Explosive environments: HAZLOC standard


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Explosive environments

1. Source of combustion (flame, spark, hot spot)

2. Oxygen in the air

3. Fuel (gas or flammable vapor, dust)


Under what conditions can an explosion occur?

There is a risk of explosion when several elements are present:

  • an oxidant: the oxygen in air, for example
  • a fuel:
    • gas or vapors: hydrocarbons, solvents, varnishes, diluents, gas, alcohol, dyes, perfumes, chemical products, agents for manufacture of plastics...
    • powders and dust: magnesium, aluminum, sulfur, cellulose, cereals, carbon, wood, milk, resins, sugars, starch, polystyrenes, fertilizer...
  • a hot spot or a source of combustion.

For example, when filling a grain silo, the concentration of dust is very high. The environment then is dangerous: a rise in temperature, or even a spark, can trigger an explosion.

If a risk of explosion is identified in an environment (gas or dust), a safety requirement is imposed for the use of equipment that is specifically designed to function without becoming a potential source of combustion. This equipment offers different types of protection designed to diminish the risk of explosion.


The HAZLOC standard

What is the HAZLOC?

The HAZLOC certification primarily concerns North America.

It aims to control the risks related to explosion in certain environments.

It comprises two elements:

  • testing and evaluation of products being used
  • inspection of the factory

How do you choose equipment that is adapted for an environment at risk of explosion?

Hazardous locations are classified in three ways under the HAZLOC standard:

  • by type
  • by conditions
  • by nature of the hazardous substance or material


Hazardous environments are divided into three classes:

  • Class I: designates a space that has become dangerous because of the possible presence of certain gases or vapors in sufficient quantity to be potentially flammable or explosive. Examples: petroleum refineries, gas distribution zones, spray finishing zones...
  • Class II: designates a space that has become dangerous because of the presence of flammable air-borne dust. Examples: grain silos, manufacturers of plastics, aluminum, pharmaceutical products and fireworks...
  • Class III: designates a space in which airborne fibers and particles can accumulate around a machine or on lighting equipment and become ignited by heat, a spark or a hot metal. Examples: textile factories, flax processing plants, factories that produce wood shavings or flying particles...


There are two types of conditions:

  • Division 1 (average conditions): the risk is present during regular production operations, or during ongoing repair or maintenance operations.
  • Division 2 (unusual conditions): the dangerous substance is only present in the case of an accidental break or defective functioning.

Nature of the hazardous substance or material

  • The gases and vapors of class I hazardous environments are divided into four groups: A, B, C and D (these substances are grouped according to their combustion temperature, their explosion pressure and other combustion characteristics).
  • The dangerous substances of class II hazardous environments are divided into three groups: E, F and G (these substances are grouped according to their combustion temperature and their conductivity). Conductivity relates particularly to metal dusts.







I Gases, vapors, liquids

A: Acetylene

B: Hydrogen...

C: Ether...

D: Hydrocarbons, fuels, solvents...

Explosive and always dangerous

Normally not present in quantities sufficient for explosion (but this situation may accidentally arise)

II Dust

E: Metal dusts (conductive and explosive)

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

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

The quantity of dust is sufficient to be flammable, or the dust is conductive under normal conditions.

Normally not present in quantities sufficient for explosion (but this situation may accidentally arise)

III Air-borne fibers and particles

Textiles, wood debris...

Manipulated or used during manufacture

Stored or manipulated in a storage area (away from manufacturing)


What are the specific features of certified headlamps?

The more restrictive the mode of protection of a headlamp is, the less powerful the lighting will be. The intensity and voltage that is permitted may be low in order to ensure that the device does not produce an arc, spark or dangerous temperature.

What does the marking mean?

All products designed for use in explosive zones have a specific marking on them. This marking contains all the information necessary to determine the zones in which the product may be used.

Example of marking:



  • Class I: gaseous environment

    (Class I = gas, Class II = dust, Class III = fibers)
  • Div. 2 = type of conditions

    (Div 1: normal conditions, Div 2: abnormal conditions)
  • GROUPS C/D: corresponds to the classes of gas covered by the product
  • Class II: dusty environment
  • Div. 2: present under abnormal conditions
  • GROUP G: corresponds to the classes of dust covered by the product

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