Two catastrophic sawmill explosions that killed four people and injured dozens more originated in contained spaces in which electrical and or mechanical equipment was running, says WorkSafeBC.
The provincial agency held a conference call Monday to update its investigations into the fires and explosions at the Babine Forest Products mill in Burns Lake in January, as well as last month at Lakeland Mills Ltd. in Prince George.
"In both investigations, the ignition sources appear to have been located at the conveyor level, where electrical and or mechanical equipment was in operation in areas contained by walls and equipment. These areas are the basement or lower level of both the mills under investigation," said Jeff Dolan, director of investigation for the workers' compensation board.
Mr. Dolan stressed these are observations and no conclusions have been reached when it comes to cause and underlying factor.
"They may be coincidental, but they certainly cannot be ignored," he said.
WorkSafeBC said it directed employers' attention to the similarities as part of its commitment to provide as much information as possible to industry. It said five elements are required for an explosion: fuel, ignition, dispersion, oxygen and containment.
WorkSafeBC previously said it had removed exhibits pertaining to possible ignition sources at Babine from an area 50 feet by 50 feet. Mr. Dolan wouldn't provide a containment area size on Monday. He said WorkSafeBC didn't want to limit the scope for employers.
When asked how WorkSafeBC zeroed in on a location within the Prince George mill quicker than it did in Burns Lake, Mr. Dolan pointed to the weather.
"When Babine occurred, the weather was very different, Environment Canada telling us that it was as low as -41," he said. "As a result, all the water that was used by the fire department to suppress the fire on site froze. That was one factor the investigators didn't have to work through in Lakeland. As we're now in Week 3 of the Lakeland investigation, we were closer to Week 10 at Babine before we were able to access the area which we believe to be the ignition source."
Workers, industry experts and the media have for months pointed to the cutting of wood harvested from forests ravaged by the mountain pine beetle as a possible explanation for the explosions. The wood produces a fine, dry sawdust that is more likely to explode than the normal, wetter timber.
Earlier this month, in its first update into the Babine blast, WorkSafeBC said sawdust is one of the potential fuel sources being investigated. Natural gas and propane are also possibilities.
Like the fuel source, the ignition source remains unclear. Investigators have ruled out arson and lightning strikes (some Burns Lake residents had raised that as a possibility). WorkSafeBC said it continues to examine ignition sources such as hot surfaces and electrical components.
Possible factors in the explosion, WorkSafeBC said, include the type of wood being milled, the exhaust and ventilation systems and the cold weather.
The explosions led to an unprecedented safety crackdown at sawmills across the province. WorkSafeBC ordered more than 300 mills to remove all accumulated sawdust from their premises and ordered inspections.
The Globe and Mail reported last week that a portion of Canfor's mill in the northern town of MacKenzie was temporarily closed earlier this month because of a sawdust buildup. The closing order has since been lifted.
B.C. sawmill operators are also dealing with soaring insurance costs, because of the accidents and one underwriter's departure from the Canadian market.