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

Table 2
Dust Properties for Determining Fire and Explosion Hazards (a)
Elements Properties Significance
Fuel
Explosion
Severity (Kst)
value
Maximum rate of pressure rise normalized to a 1.0-m 3
volume, which is a relative measurement of energy of the
dust explosion. The greater the Kst value, the more
energetic the explosion.
Moisture content Affects ease of ignition and ability to sustain an explosion.
Increasing moisture content increases ignition energy (for
some dusts, the increase may be exponential) and reduces
explosion severity (i.e., water vapor acts as inert heat sink).
Ignition Minimum ignition
energy (MIE)
Provides information on the lowest energy required to ignite
the most readily ignitable dust/air mixture at atmospheric
pressure and room temperature; a combustible dust with a
low MIE is easily ignited. Ignition energies for dust clouds
are usually higher than for gases or vapors—typically a
fraction of a millijoule for gases and 1–10 millijoules for
dust.
Oxygen Oxygen content Less oxygen in the air reduces explosion severity by
limiting rate of combustion and increases ignition energy.
Suspension/
confinement
Degree of
dispersion
Particle
size/shape
Minimum
explosive
concentration
(MEC)
Usually dependent on the way dust is dispersed and level
of turbulence. An evenly suspended and less turbulent
dust cloud is more easily ignited and burns more easily.
Reduction in particle size increases surface area and
decreases MIE; the smaller the dust particle, the more
easily it is suspended. Particles with high surface area per
unit volume exhibit low MIE, low MEC, and high Kst.
(a) This table highlights the main characteristics of combustible dusts.
Dusts, like gases and vapors, form explosive clouds only if
dust concentration lies between certain limits, known as the
lower (LEL) and upper explosive limit. For dusts, LEL is
also commonly referred to as MEC.
50