A nameplate that reads Ex db IIC T6 Gb is carrying at least five separate decisions in nine characters — which protection concept, which gas group, which surface temperature, and which equipment protection level. Read one of them wrong and the right product goes into the wrong place.
This guide walks a marking left to right, in the order the standard writes it, and then covers the three things buyers most often miss: the letter after the protection concept, the dust marking that sits next to the gas marking, and the ambient temperature range that quietly limits where the equipment can be installed.
The marking, left to right
Every IEC 60079 marking is built from the same blocks in the same order. Once you know the order, you can read any nameplate on any manufacturer’s equipment.
| Block | Example | What it tells you |
|---|---|---|
| Prefix | Ex | Built to the IEC 60079 / EN 60079 series for explosive atmospheres |
| Protection concept | db | How the equipment is protected — and the EPL that concept achieves |
| Gas group | IIC | Which gases or vapours the equipment is certified for |
| Temperature class | T6 | The highest surface temperature the equipment can reach |
| Equipment protection level | Gb | Which zone the equipment is allowed to work in |
| Certificate reference | IECEx XYZ 21.0001 | The certificate you should be able to download and check |
The letter after the concept: “db” is two pieces of information
This is the single most misread part of a modern marking. Since the 2017 edition of IEC 60079-0, the equipment protection level is written inside the protection concept as a small letter.
So in Ex db, the d is flameproof enclosure and the b is the EPL — not a second protection concept. It is not “Ex d and Ex b”. In Ex eb, the e is increased safety and the b is again the EPL.
When two concepts share one nameplate, each one carries its own letter. Ex db eb IIC T4 Gb means the item uses flameproof enclosure and increased safety, both at EPL b, for gas group IIC at temperature class T4, with an overall EPL of Gb. That combination is common on distribution and control equipment, where a flameproof main enclosure carries increased-safety terminals and wiring.
Protection concepts and the standard behind each one
The concept letter tells you how ignition is prevented. The mechanical answer — a strong enclosure, a sealed winding, a limited energy circuit — determines almost everything about size, weight, cost and where the item can be mounted.
| Marking | Concept | Standard | How it works |
|---|---|---|---|
| Ex d | Flameproof enclosure | IEC 60079-1 | An internal explosion is contained, and the flame path cools it before it escapes |
| Ex e | Increased safety | IEC 60079-7 | No sparks or hot surfaces in normal operation — larger clearances, better insulation |
| Ex i | Intrinsic safety | IEC 60079-11 | Energy in the circuit is too low to ignite the atmosphere, even as a fault |
| Ex p | Pressurisation | IEC 60079-2 | The enclosure is held at positive pressure with clean air or inert gas |
| Ex m | Encapsulation | IEC 60079-18 | Parts that could spark are sealed in resin or compound |
| Ex q | Powder filling | IEC 60079-5 | Sand or powder surrounds the ignition source |
| Ex o | Oil immersion | IEC 60079-6 | Live parts are submerged in oil |
| Ex n | Non-sparking | IEC 60079-15 | Zone 2 only — no sparking or hot surfaces in normal operation |
| Ex t | Protection by enclosure (dust) | IEC 60079-31 | Seals the enclosure against dust ingress and controls surface temperature |
In practice, most industrial luminaires are Ex d or Ex de: a flameproof body with the driver compartment separated from the light source. On our own range, the ZBD119 platform luminaire and the BPY fluorescent luminaire both carry flameproof markings, while the AC plug and socket uses Ex db eb, because the socket body has to be flameproof while the terminal area is built to increased safety.
Gas group: IIA, IIB, IIC
The gas group answers a single question: how easily does the gas present in your plant ignite? The test is the maximum experimental safe gap (MESG) — the widest gap through which a flame will not pass.
| Group | MESG | Typical gases | Practical effect |
|---|---|---|---|
| IIA | > 0.9 mm | Propane, methane, butane, natural gas | The easiest group to design for |
| IIB | 0.5 – 0.9 mm | Ethylene, coke oven gas, hydrogen sulphide | Flame paths must be longer and tighter than IIA |
| IIC | < 0.5 mm | Hydrogen, acetylene, carbon disulphide | The strictest group — usually the heaviest and most expensive enclosure |
Equipment marked IIC can be used where IIA or IIB is required, because it is certified to the hardest case. The reverse is never true. If you see IIA on a nameplate, ask for an IIC certificate before you put it anywhere near a hydrogen or acetylene line.
