Explosive atmosphere (Ex) terminology intimidates buyers, and suppliers exploit that: 'Ex-rated' without a zone, a gas group or a certificate number is marketing, not specification. The system is actually logical once you see the structure.
This guide explains zones, gas groups and temperature classes in practical terms — enough for a project engineer to specify correctly and check a quotation critically.
Zones: how often is the atmosphere explosive?
Zones classify areas by how likely and how long an explosive gas atmosphere is present.
- Zone 0: explosive atmosphere present continuously or for long periods (inside tanks, gas space). Actuators are rarely installed here — the valve itself usually is.
- Zone 1: likely in normal operation (around vents, seals, regular release points). Requires flameproof Ex d / Ex db or similarly robust protection.
- Zone 2: unlikely in normal operation, short duration if it occurs (well-ventilated process areas). Allows increased-safety Ex ec — certified but more economical.
- Dust has its own parallel system: Zones 20/21/22 with IIIC/IIIB/IIIA dust groups.
Gas groups and temperature classes
Two more labels complete the match between hazard and hardware.
- Gas groups: IIA (propane-like), IIB (ethylene-like), IIC (hydrogen/acetylene — the hardest to contain). The enclosure certificate must cover your gas group.
- Temperature class: T1 to T6 — the maximum surface temperature the certified equipment may reach. T6 is the strictest. Match to the auto-ignition temperature of your gas with margin.
- Example full marking: II 2G Ex db IIB T4 Gb — equipment group II, Zone 1 category, flameproof, gas group IIB, T4.
What to demand from a supplier
Three checks that separate real Ex suppliers from certificate-wavers.
- Certificate number per unit type — issued by a notified body, verifiable. 'Complies with' without a number is not certification.
- Zone and gas group stated explicitly in the offer: 'certified for Zone 1, IIB, T4' — not just 'Ex-rated'.
- Matched temperature class to your gas, not a blanket T6 claim that ignores your actual medium.
Quick zone-to-actuator reference.
How SJMC handles Ex procurement
SJMC quotes Ex actuators with the certificate number, zone, gas group and temperature class stated explicitly in the offer. If your area classification is ambiguous, our engineers review it with you before quoting — the wrong certificate is a safety finding, not a discount opportunity.
- JVX-04 Explosion-proof — Certified Ex enclosures, 50–50,000 Nm, matched to zone, gas group and temperature class.
- Certificate package — Notified-body certificate numbers verifiable by your HSE department.
- Zone consultation — We review your area classification drawing before quoting — free of charge.
Frequently asked questions
What is the difference between Ex d and Ex ec?
Ex d (flameproof) contains an internal explosion and cools escaping gases — required for Zone 1. Ex ec (increased safety) prevents ignition through construction — sufficient for Zone 2 and more economical.
Is 'ATEX-certified' enough information to buy?
No. ATEX is the directive framework, not the protection level. You need zone, gas group and temperature class on the certificate — e.g., II 2G Ex db IIB T4.
Do I need Ex equipment in a well-ventilated compressor building?
Depends on your area classification study. Well-ventilated areas around gas handling are commonly Zone 2 — which allows Ex ec certified equipment rather than the more expensive Zone 1 hardware.