NFPA 68: Explosion Protection
The National Fire Protection Association’s NFPA 68-2018: Standard on Explosion Protection by Deflagration Venting provides benchmarks for deflagration vents to diminish the potential harm brought on by the dispensation of combustible dust, which is surprisingly abundant in some work facilities.
Deflagration is a combustion that spreads through a gas or along the surface of an explosive at a swift rate, driven by the transfer of heat.
Many voluntary consensus standards were/are aimed towards providing safe environments when combustible dusts and particulate solids are present. NFPA 652-2019: Standard on the Fundamentals of Combustible Dust outlines the basic principles on these, while NFPA 654-2017: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids complements it, contributing rules and strategies for the stages of the manufacturing, processing, blending, conveying, repackaging and handling of combustible particulate solids/hybrid mixtures.
The NFPA guide lists the following basic principles that are common to the venting of deflagrations:
1. The vent design must be sufficient to prevent deflagration pressure inside the dust collector from exceeding two-thirds of the ultimate strength of the weakest part of the dust collector, which must not fail. This principle does anticipate that the dust collector may deform. Expect some downtime with the dust control system after an explosion.
2. Dust vent explosion operation must not be affected by snow, ice, sticky materials or comparable interferences.
3. Dust explosion vent closures must have a low mass per unit area to reduce opening time. NFPA recommends a maximum total mass divided by the area of the vent opening of 2.5 lbs./ft2.
4. Dust explosion vent closures should not become projectiles as a result of their operation. The closure should be correctly restrained without affecting its purpose.
5. Vent closures must not be affected by the process settings which it protects or by conditions on the non-process side.
6. Explosion vent closures must release at overpressures close to their design release pressures. Magnetic or spring-loaded closures will satisfy this criterion when properly designed.
7. Explosion vent closures must reliably withstand fluctuating pressure differentials that are below the design release pressure.
8. Dust explosion vent closures must be inspected and properly upheld in order to ensure dependable operation. In some cases, this may mean replacing the vent closure at appropriate time intervals.
9. The supporting structure for the dust collector must be strong enough to endure any reaction forces developed as a result of operation of the dust explosion vent. 10. Industrial exhaust system ductwork connected to the dust collector could also require explosion venting.
Why Standard is Important:
When deflagrations or explosions befall, vents can help. These frequently are installed in numerous at-risk industrial process components, including those designed to alleviate or control hazards of combustible dust, such as dust collectors, process vessels, duct/piping networks and industrial assemblies.
OSHA has presented evidence that facilities which process agricultural products, agricultural dusts carbonaceous dusts, chemical dusts, metal dusts, or plastic dusts are in danger of experiencing a combustible dust explosion.
Many of these solid, organic materials, metals and non metallic inorganic materials are not normally combustible, but if the particles are of a certain size or concentration, they present fire or deflagration hazards. The standard helps eliminate the chance of an explosion occurring.
The full standard requirement can be downloaded on the Nation Fire Protection Association’s official website: https://bit.ly/2EdcBfN
SPONSORED BY: Camfil APC
“Our mission is to provide dust collection equipment that is compliant to all relevant standards in the safety and NFPA world. NFPA 68 is imperative in our ability to design safe, reliable and cost-effective systems that help prevent and mitigate combustible dust hazards.” – Brian Richardson, Technical Departments Manager for Camfil APC Camfil APC, (870)933-8048, www.camfilapc.com
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