Firefighters work at the scene of a gas explosion at Sunrise Propane in Toronto in the early morning of Aug. 10. The company exhibited a 'lack of safety culture,' according to Ontario's safety regulator for fuels. (Angela Deluce/Canadian Press)

Almost two weeks after a gas explosion rocked northern Toronto, leaving two people dead, a possible cause of the blast has emerged.

The Technical Standards and Safety Authority, Ontario's independent safety regulator for fuels, released a statement on its website on Thursday saying that just before the Sunrise Propane Industrial Gases plant in Toronto's Downsview area blew up, a truck driver was illegally transferring propane from one truck to another.

The statement says in part that, "prior to the fire and explosion, a truck driver at the Murray Road facility was engaged in a truck-to-truck propane transfer. The practice of transferring propane from one truck to another is prohibited in Ontario. The investigation further determined that the prohibited unsafe practice of transferring propane product from one truck to another was a frequent and routine operating practice at the facility."

Direct truck-to-truck propane transfers are illegal because they increase the risk of a gas leak or a fire.

The safety agency also says that in November 2006, Sunrise Propane was warned that it showed a "lack of safety culture or commitment" by not putting an end to the truck-to-truck transfers at the company's facilities.

The TSSA sent out an order on Thursday suspending the operating licences for three Sunrise Propane sites: the 54 Murray Rd. facility in Toronto, where the explosion occurred in the early hours on Aug. 10; 1201 Dundas St. E. in Toronto; and 3171 Derry Rd. E. in Mississauga.

"This action results in the immediate shutdown of the propane filling activities at the two remaining sites," the statement says.

"This decision was based on a thorough review of the information currently available and the immediate nature of the potential hazards associated with operations at those particular sites," said John Marshall, director of TSSA's fuels safety program, in a news release.

Two deaths were connected to the explosion at the Murray Road propane facility.

An unidentified body was found at the site. It is believed the body may be that of Parminder Saini, an employee who was working at the plant at the time of the explosion.

Toronto firefighter Bob Leek also died at the scene.

The City of Toronto said the $1.5-million cleanup of the explosion site and surrounding neighbourhood should be complete late Friday, with a final inspection on Saturday. The area was contaminated with asbestos.