The sawdust from green wood is just as likely to ignite as the sawdust from dead pine beetle trees, according to WorkSafeBC officials investigating the fatal explosions and fires at Babine Forest Products and Lakeland Mills.
The officials stressed, however, that wood dust is still not known to have caused any part of those incidents.
The explosive properties of green wood dust were discovered during background testing by a lab helping with the Babine/Lakeland investigations.
"If there is one mill out there that feels they are exempt [from province-wide cleanup orders] because they are not milling beetle-kill wood, that is who we are communicating to today," said Jeff Dolan, director of investigations for the workplace safety agency. "We were confident beetle-kill wood is explosive. All dust under, certain circumstances, also has that volatility."
He said that the U.S. lab concluded that green wood with a moisture content below five per cent and with particle sizes less than 75 micrometres was just as dangerous, when combined with other explosion factors, as the long-dead pines being milled heavily around the region.
"Dust with this moisture content and particle size is found on elevated surfaces such as rafters, beams, inside dust collectors, and on the surface of air separation systems as well as in hot dry environments such as process equipment and light covers," said Dolan.
Not long after the incident at Lakeland Mills in Prince George on April 23 and the earlier one at Babine in Burns Lake on Jan. 20, WorkSafeBC issued a blanket directive for all 173 B.C. sawmills to clean up the wood dust inside their milling rooms and keep it clean. As of Thursday, 12 of them were not in full compliance-- reasons and locations were undisclosed -- although WorkSafeBC's vice president of corporate services Roberta Ellis said none were under shutdown orders due to imminent danger.
"There was certainly a lot of speculation on beetle-kill wood being the ignition source [for Babine and/or Lakeland]. It is import for operators processing green wood to not feel complacent," Ellis said. "We were very clear when we began the inspection process that the milling of green wood or beetle-kill wood was irrelevant. We were not at all confused about that issue and I don't think the mills were, but we want there to be no complacency. Whether it is beetle-kill or green, the directives are the same."
The specific wood profile of Babine's and Lakeland's sawing operations are known to investigators, said Dolan, so that helps the forensic process. Dust is a suspected factor in both blasts, although propane and natural gas is also being considered for the Babine incident and gas sources at the Lakeland site are also being examined.
Some forensic results were already back from the lab, he said, but interpreting the data was a complex process and that part of the investigation was still underway.
Dolan said cold weather was thought to be perhaps a factor in one or both blasts so he was hopeful the investigations would be complete before cold weather set in again, although he also clarified that investigative shortcuts would not be taken just to hit an arbitrary deadline.