Police say a second victim of an explosion at an industrial facility in Sarnia is now in critical condition.

Staff-Sgt. David Bonnema says the worker at the Veolia ES Canada Industrial Services Inc. plant in Sarnia has been airlifted to a hospital in London.

The explosion ripped through the industrial cleaning and maintenance services facility Saturday afternoon, sending five workers to hospital with burn injuries -- one of whom is also critically injured and transferred to London.

Bonnema says the Ontario Fire Marshal is investigating the cause of the blast, which tore a hole in the building's wall, and that the Ontario Ministry of Labour and Ministry of Environment are also at the scene.

He says no chemicals were released in the explosion.

Sarnia Fire Capt. Dan Nelles says a "small, smoldering fire" continues to burn inside the destroyed facility, but crews haven't reached it yet due to danger from the partial collapse of the roof.

"It just puffs a little smoke now and then. So we're still sitting on it, and then trying to deal with that as safely as we can," Nelles said Sunday.

A Veolia spokeperson could not immediately be reached for comment.