Explosions ripped through Sunrise Propane Industrial Gases on Aug. 10, 2008, lighting up the sky in northwest Toronto between Highway 401 and Downsview Park. ((Submitted by Andrew Erlich))

The deadly 2008 explosion and fire at Sunrise Propane in Toronto was traced to a gas hose leak and an accidental "mechanical failure," but the exact ignition cause may never be known, says a confidential report by the Ontario Fire Marshal's Office, obtained by CBC News.

The initial blast and subsequent explosions at the propane fuel site in the city's north end in the early morning of Aug. 10, 2008, could be heard seven kilometres away. It damaged homes, businesses and schools in the surrounding area.

An employee of Sunrise Propane, Parminder Singh Saini, 25, died in the explosion. 

The report says an illegal "tank-to-tank transfer was in progress at the time of the accident" and a propane leak resulted from a hose failure.

About six minutes before the explosion, the leaked liquid propane turned to vapour, the report says. That vapour cloud ignited, but the investigators said they don't know the exact cause.


Firefighters gather several blocks from the site of the propane depot fire. ((J.P. Moczulski/Canadian Press))

"This explosion and fire will be classified as accidental — mechanical failure," the report concludes.

The report notes that tank-to-tank or truck-to-truck transfers are both highly dangerous and illegal in Ontario. Sunrise had already been warned about the practice previously.

The report has several sections blacked out, including information on witnesses and damage to homes.

The report does make recommendations calling for improved standards for equipment and employees. Another recommendation says consideration should be given to how much propane is stored at specific sites, saying the Sunrise site was too congested. 

Finally, the report says even though Sunrise did fit standard site criteria, more consideration should have been given to whether its location so close to a residential area was appropriate.

There is a major class-action lawsuit underway against Sunrise Propane and the owners of the site.