Hazardous-area equipment avoids ignition in one of three ways: contain an explosion (flameproof, Ex d), prevent sparks and heat (increased safety Ex e, non-sparking Ex n or ec, encapsulation Ex m), or limit energy (intrinsic safety Ex i), or keep the gas out (pressurised or purged enclosures, Ex p). The right concept depends on the device, the zone and the gas group.
- Describe each protection concept in one sentence
- Match concepts to equipment types
- Understand why ACCURRA-Hz is flameproof
The concepts
| Concept | Marking | Principle | Typical use |
|---|---|---|---|
| Flameproof | Ex d | The enclosure withstands an internal explosion and cools escaping gas through narrow joints so it cannot ignite the outside atmosphere | Analysers, motors, switchgear, junction boxes |
| Increased safety | Ex e | No arcs, sparks or hot surfaces under normal operation; terminals and insulation are reinforced | Terminal boxes, lighting |
| Intrinsic safety | Ex i | Electrical energy is limited so no spark or heat can ignite; used with barriers or isolators | Low-power transmitters, sensors, instruments |
| Pressurised or purged | Ex p | The enclosure holds clean air or inert gas at a slight positive pressure so the surrounding gas cannot enter | Large cabinets and analyser houses |
| Non-sparking, encapsulation | Ex n or ec, Ex m | Equipment designed not to spark, or sealed in compound so gas cannot reach it | Simple devices, electronics |
Intrinsic safety has levels ia, ib and ic for Zones 0, 1 and 2.
Flameproof in practice
In a flameproof enclosure, joints are machined so that a flame trying to leave is cooled below ignition by the long, narrow gap. The enclosure is strong enough to hold the pressure of an internal explosion. Gas Group IIC needs the narrowest gaps. Covers must not be opened while the circuit is live in a hazardous area, unless the design allows. ACCURRA-Hz uses a flameproof enclosure certified for Group IIC, Zone 1 and 2, T6, and calibration is possible without opening the covers: Hazardous area gas analysers explained.
Intrinsic safety in practice
An intrinsically safe loop limits voltage and current through a barrier or isolator in the safe area, so that even a fault in the field cannot release enough energy to ignite gas. It suits low-power loops such as a two-wire transmitter: INFINITY-Tx is a loop-powered two-wire transmitter for percent oxygen and trace CO in hazardous areas. The certificate and the barrier or isolator must match: check the entity parameters.
Purging in practice
A purged cabinet is filled with clean air or inert gas, kept at positive pressure and monitored. It lets standard equipment run inside a classified area, but needs a purge control system, a supply of gas and a purge before power-up.
Choosing
- Low-power field instruments: consider Ex i.
- Analysers and enclosures with larger power: Ex d or Ex p.
- Terminal and junction boxes: Ex e or Ex d.
- Always match zone, gas group and temperature class: Hazardous area classification: zones, gas groups, T-Classes.
Protection concepts say the equipment will not ignite gas. They say nothing about measurement reliability or SIL: What SIL means for gas analysers, and what it does not.
- Concepts: contain (Ex d), prevent (Ex e, n, m), limit energy (Ex i), keep gas out (Ex p).
- Flameproof joints cool escaping flame; IIC needs the narrowest gaps.
- Intrinsic safety suits low-power loops with barriers.
- Certification covers ignition, not measurement integrity.
Check your understanding
Answer in your head or on paper first, then open the answer. Recalling an answer teaches more than rereading.
What does a flameproof enclosure do?
It contains an internal explosion and cools escaping gas so it cannot ignite the outside atmosphere.
Which concept suits a low-power two-wire transmitter?
Intrinsic safety, Ex i, usually with a barrier or isolator.
What does a purged cabinet rely on?
A slight positive pressure of clean air or inert gas that keeps hazardous gas out.
Key terms
Frequently asked questions
What does Ex d mean?
Flameproof: the enclosure contains an internal explosion and prevents it igniting the outside atmosphere.
What is intrinsic safety?
A concept that limits electrical energy so no spark or heat can ignite gas.
Can I open a flameproof analyser in a hazardous area?
Only following the manufacturer's rules; ACCURRA-Hz allows calibration without opening the covers.
Do I need a barrier for INFINITY-Tx?
Check the certificate and the loop's entity parameters; ask us for the installation requirements.
Related products
ACCURRA-Hz
Process gas analyser in an enclosure certified for Gas Group IIC, Zone 1 and 2, T6.
View ACCURRA-Hz
INFINITY-Tx
Loop-powered two-wire transmitter for percent O2 and trace CO in hazardous areas.
View INFINITY-Tx