experimental systems 3

2. Furnace temperatures in the 20-L furnace at a set temperature of 1,000 °C .. . . . .. .. . . . . .. . . . . . .. . . . . . . . . . . . 4

3. Correlations between the HC], HCN, N02, and CO gas yields and the percentage of chlorine, nitrogen, and carbon

contents in the original materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4. Toxicity index parameter for the 20-L furnace and laboratory fire tunnel experimental systems 9

TABLES

1. Description and analyses of conveyor belt materials ,. 4

2. Toxic gas yields measured in the 20-L furnace and laboratory fire tunnel experimental systems . . . . . . . . . . . . . . . . 6

3. CO concentration, sample temperature, and total airflow measured in the 20-L furnace and laboratory fire tunnd

experimental systems 7
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

em centimeter m3

jg cubic meter per gram

g gram m3

js cubic meter per second

gig gram per gram mm minute

gi S gram per sec..:md mL mi1liliter

g/(m3 x ppm) gram per cubic meter multiplied mm millimeter

by part per million

mm'2 square millimeter

L liter

pct percent

Us liter per second

ppm part per million

rng milligram

s second

mgig milligram per gram

°C degree Celsius

m2 square meter

m3 cubic meter

Mention of any company name or product: does not constitute endorsement by the U.S. Department of Energy, Pittsburgh Research

Center.
A 20-LITER FURNACE TEST METHOD TO DETERMINE THE

COMBUSTION GAS TOXICITY OF CONVEYOR BELTS

By Maria I. De Rosa'

ABSTRACT

The u.s. Department ofEnergy Pittsburgh Research Centei conducted experiments with mine conveyor belt

samples in a 20-L furnace and in a laboratory fire tunnel to measure and compare the major toxic gas

concentratioris evolved during the combustion of the materials. The toxic gas concentrations, measured

simultaneously through a multiport sampling device and treated as yield values, included hydrogen chloride

(HO), hydrogen cyanide (HeN), oxides of nitrogen (NOx treated as NOJ, and carbon monoxide (CO). The data

obtained from the two experimental systems were in good agreement. Correlations were developed for the toxic

gas yields as a function of the percentage of chlorine (for HO gas), nitrogen (for HCN and NOz gases), and

carbon (for CO gas) contained in the original materials.

The toxic gas yields were also used to calculate a toxicity index (TI) parameter to assess the potential gas

toxicity of belt materials during a fire. Furthermore, the TI and the mass loss burning rate values were used to

calculate a toxicity hazard (TH) parameter to estimate the toxic gas hazard produced by a burning belt in a

ventilated system.

Results show that polyvinyl chloride (PVC) belts released higher HCl concentrations because of the higher

chlorine content; styrene-butadiene rubber (SBR) belts released higher CO, HCN, and NOz concentrations

because of the higher carbon and nitrogen contents. The TI's, however, were greater for the PVC belts due

primarily to the higher levels of HCl produced. The fire tunnel data indicate that the SBR belts can bum with

higher mass loss rates than the PVC belts, resulting in a potentially higher toxic hazard (higher TH values) even

though their TI values were lower than those of the PVC belts.

lIndustrial hygienist, Pittsburgh Research Center, U.S. Department of Energy, Pittsburgh, PA.

1'his work originated under the U.S. Bureau of Mines prior to transferring to the U.S. Department of Energy on April 4, 1996.
2

INTRODUCTION

Underground mine fires pose a serious threat to the lives of

miners. Fire deaths are considered to be mainly attributable to

the inhalation of toxic combustion products (1-2).3 The introduction of a variety of new synthetic materials, treated with

adJitivcs and fire retardants, has made the compositions of the

crmbustion products far more complicated and their toxic

hazard more difficu1t to assess (3-5).

The toxic gases that can occur in fires are CO, HCl, HCN,

and N02 (6-7). CO is produced by the combustion of carboncontaining materials, hydrogen chloride by the combustion of

chlorine-containing materials, and hydrogen cyanide and

oxides of nitrogen by the combustion of nitrogen-containing

materials (8).

