After more than 30 years in the field and a continued interest long after retirement, the most important thing Dr. Robert Schoeff has learned about dust explosions can be summed up in one basic sentence.
"All organic material, if it's in a right condition, right situation, can be ignited into combustion," he said.
At 90 years old, the Kansas-based retiree has an overarching insight into the development of standards that were adopted by regulatory agencies and are still used today around the world when it comes to combustible dust.
Regulations regarding dust have come onto the provincial radar in a large way in the wake of two fatal sawmill mill fires this year in Prince George and in Burns Lake.
While investigations into both the Jan. 20 Babine Forest Products explosion and the April 23 Lakeland Mills blast are ongoing, a possible culprit is the dust generated by the pine-beetle killed timber both mills were processing.
Following the Prince George incident, WorkSafeBC issued orders to mills across B.C. to carry out a thorough risk assessment on combustible dust hazards and to develop a dust control program.
On Friday, WorkSafeBC released an update on the status of those orders. One hundred and seventy six locations received orders and 108 have received follow up visits with the vast majority still working towards compliance.
The science behind how dust can lead to an explosion comes down to two conditions, Shoeff explained.
"Firstly, dust must be in suspension, in a dust cloud - not just laying on the floor. Number two, it must also be a minimum concentration and particle size is very critical with that."
When Schoeff got into the dust explosion field, focusing mainly on those in the agricultural industry and grain elevators, it was from a standpoint of trying to learn why it was happening and how it could be prevented.
The danger posed by combustible dust is two-fold, in the form of a primary and secondary explosion.
The initial explosion creates a vibration to suspend a lot of dust in a room. If not properly contained, that can trigger a second blast.
Determining how dangerous the dust is can be done through a series of tests, one of which is to measure the particle size of the dust.
"If the particle size distribution is towards the smaller particle sizes, than you are in a much riskier environment," said Ali Rangwala, an associate professor at the Worcester Polytechnic Institute's department of fire protection engineering in Worcester, Mass. There are also tests to determine the explosive strength of a given material and the minimum concentration required to explode.
A series of explosions in American mills in the 1970s got the attention of workers and industry. By 1987, the Occupational Safety and Health Administration (OSHA) set out a recommended standard that limits dust accumulation to one-eighth of an inch. That standard is listed in the WorkSafeBC order to employers.
"That standard was to prevent the secondary explosion," Schoeff said. "It was up to good housekeeping to make sure there wasn't that one-eighth inch or more and it was already that much at many of the facilities that accumulated on ledges, walls, spouts and the floor itself. If there was a secondary explosion, that typically did the most damage."
But this standard may be out of date.
"Many of these standards are designed specifically to address a certain kind of dust that were around back then, but if you compare that class of dust to what we have right now, it's completely different," said Rangwala, who has been in the field for the last five years. "So if you deal with wood dust, the wood dust that was generated 20, 30, 40 years ago is completely different from the wood dust that is generated by a modern sawmill."
The question of changing the one-eighth-inch standard came up at a recent OSHA technical group panel that Rangwala took part in.
"Because, after all, you must remember, it's a number and that number will change dramatically based on the environmental conditions and the type of dust. So what number do you choose?" he said of the discussion. "There definitely will be certain cases where the dust will be so hazardous that it will not be enough. And there will be certain cases where that number will just be overkill."
"The standard preventative measure is recognizing what happens," said Schoeff. "You try and minimize the dust problem in the handling systems."
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