A forklift battery that kept charging after it was fully charged caused a Canadian plant to be evacuated this month.

Workers next to EM Plastics, in St John's, Newfoundland, noticed a rotten egg smell and notified the fire department, the Canadian Occupational Health & Safety News reported.

St John's Fire Department superintendent Don Barnes said the hydrogen level in the plant was found to be 4,200 parts per million (ppm), 10 per cent of Canada's lower explosive limit for hydrogen (41,000ppm).

An Occupational Health & Safety (OHS) spokesperson said the battery overheated and produced excess gases. The cause of the malfunction was being investigated.

The OHS ordered EM Plastics to buy a new battery and charger, and develop safe work procedures for battery charging.