A little more than three months after two men were killed in a sawmill explosion in Burns Lake, WorkSafe BC says that dust levels and processing of low quality beetle-killed wood are both possible factors in the blast.

The workplace safety body released an update on its investigation into the fatal blaze on Wednesday and said that since the Jan. 20 incident, investigators have interviewed more than 80 witnesses, including people who came forward as early as last week. While the probe is not yet complete, WorkSafe BC says it released the update to clear up any "misinformation" spreading in the wake of a second fatal sawmill blast that happened last week in Prince George.

Apart from sawdust accumulation and the type of wood being milled, the team says that production levels, ventilation and recent cold temperatures reaching as low as -41 C at the Babine Forest Products mill in Burns Lake are also being considered as possible factors.

Investigators have already ruled out hot oil, hydraulic and gear oil, oxygen and acetylene as the fuel sources for the explosion, and say they have not found any evidence of arson or a lightning strike.

At the same time, WorkSafe BC says it's impossible to eliminate open flames like welding torches, high-temperature metal halide lights or static electricity as factors in the blaze. Investigators are exploring a number of different possible ignition sources, including surface heat from motors and electrical sources.

Since the April 23 explosion at Lakelands Sawmill in Prince George, dust levels at mills across B.C. have been under scrutiny, and WorkSafe BC ordered operators to survey the dust in their facilities, clean it up and develop a plan to keep it under control.

WorkSafe BC inspection reports showed concerns over dust levels in Burns Lake leading up to the blast, and dust is mentioned twice in five years' worth of Lakelands inspection reports. Some forestry experts have speculated that processing older wood killed by the mountain pine beetle could be creating finer, more combustible dust.

About 70 per cent of the wood milled at Lakelands was killed by pine beetle. Investigators have not determined what caused the blast at that mill, but have ruled out criminal involvement.