It happened at a plant that recycles hazardous materials.
Firefighters say they received several calls to 911 after the incident at the Newalta plant on Bélanger Street on Montreal's South Shore.
The 12:30 p.m. explosion happened after water was added to some chemicals that were supposed to have been neutralized.
The incident took place in a pit where the chemicals are neutralized.
No injuries were reported.
Firefighters say Environment Quebec has given the all-clear that there is no risk to the public.