| Term | What it means | Where it comes from |
|---|---|---|
| Zone 0 | Explosive atmosphere present continuously | Area classification drawing |
| Zone 1 | Likely in normal operation | Area classification drawing |
| Zone 2 | Unlikely, and short-lived if it happens | Area classification drawing |
| Group IIA | Propane-like gases | Process gas list |
| Group IIB | Ethylene-like gases | Process gas list |
| Group IIC | Hydrogen and acetylene | Process gas list |
| T1 to T6 | Maximum surface temperature, 450 °C down to 85 °C | Auto-ignition temperature of the gas |
| Ex d | Flameproof — contains an internal explosion | Protection concept |
| Ex i | Intrinsically safe — limits energy so ignition cannot occur | Protection concept |
Zone is a legal designation set by the plant designer, not something a supplier can infer from the process. If the drawing says Zone 1 and you order a Zone 2 instrument, the installation is non-compliant regardless of intent.
IIC is the strictest. An instrument certified for IIB is not acceptable in a hydrogen area. Certification for IIC covers IIB and IIA as well.
T6 is the strictest — the instrument surface must stay below 85 °C. Ambient temperature in an Indian plant room in May matters here, and it is often what forces a step down in class.
Ex d puts the electronics in an enclosure strong enough to contain an internal explosion — simple wiring, heavy enclosure. Ex i limits the energy in the circuit so an explosion cannot start — light instrument, but you need a certified barrier and the whole loop has to be documented. For a handful of points, Ex d is usually simpler and cheaper.
A certified enclosure with an uncertified gland is not a certified installation. Ex d double compression glands, the right thread, and blanking plugs for unused entries — all of it forms part of the certification.
Every flameproof item we supply ships with a copy of its CCoE / PESO certificate. Your safety file needs it, and an auditor will ask.
Ex d IIC T6 as a default for field instruments, with CCoE certificate copies filed for each tag.
Usually Zone 1 IIA or IIB — check the solvent list, because some ketones and ethers move the group.
Dust zones 20/21/22, not gas zones. The certification is different and often overlooked.
Ex d flameproof contains an internal explosion inside a strong enclosure. Ex i intrinsically safe limits the electrical energy so an explosion cannot start. Ex d is simpler for a few points; Ex i suits many low-power instruments with barriers.
PESO is the organisation; CCoE was its earlier name and the term is still used for the approval. In India this is the approval that matters for flameproof equipment.
Not by itself. Indian installations require CCoE / PESO approval. Many manufacturers hold both, but you should state which the project needs.
It follows from the auto-ignition temperature of the gas present. T6 (85 °C) is the strictest and is common in refineries; T3 (200 °C) is often sufficient elsewhere.
No. The gland is part of the certified assembly. An uncertified gland invalidates the protection and the installation.
Send the zone, gas group and temperature class from your area classification drawing. We build and certify to it, and the CCoE certificate copy ships with the goods.
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