Hazardous location classification system for electrical equipment

In electrical and safety engineering, hazardous locations are defined as places where fire or explosion hazards may exist. Sources of fire include combustible and flammable liquids, gasses or solid material like fibers or dust. Electrical equipment installed in such locations could provide an ignition source due to electrical sparking, arcing, or high operating temperatures of the equipment.

When purchasing electrical equipment for your facility, knowing that the equipment you purchase will be safe operating in a hazardous location is essential. While meeting industry and governmental requirements for safe operations is imperative, having equipment that will efficiently operate and is adjustable for changing demands at your facility will ease your mind and increase your comfort level.

Below are the details of the classification system for electrical equipment.


Location classification

The National Electrical Code (NEC; also known as NFPA 70 National Electrical Code) defines hazardous locations as those areas “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids combustible dust, or ignitable fibers or flyings.” Articles 500 through 504 and 510 through 517 provide classification and installation standards for the use of electrical equipment in these areas.

Hazardous locations are classified in three ways by the National Electrical Code: type, condition, and nature.


There are three types of hazardous locations:

  1. Type (Class) 1 Hazardous location is created by the presence of flammable gases or vapors in air, such as methane or gasoline vapor in enough quantities to be explosive or ignitable.  Typical Class 1 locations include petroleum foundries, flammable and combustible liquid storage and dispensing areas, and spray finishing areas. These locations would require equipment specifically made for that environment.
  2. Type (Class) II Hazardous locations are made hazardous by the presence of combustible dusts. Finely pulverized air suspended material can cause an explosion just as powerful as a petroleum refinery explosion. Class II locations include producers of plastics, medicines and fireworks, plants that use magnesium or aluminum powders, grain mills, candy plants, and spice grinding plants.
  3. Type (Class) III Hazardous locations are areas where there are easily ignitable fibers or flyings present due to the type of material handled, stored, or processed. Fibers and flyings are not only present in the air but can accumulate around machinery or lighting fixtures where a spark or accumulated heat can ignite them. Typical Class III locations include woodworking plants and textile mills.


Hazardous materials location conditions can be classified as normal or abnormal.

In the normal condition, the hazard is expected to be present on an everyday basis. This is described as Division 1 Condition.

An abnormal condition is described as when the hazard is present on an incidental basis or due to accident. While it is normal to store flammable liquids in a flammable liquid cabinet or storage room, the only time when one would expect flammable gases or vapors present is if there was a leak in the flammable liquids container.  This is described as Division II condition.


Class I hazardous locations are broken into four groups by code A, B, C and D. Materials within the codes are grouped by the ignition temperature of the substance, its explosion pressure, and other flammable characteristics.

  • The only substance in Group A is acetylene.
  • Group B is also a small, classified area and includes hydrogen and other materials with similar characteristics.
  • Group C and D are the more usual Class I materials such as butane, gasoline, propane, and natural gas.

Class II hazardous locations contain code groups E, F and G, which are classified according to the ignition temperature and conductivity of the hazardous substances.

  • Group E comprises metal dusts, and the physical characteristic of electrical conductivity is important here. This includes aluminum, magnesium, titanium and similar nature dusts.
  • Group F atmospheres contain materials such as carbon black, charcoal dust, and coal dust.
  • Group G contains the grain dusts, flour, starch, cocoa, and similar types of dusts.

NFPA 70 NEC Hazardous Locations Classes, Divisions and Groups


Class Division Group
I: Flammable gases or vapors may be present

I: Ignitable hazard concentration exists under normal conditions


2: Ignitable hazard concentration exist under incidental or abnormal operation conditions

Group A ― Acetylene


Group B ―  Hydrogen, ethylene oxide, propylene oxide, acrolein, and butadiene


Group C― ethylene, cyclopropane, and ethyl ether


Group D ―  Acetone, ammonia, butane, benzene, methane, ethanol, and gasoline
II: Combustible dusts may be present  I: Ignitable hazard concentration exist under normal operation conditions


2: Ignitable hazard concentration exist under incidental or abnormal operation conditions

Group E ― Combustible metal dusts: aluminum and magnesium, titanium and other commercial alloys


Group F ― Combustible dusts of carbon black, charcoal, and coal


Group G ― Other combustible dusts and chemicals: wood, plastic

III: Ignitable fibers or flyings present

I: Ignitable hazard concentration exist under normal operation conditions


2: Ignitable hazard concentration exist under incidental or abnormal operation conditions
Not applicable

Determining the class, division and group in hazardous environments is critical in determining which equipment to place in that environment while controlling property loss from fire or explosion. Which system is deemed preferable depends on the owner’s preference, how the area is classified, and the electrical wiring system used? Industrial electrical equipment for a hazardous area needs to conform to appropriate standards to reduce danger to life and property.



  1. NFPA 70, National Electrical Code, 2020 edition.
  2. OSHA 29 CFR 1910.307 Hazardous (classified) Locations.
  3. IEC 60079:2020 SER Series- Explosive atmospheres; International Electrical    Commission 2020-06-26.


This material is provided for informational purposes only and does not provide any coverage or guarantee loss prevention. The examples in this material are provided as hypothetical and for illustration purposes only. The Hanover Insurance Company and its affiliates and subsidiaries (“The Hanover”) specifically disclaim any warranty or representation that acceptance of any recommendations contained herein will make any premises, or operation safe or in compliance with any law or regulation. By providing this information to you. The Hanover does not assume (and specifically disclaims) any duty, undertaking or responsibility to you. The decision to accept or implement any recommendation(s) or advice contained in this material must be made by you.

LC 2022-345