# Gas Groups IIA, IIB and IIC: Why the Safest Radio May Not Be the Right One
Two watts against four.
That is the trade-off buried inside the ATEX gas group, and almost nobody mentions it at the point of sale.
Let me explain what you are actually choosing between.
## What the gas group measures
Gases do not ignite equally easily.
The classification is based on how readily a gas can be ignited and how easily a flame can pass through a narrow gap. Hydrogen is far more dangerous on both counts than propane.
So gases are sorted into groups.
**IIA** — propane, petrol, methane, most solvents. The largest group by far.
**IIB** — ethylene, ethylene oxide, coke oven gas.
**IIC** — hydrogen and acetylene. The most easily ignited.
The rule is cumulative. Equipment certified IIC is also acceptable for IIB and IIA. IIB covers IIA. IIA covers only IIA.
So IIC is the safest choice. Why would anyone buy anything else?
## Because of the power cap
An intrinsically safe radio is safe because its energy is limited below the level that could ignite the atmosphere. That applies to the radio-frequency energy it transmits, not just the sparks inside it.
The lower the ignition energy of the gas, the lower the permitted RF power.
For **IIC**, the standards cap transmit power at **2 watts**. Motorola state it plainly in the R7Ex data sheet: max 2 W allowed per ATEX/IECEx standards.
For **IIA**, there is more headroom. The same radio families are typically sold at **4 watts** UHF, and 5 watts on VHF.
Compare like for like:
- Entel DT982 (IIC): 2 W EIRP
- Entel DT882 (IIA): 4 W
- Hytera HP715Ex IIC: 2 W
- Hytera HP715Ex IIA: 4 W UHF, 5 W VHF
- Motorola R7Ex IIC: 2 W
- Motorola R7Ex IIA: 4 W
Same radio. Same body. Double the power on the IIA version.
## What double the power buys you
Not double the range. RF does not work that way.
Going from 2 W to 4 W is a 3 dB gain. In free space that is roughly a 40% increase in distance. Inside a plant, with steel structures, tanks and reinforced concrete in the way, the real-world gain is smaller and harder to predict.
But it is not nothing. It can be the difference between a usable talk-path across a site and a dead spot at the far end of the tank farm.
Entel quote a further practical difference. Their IIC models run 16.5 hours analogue and 19.5 hours digital. Their IIA models, transmitting at higher power, run 13.5 and 16.5. Better range, shorter shift life.
## So which do you buy?
Go back to the hazardous area classification.
Your site drawing does not just say "Zone 1". It says which substances create the hazard. From that comes the gas group.
If your dangerous substances are all IIA — and on a great many sites they are — then a IIA radio is fully compliant and gives you materially better coverage.
If you have hydrogen anywhere in the process, you need IIC. Refineries with hydrotreaters, chlor-alkali plants, battery charging rooms, ammonia production. No debate.
If you are not sure, or you have a mixed site, or the process may change, IIC is the defensible choice. You take the range penalty and you fix coverage with infrastructure instead.
## Fixing coverage the right way
If IIC is genuinely required and 2 watts will not reach, do not start hunting for a workaround. The power limit exists for a reason.
Reach further with the system, not the handset.
- A repeater lifts the effective coverage of every radio on the site.
- Better antenna siting often gains more than a power increase would.
- DMR digital holds usable audio further out than analogue, because it does not degrade into static the same way.
- Bi-directional amplifiers or leaky feeder can cover tanks, tunnels and voids that no handheld will reach.
Just imagine sizing the system properly once, rather than fielding complaints about dead spots for the next five years.
## The question to ask your supplier
Not "what is your best ATEX radio."
Ask: "Which gas group does my site actually require, and what does that cost me in transmit power?"
If they cannot answer, that tells you something.
Craig