ATEX Zones Explained: Choosing Explosion-Proof LED Lighting for Hazardous Areas

Anywhere flammable gas, vapour, mist or combustible dust can build up in the air — a paint shop, a flour mill, a distillery, a fuel depot, a waste-water works, a grain store — is a potentially explosive atmosphere, and the lighting in it must be incapable of setting it off. In the UK that is a legal duty under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR), which require the employer to classify the hazardous areas into zones and to install only equipment certified for the zone. This guide explains the zones, the equipment categories and the markings, so that an explosion-proof lighting specification can be read and checked rather than taken on trust.

The zones: how often the hazard is present

Zoning describes how likely an explosive atmosphere is, not how dangerous the substance is. For gases and vapours: Zone 0 is an area where an explosive atmosphere is present continuously or for long periods — inside a tank, for example. Zone 1 is where it is likely to occur in normal operation, occasionally — around a filling point or a vent. Zone 2 is where it is not likely in normal operation and, if it does occur, will persist only briefly — the wider area around a process. For combustible dusts the equivalents are Zones 20, 21 and 22. The zone classification is produced by a competent person as part of the DSEAR risk assessment and recorded on a hazardous-area drawing; it is that drawing, not the lighting supplier, that decides what is needed where.

Equipment categories and protection levels

Equipment is certified into categories that map onto the zones. Under the UK regime — the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016, marked with UKCA and the Ex hexagon (UKEX in industry shorthand) in Great Britain, mirroring the EU's ATEX Directive 2014/34/EU which still applies in Northern Ireland, and with CE/ATEX-marked equipment continuing to be accepted in Great Britain — Group II equipment for surface industries is divided into Category 1 (Zones 0 and 20), Category 2 (Zones 1 and 21) and Category 3 (Zones 2 and 22). The international IECEx scheme, built on the same IEC 60079 standards, expresses the same idea as Equipment Protection Levels: Ga/Da, Gb/Db and Gc/Dc. A Category 2 or Gb fitting may be used in Zone 1 or Zone 2; a Category 3 or Gc fitting only in Zone 2. Buying a higher category than the zone requires is legitimate; buying a lower one is illegal.

Protection concepts: how the fitting stays safe

The letters after "Ex" on a label describe the method used to prevent ignition. Ex d, flameproof, encloses the electrics in a housing strong enough to contain an internal explosion and cool the gases as they escape — the traditional heavy, cast-alloy luminaire. Ex e, increased safety, uses construction that prevents arcs, sparks and hot spots occurring in the first place, and is common for LED luminaires and their terminal boxes. Ex nA or Ex ec, non-sparking, is a lighter form for Zone 2 only. Ex t is protection by enclosure for dust atmospheres, relying on a sealed IP6X housing and controlled surface temperature. Ex m encapsulates components in resin, often used for LED drivers. A modern explosion-proof LED luminaire typically combines two or more — for example Ex db eb — to cover the driver, the LED board and the wiring compartment appropriately.

Gas groups and temperature classes

Two further codes narrow the certification to the substance present. The gas group ranks how easily the gas is ignited: IIA (propane and most fuels), IIB (ethylene and similar) and IIC (hydrogen and acetylene, the hardest to protect against); a IIC-rated fitting covers all three. The temperature class states the maximum surface temperature the equipment can reach, from T1 (450 °C) down to T6 (85 °C), and must be below the auto-ignition temperature of the gas or the ignition temperature of the dust layer. T4 (135 °C) is a common requirement; T6 is the most demanding. LED luminaires, which run cool compared with discharge lamps, usually achieve T4 without difficulty and often T5 or T6, sometimes at a reduced ambient rating, which is one of the reasons LED has replaced older sources in hazardous areas so quickly.

Reading a marking and checking a specification

• A typical marking reads: II 2 G Ex db eb IIC T6 Gb, and for dust II 2 D Ex tb IIIC T85°C Db. That is: surface industry, Category 2, gas (or dust), protection concepts, gas or dust group, temperature class (or, for dust, maximum surface temperature), protection level.
• Match the category and EPL to the zone on the hazardous-area drawing; match the gas group and temperature class to the substances listed in the DSEAR assessment.
• Ask for the certificate, not just the marking. For Category 1 and 2 equipment, a UKEX or ATEX certificate from an approved or notified body — and ideally an IECEx certificate — should name the exact product and any conditions of use, marked by an X suffix on the certificate number. Category 3 electrical equipment may legally be self-declared by the manufacturer, so a third-party certificate there is a sign of diligence rather than a requirement.
• Check ambient temperature and IP rating separately: a fitting certified for −20 °C to +40 °C is not certified at +55 °C in a plant room, and dust zones need IP6X as part of the protection (IP5X is permitted for Ex tc with non-conductive dusts). Our guide to IP ratings covers the second point.
• Plan for emergency lighting in the same terms: escape routes through hazardous areas need emergency luminaires certified for the zone, not standard ones.
• Install and maintain to BS EN 60079-14 and -17, by competent persons; a certified fitting installed with the wrong gland or an unsealed conduit is no longer a certified installation.

The zone comes from the risk assessment. The category comes from the certificate. A hazardous-area lighting specification is simply the discipline of making the second match the first.

Explosion-proof lighting used to mean heavy, hot, high-maintenance fittings. LED has changed that: lower surface temperatures, longer life and far fewer relamping visits into areas where every intervention is a permit-to-work. Regents LED's explosion-proof range covers Zone 1/21 and Zone 2/22 applications for the industrial and process sector, with certificates supplied with every quotation so the match to the hazardous-area drawing can be checked before anything is ordered.