It warned the site safety and health management system must also ensure ERBs were installed, operated and maintained according to original equipment manufacturer recommendations.
“A periodic inspection of an underground rescue air emergency refuge bay found that an explosion had occurred inside,” the inspectorate said in a safety alert.
“It is believed that an explosive atmosphere was created by the hydrogen generated when the EverExceed VRLA (valve regulated lead acid) batteries were overcharged.”
Factors contributing to the incident included the EverExceed battery-charging system not switching off when the manufacturer’s fully charged battery voltage was reached.
The overcharging batteries produced hydrogen which vented into the ERB.
An ERB inspection procedure was not followed correctly by personnel and the gas was ignited by an unknown energy source.
The batteries were housed under a seat within the ERB.
The gas expelled from the overcharged batteries was circulated around the airtight ERB by the air-conditioning unit.
While the ignition source hasn’t been positively identified, the battery charger is suspected.
Other potential ignition sources inside the ERB include lights, two-way radio and an air conditioner.
“ERBs form an integral part of an underground mine’s emergency response plan and system,” the inspectorate said.
“Where OEM recommendations are not followed, suitable risk and change management processes must be applied to ensure that the risk remains at an acceptable level.”
The inspectorate also recommended all ERB battery and battery-charging systems were inspected to ensure they were compatible with and installed and operating within OEM specifications.
All ERBs should be subject to scheduled inspection and maintenance by suitably qualified personnel, covering OEM specifications as a minimum.
Regular inspections of batteries for signs of gasification (swelling) or other defects such as cracking of cases and deterioration of terminations should be carried out and batteries should be relocated to a place where flammable gases cannot accumulate.
Batteries which do not expel hydrogen in the event of overcharging should be used, and battery cell monitors should be installed on each battery to ensure that the internal impedance of the battery is within acceptable limits.
Where a defect is detected, the alarm should be initiated.
