What is dust zone?
A Zone 22 area is classified as an atmosphere where a mixture of air and flammable substances in the form of powder or dust is not likely to occur in normal operation, but if it does occur, will persist for a short period only. These are typically storage areas but can also be process areas.
In which zone is high probability of explosion with atmosphere?
Zone 20
Zone 0, Zone 20 – High probability (A flammable atmosphere is present continuously, for long periods or frequently) Zone 1, Zone 21 – Medium probability (A flammable atmosphere is likely in normal operation occasionally)
What is a dust zone?
A Zone 21 area is classified as a place in which an explosive atmosphere consisting of a mixture with air or flammable substances in the form of powder or dust is likely to occur in normal operation occasionally. These are typically process areas where dusts and powders are more likely to be present.
What hazard class is combustible dust?
Class II hazardous
NFPA 70, National Electrical Code , defines a Class II hazardous (classified) location as one that is hazardous because of the presence of a combustible dust.
Where do the majority of dust explosions start?
Dust explosions in the process industries most often start inside some process unit (a mill, a filter unit, a cyclone, a storage silo, etc.). This kind of initial explosion event inside some process unit is called a primary explosion.
How can you tell if dust is combustible?
A combustible dust is any material (finely divided solid particles) that has the ability disperse in air and catch fire and explode when exposed to an ignition source. Combustible dust may include materials that are in the physical states of powders, flakes, fines, fibers, etc.
How do you know if dust is combustible?
If the material will burn and contains a sufficient concentration of particles 420 microns or smaller to create a fire or deflagration hazard, it should be classified as a combustible dust.
Which of the following locations are hazardous due to the presence of combustible dust?
Class II Locations
Class II Locations The second type of hazardous location is called a “Class II Location”. This classification is created by the presence of combustible dust in the air in sufficient quantities to be explosive or ignitable.
How powerful is a dust explosion?
Effects. A dust explosion can cause major damage to structures, equipment, and personnel from violent overpressure or shockwave effects. Flying objects and debris can cause further damage. Intense radiant heat from a fireball can ignite the surroundings, or cause severe skin burns in unprotected persons.
How do you trigger a dust explosion?
In practice, for a dust explosion to occur, a number of conditions must be met including:
- The dust must be combustible and release enough heat when it burns to sustain the fire.
- The dust must be capable of being suspended in air.
- The dust must have a particle size capable of spreading the flame.