Two people suffered serious burns in an explosion at a business in Leduc, Alta., on Tuesday morning.
RCMP said the injured employees work for Clean Harbors, an industrial services and hazardous waste business.
Brookes Merritt with Occupational Health and Safety said something went wrong when the two men were flushing out a tanker trailer unit in a wash bay.
"Essentially the procedure is to use a power washer to flush out the inside of a tanker trailer unit which may have been in this case, a petrochemical product," said Merritt.
"There might have been some kind of ignition. We don't know what went wrong. OHS is investigation along with the Leduc fire department."
Merritt said the men were 28 and 49 years old and were taken to Edmonton's University Hospital.
Company officials were not immediately available for comment.