Reading ATEX markings — what does the Ex marking mean?
An Ex equipment marking tells you exactly where and in which atmosphere it can be used safely. Below I break down a typical gas and dust marking piece by piece — so you can tell at a glance whether a piece of equipment belongs in its zone.
How to read it — gas marking
Take a typical gas marking and split it into pieces:
ExExplosion-protected design.IISurface industry (I = mining).2GEquipment Category 2, for gas (G).Ex dbFlameproof enclosure (d), protection level "b".IICGas group (the strictest: hydrogen, acetylene).T4Max. 135 °C surface temperature.GbEPL — high protection level (Zone 1).How to read it — dust marking
The logic of a dust marking is similar, but with its own groups and the IP rating:
Ex tDust protection by enclosure.IIICConductive dust.T85°CMax. surface temperature (in °C for dust).DbEPL for dust (Zone 21).IP6XFull ingress protection against dust.Ex tD A21 IP6X — here A21 indicated Zone 21.
More real Ex markings, decoded
The same logic applied to markings you will actually see on nameplates:
Ex de IIC T4 Gb — a flameproof enclosure (d) combined with increased-safety (e) terminal chambers; gas group IIC, surface temperature ≤ 135 °C, EPL Gb for Zone 1.
Ex ia IIC T6 Ga — intrinsic safety at the highest level (ia), so it is permitted in Zone 0; T6 means a surface temperature ≤ 85 °C.
Ex db IIC T6 Gb — same as the first example, but rated to the stricter T6 class (≤ 85 °C), for atmospheres with a low ignition temperature.
Temperature classes (T1–T6) — gas
The T-class is the maximum permitted surface temperature of the equipment. It must always be lower than the ignition temperature of the gas present:
| T-class | Max. surface temperature |
|---|---|
T1 | 450 °C |
T2 | 300 °C |
T3 | 200 °C |
T4 | 135 °C |
T5 | 100 °C |
T6 | 85 °C |
EPL protection levels and zones
EPL (Equipment Protection Level) links the equipment to the zone. Read this alongside the zone classification:
| EPL | Atmosphere | Permitted zone |
|---|---|---|
Ga | Gas | Zone 0 (and 1, 2) |
Gb | Gas | Zone 1 (and 2) |
Gc | Gas | Zone 2 |
Da | Dust | Zone 20 (and 21, 22) |
Db | Dust | Zone 21 (and 22) |
Dc | Dust | Zone 22 |
Common Ex protection types
The letter in the marking tells you on which principle the equipment is protected against ignition:
Flameproof enclosure — the enclosure contains an internal explosion.
Increased safety — no ignition source in normal operation.
Intrinsic safety — energy limited so it cannot ignite (ia/ib/ic).
Pressurised — clean gas/air keeps the explosive atmosphere out.
Encapsulation — parts sealed inside a solid compound.
Dust protection by enclosure (for dusty areas).
Used for Zone 2; non-igniting in normal operation (formerly "n" type).
Ex marking — frequently asked questions
What does Ex db mean?
“Ex d” is a flameproof enclosure: it withstands an internal explosion and prevents it from spreading to the surrounding atmosphere. The “b” is the protection level (EPL Gb), suitable for Zone 1.
What is the difference between Ex db and Ex de?
Both use a flameproof enclosure (d). “Ex de” adds increased-safety (e) terminal or connection chambers, so the wiring compartment is protected by a second, complementary method.
What does Gb (or Ga, Gc) mean?
It is the Equipment Protection Level (EPL) for gas: Ga = Zone 0, Gb = Zone 1, Gc = Zone 2. Each level also covers the higher-numbered, less strict zones.
What does T4 mean on an Ex marking?
T4 is a temperature class — the maximum surface temperature of the equipment is 135 °C. It must always stay below the ignition temperature of the gas present.
Is an ATEX marking the same as an IECEx marking?
The core Ex marking (e.g. Ex db IIC T4 Gb) is essentially the same. ATEX adds the EU category format (e.g. II 2G) and the Ex hexagon; IECEx is the international scheme. More on what ATEX is.
Not sure whether the equipment belongs in its zone?
During an inspection I check the markings, the zone classification and the Ex compliance on site. Book a free 30–60 minute online needs assessment.