By Jamison J. Scott
As soon as a floor sander touches wood, the composition of the wood changes, and fine wood dust, also known as “wood flour,” is created. Wood flour in a large enough concentration in an enclosed area can become the source of a combustible dust explosion if an ignition source from a spark is introduced. This spark can originate from anything, including an overheating motor on a floor sander, to an electrical shortage within the enclosed environment.
According to the Occupational Safety and Health Administration (OSHA), combustible dusts “are fine particles that present an explosion hazard when suspended in air in certain conditions.” “Certain conditions” refer to two parameters that differentiate a fire triangle from an explosion pentagon; they are dispersion and confinement. A potentially combustible wood particle additionally is defined by size, shape, age, moisture content, and other factors. If there is any doubt of combustibility, the dust must be sent to a certified facility to be tested. National Fire Protection Association (NFPA) 652 states, “To determine if the dust can present an explosion hazard, the simplest test that can be performed is known as the ‘go/no go’ test ‘yes, it blows up, or no, it doesn’t’ according to ASTM E-1226 Standard Test Method for Explosibility of Dust Clouds.” Additional tests include Minimum Ignition Energy (MIE) test ASTM E-2019, and Explosion Severity Test (KSt and PMAX) ASTM E-1226. Testing prices range from approximately $350-$1,300, up to $3,850 or more for a full OSHA National Emphasis Programs (NEP) Package.
There are various organizations that provide guidance on combustible dust, they include: OSHA, NFPA, and FM Global, representing the insurance industry. Additionally, the Authority Having Jurisdiction (AHJ), which can be anyone from a fire marshall, building inspector, or any other local, state, or federal agency, has potential oversight of your jobsite or facility.
While OSHA currently does not have a combustible dust regulation, they have been exploring the possibility of regulation since 2009, when they first issued the Advanced Notice of Proposed Rule Making (ANPRM). In 2013, OSHA addressed combustible dust by incorporating it into an updated Hazard Communication Standard, where according to OSHA, combustible dust is noted as a “hazardous chemical.” That same year, OSHA also created “Precautions for Firefighters to Prevent Dust Explosions. OSHA QuickCard, Publication 3674” and “Firefighting Precautions at Facilities with Combustible Dust. OSHA Publication 3644.” While nothing has happened during the last few years, as it was placed on the back burner by the prior administration, I have a strong suspicion the new administration will revisit the importance of this possible regulation in the near future.
NFPA is an “International Codes and Standards Organization” that creates voluntary consensus standards. According to OSHA, “These standards are not OSHA regulations. However, they do provide guidance from their originating organizations related to worker protection. In some cases, they may be mandated by state or local governments, or individual companies.”
There are several relevant NFPA standards related to combustible dust, a few of the most relevant to wood-related industries include, but are not limited to:
NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. NFPA states, “This standard presents safety measures to prevent and mitigate fires and dust explosions in facilities that handle combustible particulate solids, which includes combustible dusts, fibers, flocks, flakes, chips, and chunks.”
NFPA 664: Standard for the Prevention of Fires and Explosions on Wood Processing and Woodworking Facilities. NFPA describes, “This standard provides requirements for fire and explosion prevention and protection of industrial, commercial, or institutional facilities that process wood or manufacture wood products in order to protect life, property, and mission continuity.”
NFPA 652: Standard for the Fundamentals of Combustible Dusts. According to NFPA, “This standard shall provide the basic principles of and requirements for identifying and managing the fire and explosion hazards of combustible dusts and particulate solids.”
FM Global has a data sheet available called 7-76 Prevention and Mitigation of Combustible Dust. This data sheet describes recommended preventive measures to reduce the frequency of combustible dust explosions, and protection features to minimize damage from a combustible dust explosion.
Referring to various resources such as OSHA, NFPA, and FM Global are helpful in understanding and addressing mitigation of combustible dust. However, one of the first steps is simply housekeeping. If you can see dust, don’t ignore it. If underlying surface colors are not readily discernible, this warrants immediate cleaning of the area. Flat surfaces are detrimental, as they are collection zones for dust. Ensure areas such as rectangular HVAC ducting, overhead beams, electrical cable trays, and areas above suspended ceilings all are inspected for fugitive dust as part of housekeeping. Finally, addressing the source(s) of the dust and properly addressing them will prevent build-up of fugitive dust.
Worker training is very important. Have workers been trained and do they understand the hazards of combustible dust? Explosions can be prevented. In one situation, employees were trying to unclog a metal dust collector with a metal rod, which created a spark upon contact, creating an explosion. “Safe work habits are developed and do not occur naturally,” as noted in NFPA 652.
If you deal with wood dust, you need to determine if it is combustible dust, and you need to be aware of the situation and determine the severity to you, your staff, your facility, and your customers.
Jamison J. Scott serves as Executive Vice President of Air Handling Systems, a third-generation family-owned business in Woodbridge, Connecticut. He can be reached at email@example.com or 203.389.9595.
I have always known that in wood processing plants this is a risky issue. Specially with static electricity and air handling ducting for dust extraction.
I think this video is quite informational also.
( https://www.youtube.com/watch?v=70fZqHsEdMo ).
In our trade particularly sparks from hitting nails can cause smoldering fires, in that case we talk about combustible, only when fine wood dust is suspended in air does it become an explosive risk as I always understood.