CompEx is the UK's leading scheme for assessing the competency of electrical workers to carry out work on electrical equipment in explosive atmospheres — commonly known as hazardous areas. If you work on or around oil and gas facilities, offshore platforms, chemical plants, pharmaceutical manufacturing, distilleries, or any site where flammable gases, vapours, or dusts are present, you will almost certainly need a CompEx certificate.
What Does CompEx Stand For?
CompEx stands for Competency in Explosive Atmospheres. It is administered by JTL Training on behalf of the industry and is recognised internationally as evidence of competency for electrical work in hazardous areas. The scheme was developed in partnership with the offshore oil and gas industry in the 1990s and has since expanded to cover all industries where explosive atmospheres may be present.
Who Needs CompEx?
CompEx certification is required or strongly expected for:
- Electricians working on offshore oil and gas installations
- Electrical engineers on petrochemical and refinery sites
- Instrument technicians working with hazardous area equipment
- Maintenance electricians at chemical plants, distilleries, pharmaceutical facilities
- Electrical contractors tendering for work on COMAH sites
- Anyone inspecting, installing, or maintaining Ex-certified equipment
CompEx is not a legal requirement in the UK — but the ATEX Directive (2014/34/EU retained in UK law) and DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002) require that work on electrical equipment in hazardous areas is carried out by competent persons. CompEx has become the de facto industry standard for demonstrating that competency.
The CompEx Units — Ex01 to Ex06
CompEx is divided into units, each covering a different scope of work:
| Unit | Scope | Gas Groups |
|---|---|---|
| Ex01 | Installation of Ex equipment | IIA and IIB (most gases) |
| Ex02 | Installation of Ex equipment | IIC (hydrogen and acetylene) |
| Ex03 | Inspection of Ex equipment | IIA and IIB |
| Ex04 | Inspection of Ex equipment | IIC (hydrogen) |
| Ex05 | Instrumentation (intrinsic safety) | All groups |
| Ex06 | Cathodic protection | All groups |
Most offshore and petrochemical workers will hold Ex01 and Ex03, or Ex02 and Ex04 for IIC sites. Ex05 is common for instrument technicians working with intrinsically safe systems.
What Does the CompEx Assessment Cover?
The CompEx assessment has two components:
Written Assessment
A formal written paper covering the underpinning knowledge required for the unit. This includes zone classification, protection types, IEC 60079 standards, equipment selection, inspection grades, deficiency classification, and safe working practices. The pass mark is 70%.
Practical Assessment
A practical demonstration of competency assessed by a CompEx assessor. For inspection units (Ex03/Ex04) this includes performing a structured inspection of Ex equipment and correctly identifying and classifying deficiencies. For installation units (Ex01/Ex02) this includes correctly installing and connecting Ex equipment including cable glands, stopping plugs, and earthing arrangements.
How Long Does CompEx Last?
CompEx certificates are valid for 5 years. After 5 years you must renew by completing a reassessment. Many employers and clients require evidence of a current (in-date) CompEx certificate before permitting work on their sites.
How to Prepare for CompEx
Effective CompEx preparation requires understanding both the theory (standards, principles, rules) and the practical application (what to look for, what decisions to make, how to classify what you find). Many candidates underestimate the depth of knowledge required — particularly for the inspection units where you need to understand not just what constitutes a deficiency, but how to classify it correctly under IEC 60079-17.
EX Academy is built specifically around this challenge — putting you in real inspection and equipment selection scenarios so that when you face the practical assessment, the decisions feel familiar.
The most common area where candidates lose marks in the Ex03/Ex04 written assessment is deficiency classification — knowing the difference between Category X (take out of service immediately), Category A (rectify at next scheduled maintenance), Category B (monitor), and Category C (note in records). EX Academy's inspection simulations drill this decision process across 15 different scenarios.