British Columbia Combustible Dust Hazards Awareness Workshops

Workplace combustible dust related fires and explosions occur with alarming regularity in the global grain, mining, forestry and manufacturing sectors. Although the majority of incidents do not result in fatalities, injuries, or property damage, historically many of these non-consequential incidents have been precursors to catastrophic events.

The complex topic of combustible dust hazards recently came to the forefront in British Columbia when WorkSafeBC issued a directive order for all sawmills to conduct a comprehensive risk assessment resulting in an effective dust control program. 

In conjunction with FireWise Consulting Ltd., John Astad, Director and Research Analyst from the Combustible Dust Policy Institute (CDPI) will be presenting a series of one day Combustible Dust Hazards Awareness Workshops throughout British Columbia. The goal of the CDPI is to minimize the severity and reduce the occurrence of combustible dust related fires and explosions through research of combustible dust related incidents. For more information on the CDPI  view brochure here.

The Combustible Dust Hazards Awareness Workshop will provide stakeholders with the knowledge to minimize the probability of occurrence and severity of consequence of future combustible dust related incidents. In addition the workshop will assist stakeholders in developing a comprehensive dust control program as noted in the revised WorkSafeBC OHS Guidelines. Key aspects of the workshop are identifying, evaluating, and controlling combustible dust hazards in addition to providing guidance in conducting facility inspections and risk assessments.

Facility owners and managers concerns in reducing the probability of a catastrophic secondary dust explosion include good housekeeping, employee training, maintenance, and management of ignition sources. Prevention of future incidents begins with awareness of the problem and a robust hazard mitigation framework which consists of a facility risk assessment, written combustible dust program, and hazard communication.

This combustible dust workshop will discuss the importance of these topics and more in addition to the BC Fire Code referencing the National Fire Protection Association (NFPA) combustible dust standards. NFPA best industry practices include engineering controls for deflagration suppression, deflagration isolation, and explosion venting in the mitigation of combustible dust explosions. The NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities provides excellent guidance in this area and is a key resource for the workshop.  Click here for a detailed course outline.

COURSE DETAILS


June 11, 2012  Prince George

June 12, 2012  Williams Lake

June 14, 2012  Vernon

June 18, 2012  Port Alberni

June 19, 2012 Township of Langley


Time: 0800 to 1600
Registration Fee: $149.00 plus tax (includes lunch)

Register on-line by clicking on the FireWise Consulting Registrations link or register by mail, e-mail or fax by printing and filling out the form at the following link: Registration Form

Mystery of Airborne Combustible Dust Concentrations

So at what threshold should airborne concentrations of combustible dust trigger a concern for combustible dust related fires and explosions? Mention of industrial hygiene issues is reminiscent of the 2011 Foxconn catastrophic dust explosion in China, where initially workers complained of high levels of aluminum dust respiratory exposure during polishing operations.

Confusion still exists according to media accounts of the high airborne dust levels discovered in the WorkSafeBC inspections at the British Columbia, Canada facility a few weeks prior to Fridays catastrophic explosion. These high levels were for airborne concentrations in regards to respiratory exposure not combustible dust explosive concentration levels. Explosive airborne dust concentrations would require approximately 30,000 times more than the concentration found in the inspections depending on moisture content and particle size. For example, the highest airborne concentration was 5.9 milligrams/cubic meter, which was 2 times over the acceptable threshold of 2.5 milligrams/cubic meter, according to WorkSafeBC inspection reports released to the media.

To put this into perspective we must ask what exactly is 2.5 milligrams? Well if you put a pesky mosquito on a laboratory scale that would be your answer. Of course mosquitoes are not processed in sawmills, lumber is. But this does provide a general idea of 2.5 milligrams of mass. Alternately, using the mass of wooden toothpick provides better idea of how high suspended dust concentrations would be in one cubic meter of volume, such as the volume of a huge glass fish tank.

So here is the math. On an average, a wooden toothpick weighs approx. 100 milligrams on a laboratory scale. Now dissect the toothpick into 40 parts, which would equate to each of the forty toothpick parts weighing the same as a 2.5 milligram mosquito.

Now take three of those individual 2.5 milligram toothpick parts and grind them up to the consistency of sawdust. This would provide about total 7.5 milligrams of mass, a little over the 5.9 milligrams of the high airborne dust level that inspectors found in a cubic meter during the prior facility inspection.

So one must ask, is approx. 1/10 of wooden toothpick sawdust explosive in a cubic meter volume of air? The basis of a combustible dust explosive atmosphere is that the minimum explosive concentration (MEC) must be sufficient to have ignition while in suspension when combined with the fire triangle.Think of MEC analogous to the lower flammable/explosive level LFL/LEL of a flammable vapor or gas.

In contrast a minimum explosive concentration (MEC) of sawdust depending on moisture content and particle size is approximately 300 wooden toothpicks, weighing approximately 30 grams or 30 grams/cubic meter.Hope this helps obtaining insight in the difference between airborne respiratory hazards (milligrams) in contrast to airborne explosive concentrations (grams) of combustible dust. Of extreme importance is to ensure horizontal layers of dusts do not become airborne where a safe respiratory concentration can escalate rapidly into a minimum explosive concentration (MEC). Good housekeeping is key in this respect.

Wood Pellet Dust Fire Non-Issue?

A New England wood pellet manufacturer experiences a second dust related fire in two weeks. In the prior fire, an ignition source from the pellet mill caught pellets on fire and subsequently the conveyor feeding wood pellets to the outside silo also caught fire. The fire in the silo smoldered for over a day.

Last month a similar combustible dust related fire at a wood pellet plant occurred at Westwood Fibre Products in Kelowna, British Columbia in which the conveyors were ablaze with wood pellets. The fire chief who responded to the Westwood fire seems to concur regarding a non-issue with such fires when he stated to the news reporter that, 'of course being a wood fibre plant with dust and sawdust it's not uncommon to have small fires in these types of operations."

From viewing the above picture, it wasn’t much of a non-issue, when last year in Monticello, WI, Risley Pellet Solutions exploded, injuring two workers. Over the last six weeks in Marion, PA., AJ Stoves and Pellets, has experienced hopper explosions twice due to combustible dust. Since there were no fatalities or three or more injuries, it's like the tree fell in the forest, yet no one heard it. So did the tree fall?

It's highly advisable that all wood pellet manufacturers install spark detection and extinguishment systems adjacent to their conveyors. If that is to expensive, then at least shutdown the conveyor at the first sign of fire so burning pellets will not enter the adjacent bulk storage unit.

As a matter of any fire occurring where combustible particulate solids are handled, you be the judge of whether it is a non-issue or not. Hopefully the prior examples will add light to the subject in whether preventative and mitigative measures should be implemented according the the NFPA combustible dust standards.

Recent Wood Pellet Mfg. Explosions and Fires

8/22/08-AJ Stoves & Pellets- dust explosion/hopper
8/15/08 Corinth Wood Pellets- fire/sawdust dryer
8/10/08 New England Wood Pellets- fire/pellet mill
7/15/08-AJ Stoves & Pellets- dust explosion/hopper
5/20/08 Corinth Wood Pellets- fire/exterior burner

Photo Credit: Monticello Fire & Rescue