Over the years I have helped protect many of these wood flour producers.
This fire was likely caused by the dryer.
Although many are also started in the grinding process.
For a wood flour composite extrusion process like this,
they will typically dry wood flour to just below combustion
point, creating a highly flammable combustible material and dust in the process.
They will typically use pneumatic
conveying of the dried wood flour from the dryer to the process.
Depending on how the conveying, collection and storage systems
are designed, this wood flour can also agglomerate and create
stalactites and material build-up within the ductwork at any joints, elbows and transitions,
and also any joints or corners of the dust separator or collector.
These stalactites can super heat 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.
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 super heat 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.
Plants like this need process design and safety system design
review; Fire Prevention equipment like Spark Detection and
Suppression systems on all of the ductwork, CO detection
within storage bins; Fire Protection Equipment like sprinkler and
deluge systems in the collectors and silos; and Explosion Protection equipment like venting and suppression in all critical collectors and storage equipment.
All of the process and safety systems must also meet current standards such as NFPA 664 in this case.
Factory fire causes $350000 damage Wilmington News Journal, OH
The presence of combustible dust was a concern for firefighters, he said. “The dust, as with grain bins, can make for an explosive situation. ...