1. Start with the area classification, not with the fixture
Choosing a luminaire before the area classification drawing is frozen is the most expensive mistake in this category. Zone and Division describe how often a flammable atmosphere is expected, and that drives the protection concept, the certificate and the price.
| Same question | IEC / ATEX (Zone) | NEC / CEC (Division) |
|---|---|---|
| Gas present continuously | Zone 0 | Class I, Division 1 |
| Gas likely in normal operation | Zone 1 | Class I, Division 1 |
| Gas only in abnormal conditions | Zone 2 | Class I, Division 2 |
| Combustible dust | Zone 20 / 21 / 22 | Class II, Division 1 / 2 |
| Ignitable fibers | — | Class III |
"Zone 2 is roughly Class I Division 2" is a useful first estimate and a dangerous final specification: a luminaire listed only to NEC Article 500 cannot go into an IECEx Zone 2 project just because the risk looks similar.
Gas group and dust group decide how strict
The group describes what is flammable, not how often. IEC gas groups run IIA (propane), IIB (ethylene) and IIC (hydrogen, acetylene), with IIC the strictest. Dust groups are IIIA (flyings), IIIB (non-conductive) and IIIC (conductive metal and carbon dust). NEC uses Groups A–D for Class I gases and E–G for Class II dusts. Grain silos are mis-specified most often, because dust settles in layers and insulates the fixture — which is why dust certifications state a maximum surface temperature measured with a dust layer present.
2. Read the Ex marking like a spec sheet
A nameplate line such as Ex ec IIC T4 Gc / Ex tc IIIC T90 °C Dc, IP66, Ta −40 °C to +55 °C, II 3GD is a complete, compressed specification.
| Field | Example | What it tells you |
|---|---|---|
| Protection concept | Ex ec | Non-sparking, increased safety (IEC 60079-7), Zone 2 only |
| Gas group | IIC | Safe for hydrogen and acetylene, so also IIA / IIB |
| Temperature class | T4 | Maximum surface temperature 135 °C |
| Dust line | Ex tc IIIC T90 °C Dc | Dust-protected enclosure (IEC 60079-31), Zone 22 |
| ATEX coding | II 3GD | Group II, Category 3 (Zone 2 / 22), gas and dust |
| Ambient range | Ta −40 to +55 °C | The range the whole rating is valid for |
Ex d (flameproof, IEC 60079-1) contains an internal explosion and cools the escaping gases; heavy, and the standard choice for Zone 1. Ex ec (increased safety, 60079-7) is non-sparking construction — what most Zone 2 LED fixtures carry, far lighter and cheaper than Ex d but not valid for Zone 1. Ex t / Ex tc (60079-31) is the dust-protected enclosure for Zones 21 and 22. Ex i (60079-11) is intrinsic safety, used for portable inspection lamps rather than mains lighting.
The temperature class is where projects fail
| T-code | Max surface | Typical substance |
|---|---|---|
| T1 | 450 °C | Acetylene, hydrogen |
| T2 | 300 °C | Many bulk industrial gases |
| T3 | 200 °C | Gasoline vapour, hexane |
| T4 | 135 °C | Diethyl ether, ethylene oxide |
| T4A | 120 °C | NEC-only code, common on Class I Div 2 LED |
| T5 | 100 °C | Carbon disulphide |
| T6 | 85 °C | Most restrictive in practice |
A T6 fixture can go anywhere specified T1 to T6; a T3 fixture cannot enter a T4 area. But read the fine print: the T-code is only valid inside the certified ambient range, so on a 50–55 °C design ambient this one line decides whether the fixture is legal.
3. Certificates: ask for the number, then verify it
A printed Ex logo on a datasheet is marketing. What your inspector needs is a number that resolves in the issuing body's database.
- EU: ATEX Directive 2014/34/EU. Categories 2 and 3 need an EU-type examination certificate from a Notified Body; a number ending in "X" carries special conditions for safe use that bind the installer.
- International: IECEx Certificate of Conformity, verifiable in the IECEx online system and widely accepted in the Gulf, Australia and much of Asia.
- UK: UKEX under SI 2016 No. 1107.
- North America: NEC Article 500 (Division) and Article 505 (Zone) in NFPA 70; hazardous-location luminaires are evaluated to UL 844, usually with UL 1598 or UL 1598A and CSA C22.2 No. 137 for Canada.
When the certificate arrives, check that the model number matches your quotation, the marking matches the classification, and the certificate is not suspended in the issuing body's register.