Group I is a separate case: it covers mining applications with firedamp, and it is certified under different rules from the surface-industry groups.
Temperature class: the number that decides whether the luminaire is allowed
The temperature class caps the highest surface temperature the equipment can reach, compared against the ignition temperature of the gas. T6 is the most restrictive and T1 the least.
| Class | Max surface temperature | Gases this class covers as an example |
|---|---|---|
| T1 | 450 °C | Hydrogen |
| T2 | 300 °C | Ethylene |
| T3 | 200 °C | Petrol, hexane |
| T4 | 135 °C | Acetaldehyde |
| T5 | 100 °C | Carbon disulphide |
| T6 | 85 °C | — |
The same logic runs the other way on dust. There is no T-class for combustible dust; instead the marking states the surface temperature directly, as in Ex tb IIIC T80°C Db. Note that T80°C and T6 are not interchangeable. A dust layer sitting on a hot surface ignites far more easily than a gas cloud, so dust markings are usually set well below the gas class on the same item.
Equipment protection level and which zone it allows
The EPL is the block most often skipped, and the one that decides whether you may install the item at all.
| EPL | Atmosphere | Permitted zone |
|---|---|---|
| Ga | Gas | Zone 0, 1 and 2 |
| Gb | Gas | Zone 1 and 2 |
| Gc | Gas | Zone 2 |
| Da | Dust | Zone 20, 21 and 22 |
| Db | Dust | Zone 21 and 22 |
| Dc | Dust | Zone 22 |
A common and expensive mistake is to buy Ga equipment for a Zone 2 area “for safety”. It is not wrong to install it, but you pay for enclosure strength you will never need. The opposite mistake — Gc equipment on a Zone 1 pipe rack — is a compliance failure and a rejection at the gate.
Two markings on one nameplate
Equipment certified for both gas and dust carries both strings, separated by a semicolon. Both must be satisfied for the installation; the dust marking does not excuse the gas one.
A real example from our BBJ sound and light alarm reads:
Three things that quietly limit an installation
The ambient range. Unless the nameplate says otherwise, certification assumes an ambient temperature between −20 °C and +40 °C. If the marking states an extended range such as −40 °C ≤ Ta ≤ +55 °C, that range was tested and certified. If your site sits at +50 °C in summer and the nameplate still says the default, the certificate does not cover your installation.
The “X” after the marking. An X suffix means the certificate carries specific conditions of use. Those conditions live in the certificate schedule or the instruction sheet, not on the nameplate — and they are binding. Typical conditions cover the cable entry, the gland, or a maximum ambient.
The cable entry. The thread on the enclosure (G, NPT or metric) is part of the certified assembly. A gland that does not match the thread, or an adapter that is not covered by the certificate, breaks the marking even if every other component is correct.
What to check before you accept a quotation
- Write down the zone, the gas or dust group, and the ignition temperature at the installation point.
- Convert that into a required EPL, group and temperature class.
- Ask for the certificate, not a datasheet, and check that the certificate covers the exact model and configuration quoted.
- Compare the certificate’s ambient range against your site’s extremes.
- Confirm the cable entry thread and the gland that goes with it.
If a supplier cannot produce the certificate for the quoted model within a day, that is the answer to a different question.
Common questions
Can I use IIB equipment in a IIC area?
No. Group ordering is one-directional: equipment certified for the harder group (IIC) may be used in areas requiring an easier group (IIA or IIB), but IIB equipment is not certified for IIC gases such as hydrogen or acetylene.
Is T6 always better than T4?
T6 is more restrictive on surface temperature, so it survives a stricter ignition temperature. But T6 equipment is not automatically the right choice: it can be larger, heavier and more expensive, and on dust installations the controlling number is the stated surface temperature in °C rather than a T-class.
What does the “b” in Ex db mean?
It is the equipment protection level, not a second protection concept. Ex db is a flameproof enclosure (d) certified to EPL b, which permits Zone 1 and Zone 2.
Where can I check an IECEx certificate?
Issued IECEx certificates, reports and licences are public. They can be searched on the IECEx On-Line Certification System; the IECEx site itself explains the system at iecex.com. We cover the checking process in detail in how to verify an explosion-proof certificate.
Send us your area classification and we will match the marking to it. Zone, gas or dust group, ambient range and the equipment you need — we will come back with the exact marking the installation requires.
