CTA Report, Draft 1, ISP Review - US Chemical Safety and Hazard ...

6.0 Understanding Combustible Dust Hazards
6.1 Introduction
Most organic materials and many metals—and even some nonmetallic inorganic materials, if finely
divided and dispersed in suitable concentrations—will burn or explode if they contact a sufficient ignition
source. 13 Not all small particles burn, however. For example, salt and baking soda, no matter how finely
powdered, will not burn because they contain no combustible material. Coffee creamer, on the other
hand, will burn because it contains fat (organic material). Materials that are capable of burning in air are
called combustible materials.
Combustible dusts can be generated when solid combustible materials are handled or processed due to
gradual reductions in the particle sizes and/or segregation of the particles. They are defined by NFPA 654
(2000) (Table 1, see page 48) as any finely divided solid material 420 microns or less in diameter that
presents a fire or explosion hazard when dispersed and ignited in air. The combustibility of dust is
established through materials testing (FM Global, 2004). Awareness of combustible dust hazards is
important to ensure employee safety, to ensure proper facility design, and to develop adequate operations
and maintenance procedures.
6.2 Dust Fire and Explosion Hazard Characteristics
Like all other fires, a dust fire occurs when fuel (the combustible dust) comes in contact with heat (an
ignition source) in the presence of oxygen (air). Removing any one of these elements of the fire triangle
eliminates the possibility of a fire. A dust explosion requires the simultaneous presence of two additional
13 Ignitability and Explosibility of Dusts, Table A.1, Appendix A.2 (Eckhoff, 2003).
45