Fires in sawmills and other forestry product plants are a real threat. Production environments in these facilities are filled with wood, the combustible nature of which is exacerbated by large amounts of sawdust and fine wood particles in the air. Fires in such facilities have been a problem in Europe recently, with 79 sawmill fires in Germany, Austria, and Switzerland alone between 2015-17. In British Columbia, Canada, 89 fires were reported between 2001 and 2011. And in the United States, sawdust is one of several flammable materials associated with 130 reported non-house structural fires between 2010-14.
Due to the risk of fire, the National Fire Protection Agency in the U.S. has required sawmills and other facilities that handle flammable dust—such as ethanol plants—to have a dust hazard assessment (DHA) performed at their facility by September 7, 2020. The companies will need to update the assessment every five years.
While the DHA will identify specific threats to these production facilities, there are some general safety measures companies that handle flammable dust can take to reduce the risk of fire. These measures include fire suppression systems, ensuring a system for explosion protection and isolation is in place, and replacing open-air equipment such as conveyors and storage units with dust-tight alternatives.
Sources of Fire in Sawmills and Other Forest Industry Plants
Facilities that handle combustible dust are at risk for explosions and fire for obvious reasons. A spark can ignite a large fire very quickly. Sawdust, specifically, has been proven the culprit in many fires. Of the 89 sawmill fires in British Columbia, sawdust was listed as the material that initially caught fire in half the situations.
Sawmills and forest product mills hold additional threats because of the large fire load (wood) they house. Oftentimes, the structures are also made of the same combustible material. Adding to the threat is a cramped environment through which fire can spread quickly and which can be difficult for fire personnel to navigate. What’s more, these facilities are often in rural areas, where the response from firefighters is slow and, in some cases, impossible, as was the case initially in the Arizona sawmill fire.
While managers and supervisors might like to think special circumstances led to the fires, the opposite is true. According to the NFPA, 75 percent of non-house structural fires begin during normal production. Of the factors contributing to fire, the NFPA reports 45 percent of these fires begin when workers cut or weld too close to combustible material; 23 percent start due to a heat source too close to the material.
Many wood processing production machines themselves add to or are sources of risk. The Combustion Research Center for explosivity has identified more than 30 machines than could be included in an explosion protection strategy, as reported in the 2018 July/August edition of Pellet Mill Magazine (“Dissecting a DHA”). In Pellet Mill Magazine’s article, Jason Krbec, sales engineering manager for CV Technology, noted dust collectors, cyclones, weigh hoppers, fiber bins, forming heads, connecting conveyors, ducting, and bucket elevators of special concern.
“Mechanical conveyor equipment can often produce sparks or overheated elements. Milling is always an area of potential ignition source generation,” Krbec said.
Dust Hazard Assessment (DHA)
Due to these hazards, the NFPA has required companies that handle combustible dust to conduct a DHA by September 7, 2020. A DHA is an evaluation that identifies potential risks for dust explosion in equipment and compartment areas in a production facility. Its basic goals “are to evaluate the hazard, determine what safeguards exist, and identify where safeguards are needed,” said Krbec. If no risks are identified, the document becomes a comparison point for future and further risk assessment.
Decreasing Fire Risks
As it stands, facilities with explosive dust should already have a system of explosion protection and isolation in place. (See NFPA 69, Standard on Explosion Prevention Systems.) If an explosion or fire does occur, nobody wants it to spread to multiple machines or compartments. If such a system is not in place, the DHA will address it and other issues unique to your facility.
As part of your process of decreasing fire and explosive risks, you will inevitably work to control dust. Cleanliness is the best fire prevention technique you can employ. Enclosed equipment, such as Biomass Engineering & Equipment’s SMART Conveyor™, is one way to stop dust from spreading. BE&E’s SMART Containers, too, provide dust-tight storage. Considering that dust enters the air readily where the material is dumped and transferred, investing in enclosed equipment is an important strategy for addressing fire hazards.
Also, facilities handling combustible materials should have a proper fire suppression system. While most sawmills have these systems in place, older and smaller facilities might not be properly equipped. If a fire occurs, you will want to control it as fast as possible to minimize damage to your facility and machines. The cost of such a system is far less than the loss of revenue you will incur if your facility is destroyed.
For more information about DHAs, check out NFPA’s Dust Hazard Assessments PowerPoint.
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