Friday, August 29, 2008

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


Stephan Zimmerman said...

Hazards like this one can effectively be prevented by use of a spark extinguishing system.
Do not be afraid of the mentioned costs, since such a system will be much cheaper than explosion suppression, which picks up its action after the explosion already started.
The clear advantage of a spark extinguishing system is, that it can, if applied to professional standards, take most of the dangers leading to an explosion out, without the interruption of the running pellet production.
To manage this task, a system should be required to have a wide range of manufacturing and performance standards. E.g., if a system shows the Factory Mutual Approval, the NFPA, and as well as international accepted specifications according to expert associations like ATEX Explosion Protection, it will be the right one for this application.
Even if the spark detection and extinguishing system can dependably reduce the risks of fires and explosions in the pellet industry, there will always be, depending on local circumstances, a residual risk for those occurrences. Therefore, to track the real time development of an explosion later on accurately for analysis, insights and future prevention, the spark extinguishing system must be able to operate in explosion speed as well. Those spark detection systems, proven to operate and track in milliseconds only are available in the market and have been successfully installed in the pellet production industry.

Jeffrey C. Nichols said...

Yes, of course. Combustible dust should be a major source of concern in these plants. When you are drying, grinding, conveying, and compressing wood flour (or other), you are creating the perfect storm for a combustible dust fire or deflagration. Every time you move or manipulate this product in the process you are creating combustible dust. Then all you need is an ignition source for combustion. Ignition sources are plentiful in the drying, grinding and pellitizing stages. And it is very easy to convey a spark or ember into a combustible dust cloud within the pellet cooler, dust collector, and storage bin. The small fires they are experiencing are warning signs, simply precursors to a potential larger event.

OSHA requires these plants to provide a safe working environment. Dust control and ignition control are vital. To reduce risk you must control the probability and severity of possible events. Spark detection & extinguishing systems as required by NFPA 664 (for wood processes) are the most cost effective way to reduce fires in these processes. Along with deluge and sprinkler systems, and explosion venting, these are minimum requirements for preventing most fires and deflagrations. Additional layers of protection may also be added by means of explosion suppression and isolation. Along with these prevention and protection systems, proper design and controls, housekeeping, maintenance, lockout-tagout, and hotwork procedures must be in place.

OSHA General Duty Clause, and National Emphasis Program.
NFPA: 654, 664, 61, 68, 69

Jeffrey Nichols

thomas mason said...

what about the possibility of adding a tackifier agent to the mix to suppress in effect the dust , thereby eliminating the conditions for an explosion?

we have such a product


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