Flammability of wider conveyor belts 


using large-scale fire tests
 

J.H. Rowland III and A.C. Smith 

National Institute for Occupational Safety and Health (NIOSH), Pittsburgh, PA 

Abstract 

The Mine Improvement and New Emergency Response Act of 2006 (MINER Act) established a Technical 

study panel (the Panel) to provide recommendations on the utilization of belt air and new technology that 

may be available for increasing the fire resistance properties of conveyor belt used in underground coal 

mines.The Panel Report recommended use of the belt evaluation laboratory test (BELT) as the method 

for testing and approval of flame resistant conveyor belts used in underground coal mines.The research 

conducted to establish the correlation of the BELT with large-scale belt fire flammability tests was done 

using 91 - 107 cm (36- to 42-in.) wide conveyor belt. Due to today’s coal haulage capacity, the mining 

industry is using 183 cm (72 in.) and wider conveyor belts.The U.S. National Institute for Occupational 

Safety and Health (NIOSH) conducted a study to determine if the BELT will also qualify wider belts as 

fire resistant for use in underground coal mines. This paper describes the results of recent experiments 

comparing results from using the BELT and the large-scale tests for six different belts. 

Introduction 

The 2G test, described in 30 CFR 18.65, has been used for 

acceptance of fire-resistant belting since 1955. The accepted 

method was mandated by the Federal Coal Mine Health and 

Safety Act of 1969 to qualify a belt as fire-resistant for use 

in underground coal mines in the United States. To conduct 

the 2G test, a 15-cm-long by 1.3-cm-wide (6 in. by 0.5 in.) 

sample of belt is exposed to a flame from a Bunsen burner in 

still air for one minute, with the transverse axis at 45 ̊ inside 

a 53-cm (21-in.) cubical test gallery. After one minute, the 

flame is removed, and the sample is exposed to air at a velocity of 91 m (300 ft) per minute. The belt passes the test if the 

flame duration is less than one minute for four samples of the 

same belt, or if the afterglow is less than an average of three 

minutes. In their report, the Technical Panel on the Utilization 

of Belt Air noted that the 2G test has various deficiencies, as 

seen in the persistence of belt fires in underground coal mines 

(Mutmansky et al., 2007).

The U.S. Bureau of Mines (USBM), in cooperation with 

the Mine Safety and Health Administration (MSHA), first 

addressed the use of the 2G test to evaluate conveyor belt fire 

resistance in laboratory-scale tests in the early 1980s (Sapko et 

al., 1981). Large-scale tests were conducted in the mid 1980s 

to compare the results of the 2G test to results in large-scale 

conveyorbeltfire tests(Lazzara andPerzak,1989).Inthisstudy, 

nine synthetic rubber belts and eight PVC belts were evaluated 

in full-scale fire tests in the Lake Lynn Fire Gallery. Of the 17 

belts tested, 16 were rated as MSHA-accepted fire-resistant 

based on the 2G test. One belt was rated as non-fire-resistant. 

Of the 16 belts that passed the 2G test, 11 belts failed the Fire 

Gallery test criteria, exhibiting flame spread and belt damage beyond the ignition area, while five belts passed the test. 

Based on these results, the National Institute for Occupational 

Safety and Health (NIOSH) and MSHA worked to develop a 

new laboratory-scale test apparatus and method for evaluating 

the fire resistance of conveyor belts that more closely correlated with the results of the large-scale Fire Gallery results 

(Verakis, 1991; Verakis and Dalzell, 1988). Further research 

was completed comparing the apparent fire resistance of 21 

conveyor belts based on tests conducted in the Fire Gallery 

and a new laboratory apparatus (Lazzara and Perzak, 1990). 

Of the 21 belts tested, the results showed that 19 were in 

full agreement based on the pass/fail criterion developed for 

the two test methods. Based on the results of the large-scale 

conveyor belt fire tests and new laboratory-scale test work, 

MSHA published a proposed rule in 1992 to replace the 2G 

test with this new laboratory method, belt evaluation laboratory test (BELT) (1992). In July 2002, the proposed rule was 

withdrawn. MSHA cited a significant decline in conveyor belt 

fires from 1993-2002, belt monitoring improvements, such as 

fire detection, and technological advancement, such as roller 

and bearing improvements to minimize friction on the belt, 

as reasons for withdrawing the proposed rule (MSHA, 2002).

