Hazardous Areas - North America Classification

A comprehensive tool for understanding and classifying hazardous areas in North America using both the Class/Division/Group system and the Zone/Group system. Determine required protection techniques for electrical installations in locations with flammable gases, vapors, combustible dusts, or ignitable fibers.

Hazardous Areas - North America Classification

Electrical equipment installation in atmosphere with flammable gases or vapors, flammable liquids, combustible dusts, ignitable fibers or flyings represents a risk for fire and explosion.

Areas with possible fire or explosion risks due to explosive atmospheres are classified using the Class/Division system (North America) or the Zone system (Europe and increasingly North America).

Classification Systems

Class/Division/Group System

Based on Article 500 of the National Electrical Code (NEC):

  • Classes - General nature of the hazardous material
  • Divisions - Probability of hazardous material being present
  • Groups - Type of the hazardous material

Zone/Group System

Based on Articles 505/506 of the National Electrical Code (NEC):

  • Zones - General nature and probability of hazardous material
  • Groups - Type of hazardous material and location
Calculator

Inputs

Results

Hazardous Area Classification--
Hazard Description--
Probability of Hazardous Material--

Class/Division/Group System Details

Classes

  • Class I: Flammable gases or vapors
  • Class II: Combustible or conductive dusts
  • Class III: Ignitable fibers or flyings

Divisions

  • Division 1: High probability - continuous, intermittent, or periodic presence under normal operating conditions
  • Division 2: Low probability - abnormal conditions only, short duration

Groups (Class I: A-D for Gases)

  • Group A: Acetylene
  • Group B: MESG ≤ 0.45mm or MIC ≤ 0.40 (Hydrogen, Fuel gases with >30% hydrogen)
  • Group C: MESG > 0.75mm or 0.40 < MIC < 0.80 (Carbon monoxide, Ether, Hydrogen sulfide)
  • Group D: MESG > 0.75mm or MIC > 0.80 (Gasoline, Acetone, Ammonia, Benzene, Propane)

Groups (Class II & III: E-G for Dusts)

  • Group E: Combustible metal dusts (Aluminum, Magnesium, Titanium, Zinc)
  • Group F: Carbonaceous dusts (Coal, Carbon black, with >8% volatiles)
  • Group G: Other combustible dusts (Flour, Grain, Starch, Sugar, Wood, Plastics)

Zone/Group System Details

Zones - Gases, Vapors, Mists

  • Zone 0: Present continuously or for long periods
  • Zone 1: Likely to occur under normal operating conditions
  • Zone 2: Not likely under normal conditions, short period only

Zones - Dusts

  • Zone 20: Dusts present continuously or for long periods
  • Zone 21: Dusts likely to occur under normal operating conditions
  • Zone 22: Dusts not likely under normal conditions, short period only

Groups

  • Group I: Mining locations with firedamp
  • Group II: Explosive gas atmospheres (Zones 0, 1, 2)
    • IIA: Propane, Acetone, Benzene, Butane, Methane, Petrol
    • IIB: Ethylene, Propylene oxide, Ethylene oxide, Butadiene
    • IIC: Acetylene, Hydrogen, Carbon disulphide
  • Group III: Explosive dust atmospheres (Zones 20, 21, 22)
    • IIIA: Combustible flyings
    • IIIB: Non-conductive dust
    • IIIC: Conductive dust

Example

A propane gas installation would typically be classified as:

  • Class/Division: Class I, Division 2, Group D
  • Zone System: Zone 2, Group IIA