Page 56 - Occupational Health & Safety, October 2019

COMBUSTIBLE DUST
Important NFPA Standards for Manufacturing Processes thIat Create Combustible Dust
BY BRIAN RICHARDSON
and concentrated combustible dust cloud comes into contact with an ignition source. A primary explo- sion is the first point where an explosion occurs and is often an isolated incident. A secondary explosion occurs when the primary explosion pressure disturbs dust that has collected in the workplace, resulting in a much more extensive explosion.
Maintaining a clean facility and operating a dust collection system that is properly designed for your specific operation can significantly reduce combus- tible dust in the work environment. The National Fire Protection Association (NFPA) sets safety standards for managing combustible dust. Most insurance agen- cies and local fire codes require companies to follow NFPA standards. Exceptions are made when the au- thority having jurisdiction (AHJ), such as Factory Mutual or local fire marshals, specifies an alternative safety approach. However, the alternative approach might be even more stringent.
Here are important NFPA standards you need to be aware of if your facility handles combustible dust:
NFPA 652—Standard on the Fundamentals of Combustible Dust. This standard covers the require- ments for managing combustible dust fires and explo- sions across industries, processes, and dust types. It requires the owner or operator of any facility where combustible dust exists to conduct a dust hazard analysis (DHA), develop a plan for managing fire and explosion dangers, and provide training for workers who potentially could be affected by the hazards.
Facility operators and their health and safety man- agers can conduct the DHA internally or use an inde- pendent consultant. Ultimately, the authority having jurisdiction will review the findings and grant approval. The DHA must be completed by the fall of 2020 and demonstrate reasonable progress toward completion of the DHA in each of the years approaching the deadline.
A complete dust hazard analysis includes the process machinery that produces dust and the dust collection system itself. Many dust collector fires and explosions occur after a fire outside the collec- tor produces flames or sparks that are drawn into the collector. DHA considerations for the dust collection system include documenting all possible hazards as- sociated with the dust collector and the controls used to mitigate them. Appendix B of NFPA 652 provides guidance on performing a thorough DHA.
NFPA 654—Standard for the Prevention of Fire
52 Occupational Health & Safety | OCTOBER 2019
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f your facility handles, transfers, packages or pro- cesses dust-producing materials or powders, you could face an explosion risk from combustible dust. A dust explosion occurs when a confined
and Dust Explosions from the Manufacturing, Pro- cessing, and Handling of Combustible Particulate Solids. This is an all-encompassing standard on how to design a safe dust collection system. It points to more specific standards, depending on the nature and severity of the hazard potential, that deal with differ- ent types of dust and explosion protection equipment, such as explosion venting and deflagration protection.
NFPA 68—Standard on Explosion Protection by Deflagration Venting. This standard focuses on explosion venting on devices and systems that vent combustion gases and pressures resulting from a def- lagration within an enclosure in order to minimize structural and mechanical damage.
NFPA 69—Standard on Explosion Prevention Systems. This standard extends beyond explosion venting to address the whole dust collection system. It includes inlet and outlet ducting, spark-extinguishing systems, and methods for preventing an explosion from traveling back into the building or to process lo- cations upstream of inlet duct work.
NFPA 70—National Electrical Code (NEC). The NEC covers everything related to the installation of electrical equipment across all industries and all types of buildings. This code is enforced in all 50 states. Two sections of NFPA 70 apply to housekeeping: combus- tible dust definition and hazardous locations. NFPA 70 defines combustible dust as “dust particles that are 500 microns or smaller and present a fire or explosion hazard when dispersed and ignited in air.” The NEC defines different classes of hazardous (classified) and non-hazardous locations. These classes determine the wiring of buildings and also the equipment and housekeeping procedures that can be used in different areas of facilities.
NFPA 91—Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids. This standard includes duct system designs that enable the correct velocity to keep the duct clean and the correct strength to keep the duct from rupturing.
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