Thepanel’sreportrecommendedtheimmediateimplementation of BELT as the method for testing and approval of flame 

resistant conveyor belts (Mutmasky et al., 2007). However, 

since the correlations between the laboratory-scale tests and 

the full-scale tests used to establish the BELT method were 

based on 91-to-107-cm- (36-to-42-in.)-wide conveyor belts, 

NIOSH and MSHA decided to conduct experiments to determine if the correlation is still valid for the wider conveyor 

belts typically used in mines today. This report describes the 
results of experiments conducted on a number of wider belts 

using the laboratory-scale BELT method and large-scale tests 

in the NIOSH Fire Suppression Facility. 

Belts evaluated 

The conveyorbeltingchosenforthisresearchwaspurchased 

as brand new conveyor belting from each manufacturer. Each 

belt is 183 cm (72 in.) wide. The goal in choosing the conveyor 

belts was to evaluate different types of belts used in the mining 

industry in the U.S. and other countries today. Three different 

types of belt material were selected: polyvinyl chloride (PVC), 

styrene butadiene rubber (SBR) and chloroprene. Three of the 

belts meet three different U.S. standards, non-fire resistant, 

2G-accepted and BELT-approved. The three other belts meet 

foreign fire resistance standards (Australian, British and German).Table1showsthe typeofbeltmaterial,standardapproval, 

construction, strength and cover dimensions. 

Table 1 — Conveyor belts evaluated. 

Belt Standard Ply 

Strength, 

piw7 Covers 

1 N1 Australian 3 600 3/16 x 1/16 in.

2 PVC2 British SW6 800 2 x 2 mm

3 SBR3 NFR5 US 4 800 3/8 x 3/32 in.

4 SBR3 2G US 3 600 3/16 x 1/16 in.

5 SBR3 BELT US 3 600 3/16 x 1/16 in.

6 C4 German 3 600 3/16 x 1/16 in.

1 Neoprene

2 Polyvinyl chloride

3 Styrene butadiene rubber

4 Chloroprene

5 Non-fire-resistant

6 Solid woven 

7 Pounds per inch of belt width (widely used in the U.S.) 

Experimental description

Large-scale test. The large-scale fire tests were conducted 

at the NIOSH Fire Suppression Facility (FSF). The FSF, shown 

in Fig. 1, is a full-scale, state-of-the-art fire test facility located 

on the surface at the Lake Lynn Laboratory in Fairchance, PA. 

Figure 1 — Fire Suppression Facility. 

The fire tunnel is configured in a T shape to simulate a main 

mine entry and crosscut. The main entry is 47 m (153 ft) long 

and the crosscut is 12 m (40 ft) long. For these experiments, 

the crosscut was closed off. The entry is 5.5 m (18 ft) wide 

by 2 m (7 ft) high. The FSF is equipped with a 1.8-m- (6-ft)-

diameter, variable speed axial vane fan, located at one end of 

the main tunnel to provide ventilation. The fan has a pneumatic 

controller to adjust the fan pitch in order to increase or decrease 

the air velocity.

The FSF is equipped with a nine-point gas monitoring array 

at the open end of the tunnel to measure the gas components 

produced from a belt burn test. The array is made of 1.3-cm 

(0.5-in.)-diameter black steel pipe positioned at the center of 

the entry. A total of nine 0.3-cm (0.125-in.) holes are drilled 

into the vertical section of the pipe to sample the gases. The 

sample holes are equally spaced vertically from the roof to the 

floor. A 1.3-cm (0.5-in.) tube is connected to the steel pipe and 

leads back to the control room to a set of infrared gas analyzers. The gas analyzers measure carbon monoxide (CO), carbon 

dioxide (CO2) and oxygen (O2) gas concentrations. The gas 

data was collected every two seconds and was recorded by a 

computer-based data acquisition system.

Figure 2 — Gas burners. 

Figure 3 — Shield for gas burners. 