'The human consequences of toxic gas poisoning, which

depends on concentrations and exposure time (9), may be:

1. Loss of mental concentration, decrease in sense of direction, drowsiness, coma, or death (CO poisoning) (10);

2. Destruction of the mucous membranes of the eyes, nose,

and respiratory tract (HCl poisoning) (11);

3. Obstruction of the utilization of oxygen by the body

tissue (HCN poisoning) (12);

4. Death from bronchospasm and respiratory failure (N02

poisoning) (13).

The National Institute for Occupational Safety and Health

(NIOSH) has established toxic gas concentrations that are

considered immediately dangerous to life and health (IDLH).

The IDIH values represent "the maximum concentration from

which, in the event of respirator failure, one could have escaped

within 30 min without a respirator and without experiencing

any escape-impairing (e.g., severe eye irritation) or irreversible

health effects" (14). The recently revised NIOSH definition for

an IDLH exposure condition is one that "poses a threat of

exposure to airborne contaminants when that exposure is likely

to cause death or immediate or delayed permanent adverse

health effects or prevent escape from such an environment"

(15). The purpose of establishing an IDLH exposure concentration is "to ensure that the worker can escape from a given

contaminated environment in the event of failure of the respiratory protection equir'1lent" (15). For the toxic gases investigated in this study, the previous and revised IDLHs, respectively, are: CO, 1,500 and 1,200 ppm (16-17); HCl, 100

and 50 ppm (18-19); HCN, 50 ppm (unchanged) (20-21); and

N0:z, 50 and 20 ppm (22-23). For comparison, both the

previous and revised IDUi's have been used in this study in the

calculations of the toxicity parameters.

In a previous U.S. Bureau of Mines (USBM) study (8),

experiments were conducted in a 20-L furnace using chlorineand nitrogen-containing materials to measure and correlate the

gas concentrations of HCl and HCN with the chlorine and

nitrogen contents in the original materials, respectively. It was

found that the gas concentrations were directly proportional to

the chlorine and nitrogen contents in the original materials.

This investigation expands on that approach by measuring

simultaneously additional toxic gases through a multiport

sampling device, comparing the toxic gas yields measured in

the 2O-L furnace with similar yields measured in the laboratory

fire tunnel (24), and correlating the toxic gas yields with the

percentage of the chemical contents in the original materials.

Additionally, in the course of this study, a toxicity index (TI)

and a toxicity hazard (TH) parameters, to assess the potential

gas toxicity of mine conveyor belt materials during a fire and

estimate the toxic gas hazard produced by burning belts during

a fire, were developed.

This work supports the Pittsburgh Research Center's program to develop improved methods and technology for preventing mine fires, thereby improving mine worker safety.

20-LITER FURNACE EXPERIMENTAL SYSTEM

CONFIGURATION

The 20-L furnace system (figure lA) consists of a furnace

(22.5 cm wide by 22.5 em high by 35 em long) whose inner

panels are embedded with heating elements. A quartz cup (2.5-

ern diam) containing the sample is placed on a quartz pedestal

(10 em high) that is inserted in an opening in the center of the

furnace floor. The sample and furnace temperatures are

measured with thermocouples. The temperature data (logged

in 10-s intervals) are transmitted to a laboratory-based real-time

data acquisition system and subsequently printed by means

1talic numbers in parentheses refer to items in the list of references at the

end of this report.

of a miniframe computer. During the experiments, an exhaust

pump draws ambient air at a constant rate of 0.13 Us into the

furnace through an opening at the center of the furnace door.

The combustion gases, drawn by the same pump, are directed

through a multipart sampling device into four pairs of impingers containing specific gas-trapping solutions. The device

consists of a stainless steel manifold with a single inlet, which

is inserted into the upper back of the furnace and four outlets

through which the airflow, equally divided by flowmeters (0.03

Lis through each outlet), is directed into four pairs of impingers. Each pair consists of two consecutive impingers, and

each impinger contains 15 mL of gas-trapping solution. The

combustion gases emerging from the impingers are directed
A

B

Heating

element

... Impingers with

solutions

Data

L...-------Iacquisition

Thermocouples

Sample tube

Flowmeters

To exhaust

t

3

Figure 1.-Experimental systems: A, 20-L furnace; B, laboratory fire tunnel.
4

through the pump into a large (170-L) sampling bag. The

solutions (0.1 pct) used to recover the combustion gases are

sodium hydroxide (to recover the HCl and HeN), triethanolamine (to recover the NOll' treated as NO~, and alkalinepennanganate (to recover the N02) which is used to calculate

the nitrogen oxide (NO) yields). Syringe grab samples (20 mL)

of combustion gases are taken at 2-min intervals from the

~.ampling port located before the first set of impingers and at the

.~nd of each experiment from a sampling bag to measure the CO

gas concentrations.

PROCEDURES AND DATA REDUCTION

Two sets of experiments with five different mine conveyor

belt samples were perfonned at a set furnace temperature of

1,000 0 C. A~ shown in figure 2, the furnace temperature rose

from ambient at an average rate of 32 °Clmin and reached

640°C at the 20th min. The airflow through the furnace was

0.13 Us for a 2O-min duration; the 2O-min duration was chosen

because during this time all samples burnt completely and only

ashlikc debris remained. Subsequent exposure of the debris t...l

higher furnace temperatures did not yield any significant gas

concentrations.

The combustion gases were directed into four sets of

solution-containing impingers beginning at a sample temperature of 150°C, which was reached at about the 8th min. No

appreciable gas concentrations were measured at lower temperatures. The mine conveyor belt materials used were 19 samples, of polyvinyl chloride (PVC: P1, P2), styrene-butadieneneoprene (SBR-neoprene: SN1), and styrene-butadiene rubber

(SBR: S1, S2). The description and analyses of the materials

are reported in table 1.

The percentage of chlorine, nitrogen, and carbon contents in

the original materials was detennined by the American Society

for Testing and Materials (ASTM) test methods No. 04208,

03179, and 05373, respectively. The impinger solutions were

analyzed for gas concentrations by various test methods. The

sodium hydroxide solutions were analyzed for HCI by the

ASTM test method No. 04327-88 and for HCN by U.S.

Environmental Protection Agency (EPA) test method No.

650 r r I r r I

600 ISet furnace temp, 1,000° C t::>

t::>

uJ 550f- t::>

c::: 500 lt::>

::J t::>

f- 450 l- t::> - « t::>

c::: 400 l- t::> - UJ

a.. 350 t::> - - t::>

UJ 300 - t::> -

f- 250 - t::> - UJ

U 200 - t::> - <t 6 Z 150 - a: 100 - ::J t::> -

l.L 50 t::> - t::> 6

I r I

0 2 4 6 8 10 12 14 16 18 20

TIME, min

Agure 2---furnace temperatures In the 2o-L furnace at a set

temperature of 1,000 ·C.

00720. The triethanolamine solution was analyzed for NOll

(treated as NO~ by the American Water Pollution Federation

(AWPF) test method No. 418-C, and the alkaline-permanganate

solution was analyzed for NOzby the EPA test method No. 70.

The NOz concentrations analyzed by the EPA method were

used to calculate the NO concentrations by subtracting the NOz

yields from the NOll yields and by multiplying the remainder by

the ratio of the NO and the NOzmolecular weights.

Each gas concentration (mg) was multiplied by a factor of

4 because the total airflow passing through each set of impingers was four times less than the airflow passing through the

sampling device. The product: was treated as a yield value, milligrams oftoxic gas per gram of original material burnt (mg/g),

because it evolved during the complete combustion of the 19

sample.

Syringe grab samples, taken at the sampling port and at the

sampling bag, were analyzed by gas chromatography for CO

concentrations (ppm). The average CO concentrations measured from the sampling bag were converted to mg and treated

as yield values (mg/g). Other variables measured were the

sample and furnace temperatures (OC) and the initial and final

sample weight (g). The 19 original sample weight was used to

calculate the gas yield values because only ashlike debris

remai ned after each experiment.

Table 1.--Descrlption and analyse. of conveyor belt materials

Conveyor belt material and sample

PVC: Polyvinyl chloride polymer, with fillers:

P1 .

P2 .

SBR-neoprene: Styrene-butadiene-neoprene rubber

polymer, with fillers:

SN1 .

SBR: Styrene-butadiene rubber polymer, with fillers;

treated for fire retardancy:

S1 .

