ATEX zones: definitions, zoning, solutions
Every year, 150 workplace accidents related 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 industrial environments, the risk of explosion is all the greater in the presence of flammable substances (gas, steam, dust, etc.). To eliminate any danger, it is essential to define the ATEX zones of a workplace and to take all steps to secure the areas concerned.
What is an ATEX zone?
On industrial sites and construction sites, the safety of personnel and equipment is a priority. Specific measures are put in place to prevent potential dangers. Among them, the ATEX indication.
ATEX is the abbreviation for the term "Explosive Atmosphere" . An 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 the EN 1127-1 standard, an explosion is "a sudden oxidation or decomposition reaction involving an increase in temperature or pressure or both simultaneously". The propagation of combustion is almost immediate, accompanied by flames and heat waves. An ATEX can form under normal operating conditions or accidentally by the leakage of one or more combustibles.
In an ATEX, air mixes with flammable materials. The explosion occurs when six simultaneous conditions are met:
- the presence of an oxidant (usually oxygen in the air)
- the presence of a fuel (propane, hydrogen, coal, wheat flour, etc.)
- the presence of an ignition source (spark, static electricity, heat, etc.)
- the particular state of the fuel (gas, dust, fog, etc.)
- obtaining an explosive range: the mixture is neither too lean nor too rich in fuel
- a confined space
Please note : Industrial sites are not the only places where ATEXs are formed. Any activity or installation involving the handling and manipulation of flammable substances may also be at risk.
Important definitions regarding hazardous areas
Each ATEX zone is standardized according to its degree of danger. In accordance with the ATEX directive 99/92/CE, the employer is required to assess the explosion risks on their site and to classify the risk zones.
ATEX zoning must be carried out by a competent operator, so that the workplace is defined and subsequently secured. The identification of ATEX zones involves an audit of the entire production tool.
Article 7 of the ATEX Directive 1999/92/EC specifies this obligation as follows: “The employer shall subdivide into zones the locations where explosive atmospheres may occur, in accordance with Annex I.”
How to demarcate ATEX zones?
Zoning involves defining the parts of a site where explosion hazards may occur. These locations are referred to as hazardous areas and are demarcated according to their degree of danger.
The delimitation of an ATEX zone is an important step for the safety of workers working in areas where explosive atmospheres can form. ATEX zones are defined by European Directive 1999/92/EC and are used to classify work areas according to their level of explosion risk.
The delimitation of an ATEX zone is based on a risk assessment that determines the probability of an explosive atmosphere forming in a given area. This assessment takes into account several factors, such as the frequency and duration of the presence of explosive substances, ventilation and potential ignition sources.
- Once the risk areas have been identified, they should be clearly demarcated . The methods of demarcation may vary depending on the circumstances, but here are some common options: Road markings: Areas can be demarcated by road markings of different colours for each area, which helps to better identify the boundaries.
- Signage: Signs and labels can be used to indicate the presence of ATEX areas and provide information on specific risks.
- Physical barriers: Physical barriers can be used to separate hazardous areas from areas where there is a lower risk of explosion.
- Use of specific equipment: Equipment such as lighting fixtures, fans and motors may be designed for use specifically in ATEX zones. It is important to note that the delimitation of ATEX zones must be regularly reassessed and updated according to changes in working conditions.
The regulation
An area is called ATEX when it is used to store or handle flammable materials. The degree of danger of an ATEX zone is assessed according to the quantity and nature of the latter. The higher the level, the greater the risks and the stricter the regulations.
- Directive 2014/34/EU (ATEX 95) , relating to equipment used in ATEX zones;
- and Directive 1999/92/EC (ATEX 137) , relating to the safety of workers in an ATEX zone.
These directives require employers to control explosion risks on their site, in the same way as other occupational risks. The aim is to ensure the safety and improve the health of people likely to be exposed to ATEX risks.
- assess the explosion risks on its site
- identify, classify and delimit ATEX zones
- implement technical and organizational protection measures (prevention, training, maintenance, etc.)
- provide devices and equipment specific to hazardous areas
- draft a DRCPE (document relating to protection against explosions)
Since the entry into force of Directive 1999/92/EC in July 2003, the assessment of explosion risks has been mandatory. The workplace and equipment must be brought into compliance, under penalty of a fine of up to 10,000 euros (Article L. 4741-1 of the Labour Code).
ATEX zoning includes the following steps:
- Collection of physico-chemical data of combustible products on the site
- Functional analysis of installations using flammable products
- Determination of release sources and the probability of occurrence of an ATEX (Explosive Atmosphere)
- Characterization of the area (danger and extent)
- Study of ignition sources
Classification of areas
There are three types of zones defined by the IEC (1986), by the Ministry of Labour (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: The explosive mixture is present permanently
- COMMON RISK: An explosive mixture of gases or vapours may form during normal operation of the installation.