Anine-pointthermocouple arraywas alsolocatedattheopen 

end of the tunnel to measure the average exit gas temperature 

for use in heat release rate calculations. The thermocouples 

are attached to three vertical half-diameter steel pipes spaced 

evenly across the width height of the entry. The heat release 

rate for each test is computed using the exit gas temperature by the following equation:

 Q total = Cp x ρo x Ve x Ao x ΔT (1) 

where Cp = heat capacity of air, 1.088 x 10-3 kJ/g °C

ρo = density of air, 1,200 g/m3 

Ve =average exit air velocity, m/s 

Ao = entry cross section area, m2 

ΔT =average exittemperature – initialtemperature, 

°C. 

The FSF was equipped with two video cameras 

to record each test burn. The first camera is mounted 

in the center of the roof, roughly 18 m (60 ft) from 

the fan, to give a frontal view of the conveyor belt 

structure during the test. The second video camera is 
placed on the left side of the tunnel, facing the open end of 

the tunnel, upstream from the conveyor belt structure, to view 

the underside of the conveyor belt at the point of ignition. The 

conveyor belt structure is located 26 m (85 ft) from the fan and 

is slightly off center of the entry to allow for heavy equipment 

to pass on one side to place the belting onto the structure. The 

conveyor belt structure is 15 m (50 ft) long and 2.2 m (7.25 

ft) wide. The trough idlers are 13 cm (5 in.) in diameter and 

are placed at 1.5-m (5-ft) intervals.

To ignite the belt, four sets of natural gas impinged jet 

burners, connected in series, were placed in front of the belt 

structure, as shown in Fig. 2. Each burner was equipped with 

60 stainless steel jets, having a combined rated output of 44 to 

114 kilowatts per burner. The ignition region was confined by 

metal shields on the front, left and right sides, and the top to 

form a box around the ignition zone to reduce the effects of the 

ventilation on the ignition process, as shown in Fig. 3. The back 

side was unshielded towards the open end of the fire tunnel.

To conduct a test in the FSF, a 11-m- (36-ft)-long piece of 

conveyer belt is installed on the conveyor belt structure. The 

upstream end of the belt is affixed to the burners by metal wire, 

as shown in Fig. 2. Thermocouples are installed on the center 

line of the belt at 1.5-m ( 5-ft) intervals and along the two edges 

of the belt at 3-m (10-ft) intervals, as shown in Fig. 4. 

Figure 4 — Thermocouple layout.

The first 

row of thermocouples are placed 0.6 m (2 ft) from the front of 

the belt in the ignition zone. Each thermocouple is placed just 

below the surface of the belt to measure the belt temperature 

and determine when the flame reaches that distance on the belt. 

The air velocity is defined as the airflow over the top center 

of the belt, 5 m ( 17 ft) beyond the ignition zone and 0.3 m (1 

ft) above the surface of the belt. The velocity measurement is 

made using a handheld vane anemometer. The pitch of the fan 

blade is varied to achieve the desired air velocity. Air velocity 

measurements are alsomade atthe thermocouple andgaspoints 

at the exit of the tunnel, 46 m (150 ft) from the fan. The exit 

air velocities at each point are averaged together and recorded 

as the exit air velocity. It is important to mention that once the 

air velocity was set for the test, at no time was the fan turned 

off or adjusted until the test was completed.

To ignite the belt, the four sets of natural gas burners are 

placed 1.37 (4.5 ft) in front of the structure, the belt is secured 

over the gas burners with metal wire and the gas burners are 

ignited with a propane torch. The natural gas is allowed to 

flow for 10 minutes before it is turned off. The belt is allowed 

to burn until it is just smoldering, with no visible flame, or 

until the entire length of the belt is consumed by the fire. The 

belt passes the large-scale test if, in two separate trials, there 

remains a portion of the belt across the entire width that is not 

damaged. A belt fails the test if, during any of the two trials, 

the belt burns completely to the end. 

BELTapparatus.The USBM, in cooperation with MSHA, 

developed a laboratory-scale flame test known as the BELT

test to address the deficiencies of the 2G test. The BELT test 

can be conducted in a relatively simple laboratory setting and 

does not require a full-scale fire gallery. The BELT apparatus 

is a 1.68-m- (5.5-ft)-long by 0.46-m- (1.5-ft)-square, 2.5-cm- 

(1-in.)-thick ventilated tunnel made of refractory material. 

