Ex d Flameproof Protection — Complete Technical Guide
Ex d flameproof protection is the most widely used protection type on offshore platforms, petrochemical plants, oil refineries, and process facilities worldwide. Understanding Ex d is fundamental to CompEx Ex01, Ex02, Ex03, and Ex04 preparation.
The Flameproof Principle
Ex d does not prevent an explosion — it contains it. An Ex d enclosure is designed to withstand the pressure of an internal explosion and to cool any escaping gases below the ignition temperature of the surrounding atmosphere through controlled flamepaths.
Flamepath Requirements
The flamepath is the precisely controlled gap between mating surfaces of an Ex d enclosure. IEC 60079-1 Table 1 specifies the maximum gap for each gas group and volume:
| Gas Group | Volume <100cm³ | Volume 100–2000cm³ | Volume >2000cm³ |
|---|---|---|---|
| IIA | 0.40mm max | 0.40mm max | 0.40mm max |
| IIB | 0.30mm max | 0.30mm max | 0.20mm max |
| IIC | 0.20mm max | 0.15mm max | 0.10mm max |
A flamepath gap exceeding the IEC 60079-1 Table 1 limit is a Category X deficiency. The equipment must be taken out of service immediately. Paint, burrs, corrosion, or physical damage to flamepath surfaces can all cause gaps to exceed their limits.
Common Ex d Equipment
Ex d protection is used for equipment that generates significant heat or sparks during normal operation — motors, junction boxes, control stations, isolators, solenoid valves, and lighting fittings in Zone 1 areas.
Cable Entry Rules for Ex d
The IEC 60079-1 volume rule determines whether a barrier gland is required:
- Threaded entry, ≤2 litres — non-barrier gland acceptable for SWA
- Threaded entry, >2 litres — barrier gland required for SWA
- Clearance entry, any volume — barrier gland always required for SWA
Ex d Inspection — Key Points
- All bolts must be present, correct grade, and correctly torqued
- Flamepath surfaces must be undamaged and free from paint or corrosion affecting the gap
- Cable glands must be correctly specified (barrier/non-barrier per volume rule) and fully engaged (minimum 5 full thread turns)
- Stopping plugs must have minimum 5 full thread turns engagement
- No IP washer or locknut on Ex d threaded entries
Reading about it is one thing. EX Academy puts you in the scenario — interactive inspection simulations, equipment selection decisions, and 1,185+ practice questions all referenced to IEC 60079.
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