How to Read an ATEX Marking on a Two-Way Radio

Look at the label on an intrinsically safe radio and you will see something like this:

II 2G Ex ib IIC T4 Gb

Ten characters. Six separate pieces of information.

Most people buying radios have never had it explained. So they pick on price, or on brand, and hope the supplier got it right.

That is a gamble worth avoiding. Let me take the marking apart.

II — the equipment group

The first character says where the equipment can be used.

Group I is mining. Underground coal, and the surface installations of those mines, where firedamp (methane released from coal seams) is the hazard.

Group II is everywhere else. Refineries, chemical plants, pharmaceutical processing, flour mills, paint shops, distilleries, airports.

If your site is not a mine, you want Group II.

2G — the category and the atmosphere

The number is the category. It tells you which zone the equipment is fit for.

• Category 1 — Zone 0
• Category 2 — Zone 1
• Category 3 — Zone 2

The letter is what the atmosphere is made of. G for gas, vapour and mist. D for dust.

So 2G means category 2, gas. Suitable for Zone 1.

A radio will often carry more than one of these. II 2G and II 2D and I M2 on the same label means it is certified for gas, dust and mining.

Ex — the standard

This is simply the mark that says the equipment is explosion-protected and certified to the ATEX Directive 2014/34/EU and the IECEx scheme.

In Great Britain, the same requirements sit in the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016.

ib — the type of protection

This is the one that matters most, and the one most often skipped over.

ia and ib are both intrinsic safety. The circuit is designed so that it cannot release enough energy to ignite the atmosphere, either as a spark or as heat.

The difference is how many faults it survives.

ia stays safe with two independent faults. That is why an "ia" radio can go into Zone 0.

ib stays safe with one fault. Zone 1 and Zone 2.

Nearly every ATEX handheld on the market is ib. A few, such as the Hytera PD715IS and PD795IS, are ia.

IIC — the gas group

Only appears on gas certification.

• IIA — propane and similar
• IIB — ethylene
• IIC — hydrogen and acetylene

IIC is the hardest to achieve, because hydrogen ignites with very little energy. A IIC radio also covers IIB and IIA.

There is a catch. The standards cap radio-frequency power for IIC at 2 watts. A IIA radio has no such restriction and typically transmits at 4 or 5 watts.

Buy IIC when you do not need it, and you have quietly halved your range.

T4 — the temperature class

The maximum surface temperature the equipment will reach.

• T1 — 450°C
• T2 — 300°C
• T3 — 200°C
• T4 — 135°C
• T5 — 100°C
• T6 — 85°C

It must sit below the auto-ignition temperature of whatever is in your atmosphere. T4 covers the large majority of industrial gases.

For dust, the figure is given directly instead. T130°C means exactly that.

Gb — the equipment protection level

The last piece. EPL is a plain-language restatement of the risk.

• Ga — very high protection, Zone 0
• Gb — high protection, Zone 1
• Gc — enhanced protection, Zone 2

Dust uses Da, Db and Dc. Mining uses Ma and Mb.

And the bit that is not in the marking

There is one more thing on the label that catches people out.

Ta is the ambient temperature range. Something like -20°C ≤ Ta ≤ +50°C.

Outside that range, the certification does not apply. A radio rated to -20°C is not certified on a January nightshift on an exposed gantry at -25°C.

Putting it together

II 2G Ex ib IIC T4 Gb means: non-mining, category 2, gas atmosphere, intrinsically safe to one fault, hydrogen and acetylene, surface temperature under 135°C, Zone 1.

Read it once and it looks like alphabet soup.

Read it twice and it is a complete specification.

If you want a second pair of eyes on what your site actually needs, get in touch. That conversation costs nothing and takes about twenty minutes.

Craig