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Each year, 150 work accidents linked to an explosion are recorded in France, on average. More than 15% of them cause significant human and material damage. On construction sites or in an industrial environment, the risk of explosion is all the greater in the presence of flammable substances (gas, steam, dust, etc.). To avoid any danger, it is essential to define the ATEX zones of a workplace and to take all steps to secure the perimeters concerned.

What is an ATEX zone ?

In industrial sites and construction sites, the safety of personnel and equipment is a priority. Precise devices are implemented to prevent potential hazards, including ATEX indication.

ATEX is an abbreviation for the term "Explosive Atmosphere." ATEX is an environment in which the risk of explosion is high due to the presence of combustibles, visible or not to the naked eye. According to standard EN 1127-1, an explosion is "a sudden reaction of oxidation or decomposition involving a temperature or pressure increase or both simultaneously." The propagation of combustion is almost immediate, accompanied by flames and heat waves. ATEX can form under normal operating conditions or accidentally due to the leakage of one or more combustibles.

In an ATEX, air mixes with flammable substances. The explosion occurs when six simultaneous conditions are met:

- the presence of an oxidizer (usually oxygen from the air)

- the presence of a fuel (propane, hydrogen, coal, wheat flour...)

- the presence of an ignition source (spark, static electricity, heat...)

- the specific state of the fuel (gas, dust, mist...)

- achieving an explosivity range: the mixture is neither too lean nor too rich in fuel

- confined space

Attention : Industrial sites are not the only places where ATEX can occur. Any activity or installation involving the handling and management of flammable substances can also pose this risk.

Important definitions regarding hazardous areas

Each ATEX zone is standardized according to its level of hazard. In accordance with ATEX Directive 99/92/EC, the employer is required to assess the explosion risks on their site and classify the risk zones.

An ATEX zoning must be carried out by a competent professional to define and subsequently secure the workplace. The identification of ATEX zones involves an audit of the entire production facility.

Article 7 of ATEX Directive 1999/92/EC specifies this obligation: "The employer subdivides the locations where explosive atmospheres may occur into zones, in accordance with Annex I."

How to Delimit ATEX Zones?

Zoning involves defining parts of a site where explosion risks can occur. These locations are qualified as hazardous zones and delimited based on their degree of danger.

Delimiting an ATEX zone is a crucial step for the safety of workers in areas where explosive atmospheres can form. ATEX zones are defined by the European Directive 1999/92/EC and are used to classify work areas based on their level of explosion risk.

The delimitation of an ATEX zone is based on a risk assessment that determines the likelihood of an explosive atmosphere forming in a given area. This assessment takes into account various factors such as the frequency and duration of the presence of explosive substances, ventilation, and potential sources of ignition.

  1. Once the risk zones have been identified, they must be clearly delimited. Delimitation methods may vary depending on circumstances, but here are some common options:
    - Ground Marking: Zones can be delineated by ground markings in different colors for each zone, enhancing boundary identification.
  2. Signage: Signs and labels can be used to indicate the presence of ATEX zones and provide information about specific risks.
  3. Physical Barriers: Physical barriers can be used to separate risk zones from areas where explosion risks are lower.
  4. Use of Specific Equipment: Equipment such as lights, fans, and motors can be designed for specific use in ATEX zones. It's essential to note that the delimitation of ATEX zones must be regularly reassessed and updated based on changes in working conditions.


An area is considered ATEX as soon as it is used to store or handle flammable materials. The degree of danger of an ATEX area is evaluated based on the quantity and nature of these materials. The higher the level, the greater the risks, and the stricter the regulations.

The ATEX regulations are defined by two European directives:

-        Directive 2014/34/UE (ATEX 95), concerning equipment used in ATEX areas;

-        and Directive 1999/92/CE (ATEX 137), concerning the safety of workers in an ATEX area.

These directives require employers to control the risks of explosion on their site, just like other occupational risks. The goal is to ensure the safety and improve the health of individuals exposed to ATEX risks.

An employer must:

-        evaluate the risks of explosion on their site

-        identify, classify, and delimit ATEX zones

-        implement technical and organizational protective measures (prevention, training, maintenance...)

-        provide devices and equipment specific to hazardous areas

-        coordinate ATEX interveners

-        draft an DRCPE (document on protection against explosions)

Since the entry into force of Directive 1999/92/CE in July 2003, the assessment of explosion risks is mandatory. The workplace and equipment must be in compliance, under penalty of a fine of up to €10,000 (Article L. 4741-1 of the Labor Code).

