MSHA said users of cap lamps powered by lead-acid batteries need to be aware of the possibility of explosions involving the batteries. Incidents have shown lead-acid batteries experiencing an ignition of hydrogen gas that has ruptured the battery case.

While all lead-acid batteries produce hydrogen when charging, they produce even more when older. MSHA said an older lead-acid battery will begin to produce hydrogen gas in larger amounts and earlier in the recharging cycle.

The agency pointed out the amount of water consumed by the battery during charging was a non-quantitative guide to gas generation – the more water that is used, the more hydrogen gas that is generated.

“An older lead-acid battery or one that has not been maintained properly will consume more water. As the water is consumed, the plates will be exposed causing a possible internal source of ignition from a spark," MSHA said.

The agency did point out that the ignition source does not have to be internal.

“The battery will be releasing hydrogen gas that can be ignited from any external spark or heat source,” MSHA said.

“If the hydrogen gas is ignited, the battery case can rupture with the possibility of injury to the user or a bystander from shrapnel from the case or from the acid ejected from the battery."

The key to minimising risk of this happening is a good maintenance program.

MSHA said indicators to look for that can lead to the build-up of hydrogen gas and possible internal sparking include an unusual consumption of water in the battery, and/or a charging indicator that shows the current is not decreasing into “trickle charge” (indicator light that stays on continuously or meter that never shows the charging current decrease).

The following practices were recommended by manufacturers of lead-acid cap lamp batteries:

• Leave battery on charger when not in use;
• Check electrolyte level weekly and add distilled water as necessary; and
• Add water only when the battery is fully charged.