Round stainless steel ducting is used to exhaust the fumes 

produced from the burning of the belt. A steel rack made of 

slotted angle iron is used to hold down the belt during the test, 

as shown in Fig. 5.

Figure 5 — BELT test apparatus. 

 To ignite the belt, an impinged jet methane 

gas burner containing two rows of six jets is used. The methane 

used is technical grade 2 (99.99%).

To conduct a BELT test, a belt sample is cut to the size 

of 1.5 m by 23 cm (5 ft by 9 in.). The belt is fastened to the 
angled iron rack, cover side up, using cotter pins and washers 

to prevent it from shrinking away from the burner. The front 

of the rack is then placed and centered 15 cm (6 in.) inside the 

tunnel. The ventilation for the tunnel is set at 61 m (200 ft) per 

minute using a vane anemometer to measure the air flow. The 

belt is ignited by applying the methane burner to the front edge 

of the belt with the flames distributed evenly over the top and 

bottom. The flow of methane to the burner is set at 0.034 ± 0.1 

m3/min (1.2 ± 0.1 cfm). The methane burner is removed after 

five minutes and the belt is allowed to burn until the flames 

are out. The belt passes the test if in three separate trials there 

remains a portion of the belt across the entire width that is not 

damaged. Abelt fails the test if during any of the three trials the 

belt burns completely to the end of the sample (MSHA, 2008). 

Results and discussion 

Large-scale test. Initially, tests were conducted using the 

2G-accepted SBR belt at air flows of 62, 122, 152 and 183 m 

(200, 400, 500 and 600 ft) per minute to determine the worstcase air velocity. This belt was chosen because it is commonly 

used in the U.S. coal mining industry. To calculate the flame 

spread rate, the time and distance were recorded when the fire 

reached each row of thermocouples. The points were then plotted on a graph and the data was fitted by linear regression. The 

slope of the line is the flame spread rate. The results are shown 

in Fig. 6 and Table 2. 

Table 2 — Flame spread rates.

 SBR 2G Belting 

Ventilation rate (ft/min) 200 400 500 600 

Flame spread rate (ft/min) 11.2 14.6 11.5 13.8

Figure 6 — Plot of flame spread rates of 2G-accepted SBR 

belting. 

The results indicate that the worst-case 

air flow is 122 m (400 ft) per minute. The plots in Fig. 6 show 

that the flame spread rate is linear over the 11-m (36-ft) length 

for each of the air velocities. 

After determining the worse case air flow of 122 m (400 

ft) per minute, this ventilation rate was used to evaluate all six 

belts in the large-scale test. Two tests were conducted for each 

belt. As mentioned earlier, the pass/fail criterion is based on the 

damage to the belt. A belt passes the large-scale test if, in two 

separate trials, there remains a portion of the belt across the 

entire width that is not damaged. A belt fails the test if, during 

any of the two trials, the belt burns completely to the end. The 

flame spread rate was calculated for the belts that burned out 

of the ignition zone. The peak fire size is the optimum heat 

release rate after the gas burners are turned off. The damage to 

the belt was recorded as the length of belt burned away from 

the gas burners. The flame spread rate, peak fire size, amount 

of belt damage and pass/fail results are shown in Table 3.

Table 3 — Large-scale test results.

Flame 

spread rate 

ft/min 

Peak fire size 

management 

Belt damage,

ft 

Pass/ 

Type Standard Fail 

Belt 1 T1 Neoprene Australian NA 0.22 2.5 P 

Belt 1 T2 Neoprene Australian NA 0.30 6 P 

Belt 2 T1 PVC British NA 0.15 less than 1 P 

Belt 2 T2 PVC British NA 0.13 less than 1 P 

Belt 3 T1 SBR non fire-resistant U.S. flashover 10.00 36 F 

Belt 3 T2 SBR non fire-resistant U.S. flashover 11.00 36 F 

Belt 4 T1 SBR 2G U.S. 14.6 6.00 36 F 

Belt 4 T2 SBR 2G U.S. 21.0 9.00 36 F 

Belt 5 T1 SBR BELT U.S. NA 0.12 1 P 

Belt 5 T2 SBR BELT U.S. NA 0.09 less than 1 P 

Belt 6 T1 Chloroprene German NA 0.14 2 P 

Belt 6 T2 Chloroprene German NA 0.13 2 P 

The Neoprene, PVC, chloroprene and BELT-approved SBR 

belts (belts 1, 2, 5 and 6) passed the large-scale test based on 

the stated criteria. These belts did not burn out of the ignition 

zone and were unable to reach steady-state flame propagation. 

