Combustible Dust

When it comes to combustible dusts there are many terms common to the industry that are probably not so common to you.  I will try to briefly define what some of these terms.  

Dust Class (ST)
-ST 0, ST 1, ST 2, ST 3

Volume –Normalized Rate of Pressure increase (Kst)
-The deflagration index of a dust cloud.

Rate of Pressure Rise (dP/dt)
-The increase in pressure divided by the time interval necessary for that increase to occur.

Maximum Rate of Pressure Rise [(dP/dt)max]
-The slope of the steepest part of the pressure-versus-time curve recorded during deflagration in a closed vessel.

Maximum Pressure (Pmax)
-The maximum pressure developed in a contained deflagration of an optimum mixture.

Minimum Explosive Concentration (MEC)
-The minimum concentration of a combustible dust cloud that is capable of propagating a deflagration through a uniform mixture of the dust and air under the specified conditions of test.

Minimum Ignition Energy (MIE)
-The minimum amount of energy released at a point in a combustible mixture that causes flame propagation away from the point, under specified test conditions.

Minimum Ignition Temperature (MIT)
-Minimum ignition temperature of a hot surface capable of causing ignition of dust in suspension.

Layer ignition temperature or Auto Ignition Temperature (AIT)
-Temperature at which a dust layer ignites on a hot surface (1/2” thickness test base)

Limiting Oxygen Concentration (LOC)
-To determine the highest oxygen concentration at which ignition of a dispersed dust at ambient temperature and pressure is not possible.

Electrical Volume Resistivity (Rv)
-The measure of how easily electrical charge can flow through the particulate.

Charge Relaxation Time
-The time it take for a charge to decrease to 0.37 x it’s initial value.

Powder Chargeability 
-The charge per unit mass that can be developed on a specific material during processing

Burn Rate 
-The flammability and degree of combustibility of metal powder/dust

Thermal Stability
-Process risk at higher operating temperatures and storage conditions.

Water Reactivity
-A material that chemically reacts with water, producing another compound that can represent a different set of fire protection concerns

Water-Incompatible
-A material that does not chemically react with water, but which undergoes a change of phase or state upon mixture with water that renders it permanently changed or incompatible with the remainder of the process

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