WorkSafeBC says it could be months before its investigation into an explosion and fire at a wood products mill in Quesnel is complete.

No one was injured in the blast, which occurred Wednesday at about 5:30 p.m. A cause has not been determined and the company that owns the WestPine MDF mill says it’s unclear when it could reopen.

The explosion immediately evoked memories of two fatal blasts at B.C. mills in 2012 that killed four workers and injured more than 40 others. Those explosions were triggered by dangerous levels of combustible sawdust.

Al Johnson, WorkSafeBC’s vice-president of prevention services, said Thursday the agency inspected the Quesnel mill about 10 times since 2012. He said it also conducted another five to seven consultative visits.

Mr. Johnson said orders were written against the mill over two elements of its combustible dust program. However, he said the company complied both times and has an active dust-management plan. He also stressed that the investigation into the explosion has just begun.

“We thought that they could do more thorough inspections for combustible dust. So they were doing inspections, but we thought that there were a few areas that they could inspect more regularly or more thoroughly, that sort of thing. That was one area where we had written for them to make improvements,” Mr. Johnson said in an interview.

He said WorkSafeBC also ordered the mill to fix what he described as “explosion doors.”

“In the case of an explosion, these doors blow off and release the explosion directionally, if you will, like a release valve. We saw in late 2012 or early 2013 that some of these explosion doors or release valves were aimed at areas that workers might occupy,” he said, adding the mill rectified the issue.

Mr. Johnson said the explosion and fire occurred in an area that includes dust collection. He said that could mean sawdust played a role, though it’s too early to tell.

WestPine MDF, which produces fibreboard, is owned by lumber producer West Fraser.

Tara Knight, a West Fraser spokeswoman, said in an e-mail that the mill’s employees “acted quickly, safety procedures were engaged and the mill was evacuated. Thankfully, no one was injured.”

Ms. Knight said the fire has caused damage, and the facility “will not be operational for a period of time.” She could not say how long the WestPine mill, which employs about 100 people, would remain closed.

She did not respond to questions about the WorkSafeBC orders. She also did not say how many employees were on site at the time of the explosion.

Mr. Johnson said he believed about 30 employees were at the mill when the blast occurred, as a shift change was under way.

Quesnel has a population of about 10,000 people and is located about 120 kilometres south of Prince George. Its mayor, Bob Simpson, called the explosion “significant,” and said he was told the blast was felt at another wood-products business that is located down the street.

Mr. Simpson said WestPine MDF is a “critical part of our future” and he was not aware of any issues at the mill in the past. He said West Fraser did its due diligence when it comes to combustible sawdust after the explosions in Burns Lake and Prince George in 2012. West Fraser’s website says it enhanced its housekeeping procedures and training, adding new equipment, ventilation and collection systems.

Mr. Johnson said the RCMP turned the scene over to WorkSafeBC on Thursday morning.

WorkSafeBC was heavily criticized after its investigations into the 2012 mill explosions failed to produce charges. The Crown said WorkSafeBC failed to warn the mills involved about the dangers of combustible sawdust and then conducted sloppy investigations, with some of its collected evidence likely to be deemed inadmissible.

Mr. Johnson said WorkSafeBC has since “strengthened” its investigative process. The agency also enhanced its inspection regime and imposed tougher regulations around combustible dust after the 2012 explosions.