The National Institute for Occupational Safety and Health paper - The Brookwood Disaster and Electrical Requirements for Hazardous Locations - found that over the past 30 years a number of fatal coal mine explosions have been linked to non-permissable electrical equipment ignition sources when flammable gas moved outbye the last open crosscut under unusual conditions, brought about by a lack of ventilation in the mine.
Released earlier this week, it said the Brookwood accident - in which two explosions at the Jim Walter Resources No. 5 mine killed 13 workers - involved methane and coal dust igniting in intake air entries, most likely as a result of electrical equipment.
The investigation learned that prior to the blasts, workers at the mine were mending a section of the roof that had become deteriorated. A scoop battery charging station was under the faulty roof section and adjacent to a stopping, separating methane concentrated return air from fresh ventilation air.
Before the miners were able to repair the roof, it caved in, damaging the stopping and the battery enclosure, shorting the battery and releasing methane into the battery charging station.
This build-up resulted in the first minor explosion that injured four workers, leaving one incapacitated while the other three escaped.
Within an hour 12 workers had rushed to aid the worker, unaware of the build-up of methane in the environment, and perished after the second explosion.
NIOSH investigators - led by Thomas Dubaniewicz Jnr. - concluded the ignition of the first blast was most likely a scoop battery while the second, more serious blast came about from the block light system, sparking a review of the electrical classification guidelines for underground mines and equipment approval processes.
The report recommended intake air entries that might become hazardous through failure of a ventilation system should be considered as a hazardous location in the national electrical code.
This places restrictions on equipment approved to enter the environment and will have to be taken into consideration for wireless communication systems and back-up batteries under design or currently in operation in mines.
The report also supports calls from the United Mine Workers of America to install gas detectors near a power centre and in a fresh air entry and increased insulation of batteries.
The UWMA also called for installation of rubber conduit on all cables and leads and support braces to protect batteries from roof falls.
NIOSH also recommended upgrading protection techniques for non-permissible intake-air electrical equipment that is likely to be de-energised during emergencies to Class 1, Division 2 or Zone 2, while equipment likely to remain energised should be protected by Class 1, Division 1 or Zone 1 safety requirements.