S2 .

Construction

Solid woven

Solid woven

3-ply .

3-ply '"

3-ply .

Thickness, mm

13.3

10.6

11.9

11.6

11.56

Analyses. pet

Chlorine Nitrogen Carbon

28 0.63 SO

19.2 0.65 SO.7

11.5 0.69 55.5

7.7 2.3 64

7.4 1.5 63.7
5

LABORATORY FIRE TUNNEL EXPERIMENTAL SYSTEM

CONFIGURATION

The laboratory fire tunnel (figure lB), also known as the belt

evaluation laboratory test: (BELl) apparatus, consists of a chamber

(1.8-m long by 0.46-m1 constructed of refractory material (25-em

thick). The chamber is connected to an exhaust ducting (305-emdiam galvanized steel ducting) \iia a stainless steel transition section

whose inner surfare is lined with a ceramic fibet blanket (13-mm

thick). The igniter used is a commercial U-shaped natural gas

burner with two rows of six nozzles.

The mine conveyor belt sample (23 em wide by 76.2 em

long for the tests in this study) is fastened to a steel rack

constructed of slotted angle iron and placed in the tunnel at a

distance of 20.3 or 12.7 ern from the tunnel roof. The airflow

is measured by a vane anemometer (approximately 211.7 Us)

placed on the belt surface at about 30 ern from the front of the

tunnel. The sample temperatures were monitored by thermocouples that were embedded along the centerline of the belt

(half depth of the belt thickness) at distances of 15.2, 30.5, and

45.7 cm. The temperature data were transmitted every 10 s to

a data acquisition system and were printed by means of a

computer program.

During the experiments, a small amount of the combustion

gases (0.13 Us) is drawn by an exhaust pump via a multiport

sampling device. The device consists of a stainless steel manifold with a l-em-diam, 30-em-long perforated inlet tube (three

equidistant perforations along the tube) inserted horizontally

into the tunnel transition section. The combustion gases are

then directed equally by flowmeters through four manifold outlets into four sets ofsolution-containing impingers as described

in the "20-Liter Furnace Experimental System" section earlier

in this report. The gases emerging from the impingers flow

through the pump into a large (170-L) sampling bag. Syringe

grab samples are taken at a sampling port at 4-min intervals and

from the sampling bag at the end of each experiment.

PROCEDURES AND DATA REDUCTION

Experiments with the same mine conveyor belt materials

described in table 1 were performed in the laboratory fire

tunnel. The sample weights were: PI = 2,926 g; P2

= 2,335 g; SNI = 2,812 g; Sl = 2,495 g; and S2 = 2,445 g. The

experiment with sample S1 was repeated to verify the gas

concentrations.

During the experiments, a belt sample was fastened to a steel

rack with 1.4-mm-diam cotter pins and thin washers to prevent

the belt from shrinking away from the burner. The fastened

belt was placed in the fire tunnel at a distance of 20.3 em (S1

and S2 samples) or 12.7 em (PI, P2, and SN1 samples) from

the fire tunnel roof. The shorter distance from the roof

facilitated the combustion of these samples which, otherwise,

would not have completel y burnt. The flames from the gas

burner impinged equally upon the upper and lower surfaces of

the sample for a duration of 5 min (S1, S2, SN1, and P2

samples) or 8 min (P1 sample). The longer flame impingement

time for sample P1 was required to maintain the combustion

process, which otherwise would have not been sustained.

Because only ashlike debris remained after each experiment,

the initial sample weight was used to calculate the toxic gas

yields. The gas solutions and the syringe grab samples were

analyzed in the same manner as described for the 20-L furnace.

Each toxic gas concentration value (mg) was first multiplied by

a factor of 4 for the reasons given earlier in the "20-Liter

Furnace Experimental System" section, and then normalized to

a yield value (mg/g). The normalization was accomplished by

multiplying the toxic gas concentration value (mg) by the ratio

of the total volumetric airflow in the tunnel and the total

volumetric airflow in the sampling device during the test

duration; the product was then divided by the initial sample

weight.