4. Where the money actually goes
Two fixtures can carry the same Ex rating and differ 40% in price.
Zone 2 LED luminaires are typically IP66 — here is what those numbers really test. Impact ratings run IK08 at the lens to IK10 at the housing. Coastal, offshore and chemical duty needs a defined coating system: epoxy primer plus polyester topcoat over marine-grade aluminium, with 316 stainless brackets. Gaskets are the quiet failure point, so confirm silicone compatibility with the solvents actually present.
Thermally, LED wins outright. A 150 W explosion-proof LED high bay replacing a 400 W metal halide typically lands at T4 or T5, where the HID fixture sat at T2 or T3 — so the LED is legal where the old fixture never was, without paying for a higher T-class enclosure. That advantage disappears if the driver runs hot, because the driver's Tc point is the real lifetime limiter. Check the L70 lumen maintenance data at your ambient, not at 25 °C on a bench, and specify PF ≥ 0.95 with THD ≤ 20% (see our load calculation guide). Surge protection of 4 kV line-to-earth, and 6–10 kV on lightning-prone sites, is cheap insurance.
Cable entry is the detail that voids everything: a certified luminaire fitted with an uncertified gland is an uncertified installation. Specify certified Ex glands and stopping plugs in the thread you need — 3/4 inch NPT in North America, M20 or M25 elsewhere — and plug every unused entry. Never drill, thread or swap glass on a certified enclosure.
5. Match the fixture to the plant
| Application | Typical classification | What to specify |
|---|---|---|
| Refinery process units | Zone 2 / Class I Div 2 | Ex ec or Ex d, IIC where hydrogen is present, IP66, anticorrosion coating |
| Tank farms, loading gantries | Zone 1 / 2 | Ex d, medium beam, low glare for operator visibility |
| Chemical and paint booths | Zone 1 / 2 + Zone 21 / 22 | Ex d plus dust protection, solvent-resistant gaskets |
| Grain silos, flour mills | Zone 21 / 22, Class II Div 1 | Ex tc IIIC, dust-layer surface temperature, low-dust housing |
| Offshore platforms, rigs | Zone 1 / 2, salt spray | Marine-grade aluminium or 316 stainless, UL 1598A, IK10, vibration-tested bracket |
| Wastewater digesters | Zone 2 (methane, H2S) | Ex ec IIC to cover both gases, heavy-duty anticorrosion finish |
| Solvent and paint stores | Zone 1 / 2 | Ex d IIC T4 or better |
Mining is a different world: Group I equipment for underground coal mines follows its own certification path and cannot be substituted with Group II industrial product.
6. Five mistakes that show up on site
- Calling a vapour-tight or tri-proof fixture "explosion-proof". Sealed against water is not certified against ignition, and installing it in a classified area is a code violation. Our tri-proof guide covers where those products belong.
- Buying on Zone alone, then finding the gas group or temperature class does not cover the actual substance.
- Ignoring the ambient range attached to the T-code — the most common cause of late substitution on hot-climate projects.
- Using uncertified glands and plugs, or drilling an extra entry into a certified enclosure.
- Accepting a certificate whose model number does not match the shipped product, or that has since been withdrawn.
7. The RFQ fields that save two rounds of emails
Send these seven items with your enquiry and the quotes you get back are comparable and binding: area classification (Zone, gas group, dust group, or NEC Class / Division / Group); required certificate (ATEX, IECEx, UKEX, UL 844); temperature class and design ambient range; photometry (lumens, wattage, beam angle, mounting height, IES file); electrical (voltage range, PF, THD, surge rating, dimming); mechanical (IP, IK, cable entry thread, coating); and documentation (certificate, Ex marking drawing, installation manual, spare glass and gasket list).
Conclusion
Explosion-proof LED lighting is specified backwards compared with normal fixtures: classification, gas group and temperature class come first, and the product is chosen to fit.
Solarix Lighting builds LED luminaires for exactly these conditions. Our DS Series explosion-proof LED high bay covers 50–300 W in a sealed, impact-resistant housing for Zone and Class-rated hazardous areas, alongside industrial LED high bay, street, tunnel and panel ranges for plant-wide projects. With CE, CCC, PSE and RoHS certification and 20+ metro and rail transit projects behind us, we supply the Ex marking, certificate number, temperature class and ambient range matched to the classification on your drawings, with IES files and samples so your designer can verify before you commit. Send us your area classification and target lux levels and we will quote against a complete specification, not a part number.