Effective September 2015, the NFPA 652 Standard outlines the requirements for controlling combustible dust hazards. The Standard specifies guidelines on dust combustibility and emphasizes the importance of fire protection and explosion prevention. It states that within three years, starting from October 2015, a Dust Hazard Analysis (DHA) must be performed by all enterprises that generate combustible dusts. It is also good to know the difference between NFPA 652 and NFPA 654 standards: the first one focuses on combustible dust hazards, the second one - on explosion protection in chemical processing facilities.
Combustible dust explosion hazards exist in a variety of industries including:
- Agriculture, fertilizer, grain, tobacco, food processing (for example, candy, sugar, spice, starch, flour)
- Rubber, tire manufacturing
- Wood and paper processing facilities, furniture, textiles, dyes
- Chemical processing, pesticides, pharmaceuticals
- Plastics and recycling operations
- Fossil fuel power generation (coal)
- Metal processing (aluminum, chromium, iron, magnesium, and zinc) and welding
In general, about 70% of dusts are explosive. In addition, non-explosive materials (sand or silica, for example) could become explosive when mixed with other explosive materials (such as organic or metal dust) in sufficient concentration.
Why Do Explosions Happen?
The five factors - oxygen, heat, fuel, dispersion, and confinement - are known as the “Dust Explosion Pentagon”. A rapid combustion of dust particles is more likely to happen in a closed area where their concentration in the air is the highest. Keep in mind that secondary explosions could be even more dangerous than the initial ones: they claimed many lives of workers who were not aware of this danger. Why do secondary explosions occur? Because a primary explosion may release more accumulated dust into the air, or may damage a containment system (such as a vessel or a duct), which may cause multiple secondary explosions.
How to Prevent Catastrophic Explosions
OSHA recommends identifying factors that may contribute to an explosion and completing a thorough hazard assessment of all materials handled, all operations conducted (including by-products), all hidden spaces, and all potential ignition sources.
How to Comply with Combustible Dust Standard NFPA 652
The Standard dictates the following 10-step action plan that you need to implement in order to comply:
- Detect the combustibility and the explosibility of the materials being handled
- Identify fire, flash fire, and explosion hazards
- Manage these hazards: considerations must be given to the safety of building and equipment design, house-keeping, PPE, dust control, explosion prevention, protection, isolation, and fire protection.
- Educate all employees about the hazards and train them on protective measures
- Improve housekeeping procedures: do not clean with compressed air
- Use effective dust collection systems
- Use venting systems that comply with NFPA 68
- Direct exhaust air outside
- All central vacuum systems must be equipped with attachments made of static dissipative material, and all vacuum hoses must be grounded
- Develop MOC (Management of Change) procedures to be implemented prior to any changes to materials, equipment, technology, or work tasks.
How to Protect Workers: Explosion Prevention and Proper PPE
Unfortunately, combustible dust fires and explosions continue to occur on a regular basis. For example, 14 workers were killed in a sugar dust explosion in Georgia in 2008, and 3 workers were killed in a titanium dust explosion in West Virginia in 2010.
When properly designed, installed and maintained, explosion prevention systems protect well from the explosion hazards posed by combustible dusts. However, these systems provide little protection for the employees being exposed to combustible dust flash fires. Some employers tend to focus on wearing simple PPE (safety glasses, hearing protection, gloves) that only protects workers from easily recognized hazards. OSHA’s Personal Protective Equipment Standard (29 CFR 1910.132(d)(1)) requires employers to “assess the workplace to determine if hazards are present, or are likely to be present, which necessitate the use of PPE.” Often overlooked, Flame-resistant garments (FRGs) and ARC Flash Clothing can help protect employees from thermal and other hazards associated with combustible dust.
A significant portion of industrial explosions and fires are attributed to static electricity: fine dust in grain elevators has been ignited by static electric sparks, coal dust explosions happen in coal mines, and explosions in wood-working facilities have been reported every year. Preventing these explosions is possible by the elimination of static electricity with the help of grounding devices. Heavy-duty grounding clamps and static grounding cable reels from Stewart R. Browne are built for grounding in various industrial applications. These products are designed to prevent static build-up and control static charges in hazardous environments where equipment may be surrounded by dust or flammable liquids.
Additional Resources:
Read our previous blog posts on Arc Flash Clothing and Safety.
Download Combustible Dust poster: osha.gov
Check out OSHA website: Hazard Communication Guidance for Combustible Dusts
If you have questions or would like help selecting the right PPE, please give us a call at 1-800-829-9580, or visit us online at pksafety.com.