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NEC Hazard Zone Classifications
NEC Hazard Zone Classifications


Hazardous Zone Classifications (defined by National Electrical Code (NEC))







Class I:

Gases, vapors, and liquids
(Art. 501)

A: Acetylene

B: Hydrogen, etc.

C: Ether, etc.

D: Hydrocarbons, fuels, solvents, etc.

Normally explosive and hazardous

Not normally present in an explosive concentration (but may accidentally exist)

• Petroleum refineries, and gasoline storage and dispensing areas.

• Industrial firms that use flammable liquids in dip tanks for cleaning parts or 
other operations

• Petrochemical companies that manufacture chemicals from gas and oil.

• Dry cleaning plants where vapors from cleaning fluids can be present.

• Companies that have areas dedicated for spraying products with paint or plastics.

• Aircraft hangars and fuel servicing areas.

• Utility gas plants, and operations involving storage and handling of liquefied petroleum gas or natural gas.

Class II:

(Art. 502)

E: Metal dusts (conductive,*and explosive)

F: Carbon dusts (some are conductive,and all are explosive)

G: Flour, starch, grain, combustible plastic or chemical dust (explosive)

Ignitable quantities of dust normally are or may be in suspension, or conductive dust may be present

Dust not normally suspended in an ignitable concentration (but may accidentally exist). Dust layers are present.

• Grain elevators, flour and feed mills.

• Plants that manufacture, use or store magnesium or aluminum powders.

• Plants that have chemical or metallurgical processes, producers of plastics, 
medicines, and fireworks etc.

• Producers of starch or candies.

• Spice grinding plants, sugar plants and cocoa plants.

• Coal preparation plants and other carbon handling or processing areas.

Class III:

Fibers and flyings
(Art. 503)

Textiles, wood-working, etc. (easily ignitable, but not likely to be explosive)

Handled or used in manufacturing

Stored or handled in storage (exclusive of manufacturing)

• Textile mills, cotton gins, cotton seed mills and flax processing plants.

• Clothing manufacturing plants

• Any plant that shapes pulverizes or cuts wood and creates saw dust or shavings.


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