DISCUSSION AND TREATMENT OF EXPERIMENTAL RESULTS

The gas yields (mg/g) ofHCI, HCN, N02, and CO measured

in the 2O-L furnace and in the laboratory fire tunnel are shown

in table 2. The calculated NO yields for both systems also are

shown in table 2. The CO gas yields measured in the fire

tunnel were higher (average for all belt materials, 43 pct) than

those measured in the 20-L furnace; the HCI and HCN gas

yields were slightly higher (average for all belt materials, 16

and 20 pet, respectively), and the N02 and NO gas yields were

slightly lower (average for all belt materials, 11 and 20 pct,

respectively). The difference between the gas yields measured

in the fire tunnel and those measured in the 20-L furnace is due

perhaps to the use of a horizontal sampling inlet only. The use

of vertical and diagonal inlets, intersecting the horizontal one,

may yield better results by drawing representative samples of

the combustion air in the fire tunnel ventilation system.

Considering the significant differences in the experimental

systems, however, the toxic gas yields measured in both

systems may be considered in good agreement.

For all samples, the HCl and CO yields were much higher

than the HCN, N02' and NO yields. As expected, samples P1

and P2, followed by sample SN1, released the highest HCl

yields because of the high percentage of chlorine content in the

original materials; they released the lowest HCN, N02' and CO

yields because of the low percentage of nitrogen and carbon

contents in the original materials. On the other hand, samples

S1 and S2 produced the lowest HCl yields because of the low

percentage of chlorine content of the materials and the highest

HCN, N02' and CO yields because of the high percentage of
6

Table 2.-Toxlc gas yields measured In the 2o-L furnace and laboratory fire tunnel

experimental systems (mg/g)

Conveyor belt

material and sample1 Hcr

2O-L furnace

HCN NO?z co HCI

Laboratory fire tunnel

co

96

90

68

164

145

172

0.21

0.26

0.20

0.09

0.09

0.11

0.26

0.27

0.66

0.59

0.60

0.12 0.22

0.26

0.34

0.23

0.17

0.16

94

30

25

24

69

59

69

70

71

71

61

54

0.09

0.11

0.16

0.16

0.11

0.12

0.36

0.38

0.25

0.30

0.30

0.44

0.11

0.11

0.14

0.09 -

0.07

0.11

46

48

73

90

53

50

pvc:

Pl .

P1 4 ••••••••••••

P2 .

P24 ••••••••••••

5BR-neoprene:

5Nl .

5N1 4 .

5BR:

51 33 0.28 0.67 0.29 99

51 4 30 0.18 0.73 0.31 114

52 . . . . . . . . . . . . . 23 0.25 0.39 0.26 98

524 26 0.21 0.64 0.19 103

12O_L furnace: all samples = 1 g. Laboratory fire tunnel (normalized to 1g sample):

5Nl =2,812 g, 51 =2,495 g, 52 =2,445 g.

zNO. treated as NOz.

3Ca1culated values.

45econd set of experiments.

Pl = 2,926 g, P2 = 2,335 g,

nitrogen and carbon contents of the materials. It is important

to note that the HO yields measured in this study are at least

50 pet higher than similar yields measured in a previous U5BM

study (8) using materials with comparable chlorine contents.

The increase in HO recovery is due to the longer contact time

ofthe combustion gases with the gas-trapping solutions. However, even the present HO yield values are at least 50 pct below

the theoretical HCI values based on the percentage of chlorine

in the original material (25-27). The difference between the

theoretical HO yields and the measured ones may be the result

of HO decay by deposition on the furnace walls and floor and

on sampling lines (28-29).

Table 3 shows the CO concentrations and sample temperatures versus time measured in both experimental systems. For

the 2O-Lfurnace system, all samples released high CO concentrations at sample temperatures above 300 °C. However, sample 51 released the highest CO concentration at the lowest sample temperature. Furthermore, this sample, together with samples 52 and 5N1, continued to release high CO concentrations

for the longest duration. For the fire tunnel system, samples 51

and 52 burnt within shorter periods of time than the other samples, releasing high CO concentrations. Of further importance

is that samples 51 and 52 reached high temperatures (above

400 0c) simultaneously along their entire lengths. These belts

burnt completely within a very short time, thus releasing the

toxic gases earlier and at faster rates.