- OCCASIONAL RISK: An explosive mixture can only appear in the event of abnormal operation of the installation
| AREAS | MATERIAL CATEGORY | |
|---|---|---|
| GAS | 0: Permanent presence 1: Occasional presence 2: Rare presence | -> 1G -> 2G or 1G -> 3G, 2G or 1G |
| DUST | 20: Permanent presence 21: Occasional presence 22: Rare presence | -> 1G -> 2G or 1G -> 3G, 2G or 1G |
These risks have 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 persist for a short period.
| DEVICE CATEGORY | FLAMMABLE SUBSTANCE | DEGREE OF PROTECTION | PROTECTION, DEFAULT VALUES | |
|---|---|---|---|---|
| GROUP I DEVICE (mines) | M1 | Methane, dust | Very high level | 2 protection channels or default values |
| M2 | Methane, dust | High level | 1 way protection Standard operation | |
| GROUP II DEVICE (mines) | 1 | Gases, vapors, mists, dusts | Very high level | 2 protection channels or default values |
| 2 | Gases, vapors, mists, dusts | High level | 1 way protection Common and frequent disturbance | |
| 3 | Gases, vapors, mists, dusts | Standard | Required level of protection |
The marking
ATEX regulatory marking refers to the marking requirements for equipment intended for use in hazardous (explosion-risk) areas. Equipment must be marked with the ATEX directive number, zone category and manufacturer information.
ATEX normative marking refers to specific standards that define the requirements for equipment used in hazardous areas. ATEX standards include requirements for the design, construction, performance and marking of equipment to ensure its safe use in potentially explosive environments.
Zoning is used to identify locations where an ATEX may form , but also to determine the appropriate equipment to use in risk areas. Each device present on the premises, whether electrical or not, must comply with the technical requirements associated with each type of zone. Only certified products with specific markings can be used in an ATEX zone.
The specific ATEX marking is a requirement of the European ATEX Directive. It allows the employer to ensure the conformity, required by the ATEX Directive 2014/34/EU, of its equipment. An ATEX marking must include:
- The “CE” symbol of the European Commission
- a sequence of four digits corresponding to the notified body responsible for conformity control
- the ATEX logo (a hexagon in which the letters “E” and “x” are inscribed)
- a series of numbers and letters indicating the nature and intensity of the explosive risk
There are different ATEX zones that determine the level of potential danger in a given area. The zones are defined as follows:
Zone 0: An area in which a gas, vapor or dust explosion may occur continuously.
Zone 1: An area in which an explosion of gas, vapour or dust may occur occasionally.
Zone 2: An area where a gas, vapor or dust explosion is unlikely.
ATEX zones are determined based on the quantity, nature and duration of the presence of explosive gas, vapour or dust 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 classification of hazardous zones for the 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 an explosive mixture occurring. Outside the classified zone, it is therefore possible to use the industrial standard.
Remarks
- 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 areas where there is fixed electrical equipment (except sensors).
- Devices certified for zone 21 cannot be used in zone 1.
- ATEX “gas” certified devices (including 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 casing. However, there are many devices with dual "gas" and "dust" certification that can be used in both types of environment./p>
Classification of equipment for use in ATEX zones
| CLASSIFICATION OF DANGEROUS AREAS | EUROPEAN/IEC CLASSIFICATION | |||
|---|---|---|---|---|
| Substances flammable | Temporary behavior of flammable substances in hazardous locations | Areas types | Equipment required for installation | |
| Equipment group | Hardware protection level | |||
| Gas Vapors | is present permanently, for long periods or frequently | Zone 0 | II | Ga |
| is likely to occur occasionally during normal operation | Zone 1 | II | Gb | |
| is not likely to occur during normal operation, or, if it does occur, is only of short duration | Zone 2 | II | Gc | |
| Dust | is present permanently, for long periods or frequently | Zone 20 | I | Yes |
| is likely to occur occasionally during normal operation | Zone 21 | I | Db | |
| is not likely to occur during normal operation, or, if it does occur, is only of short duration | Zone 22 | I | Dc | |
| Dust | - | Mines | III | My |
| - | Mines | III | Mb | |
| SUBDIVISION OF GASES AND VAPORS | ||||
|---|---|---|---|---|
| Equipment usable in the group | Gas or vapors | |||
| ammonia methane ethane propane | ethyl alcohol cyclohexane n-butane | n-hexane essence | acetaldehyde | |
| city gas, acrylonitrile | ethylene ethylene oxide | ethylene glycol | ethyl ether | |
| hydrogen | ethine (acetylene) | carbon disulfide | ||
According to the same principle as for gases and vapors, dusts are divided into 3 groups.
| DUST | |
|---|---|
| IIIA | Flammable volatiles |
| IIIB | Non-conductive dust |
| IIIC | Non-conductive dust |
Each type of dust has been the subject of detailed studies to determine their flammability characteristics (INRS brochures/Silos guide, etc.). The particularity of dust is that their auto-ignition temperatures differ depending on whether the dust is in clouds or layers. As many other parameters can modify these auto-ignition values (particle size, humidity, ambient temperature, etc.), a calculation integrating a safety margin must be carried out for each case.
| SPECIFIC EQUIPMENT CONDITIONS | |
|---|---|
| Requirements | Marking |
| Equipment without specific conditions | - |
| Equipment with special protection, may be marked | X |
| Ex component that requires additional certification before any use in hazardous areas | U |
