NIOSH Office of Mine Safety and Health Research

The overarching goal of the NIOSH fire research program is to reduce the risk of mine fires through the development of new or improved strategies and technologies for mine fire prevention, detection, control and suppression. To accomplish this goal, NIOSH is conducting research aimed at ensuring that fire-safe materials are used, that combustibles are properly handled and stored, that mechanical and electrical equipment is properly used and maintained, and that personnel are adequately trained and educated in fire safety practices. NIOSH research is developing rapid and reliable fire sensing systems, guidelines for selecting and using these systems, investigating the principles of fire dynamics and the interaction of gaseous or chemical agents with an expanding flame. In addition, research is addressing the role that ventilation plays in fire control and extinguishment, and how different fire and smoke mechanisms can impact these interrelationships.

Computational fluid dynamics (CFD) simulations were conducted to investigate the spontaneous heating of coal in longwall gob areas under various ventilation schemes. These simulations confirmed the existence of the critical velocity zone behind the shields in the gob, and showed the existence of other critical velocity zones in both an active panel and a mined out panel. The results are being used to develop optimum ventilation schemes for mines with methane and to characterize gob gas flow to reduce the risk of spontaneous combustion.

Full-scale fire experiments were completed in the NIOSH Fire Suppression Facility and the laboratory-scale BELT apparatus to determine if the BELT test method to determine the fire resistance of the 72-in-wide conveyor belts correlates with the results under full-scale fire conditions. Of the six belts tested in the large-scale tests in the FSF and the BELT apparatus, five of the belts produced similar results. BELT approved SBR and two chloroprene belts passed both tests. A non-fire resistant and the 2G approved SBR failed in both tests. A PVC belt that meets the British standard passed the large-scale test, but failed the BELT test. These results indicate the BELT test represents the fire resistance characteristics of conveyor belting under full-scale fire conditions. In the case where the results did not correlate for the PVC belt, the BELT test proved to be a more conservative measure of the belt's fire resistance.

A series of large-scale experiments to evaluate to evaluate the effect of high air velocity, water sprinkler activation temperature, and water supply on the effectiveness of water sprinkler fire suppression systems to extinguish large-scale conveyor belt fires was completed. Water sprinkler systems with two different activation temperatures (68 °C, 141 °C) were tested under two air velocity conditions (0.5 m/s, 5.1 m/s) using both new and used 2G approved SBR conveyor belt. In these experiments, the water supply was turned off after 10 minutes. The results showed that the the suppression system was able to suppress the fires in ten minutes to the point that a miner could extinguish it with a fire hose. However, in several of the tests, the fire often reestablished itself a few minutes after the water supply was cut off and quickly grew out of control, indicating that the effectiveness of the suppression system is highly dependent on the water supply. The results are being used to establish guidelines for installation of suppression systems on belts.

Fire detection is a critical component in the safety of underground mines. A series of large-scale experiments were completed in the NIOSH Fire Suppression Facility (FSF) to determine if the use of wider belts and higher belt entry air velocities impacts existing fire detection guidelines for spacing and alarm levels. The results showed that the detection criteria previously developed remains valid for wider belts, higher air velocities, and larger entry cross-sections. It was found that the alarm levels for both CO and smoke optical density are functions not only of the coal fire heat release rate, but also of the ventilation air velocity and the entry cross-sectional area. These results indicate that the sensor alarm levels necessary for adequate fire detection in conveyor belt haulageways will tend to decrease as the air quantity (product of air velocity and entry cross-sectional area) increases. This would mean that in mines with larger entry cross-sections, lower sensor alarms would be required than in mines with smaller entry cross-sections, a result primarily of increased dilution of the combustion products by the ventilation airflow.