CompEx Ex01-Ex04 (Gas & Vapours)

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For professionals working in hazardous areas where explosive gases and vapours are present, the CompEx Ex01-Ex04 certification is the gold standard of competency. This guide provides a comprehensive breakdown of everything you need to know to achieve this essential qualification.

What is the CompEx Ex01-Ex04 (Gas & Vapours)?

The CompEx Ex01-Ex04 (Gas & Vapours) is the industry-leading international course and assessment for electrical and instrumentation personnel working in explosive atmospheres.

  • Official Exam Name & Acronym: CompEx Core Competency (Gas & Vapours) – Units Ex01, Ex02, Ex03, and Ex04.
  • Conducting Body/Authority: The exam is administered by JTLimited through the CompEx Scheme. Established in the wake of the Piper Alpha disaster in 1988, the scheme was developed to ensure a standard level of competency for those working in hazardous environments.
  • Purpose of Exam: Professional Certification. It validates that a technician can safely install, maintain, and inspect electrical equipment in hazardous areas.
  • Geographic Validity: Globally recognized. While rooted in UK health and safety regulations, it is the primary benchmark for competency in the EU, Middle East, Australia, and parts of Asia and the Americas, adhering to IEC 60079 international standards.
  • Level of Competence: Specialist/Practitioner level. It demonstrates that the holder is competent to work unsupervised on “Ex” equipment.
  • Brief History: Launched in 1994, the CompEx scheme was a collaborative effort between the Engineering Equipment and Materials Users Association (EEMUA) and JTLimited to drive up safety standards in the oil, gas, and chemical industries.

Who Can Take the CompEx Ex01-Ex04 (Gas & Vapours)? (Eligibility Requirements)

This is not an entry-level course for non-electricians. Candidates must demonstrate prior technical proficiency.

Eligibility Checklist

  • Academic Requirements: A recognized electrical or instrumentation qualification (e.g., NVQ Level 3, City & Guilds 2365 or 2330, or an equivalent international diploma).
  • Experience Requirements: Evidence of a formal apprenticeship or a minimum of 3-5 years of experience in electrical installation or maintenance.
  • Documentation Checklist:
    • Original certificates of electrical/instrumentation qualifications.
    • An Employer Letter of Endorsement confirming the candidate’s trade.
    • Valid Passport or National ID for identity verification.
    • Two passport-sized photographs (35mm x 45mm) for the CompEx ID card.
    • Completed CompEx Candidate Registration Form.
  • Language Proficiency: Assessments are typically in English. While no formal IELTS score is mandated, candidates must have sufficient English literacy to understand technical standards and pass a written exam.
  • Age Restrictions: Candidates must be at least 18 years old.

Table 1: Eligibility Summary

Requirement Specification
Core Trade Qualified Electrician or Instrument Technician
Minimum Qualification NVQ Level 3 or International Equivalent
ID Requirement Government-issued Photo ID
Prerequisite Knowledge Basic electrical testing and wiring skills

How to Register for the CompEx Ex01-Ex04 (Gas & Vapours)

Exam Schedule & Availability

Exam Frequency: Courses and exams are held weekly throughout the year at various licensed training centers. Because the course includes a 3-4 day training component, it is rarely “on-demand” and must be booked in advance.

Scheduling: Candidates choose a specific 5-day window (Monday-Friday) at their preferred center.

Exam Fees (Estimated Breakdown)

Fee Type Estimated Cost (GBP) Estimated Cost (USD)
Full 5-Day Course & Assessment £850 – £1,100 $1,050 – $1,350
CompEx Registration & Certification Fee £65 $80
Resit Fee (Theory Only) £150 – £200 $185 – $250
Resit Fee (Practical Only) £250 – £400 $310 – $500
Total Estimated Cost £915 – £1,165 $1,130 – $1,430

Booking Process

  1. Find a Center: Visit the official CompEx website to find a licensed provider (e.g., Intertek, AIS Survivex, or local technical colleges).
  2. Submit Evidence: Send your trade certificates and employer endorsement to the center for vetting.
  3. Payment: Pay the course fee in full to secure your slot.
  4. Confirmation: You will receive a joining instruction pack and pre-reading materials.

Retake Policy

  • Waiting Period: Candidates who fail a unit must wait a minimum of 4 weeks before attempting a resit to allow for further study.
  • Attempts: There is no hard limit on attempts, but centers may require remedial training after three failed attempts.

Score Validity

The CompEx certificate is valid for 5 years. Before the expiry date, candidates must take the Ex01-Ex04 Refresher (Ex01R-Ex04R) to maintain their competency status. If it expires, the full course must be retaken.

CompEx Ex01-Ex04 (Gas & Vapours) Exam Format & Structure

Exam Format

The assessment is split into two distinct parts:

  • Theory: Computer-Based Test (CBT) or Paper-based (depending on the center).
  • Practical: Hands-on installation and inspection in a simulated hazardous area booth.