ATEX zoning includes the following steps:

  1. Collection of physicochemical data of combustible products on the site
  2. Functional analysis of the installations using the products flammable
  3. Determination of release sources and the probability of occurrence of an ATEX (Explosive Atmosphere)
  4. Characterization of the area (dangerousness and extent)
  5. Study of sources of ignition

Area classification

There are three types of zones defined by the IEC (1986), by the Ministry of Labor (1988) and by the Ministry of Industry (1991).

This classification is refined in the ATEX directive, which no longer speaks of zones but of categories of devices, depending on the probability of the formation of an explosive mixture, and two different applications depending on the nature of the mixture (gas or dust).

  • PERMANENT RISK:</ strong> The explosive mixture is present at all times
  • FREQUENT RISK: An explosive mixture of gases or vapors is likely to form during normal operation of the installation
  • OCCASIONAL RISK: An explosive mixture can only appear in the event of abnormal operation of the installation

GAS0: Permanent Presence
1: Occasional Presence
2: Rare Presence
-> 1G
-> 2G or 1G
-> 3G, 2G or 1G
DUST20: Permanent Presence
21: Occasional Presence
22: Rare Presence
-> 1G
-> 2G or 1G
-> 3G, 2G or 1G

These risks made it possible to create 3 categories which determine the level of protection of the devices

  • CATEGORY 1: VERY HIGH LEVEL OF PROTECTION: the explosive mixture is present constantly, or for a long period, or frequently
  • CATEGORY 2: HIGH LEVEL OF PROTECTION: an explosive mixture will probably occur
  • CATEGORY 3: NORMAL LEVEL OF PROTECTION: an explosive mixture has a low probability of occurring, and will only exist for a short period.
DEVICE GROUP I (mines)M1Methane, dustVery high level2 protection paths or default values
M2Methane, dustHigh level1 protection path
Standard operation
DEVICE GROUP II (mines)1Gas, vapors, mists, dustVery high level2 protection paths or default values
2Gas, vapors, mists, dustHigh level1 protection path
Common and frequent disturbance
3Gas, vapors, mists, dustStandardRequired protection level


ATEX regulatory marking means the marking requirements for equipment intended for use in areas dangerous (at risk of explosion). Equipment must be marked with the ATEX directive number, zone category and manufacturer information.

ATEX normative marking designates the specific standards that define requirements for equipment used in hazardous areas. ATEX standards include requirements for the design, construction, performance and marking of equipment to ensure their safe use in potentially explosive environments.

Zoning allows for identifying locations where an ATEX (Explosive Atmospheres) can occur, as well as determining the appropriate equipment to use in hazardous zones. Every device on the premises, whether electrical or not, must comply with the technical requirements associated with each type of zone. Only certified products with a specific marking can be used in an ATEX zone.

The specific ATEX marking is a requirement of the European Directive on ATEX. It allows the employer to ensure compliance, as required by ATEX Directive 2014/34/EU, for their equipment. An ATEX marking must include:

-        The "CE" symbol of the European Commission

-        A series of four digits corresponding to the notified body responsible for conformity control

-        The ATEX logo (a hexagon with the letters "E" and "x" inscribed)

-        A series of numbers and letters indicating the nature and intensity of the explosive risk

There are different ATEX zones which determine the level of potential danger of a given zone. The zones are defined as follows:

Zone 0: an area in which a gas, vapor or dust explosion can occur continuously.

Zone 1: an area in which a gas, vapor or dust explosion may occasionally occur.

Zone 2: an area in in which a gas, vapor or dust explosion is unlikely.

ATEX zones are determined based on the quantity, nature and duration of presence of gas, vapor or dust explosives in the environment. Equipment used in ATEX zones must be designed and marked accordingly to ensure safety in potentially explosive environments.

These zones must take into account external parameters (ventilation, openings, heating, etc.) which can modify the extent of the zones. The illustration below shows an example of hazardous area classification for flammable liquid unloading station. The principle is the same for dust, only the zone name changes to 20, 21, 22. Beyond zone 2 or 22, there is no longer any probability of occurrence of an explosive mixture. Outside the classified area, it is therefore possible to use the industrial standard.


  • Devices certified for zone 0 can also be used in zones 1 and 2.
  • Devices certified for Zone 22 cannot be used in Zone 20 or 21.
  • Zone 0 (in a tank) and zone 20 (inside a silo) are zones where there is fixed electrical equipment (with the exception of sensors).
  • Appliances certified for zone 21 cannot be used in zone 1. Appliances certified “gas” (including ATEX high “e” safety devices) are protected in their shell, as well as each internal component.

However, ATEX “dust” certified equipment is protected by its outer envelope. However, there are many devices with dual “gas” and “dust” certification that can be used indiscriminately in both types of environment.

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