Figure 3 shows the toxic gas yields (mglg) of HCI, HCN,

NO:z, and CO measured for each material in each experimental

system plotted as a function of the percentage of the chlorine,

nitrogen, and carbon contents in the original materials. Using

the average values of each gas yield (mglg converted to gig)

measured in both systems for each belt material, least square

regression analyses were made. The regression analyses results, valid for the range of chlorine, nitrogen, and carbon

percentage encountered in this study, are reported in equations

1 through 4 below and are also shown in figure 3 as solid lines.

YHO (gig) =(0.00275) x (CI,pct) + (0.0088); (1)

the correlation coefficient (r~ = 0.93.

YHCN (gig) = (0.000093) x (N,pct) + (0.000055); (2)

the correlation coefficient (~ = 0.87.

YN02 (gig) = (0.000226) x (N,pct) +(0.000177); (3)

the correlation coefficient (r) = 0.89.

YCO (gig) = (0.00405) x (C,pct) +(- 0.136); (4)

the correlation coefficient (r~ =0.85.

The results shown in figure 3 indicate that good and direct

correlations exist between the yield values of HO, HCN, N02'

and CO and the percentage of chlorine, nitrogen, and carbon

contents of the original belt materials; the higher the chemical

contents, the higher the toxic gas yield values.
7

Table 3.-CO concentration, sample temperature, and total airflow measured In the 2G-L furnace

and laboratory fire tunnel experimental systems for first set of experiments

2O-L furnace Laboratory fire tunnel

Conveyor belt Sample Total Sample temp, °C, at thermocouple

material and Time. CO. temp, airflow, Time, CO,2 distance of- Total airflow,'

sample1 min ppm min ppm L (1~) °C L 15.2 cm 3O.5cm 45.7cm

PVC:

P1 ......... 8 44 183 3 1,000 450 205 205

10 58 262 7 1,380 375 235 205

12 1,036 356 11 950 275 250 215

14 1,263 450 96 15 780 225 265 235

16 441 533 19 500 195 315 245 508

18 508 615 23 300 175 450 325

20 300 668 27 200 150 570 400

31 180 135 600 425

35 150 125 620 475

39 100 115 620 560

P2 ......... 8 41 167 3 1,030 425 260 250 } 10 57 241 7 1,050 400 260 300

12 1,040 302 11 389 225 275 275 254

14 1,300 397 96 15 -T97 165 450 375

16 530 495 19 144 165 625 550

18 509 585

20 301 640

SBR-neoprene:

SN1 ....... 8 90 170 3 1,500 502 193 146 } 10 180 257 7 1,200 463 306 233

12 913 378 11 540 290 565 500 254

14 1,220 460 96 15 276 239 560 620

16 1,440 542 19 2n 192 620 560

18 695 604

20 368 654

SBR:

S1 ......... 8 80 165 3 800 306 142 129 } 10 104 250 7 4,504 341 285 244 190.5

12 1,428 319 11 3,994 666 752 454

14 1,290 455 96 15 1,050 341 467 822

16 1,388 545

18 541 575

20 468 660

S2 ......... 8 75 162 3 1,215 350 201

10 98 245 7 3,824 590 420

~} 127

12 1,390 370 9 1,500 530 709 503

14 1,300 460 96 11 850 340 500 850

16 1,206 540

18 490 609

20 450 658

1 2O-L furnace: all samples =1 g. Laboratory fire tunnel: P1 =2,926 g, P2 =2,335 g, SN1 =2,812 g, S1 =2,495 g, S2 =2,445 g.

2The CO concentration measured in the fire tunnel at the 3rd min has been reduced by 50 ppm, which is the CO concentration measured during

the standardization of the gas burner.

