Skip to content

Choosing equipment for hazardous areas: zones, protection types and markings

Guide · 3 min read

Where flammable gas, vapour or combustible dust can be present, every motor, light fitting and junction box must suit the area it sits in. Here is how to read the classification and the markings.

Key takeaways

  • The area classification (zone) says how often an explosive atmosphere is expected; equipment must be rated for that zone.
  • Check five things on every Ex marking: protection type, equipment group, temperature class, equipment protection level (EPL) and certificate number.
  • Certification is the start, not the end: correct installation, inspection and records keep equipment safe in service.
01

Start with the area classification

Hazardous-area classification divides a plant into zones according to how likely an explosive atmosphere is. Under the IEC 60079 series, used in most of the world, gas and vapour areas are Zones 0, 1 and 2; dust areas follow the same pattern as Zones 20, 21 and 22. Some North American projects use the Class and Division system instead, so check which scheme a project follows.

  • Zone 0: an explosive atmosphere is present continuously, for long periods or frequently.
  • Zone 1: an explosive atmosphere is likely to occur occasionally in normal operation.
  • Zone 2: an explosive atmosphere is not likely to occur in normal operation and, if it does, persists only for a short time.
02

Read the Ex marking

Every certified item carries a marking that tells you where it may be used. The main parts to check:

  • Protection type: for example Ex d (flameproof enclosure), Ex e (increased safety), Ex i (intrinsic safety) or Ex p (pressurisation). Each suits particular zones and kinds of equipment.
  • Equipment group: IIA, IIB or IIC for gases, where IIC (which covers hydrogen and acetylene) is the most demanding; IIIA to IIIC for dusts.
  • Temperature class: T1 to T6, showing the maximum surface temperature, which must stay below the ignition temperature of the gases present. T6 is the coolest.
  • Equipment protection level (EPL): Ga, Gb and Gc for Zones 0, 1 and 2, and Da, Db and Dc for Zones 20, 21 and 22. It links the equipment to the zones it suits.
  • Certificate number: usually under IECEx or ATEX, so you can check the certificate. An “X” after the number means there are specific conditions of use.
03

Match the equipment to the site

Selection starts from the area classification drawings and the hazardous-area schedule: the zone, gas group and temperature class of each location. Equipment rated for a more demanding zone, group or temperature class can be used in a less demanding one, but never the other way round. Gas and dust ratings are separate: equipment for a dust zone needs its own dust (Group III) rating.

Ambient conditions matter too. Unless the marking states otherwise, Ex equipment is certified for an ambient temperature of −20 °C to +40 °C, which Gulf sites often exceed. Check the rated ambient range, the ingress protection (IP) rating and the materials against the real site conditions, such as heat, dust and salt air.

04

Keep it safe in service

Certification only protects the plant if the equipment is installed and maintained as its certificate and the manufacturer’s instructions require. IEC 60079-14 covers design, selection and installation, IEC 60079-17 covers inspection and maintenance, and IEC 60079-19 covers repair and overhaul. A current hazardous-area register, with certificates and inspection records for every item, makes audits and later changes much simpler.

  • Use certified cable glands, adaptors and stopping plugs that match the equipment’s protection type.
  • Plan initial, periodic and sample inspections, and record the results.
  • Replace damaged or unidentifiable equipment rather than improvising a repair on site.

More insights