Wood Flour Dust Explosion/Fire. Excellent explanation by Fire Chief Andy Mason of process materials, situations, and conditions.

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Permalink Reply by John Astad on March 31, 2010 at 12:32am

The weak link in addressing combustible dust related fires and explosions in the workplace is at the local jurisdictional level. The above example provides stakeholders an excellent example idea of how EHS professional must attempt to educate the media and fire protection professionals concerning combustible dust hazard awareness. The majority of news accounts of ComDust workplace incidents never provide the detailed information that Gary and Andy shared.

Permalink Reply by ANTONI MICKIEWICZ on March 31, 2010 at 8:13am

Another major dust related event in a process with many similar operating steps to general powder handling processes. It was interesting to read about the "ductwork explosions"; this is often forgotten when combustible dust process hazards are being assessed. Thanks for sharing, John.

Permalink Reply by Jeffrey Nichols on March 31, 2010 at 9:53am

I have protected many of these wood flour producers. This fire was likely caused by the dryer. Although many fires are also started in the grinding process.

For a wood flour composite extrusion process like this, they will typically dry wood flour to almost the combustion point, creating a highly flammable combustible dust in the process. They will typically use pneumatic conveying of the dried wood flour from the dryer. Depending on how the conveying, collection and storage systems are designed, this wood flour can also agglomerate and create build-up and stalactites within the ductwork at any joints, elbows and transitions, and also any joints or squared corners of the dust separator or collector. These stalactites and build-up can superheat in the hot air stream from the dryer, creating red hot ignition points within the ductwork and collector. Many times for humidity reasons, these dust collectors are located inside the building.

So you can see that super heated combustible dust within the dust collection or storage equipment can easily combust at many points in the process, be transported to other points in the process, and can also start to degrade and superheat within the storage bin. Without proper process and safety system design, this process is a time bomb. They have many of the same issues in the wood pellet and MDF industries - any process where they are grinding and drying wood flour.

In the process described in the article, wood flour is then mixed with other polymers, and extruded into plastic-wood decking, and other components.

Employees will often say afterward that they heard small booms or smelled smoke, but could not find the source. These are precursors to an event described in the article.

This process needs a process design and safety system design review; Fire Prevention equipment like Spark Detection and Suppression systems on all of the ductwork, and CO detection within storage bins; Fire Protection Equipment like sprinkler and deluge systems in the collectors and silos; Explosion Prevention and Protection equipment like venting and suppression in all critical collectors and storage equipment.

Permalink Reply by ANTONI MICKIEWICZ on March 31, 2010 at 10:18am

Agree with your assessment, Jeffrey.

Permalink Reply by John Astad on March 31, 2010 at 11:27am

Your welcome Antoni. Thanks Jeff for providing the excellent overview concerning layers of protection.

Permalink Reply by Jeffrey Nichols on March 31, 2010 at 12:36pm

Thank you gentlemen, always appreciate feedback from my peers. We are all in this fight together.

Permalink Reply by ANTONI MICKIEWICZ on March 31, 2010 at 2:16pm

John; this brings back to mind the OSHA hearings on the proposed ComDust regs. Any guess as to when we can expect the actually regs to be acted upon by Congress. Thanks.

Permalink Reply by John Astad on March 31, 2010 at 3:27pm

Antoni, OSHA is still holding stakeholder meetings in an attempt to acquire additional input concerning a proposed regulation. In contrast, Congress is not aggressively pursuing legislation while OSHA is in the rulemaking stages.