The peak fire size these for belts ranged from 0.09 and 0.12 

megawatts (MW) for the SBR belt to 0.22 and 0.30 MW for 

the Neoprene belt. The small fire size was due to the small 

amount of belt burned in each test. The worst belt damage 

was observed for the Neoprene belt that meets the Australian 
standard, which burned 0.76 and 1.83 m (2.5 and 6 ft) in the 

two tests, while the SBR and chloroprene belts burned 0.61 

m (2 ft) or less.

Thenon-fireresistantand2G-acceptedSBRbelts(belts3and 

4) failed the large-scale test. The non-fire resistant belt flashed 

over, setting the entire belt on fire at once, causing damage to 

the thermocouples, so no flame spread rate could be obtained. 

The non-fire resistant belt burned completely to the end of the 

sample. The 2G-accepted SBR belt flame spread rate was 4.5 

m (14.6 ft) per minute for the first test and 6.4 m (21.0) ft per 

minute for the second test. The peak fire size for the non-fireresistant belts was 10.0 and 11.0 MW, while the peak fire size 

for the 2G accepted SBR belts was 6.00 and 9.00 MW. 

BELT results. The results of the BELT tests are shown in 

Table 4. In this test, the Neoprene, BELT-approved SBR and 

chloroprene belts met the pass criteria. The PVC, non-fireresistant SBR and 2G-accepted SBR belts failed. 

Summary

Six different types of 183-cm- (72-in.)-wide conveyor 

belting that were deemed acceptable by different flammability 

standards were evaluated for fire resistance under large-scale 

test conditions. Full-scale fire experiments were conducted in 

the NIOSH FSF and the results were compared to the results 

of laboratory-scale BELT. Of the six belts tested in the largescale tests in the FSF and the BELT apparatus, five of the belts 

produced similar results. The Neoprene, BELT-approved SBR 

and chloroprene belts passed both tests. The non-fire-resistant 

and the 2G-accepted SBR, as expected, failed in both tests. The 

PVC belt that meets the British standard passed the large-scale 

test, but failed the BELT test. In the case where the large-scale 

test results did not correlate for the one PVC belt, the BELT

test provided a more conservative result. Although the test 

difference is not completely understood for the one PVC belt, 

a partial explanation may be related to lower concentration of 

the combustible atmosphere generated in the full-scale test 

and greater heat loss versus the BELT during the combustion 

process of the PVC belt. Overall, these experimental results 

indicate the BELT represents a reasonable correlation of the 

fire resistance characteristics of wide conveyor belting under 

full-scale fire conditions as tested in the FSF. Also, the exTable 4 — BELT Test results. 

Belt 1

Belt 2

Type 

Neoprene 

PVC 

Standard 

Australian 

British 

Pass/fail 

P 

F 

Belt 3 SBR non-fire-resistant U.S. F 

Belt 4 SBR 2G U.S. F 

Belt 5 SBR BELT U.S. P 

Belt 6 Chloroprene German P 

perimental tests of the 183-cm- (72-in.)-wide belts in the FSF 

were comparable to the previous large-scale test results of the 

91-107-cm-(36-42-in.)-wide conveyor belts conducted by the 

USBM. As the industry moves to even wider and thicker belts 

in the future, there will continue to be a need for large-scale 

experimental studies to ensure that the correlation between the 

BELT method and conveyor belt fire resistance is maintained. 

Acknowledgments

The authors would like to thank MSHAfor assisting in conducting the BELT tests. Also, the authors would like to thank 

our Lake Lynn colleagues and the Wolverine contractors for 

setting up the experiments. Without them, this research would 

not have been completed. 

Disclaimer 

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of NIOSH. 

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