June 30, 2020 By PJ Boyd
Industrial facilities such as sawmills and pellet plants handle combustible particulate material that can become hazardous to workers. In many cases, the dust produced poses a risk of fire and explosion. To help prevent these risks becoming a reality, the National Fire Protection Association (NFPA) released NFPA 652: Standard on the Fundamentals of Combustible Dust in 2015.
The latest version of NFPA 652, published in 2019, requires that existing wood and biomass facilities adhering to the standard complete a Dust Hazard Analysis (DHA) by Sept. 7, 2020 and show reasonable progress in completing DHAs each year prior to the deadline.
To better understand what is required to comply with NFPA 652, Canadian Forest Industries and Canadian Biomass magazines hosted a free one-hour webinar on June 25, as part of our fourth annual Dust Safety Week. More than 120 attendees tuned in to hear Francis Petit, dust collection specialist with VETS Sheet Metal, and Jeramy Slaunwhite, a specialist in combustible dust explosion safety and NFPA standards and senior explosion safety engineer at Rembe North America, present an in-depth look at NFPA 652, a step-by-step explanation of what needs to be included in a DHA and how to apply it to facilities. They also shared some case studies and answered attendees’ questions.
“The NFPA is a standard, not a code, in the industry. And even though it is a standard, it may or may not be adopted by your local authority having jurisdiction. However, it remains the minimum acceptable industry best guidelines [and] it is definitely the gold standard to follow in North America,” Petit clarified at the beginning of the webinar.
What is a DHA?
As part of the NFPA 652 standard compliance process, industries that handle combustible particulate material (dust) are required to conduct a DHA. Essentially, owners of facilities that produce dust are required to address and manage all hazards associated with the production of that material. In doing so, the owner protects workers from potential dust hazards such as fires, deflagration and explosions. A DHA also acts as a documented record of awareness that the owner has identified the dust hazards and their plan to manage the risks.
“The owner is responsible for implementing and managing a system to ensure the facility, process and structure is designed, constructed and maintained […] to limit or prevent injury and keep people safe from the potential of fire or explosion of dust,” Petit explained.
DHAs, Petit said, need to be completed whenever a facility changes its operating process. They are not a one-time process that only need to be updated every five years.
Why is a DHA needed?
A study conducted by FM Global titled, “Combustible Dust Loses,” found that in industries handling and producing combustible particulate materials, woodworking facilities accounted for nearly 40 per cent of incidents related to dust fires or explosions.
“This is why different standards such as the NFPA standard have been created to come up with solutions to reduce these risks,” Petit said.
A DHA is designed to eliminate downtime due to fires or explosions, protect workers, the facility, and first responders, and comply with the Authority Having Jurisdiction. DHAs also help facilities identify the dust they are producing. Owners should have a portion of the dust produced at their facility collected and sent to a lab to help identify the dust level and concentration. The lab will also conduct a controlled explosion of the dust to let facilities know how explosive their dust is and how quickly the dust can create fires. This is an important first step in a DHA because lab results will help identify the characteristics of each facility’s dust, and therefore which actions need to be taken to reduce the hazard.
Who performs a DHA?
A DHA must be conducted by a “qualified person,” – someone with experience conducting DHAs, Petit said. The person must have the following:
- Familiarity with the process
- Understanding of operations and maintenance
- Experience with process equipment
- Experience with safety systems
- History of operation
- Understanding of material (dust) properties
- Understanding of emergency procedures
Unfortunately, there is no list of qualified persons or consultancies for conducting a DHA.
“There are some very good qualified people throughout Canada and the U.S. It’s very important you look for a consultant to do a DHA in your facility [that has] previous references to previous projects,” Petit said in response to an attendee’s question on this topic. “Regretfully, there is no certification or formal accreditation for explosion safety experts or engineers. It often comes with a lot of applied knowledge, experience and practical application,” Slaunwhite added.
How to conduct a DHA
When it comes to actually conducting a DHA, there are multiple steps to follow.
“In order to achieve a DHA there are two approaches in the NFPA 652. Essentially, everything you do within your facility must comply with the Authority Having Jurisdiction. And this performance base includes calculations, references, and assumptions of dust characteristics and any data relevant to support the design,” Petit explained to attendees. “If someone wants to venture in this approach, I would definitely recommend they be an expert. You need to be able to defend your ground with bold facts and scientific results.”
The second approach is to follow the steps prescribed by the NFPA.
Properly conducting a DHA begins with a site visit by an expert. This is imperative because the facility’s air flow and other measurements must be tested and seen in person in order to understand it. Equipment must also be inspected. Reviewing photos of the equipment rather than being physically seeing them will not produce the correct data needed for each DHA, Petit said. Petit also recommended the plant personnel, including plant managers, engineering manager and maintenance manager, be involved during each site visit.
Petit emphasized that it is important to qualify and quantify each hazard when conducting these tests. This will help identify factors including dust size and moisture content. It will also help facilities implement solutions that will bring each hazard to an acceptable level. “There is not one solution for all hazards,” Petit said. Dust can be found in several places in facilities including:
- Bins, tanks and silos
- Hammer mills, pulverizes, grinders
- Dryers and ovens
- Dust collectors
- Conveyors, screw augers, and buckets elevators
- Sifters, screens, and classifiers
Ultimately, a DHA is a guide to hazard reduction – it is a working document that illustrates efforts needed to manage risk and dust hazards, Petit and Slaunwhite said. It is an essential tool in every mill and pellet plant’s arsenal.
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