Explosive Atmosphere

Mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapor, mist or dust, in which after ignition, combustion spreads throughout the unconsumed mixture

(IEC 60079-0, definition 3.22)

This definition refers to Class 1 & Class 2 type of materials.

In reality , Class 3  (Division 1 & Division 2) type explosive atmospheres do exists and comprise of  flammable flyings, fibers and fluff  (Cotton or Woolen Fluff),  However this classification exists only in NEC 500 .

Flammable fibers or flyings not only present fire hazard but a greater risk. If  a  layer of class 3 type of material is formed throughout a facility and it gets ignited then fires  may spread all over, at very high speed.

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