1. Zones and equipment categories
European hazardous-area classification distinguishes gas zones (0, 1, 2) and dust zones (20, 21, 22). Lower number = more exposure.
- Zone 0 / 20 — explosive atmosphere is present continuously or for long periods (inside a tank vapour space, dust silo headspace).
- Zone 1 / 21 — explosive atmosphere likely during normal operation (loading station, manhole vicinity).
- Zone 2 / 22 — explosive atmosphere not likely during normal operation but may occur briefly (general process area outdoors).
The ATEX directive (2014/34/EU) maps zones to equipment categories 1, 2, 3 (gas) and 1D, 2D, 3D (dust). The shorthand: Category 1 equipment is suitable for Zone 0, Category 2 for Zone 1 (and Zone 0 with extra protection), Category 3 for Zone 2 only.
The pressure transmitter reference shows how ATEX category drives the device selection in process-plant service.
2. Protection methods
A device achieves its category through one or more protection methods identified by lower-case Ex letters. The most common in process plants:
- Ex ia (intrinsic safety) — energy is limited so any spark or hot surface cannot ignite the atmosphere. Mandatory for Zone 0.
- Ex ib — intrinsic safety for Zone 1 and 2 only.
- Ex d (flameproof) — enclosure contains any internal explosion without external ignition. Common in Zone 1 outdoor.
- Ex e (increased safety) — no internal arcing sources; enclosure provides additional mechanical protection.
- Ex ec (level of protection "c") — Zone 2 only, lower cost than full Ex e.
- Ex p (pressurized) — internal pressure of inert gas prevents atmosphere ingress. Common for analyzer cabinets.
Combinations are common (e.g., a control valve might be Ex d for the solenoid and Ex ia for the position feedback) and are stated explicitly on the nameplate.
3. Reading the nameplate
An ATEX marking string looks like:
CE 1180 II 2 G Ex db IIC T4 Gb
Decoded:
- CE 1180 — CE mark, notified body number.
- II — equipment group II = surface installations (group I is mining).
- 2 — category, so suitable for Zone 1 and Zone 2.
- G — for gas atmospheres (D = dust).
- Ex db — protection method, flameproof to EPL Gb.
- IIC — gas group, IIC covers acetylene and hydrogen (strictest), IIB covers ethylene, IIA covers propane.
- T4 — temperature class, max 135°C surface temperature.
- Gb — equipment protection level (EPL) Gb for Zone 1.
For a control valve with electric or pneumatic actuator, both the actuator body and the position feedback need their own marking; never assume one rolls up to the other.
4. ATEX vs IECEx — when each applies
ATEX is the European Directive 2014/34/EU — legally required for any equipment installed in the EU/EEA in a classified area. IECEx is the international scheme administered by the IEC.
Practically:
- EU-only installation — ATEX is mandatory and sufficient.
- Global skid that may ship to non-EU — IECEx is recognised more broadly. Many Asian and Middle Eastern markets accept IECEx directly or through a national overlay (e.g., NEPSI in China, KCS in Korea).
- US/Canada — need separate UL / CSA certification under the Class/Division or Class/Zone system. IECEx is being recognised more often through the IECEx Mark, but a separate North American mark is still usually required.
Most Tier-1 vendors ship devices with both ATEX and IECEx markings at no price premium. Asking for both during purchase is essentially free insurance against future relocation.
5. Buying with these standards in mind
Three buying habits that pay back:
- Standardise the plant on the minimum acceptable protection method for each zone. Mixing Ex d, Ex ia, and Ex e in the same area without documentation multiplies the inspection workload.
- Specify the temperature class one step stricter than the worst-case process temperature plus 20°C margin. Cheap insurance against upset conditions.
- Demand the full certification dossier (EC-type examination certificate, IECEx CoC, QAN/IECEx QAR) at PO stage. Chasing a missing CoC at commissioning is what delays projects.
6. Documentation and inspection
EN 60079-17 (and IEC equivalent) defines initial, periodic, and sample inspections for installed equipment. The inspection class (visual, close, detailed) and frequency are driven by the zone classification and environmental severity.
Plant operators must keep an Ex equipment register linking every tagged device to its certificate, declared category, and last inspection date. The register is the first thing an HSE auditor or notified body inspector asks for.
Flow instrumentation in hazardous service deserves its own column in the register: many flow meters (Coriolis, vortex, ultrasonic) ship in multiple Ex variants, and the wrong sub-model in the wrong zone is one of the easiest non-conformances to write up at audit.
Frequently asked questions
Is ATEX the same thing as Ex marking?
ATEX is the EU directive. Ex marking is the device-level identification of protection method, gas group, and temperature class — used by both ATEX and IECEx schemes. The Ex marking is a subset of the full ATEX nameplate.
Do I need IECEx if my plant is only in the EU?
No. ATEX is sufficient. But ordering devices with both marks adds no cost from most major vendors and protects you if you later ship the equipment elsewhere.
Can I use a Zone 1 device in a Zone 2 area?
Yes — equipment certified for a more onerous zone can always be used in a less onerous zone. The reverse is not true.
What's the difference between IIA, IIB, and IIC gas groups?
IIA covers propane-like gases (easier to contain). IIB covers ethylene. IIC covers acetylene and hydrogen — the most volatile, requiring the tightest enclosure gaps and lowest energy limits. Plant atmospheres rarely contain hydrogen; check the actual gas group of your service before paying for IIC equipment.
Does ATEX apply to mechanical equipment with no electrical parts?
Yes. Any equipment with a potential ignition source — including hot surfaces, friction sparks, or stored mechanical energy — falls under ATEX if installed in a classified area. Pumps, blowers, and gearboxes commonly carry ATEX marks.