This is a general overview and provided as a guide.  For actual installation please use the NEC/CEC code book and  IEC/CENELEC approvals and wiring codes as final authority on any installation.

Locations are divided into three different classes.  Each class has two divisions that further define the rule under that class.

Class I Locations – Flammable Gases or Vapors

Class 1 locations are created by the presence of flammable gases or vapors in the air in sufficient quantities to be explosive or ignitable.  When these materials are found in the atmosphere, a potential for explosion exists if an electrical or other source of ignition is present.  Some typical Class 1 locations are:

  • Petroleum refineries and gasoline storage and dispensing areas
  • Dry cleaning plants where vapors from cleaning fluids can be present
  • Spray finishing areas
  • Aircraft hangars and fuel servicing areas
  • Utility gas plants and operations involving storage and handling of liquified petroleum gas or natural gas.

Class I, Division 1

Class I, Division I locations are where hazardous atmosphere may be present during normal operations.  It may be present continuously, intermittently, periodically or during normal repair or maintenance operations, or those areas where a breakdown in processing equipment releases hazardous vapors with the simultaneous failure of electrical equipment.

Class I, Division 2

Class I, Division 2 locations are those in which volatile flammable liquids or gases are handled, processed or used.  Normally they will be confined within closed containers or in closed systems from which they can escape only in the case of rupture or deterioration of the containers or systems.


Class II Locations – Dust

Class 2 locations are reserved for the presence of combustible dust in the air in sufficient quantities to be explosive or ignitable.  Some typical Class II locations are:

  • Grain elevators
  • Flour and feed mills
  • Plants that produce or store combustible metal dust (aluminum, magnesium, titanium, etc.)
  • Producers of plastics, medicines and fireworks
  • Producers of starch or candies

Class II, Division 1

Class II, Division 1 locations include areas where combustible dust may be in suspension in the air under normal conditions in sufficient quantities to produce explosive or ignitable mixtures (Dust may be emitted into the air continuously, intermittently or periodically), or where failure or malfunction of equipment might cause a hazardous location to exist and provide an ignition source with the simultaneous failure of electrical equipment, included also are locations in which combustible dust of an electrically conductive nature may be present.

Class II, Division 2

Class II, Division 2 locations are those in which combustible dust will not normally be in suspension nor will normal operations put dust in suspension, but where accumulation of dust may interfere with heat dissipation from electrical equipment or where accumulations near electrical equipment may be ignited.


Class III Locations – Fibers or Flyings

Class III locations contain easily ignitable fibers or flyings.  Typically these fibers and flyings are not suspended in the air, but can collect around machinery or on lighting fixtures and where heat, a spark or hot metal can ignite them.  Some typical Class III locations are:

  • Textile mills, contton gins
  • Cotton seed mills, flax processing plants
  • Plants that shape, pulverize or cut wood and create sawdust or flyings

Class III, Division 1

Locations in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured or used.

Class III, Division 2

Locations where easily ignitable fibers are stored or handled.