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Safety Tips | Electrical safety

Charging safely

September 1, 2009

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Although it is a commonplace activity on many worksites, charging a lead-acid battery can be an extremely hazardous task. NIOSH identifies a number of associated hazards: the hydrogen gas formed while the battery is charging, the poisonous and corrosive sulfuric acid present in the battery fluid, the possibility of short circuits causing burns or explosions, and the risk of electric shock.

Safe work practices can help mitigate these hazards. NIOSH recommends the following:

  • Always switch off the battery charger before connecting or disconnecting a battery.
  • Always use insulated tools.
  • Never place tools or other conductive objects on top of the battery while it is being charged.
  • Remove metallic items such as jewelry from hands, wrists and neck, as these may cause short circuits.
  • Always disconnect the negative terminal first and the positive terminal last.
  • Be sure ventilation is always adequate to dissipate hazardous gases that form when a battery is charging.
  • Do not allow smoking in the charging area.
  • Before connecting the charger, add water to each cell until battery acid covers plates to help purge extra gas from cells. Do not overfill.
  • After charging, fill the battery to manufacturer-recommended levels. For maintenance-free batteries without removable caps, carefully follow the manufacturer’s charging instructions.
  • Most batteries are made with flame-arresting caps. Always charge batteries with caps in place, and do not pry caps off sealed batteries.

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