It was a trip to the washroom that likely saved his life.

Wayne Cleghorn went to the basement washroom moments before the April 23, 2012 explosion and fire that destroyed Lakeland Mills’ sawmill, killing Glenn Roche and Alan Little and injuring 22 others.

“It’s very likely he would not have survived the blast if he had been in his booth,” Paul Orr, WorkSafeBC’s lead investigator, told a six-man coroner’s inquest into the disaster Tuesday.

Cleghorn was the slasher operator, which is directly above where WorkSafeBC believes the first explosion originated.

Orr detailed the investigation, which included investigators from the B.C. Safety Authority, Lakeland Mills, the Prince George Fire Rescue Service, the United Steelworkers of America, and at least a couple of insurance companies and involved interviews of survivors.

Orr said their first job was to determine the area where the blast originated and, from there, try and determine what sparked it.

“One of the first targets was the large and small head rig areas,” he said. “Due to previous fires (in that area), dust in the area, and Glenn Roche was in the area at the time of the blast.”

The head rig was ruled out as was the power distribution centre which, he said, was one of the dustiest areas, and the millwright shop. Interviews of survivors helped immensely, he said, as it helped them determine the path of the blast.

One survivor, Joe Prince, who was on the main floor of the mill, said the blast came up from the basement. Others described feeling the wind of the explosion first, which, Orr said, indicated a deflagration … combustion across a surface at subsonic speeds. Others, farther away from the source, saw a fireball heading towards them and managed to duck for cover.

The blast, he said, hit the millwright’s lunchroom in the basement, and blew all four occupants into the yard.

“Pressure came from down below, seeking to get to the fuel up top,” Orr said. “The area of origin was below the slasher deck where the 6P conveyor was located.”

After determining that, he said, the job of the investigators was to determine what sparked the blast.

He said they examined the power distribution centre and while there a lot of dust and it was not up to code, there was no evidence the blast originated there. They examined lights, motors and switches, bearings and springs, but there was no evidence any of those items sparked the explosion. He added there was no evidence to suggest a static electricity charge, no evidence of any hot work, such as welding, going on at the time, and no indication anyone was smoking inside the mill.

The 6P conveyor was driven by a motor with a high-speed gear-reducer.

“The gear-reducer was in good shape,” Orr said. “But the fan had become disconnected off the main driveshaft and was lodged in a screen.”

He said the driveshaft would have continued to turn, heated up, and likely ignited dust in the air.

Electrician Donald Zwozdesky had earlier testified that he had walked by the slasher area shortly before the explosion and did not hear, or smell, anything out of the ordinary.

“It was extremely noisy (with other equipment operating),” Orr said. “As soon as he walked by, it could have come off … it would take less than two minutes to reach 577 degrees Celsius.”

Orr added the actual explosion might not have occurred right at the gear-reducer, but in the dust-laden air above it.

The inquest, which started March 2, will continue for at least another week.