The CompEx written assessment catches many candidates off guard — not because the material is impossibly difficult, but because the questions test application and reasoning, not just memorisation. This guide covers the most effective preparation strategies and the areas where candidates most commonly lose marks.
Understand the Standard, Don't Just Memorise It
The single most important preparation tip is to understand why each rule exists, not just what the rule is. CompEx examiners write questions that test whether you can apply principles to unfamiliar scenarios. If you understand that a missing bolt on Ex d equipment is Category X because the flamepath integrity is compromised — and that a compromised flamepath means an internal explosion could propagate to the external atmosphere — you can answer any question about Ex d bolts, not just the specific one you revised.
Master Deficiency Classification
Deficiency classification (Category X, A, B, C) is tested extensively in Ex03 and Ex04. The key principle to remember:
- Category X — the protection is compromised and there is an immediate risk of ignition. Take out of service now.
- Category A — protection is adequate but degrading. Must be rectified at next maintenance opportunity.
- Category B — minor issue, monitor and rectify within agreed timescale.
- Category C — note for records, no immediate action required.
When in doubt, ask: does this deficiency compromise the protection mechanism? If yes — Category X. If it could compromise it in the future — Category A. If it's purely cosmetic — Category B or C.
The most common mistakes in CompEx written assessments: (1) Confusing IIB and IIC gas group requirements. (2) Classifying a Category X deficiency as Category A. (3) Not knowing the difference between Visual, Close, and Detailed inspection grades. (4) Getting the barrier gland volume rule wrong. (5) Forgetting that IIC areas require every component to be IIC rated.
Know the IEC 60079 Standards Structure
You don't need to memorise every clause, but you should know which part of IEC 60079 covers which topic:
| Standard | Covers |
|---|---|
| IEC 60079-0 | General requirements — all Ex equipment |
| IEC 60079-1 | Ex d flameproof enclosures |
| IEC 60079-7 | Ex e increased safety |
| IEC 60079-11 | Ex i intrinsic safety |
| IEC 60079-2 | Ex p pressurisation |
| IEC 60079-14 | Installation of Ex equipment |
| IEC 60079-17 | Inspection and maintenance |
| IEC 60079-10 | Zone classification (gas) |
Practice Decision-Making, Not Just Reading
The most effective CompEx preparation goes beyond reading notes. You need to practise making the decisions you'll face in the assessment — classifying deficiencies, selecting the right gland for a given scenario, identifying what's wrong with a described installation. EX Academy's inspection simulations and equipment selection scenarios are built around exactly this kind of decision-based practice.
The Day Before
Don't try to cram new material. Review your notes on deficiency classification, the gas group MESG values, and the protection type summaries. Get good sleep. The CompEx assessment rewards calm, methodical thinking — not rushing through questions.