Reading an Ex marking
Equipment for hazardous areas carries a marking that says how it is protected and where it may be used. A typical ATEX and IECEx marking for a pressure transmitter reads:
II 2G Ex db IIC T4 Gb
- II: equipment group II, for places other than mines (ATEX)
- 2G: ATEX category 2 for gas, high protection, for zones 1 and 2
- Ex: explosion-protected equipment to the IEC 60079 series
- db: flameproof enclosure (IEC 60079-1) with level of protection “b”
- IIC: gas group IIC, which also covers IIB and IIA
- T4: maximum surface temperature 135 °C
- Gb: equipment protection level Gb, for zones 1 and 2
The decoder splits a marking into these parts, explains each one and works out the permitted zones, the gas or dust groups covered and the maximum surface temperature.
Zones and equipment protection levels
Hazardous areas are classified by how often an explosive atmosphere is present: zone 0, 1 or 2 for gas and zone 20, 21 or 22 for dust, from continuous to rare. IEC 60079-14 assigns the equipment protection level (EPL) each zone needs:
- Zone 0: Ga · zone 1: Ga or Gb · zone 2: Ga, Gb or Gc
- Zone 20: Da · zone 21: Da or Db · zone 22: Da, Db or Dc
The type of protection determines the level: intrinsic safety “ia” gives Ga, “ib” Gb, “ic” Gc; a flameproof enclosure “db” gives Gb.
Gas groups and temperature classes
Gases are grouped by how easily a flame passes through a gap and how little energy ignites them: IIA (e.g. propane), IIB (e.g. ethylene) and IIC (hydrogen, acetylene). Equipment for IIC may be used for IIB and IIA, not the other way round. Dusts are grouped as IIIA (combustible flyings), IIIB (non-conductive dust) and IIIC (conductive dust).
The temperature class limits the hottest surface: T1 450 °C, T2 300 °C, T3 200 °C, T4 135 °C, T5 100 °C, T6 85 °C. Dust equipment states the temperature directly, e.g. T85 °C.
Checking a site
Enter the zone, the substance group and its ignition temperature to check the equipment against IEC 60079-14:
- The EPL must be permitted in the zone
- The equipment group must cover the substance group
- For gas, the maximum surface temperature must be below the ignition temperature
- For dust, it must not exceed 2/3 of the cloud ignition temperature, nor the ignition temperature of a 5 mm layer minus 75 K
Without a marked ambient range (Ta), the equipment is rated for −20 to +40 °C.
North American markings
US and Canadian equipment may be marked to the Division system, e.g. “Class I, Division 1, Groups A, B, C, D, T4”, or to the zone system with an “AEx” prefix. The decoder explains classes (I gas, II dust, III fibres), divisions and the groups A to G.
Common mistakes
Reading the category or EPL in isolation. Both must match the zone; a Gc device is not permitted in zone 1, however high its gas group.
Ignoring the suffix X. A certificate number ending in X has specific conditions of use, such as impact protection or a limited ambient range. They are part of the approval.
Matching only the gas group. A IIC device with T6 can still be unsuitable if the ambient temperature exceeds its marked range.
Frequently asked questions
Does the decoder replace the certificate?
No. It explains the marking. The certificate, the manufacturer’s instructions and the specific conditions of use are binding.
What about intrinsically safe loops?
An “ia” or “ib” transmitter must be connected through a suitable barrier or isolator, and the loop parameters (Ui, Ii, Pi, Ci, Li) must match. The loop power calculator checks the voltage budget, including the barrier’s resistance.
Can it read several markings at once?
Enter one marking at a time, e.g. the gas marking and the dust marking of a dual-rated device separately.