DS 7-76 Prevention and Mitigation of Combustible Dust ... - FM Global

Combustible Dust Explosion 7-76
FM Global Property Loss Prevention Data Sheets Page 39
National Fire Protection Association (NFPA). Recommended Practice for the Classification of Combustible
Dusts and of Hazardous (Classified) Locations for Electrical Installation in Chemical Process Areas. NFPA
499, latest edition.
National Fire Protection Association (NFPA). Recommended Practice on Static Electricity. NFPA 77, latest
edition.
National Fire Protection Association (NFPA). Standard on Explosion Prevention Systems. NFPA 69, latest
edition.
National Fire Protection Association (NFPA). Standard on Explosion Protection by Deflagration Venting. NFPA
68, latest edition.
Verein Deutscher Ingenieure (VDI). VDI Guideline 3673, Part 1, ‘‘Pressure Venting of Dust Explosions.” Latest
edition.
APPENDIX A GLOSSARY OF TERMS
A v: Explosion venting area
Air material separator: A broad term for a device designed to separate powders from the air in which it is
transported. Most commonly, this would be a cyclone or dust collector.
Bara: bar, absolute (unit of pressure).
Barg: bar, gauge (unit of pressure)
Bonding: Electrical connection between two electrically-conductive objects that minimizes any difference in
electrical potential between them.
Damage-limiting construction (DLC): Construction designed to minimize the damage from a deflagration
(explosion) in equipment or building. This can be pressure resistive, pressure relieving, or some combination
of the two. Most commonly this would be vent panels on enclosures (buildings or equipment) releasing at
a pressure below the strength of the enclosure.
Deposit velocity: The minimum air (or other gas) velocity needed to prevent dust-particle fallout during
pneumatic-material conveying and to pick up any dust particles deposited during airflow interruption. The
velocity varies with particle weight, density, and aerodynamic properties.
Design strength: Pressure to which a vessel can be exposed without any risk of damage (because a safety
factor has been applied to the yield strength).
Double dump valve: An arrangement of two gate or butterfly valves in series. Only one is open at a time.
This valve is often used where material discharged from one vessel is gravity fed to another vessel (i.e., not
pneumatically conveyed) such as a dust collector discharging into a hopper below it or a material blender
or grinder discharging into a pneumatic conveying system.
Dust: Any sample of solid particles with a median size smaller than 500 microns. For the purposes of this
data sheet, it refers only to combustible dusts.
Dust, combustible: Established by tests that expose the material to ignition sources of various intensities,
such as a spark, a match flame, a Bunsen burner, or a Meker burner. Any organic material, unoxidized metal
particles, or other oxidizable materials (e.g., zinc stearate) should be considered combustible unless testing
proves otherwise. A combustible dust is not always an explosible dust.
Dust, explosible: Established by ASTM test E1226 (Test Method for Pressure and Rate of Pressure Rise
for Combustible Dusts) or E1515 (Test Method for Minimum Explosible Concentration of Combustible Dusts),
or National/International equivalent (e.g., ISO 6184/1, Explosion Protection Systems – Part 1: Determination
of explosion indices of combustible dusts in air). Dust with a median particle size greater than 500 microns
can be assumed to be non-explosible as long as particles smaller than 500 microns cannot be segregated
during material handling.
Explosion isolation: System or single device that prevents the propagation of explosion effects from one
volume to an adjacent volume.
Explosion mitigation: Methods used to reduce damage from the explosion after the explosion has started.
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