High dust levels in places like sawmills can pose respiratory difficulties for workers and can also be an explosion hazard, but Al Johnson, WorkSafe BC's regional director, said Wednesday it's too early to speculate whether dust played a role in last week's conflagration at the Babine Forest Products sawmill in Burns Lake.
"Certainly, sawdust can be combustible and combustible sawdust can lead to an explosion," said Johnson. "There needs to be a source of ignition, so just having sawdust around won't spontaneously combust, if you will."
He said the investigation will take into consideration concerns about dust, gas and any possible substance or situation that could have contributed to the disaster.
Some workers reported smelling gas just before the explosion and others have said they heard a series of explosions.
The WorkSafe BC inspection report shows an officer collected 10 dust samples from the mill on Nov. 22 and Nov. 23 and submitted them for lab tests.
The results released Dec. 28 found dust levels in the basement cleanup area were more than twice the acceptable level for an eight-hour exposure.
According to the report, the limit for wood-dust exposure during an eight-hour period is 2.5 milligrams per cubic metre.
Lab results, however, showed that level hit 5.94 milligrams per cubic metre in the basement, and the mill's leadhand, a roaming job in the mill, was exposed to 4.1 milligrams per cubic metre.
Levels on the log deck were just under the acceptable limit, and the levels for the graveyard chargehand and a bin attendant were far below the acceptable limit.
"Workers in various positions in the sawmill are exposed to pine wood dust in excess of the exposure limit, which suggests that the current ventilation systems and water misters are not adequately protecting some workers," states the report.
The report, released publicly Wednesday, ordered the mill to submit a notice of compliance to WorkSafe BC by Jan. 31.
Johnson said he is not aware of WorkSafe BC receiving a response from the mill.
Hugh Davies, a University of British Columbia professor who is part of a research program that studies the safety of sawmill workers, said UBC studied dust levels at 14 B.C. sawmills about 15 years ago, and he doesn't believe the dust levels reported by WorkSafe BC were great enough to play a role in what happened at Burns Lake.
"The concentrations in the air that you would need are orders of magnitude more than what we measured and what you would anticipate finding in that mill," he said. "So you would need literally 100 probably 1,000 times as much dust."
There may have been areas, such as duct work, where dust may have collected at those levels, but Davies said it's hard to imagine dust approaching any of those levels in the general mill.
Nevertheless, Kay Teschke, a University of British Columbia professor who has also studied the safety of sawmill workers, said the levels reported in the mill's basement were "pretty dusty."
"That probably means that when you were in the basement, you could see visible dust in the air," she said.
She said wood dust can cause different respiratory hazards, noting red cedar can cause asthma in some people and hardwood dust has been know to cause nasal cancer.
Johnson said Babine Forest Products was not singled out for investigation but was one of several mills in the province's interior that underwent testing by WorkSafe BC officers.
"It just so happened that this mill was one on the list," he said.
During the Friday night fire, 19 workers were sent to hospital, including at least four in critical condition, and the remains of two workers were found earlier this week.
The National Institute for Occupational Safety and Health in the United States issued a report after a worker was killed in an Oregon sawmill explosion in 2003.
It found faulty wiring sparked a series of at least three explosions in the mill. As one cloud of dust exploded, it created another cloud that then also exploded, until ultimately, there was "one very loud, superheated explosion."
Also released Wednesday were a number of other inspection reports on the Babine Forest Products sawmill. Those reports focused on issues like safety precautions around mill equipment and road maintenance crews working around dangerous trees.
One report issued Sept. 17, 2009 noted "the plant was clean of dust, debris and was well organized."
The reports also make reference to a fire at the mill in March 2011 that was described by the company at the time in news reports as "significant." The WorkSafe BC documents note management at the mill was changed a month after the fire.
WorkSafe BC has said the investigation into that fire has fallen to the B.C. Safety Authority and the authority has said the report will not be made public until officials are satisfied it conforms to privacy laws.
Johnson said WorkSafe BC officers and the RCMP will begin their investigations once the coroner's service has completed its work.
RCMP Const. Lesley Smith said in a news release that the site is still very dangerous and the investigation could take months.
She said the removal of debris and weak structures continue to pose challenges.
"Hampton Industries and their employees continue to co-operate and assist the investigators," she said. "There is no information to date that would support allegations of criminality."
WorkSafe BC will apply whatever it learns during the investigation to the entire industry, said Johnson.
"Obviously, something went wrong here," he said.
"Obviously, we have a lot of people's lives who have been turned upside down and we need to work with them and we are working with them to provide assistance and support to get them on track as best we can at this difficult time."