3 The 1DtaI airflow for the fire tunnel experiments was calculated by multiplying the experimental airflow by the time taken by each belt to burn

(P1 =40 min, P2 =20 min, SN1 =20 min, S1 =15 min, S2 =11 min).
8

20

OL.-....I...----L..----l_...l..----I...----I._...l....---.L..---I--L....-....L-----I....----l-...J

50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

CARBON CONTENT OF MATERIAL, pet

180

160

140

-2l

OJ 120

E

0- 100

.....J

L.U 80

>- I

0 60 . U I

40

Laboratory fire L ..mnel

1st set of 2nd set of 'j s! se\ uf 2n0 set uf

experIments experiments experiments experiments

• P1 • If P1

• P2 • • P2

• 5N1 If 5N1

• 51 '" t' 51

0 52 II if 52

9 11 13 15 17 19 21 23 25 27 29

CHLORINE CONTENT OF MATERIAL, pet

100

90

80

-2l 70 OJ

E 60 0-

.....J

L.U 50

>= 40 ....

u

I 30

20

10

0

7

0.34 0.8

0.30 0.7 '"

$-'

-2l 0.26 f OJ

OJ 0 0, 0.6 E E f'

0- 0.22 6 .....J

L.U .....J 0.5 L.U

>- 0.18 >=

z N

U 0 0.4

I 0.14 z

0.10

0.06 L...-_.l...-_"""--_.........._...L..-_...L..-_....L.-_....L..-_....L..-_...l

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

NITROGEN CONTENT OF MATERIAL, pet

0.3 •

.-11

If 0.2 L...-_...l....-_....L..-_....l...-_---L..._......L..._----l.._----l._----l_.--J

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

NITROGEN CONTENT OF MATERIAL, pet

Figure 3.---Correlations between the HC1, HCN, NOli and CO gas yields and the percentage of chlorine, nitrogen, and carbon contents

In the original materials.

The toxicity index (TI) parameter is a measure of the potential gas toxicity hazard of a belt material during a fire. The

TI is considered to be the sum of all the IDLHs contained in

each toxic gas yield for that material, assuming the gas toxicities are additive (30-31). The TI can be calculated according

to equation 5:

TOXICITY INDEX PARAMETER

where

T I = I,(Yx 1(IDLHx) Cx),

TI = toxicity index parameter (m3/g),

(5)

and Cx = constant to convert the toxic gas yield

from gig to ppm, as given by

(10-6/0.022414) x (molecular weight gas,

x), gI(m3 x ppm).

For CO (molecular weight = 28.01 g), the Cx value

=(28.01/0.022414) x (10-6) =0.00125 gI(m3 x ppm).

Considering the toxic gas yields measured in this study,

equation 5 can be written as equation 6:

TI (m3/g) = (YHCI)/(IDLHHc1 x ~C)) + (YHCN)/(IDLHHCN

Yx = yield of toxic gas (grams of gas produced per gram of original material

consumed during the combustion process, gig),

+ (YCO)/(IDLHeo x Cco). (6)
9

TOXICITY HAZARD PARAMETER

Ms = mass loss rate of a burning sample (gls),

where TH = toxicity hazard parameter (dimensionless),

Key

r7l 20-L furnace (prevIous

IDLHs)

f)();) 20-L furnace (revised

L2SJ IDLHs)

Fire tunnel (previous

t::J] IDLHs)

Fire tunnel (revised

IDLHs)

1.3 .---------------------.

1.2

1.1

1.0

0.9

0.8

0.1

0.3

0.2

CJ)

M 0.7

E

f=' 0.6

0.5

0.4

derived from the original sample weight and the time of

burning given in table 3. Previous data from USBM large-scale

fire gallery tests of conveyor belts (24) also indicated that the

burning rates can differ for various types of belts. Then, using

the 2O-Lfurnace revised TI values for belts S2 (0.39 m3

/g) and

P1 (1.06 m3/g) and the fire tunnel airflow (0.212 m3/s), the

calculated TH values for the fire tunnel system are 6.8 for belt

S2 and 6.1 for belt PI. The TH value for belt S2 would be

even higher if the belt had been tested under the more severe

experimental conditions (8-min flame impingement, 12.5-cm

distance from the tunnel roof) of belt P1 because these conditions would have resulted in larger mass loss rates for belt S2.

This example illustrates that, although the TI is important in

assessing the potential toxic gas hazard of belt materials, the

mass loss burning rates could be equally or more significant in

determining the actual toxic gas hazard of a burning belt in a

ventilated system.

