What is ATEX?
ATEX is a European standard for equipment and work environments where explosive atmospheres may occur. It regulates the safe use of equipment in environments with flammable gases, vapours, mist, or dust. Here, we take a closer look at the topic.
Risks and classification plan
When there is a risk of an explosive mixture of gas or dust, the facility owner or the party using the premises is obliged to ensure that a classification plan is prepared for that area. This “classification” then determines the requirements placed on the equipment to be installed within the area.
Depending on how often there is a risk of explosion in the area, it is divided into zones. The heat emitted by installed equipment is a source of ignition for the explosive substance. Therefore, the ignition temperature of the substance and the hottest point of the equipment must not be too close to each other. For this reason, temperature classes must be specified.
The speed and pressure of an explosion also vary, which means that the substance’s explosion group must be specified. When the installer then selects equipment/product, they review the Ex certificate and the product nameplate and choose the version that matches the classification.
How the marking on the nameplate should appear is determined by the certification and is stated in the Ex certificate. Standards and handbooks are available as guidance for installation and maintenance.
Classification plan
To clearly show where the risk areas are and to document this, it must be possible to see on layout plans and building drawings how these so-called zones extend. The zones—six in total—are marked with lines, squares, and circles on the drawings so that the correct equipment can be selected for a specified installation location.
Please note that it is not only in the horizontal plane that it is important to see the zone boundaries, but also vertically. For example, with heavy gases, the lighting may not need to be selected as Ex-rated, whereas with light gases it is precisely the lighting that is most important to select correctly.
Zones
Explosive gases:
Zone 0 Risk area in which an explosive gas atmosphere is present continuously, for long periods, or frequently.
Zone 1 Risk area in which an explosive gas atmosphere is expected to occur regularly or occasionally during normal operation.
Zone 2 Risk area in which an explosive gas atmosphere is not expected to occur during normal operation, but if it does occur, it will only be for a short duration.
Explosive dust:
Zone 20 Risk area in which an explosive dust atmosphere is present continuously, for long periods, or frequently.
Zone 21 Risk area in which an explosive dust atmosphere is expected to occur regularly or occasionally during normal operation.
Zone 22 Risk area in which an explosive dust atmosphere is not expected to occur during normal operation, but if it does occur, it will only be for a short duration.
Temperature class
Flammable substances such as gas, vapour, or dust are divided (classified) into different temperature classes according to their ignition temperature—that is, the lowest temperature at which the substance self-ignites upon contact with a surface. T1 is the lowest class and T6 is the highest class.
Explosive gases:
T1 450°C< ignition temperature for the gas
T2 300°C< ignition temperature for the gas <450°C
T3 200°C< ignition temperature for the gas <300°C
T4 135°C< ignition temperature for the gas <200°C
T5 100°C< ignition temperature for the gas <135°C
T6 85°C< ignition temperature for the gas <100°C
Explosive dust:
Written in plain text as the number of degrees (e.g., 65°C)
Standards and handbooks
EN IEC 60079-0 General requirements
EN IEC 60079-1 Exd Flameproof enclosure
EN IEC 60079-2 Exp Pressurization
EN IEC 60079-5 Exq Powder filling
EN IEC 60079-6 Exo Oil immersion
EN IEC 60079-7 Exe Increased safety
EN IEC 60079-11 Exi Intrinsic safety
EN IEC 60079-15 Exn Type of protection for zone 2
EN IEC 60079-18 Exm Encapsulation
EN IEC 60079-10 Handbook 426 Classification of hazardous (explosive) areas
EN IEC 60079-14 Handbook 427 Electrical installations design, selection and erection
EN IEC 60079-17 Handbook 427 Inspection and maintenance of electrical installations
EN IEC 60076-32 Handbook 433 Static electricity in hazardous (explosive) areas
Explosion group
Flammable substances are classified into explosion group IIA, IIB, or IIC based on the energy with which they can be ignited by sparks and their ability to propagate a flame through a gap. This classification is used to standardize the protective properties of equipment that could normally be an ignition source. Group I refers only to methane–air mixtures in mines. Group II is divided into different subgroups depending on the type of gas mixture, where IIC is the highest-risk group.
Explosive gases:
IIA E.g., propane, butane, kerosene, aviation gasoline, and methane
IIB E.g., carbon monoxide, ethanol, ethene, and acrylic acid
IIC E.g., hydrogen, acetylene, and carbon disulfide
Dust is classified in a different way.
Explosive dust:
IIIA Combustible dust particles larger than 0.5 mm
IIIB Non-conductive dust particles smaller than 0.5 mm
IIIC Conductive dust particles.
Marking
The product must bear a marking that corresponds to the Ex certificate.
It must include: