CompEx is the industry-standard qualification for working in explosive atmospheres. This guide covers all units (EX01–EX07), the 5-day assessment process, approved training centres, costs, and the career opportunities CompEx unlocks.
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CompEx (Competency in Explosive Atmospheres) is the industry-standard competency assessment scheme for people who work with electrical and instrumentation systems in potentially explosive atmospheres. It is administered by EAL (Awards for Business and Industry) and is recognised by the Health and Safety Executive (HSE) as evidence of competency under DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002).
Without CompEx, an electrician cannot legally be considered competent to carry out work in hazardous areas under DSEAR. In practice, this means that major oil and gas operators, chemical companies, and their principal contractors will not permit ATEX electrical work without a valid CompEx certificate. It is the key that unlocks some of the best-paid electrical contracting work available in the UK.
For the full technical background on ATEX hazardous area electrical installations including zone classification, Ex equipment markings, and the installation and inspection standards, see the dedicated guide.
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CompEx is divided into units, each covering a specific aspect of work in explosive atmospheres. The units relevant to electricians are EX01 to EX04. EX05 to EX07 are primarily for instrument technicians.
CompEx is a competency-based assessment — it evaluates what you can actually do, not just what you know. The assessment has two components:
An EAL-approved assessor observes you carrying out practical tasks relevant to the unit being assessed. For EX02, this includes: selecting appropriate Ex equipment for a given zone and gas type; installing a certified Ex d enclosure and making correct cable entries using certified glands; completing an inspection record to BS EN 60079-17; and verifying equipment certification markings. Assessment typically takes one to two days per unit.
An oral or written knowledge assessment covering the theoretical underpinning of each unit. For EX01, this includes questions on zone classification, Ex markings, temperature classes, and legislation. The assessor will probe your understanding of why requirements exist, not just what they are. A portfolio of workplace evidence (previous installation and inspection records from real work) can support and accelerate the assessment.
Most candidates attend a 5-day preparation course at an approved training centre before formal assessment. The course covers the technical content, introduces the assessment requirements, and provides hands-on practice with Ex equipment before the formal assessment. The 5-day course and assessment are typically packaged together by training centres.
CompEx training and assessment must be carried out at an EAL-approved centre or by an EAL-approved assessor in the workplace. The main approved centres include:
The full list of approved training centres is maintained by EAL and can be found on the CompEx Certification Scheme website. Always verify that your chosen centre is currently approved before booking — approval status can change.
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CompEx is a significant investment, but the return in terms of increased earning potential is substantial. Typical costs for the electrician units (EX01–EX04):
Some employers in the oil and gas sector will fund CompEx training for employees as part of a skills development programme. It is worth asking prospective employers about funding before self-funding. The upfront cost is recovered quickly — a CompEx-certified electrician on a North Sea offshore contract can earn the cost of the qualification in a single week.
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Try it free for 7 daysThe legal basis for CompEx comes from DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002), specifically Regulation 7, which requires that employers ensure that work involving dangerous substances is carried out only by competent persons using appropriate equipment and procedures.
The HSE's guidance on DSEAR recognises CompEx as an appropriate means of demonstrating competency for electrical and instrumentation work in hazardous areas. Major operators (Shell, BP, TotalEnergies, INEOS, and others) have adopted CompEx as a contractual requirement for all electrical contractors working in ATEX-classified areas on their sites. This means that, in practice, CompEx is effectively mandatory for this type of work — even though the legislation does not name it explicitly.
See the full guide to ATEX hazardous area electrical installations for the complete legal and technical context.
CompEx certification opens doors to some of the highest-paid electrical contracting work in the UK:
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