P1 P2 SN1 S1 S2

BELT SAMPLES

Figure 4.-ToxJcity Index parameter for the 2~L furnace and

laboratory fire tunnel experimental systemL

TH =TI (Ms/Q), (7)

Good agreement exists between the TI's calculated for the

2O-Lfurnace and those calculated for the fire tunnel, as shown

in figure 4. As expected, the TI's calculated with the revised

IDLH's (revised TI's) are about twice as high as the TI's

calculated with the previous IDLHs (previous TI's) for all of

the belt materials in both experimental systems. The higher the

TI, the greater the potential toxicity of a conveyor belt during

a mine fire.

The TI's were the highest for sample PI, followed by

samples P2 and SN1, and the lowest for samples S1 and S2 in

both experimental systems. For sample P1, the revised TI's

were 1.06 and 1.22 m3

/g (20-L furnace and fire tunnel,

respectively), and the previous TI's were 0.54 and 0.64 m3

/g

(20-L furnace and fire tunnel, respectively). For sample S2, the

revised TI's were 0.39 and 0.43 m3

/g (20-L furnace and fire

tunnel, respectively), and the previous TI's were 0.21 and 0.23

m3

/g (20-L furnace and fire tunnel, respectively).

The toxicity hazard (TH) parameter estimates the level of

toxic gas hazard produced by a burning belt material in a

ventilated system. The TH is the product of the TI and a ratio

of mass loss to ventilation airflow rates; it corresponds to the

number of IDLH's contained in an airflow during the burning

of a belt; the higher the TH value, the greater the toxic gas

hazard. The TH parameter is given by equation 7:

and Q = volumetric airflow rate (>0) into which the

toxic gas concentration is mixed (m3

/s).

In calculating the TH parameter, consideration must be

given to the mass loss rate of a burning belt, because different

belts may burn at different rates. For example, the fire tunnel

data indicated that the average mass loss rate for belt S2

(3.7 gls) was about three times greater than that for belt P1

(1.2 g/s) at an airflow of 0.212 m3

/s. These values were

CONCLUSIONS

The toxic gas yields of Ha, HCN, N02, and CO measured

in the 2O-L furnace system are in good agreement with similar

yields measured in the laboratory fire tunnel system. Thus,

either system could be used to obtain the gas yield data for

mine conveyor belts. However, the 20-L furnace system is

preferred due to the smaller sample size and less time required

to set up and run an experiment.

Good and direct correlations were found between the percentage of chlorine, nitrogen, and carbon contained in the

original materials and the HCl, HCN, N02J and CO gas yields.

Both experimental systems produced essentially the same results. The greater the percentage of chemical contents, the

higher the corresponding toxic gas yield values. As expected,

the PVC belt samples with the highest percentage of chlorine
10

released the highest HO. The SBR belt samples with the highest percentage of nitrogen and carbon released the highest

HCN, N02' and CO.

Using the toxic gas yield data, a toxicity index (TI) and a

toxicity hazard (TH) parameters were calculated for each belt

material. The TI is a measure of the potential gas toxicity that

a belt can produce during a fire; the higher the TI value, the

greater the potential toxicity. As expected, the TI was the highest for the PVC belts and the lowest for the SBR belts. The TH

parameter is the product of the TI and a ratio of mass loss

burning rates to ventilation airflow rate. It can be used to estimate the level oftoxic gas hazard produced by a burning mine

conveyor belt in a ventilated system. In some cases, the mass

loss rates may be sufficiently great that a belt with a low TI

actually produces a more severe toxic gas hazard than one with

a much higher TI. For example, for the fire tunnel system, the

TIl value calculated for belt S2, whose TI is 60 pet lower than

that for belt PI, was higher than the TH value calculated for

belt PI because ofthe higher mass loss burning rate of belt S2.

ACKNOWLEDGMENTS

The author wishes to thank Nick Harris (deceased), Mine

Safety and Health Administration, for conducting the combustion experiments in the laboratory fire tunnel; Frank J. Perzak,

U.S. Department of Energy Pittsburgh Research Center, for

measuring the conveyor belt sample temperatures during the

experiments in the laboratory fire tunnel; and C. D. Litton, also

with the U.S. Department of Energy Pittsburgh Research

Center, for his technical assistance in developing the equations

in this report.

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