Timing & Duration

Component Duration Format
Theory Exam 90 Minutes 60 Multiple Choice Questions
Ex01 Practical (Installation) 3.5 Hours Glanding and wiring into Ex d, Ex e, and Ex n enclosures
Ex02 Practical (Maintenance) 1.5 Hours Fault finding and maintenance on Ex equipment
Ex03 Practical (Inspection) 3 Hours Detailed inspection of a pre-installed rig
Ex04 Practical (Inspection) 1.5 Hours Visual and close inspection of a pre-installed rig

Syllabus & Content Domains

Domain Topics Covered Weightage
Area Classification Zone 0, 1, 2; Gas Groups (IIA, IIB, IIC); T-Ratings 15%
Ex Protection Types Ex d, Ex e, Ex n, Ex i, Ex p, Ex m, Ex o, Ex q 30%
Installation Standards IEC 60079-14; Cable entry systems; Glanding; Earthing 25%
Inspection & Maintenance IEC 60079-17; Visual, Close, and Detailed inspections 20%
Marking & Certification ATEX Directives; IECEx markings; Labeling requirements 10%

Official Reference Materials

  • EEMUA Publication 186: A Practitioner’s Handbook (The primary textbook).
  • IEC 60079-14: Design, selection, and erection of electrical installations.
  • IEC 60079-17: Inspection and maintenance of electrical installations.

How is the CompEx Ex01-Ex04 (Gas & Vapours) Scored?

Passing Score

Candidates must achieve a minimum score of 80% in the theory exam. For the practical assessments, the criteria are competent or not yet competent. A single “critical fail” (such as a safety-critical error in a practical booth) results in a fail for that unit.

Scoring Mechanics

  • Negative Marking: None. It is always better to guess than to leave a question blank.
  • Partial Credit: Not available for the theory exam. In practicals, you must pass every mandatory check-point.
  • Sectional Cut-offs: You must pass all four practical units (Ex01, Ex02, Ex03, Ex04) AND the theory exam to receive the full certification.

Result Declaration

Results are typically processed by JTLimited and sent to the training center within 3 to 6 weeks. Successful candidates receive a credit-card-sized ID badge and a formal certificate.

How Difficult is the CompEx Ex01-Ex04 (Gas & Vapours)?

Overall Difficulty Rating: Challenging.

While the theory is manageable for those who study the standards, the practical installation (Ex01) is where most candidates struggle. Precision is required—specifically in the termination of flameproof (Ex d) glands and maintaining the integrity of increased safety (Ex e) enclosures.

Historical Pass Rates

Category Pass Rate (Approx.)
First-time Pass Rate 70% – 75%
Theory Exam Pass Rate 85%
Practical Units Pass Rate 72%

CompEx Ex01-Ex04 vs. Similar Certifications

Feature CompEx Ex01-Ex04 IECEx CoPC (Unit 001, 003, 004, 007, 008) ATEX Awareness
Authority JTLimited (UK Based) IECEx (International) Various Providers
Practical Assessment Yes (Rigorous) Yes No (Theory only)
Global Recognition Highest in Oil/Gas Highest in Australia/Global Low (Introductory only)
Cost ~£1,000 ~£1,500+ ~£150

When to choose CompEx: If you are working in the UK, Europe, or for any major international oil company (Shell, BP, Exxon), CompEx is the mandatory requirement.

How to Prepare for the CompEx Ex01-Ex04 (Gas & Vapours)

Recommended Study Timeline

  • 4 Weeks Before: Read the EEMUA 186 Handbook from cover to cover.
  • 2 Weeks Before: Memorize Gas Groups, Temperature Classes, and the specific requirements for different protection concepts (e.g., the difference between a “Visual” and “Detailed” inspection).
  • 1 Week Before: Practice glanding—specifically armored cables (SWA) and braided cables using Ex d and Ex e glands.

Best Study Resources

  • Official: EEMUA 186 Practitioner’s Handbook.
  • Standards: IEC 60079-14 and IEC 60079-17.
  • Online: CompEx Tool Box (Official App).

What to Expect on CompEx Ex01-Ex04 Exam Day

  • PPE: You must bring your own safety footwear and flame-retardant workwear for the practical sessions.
  • Tools: Most centers provide calibrated tools (torque screwdrivers, multi-meters), but some allow you to bring your own hand tools (side cutters, wire strippers).
  • Prohibited Items: Mobile phones, smartwatches, and non-approved reference materials are strictly banned in the exam room.
  • Check-in: Arrive 30 minutes early for ID verification.

After Passing the CompEx Ex01-Ex04

Once certified, you are qualified to work as an Ex-Technician. This often leads to a significant pay increase, with many contractors earning 20-30% more than non-Ex qualified electricians. Career paths include Hazardous Area Inspector, Offshore Electrical Technician, or Site Safety Supervisor.

Frequently Asked Questions

  1. Is CompEx recognized in the USA? Yes, although the US uses the NEC “Class/Division” system, most major US-based international firms recognize CompEx for their global projects.
  2. Can a non-electrician take the course? No. You must provide evidence of a core electrical or instrumentation trade.
  3. What happens if I fail one unit? You only need to resit the specific unit you failed.
  4. Is the exam open-book? No, but you are often provided with certain “Standard Sheets” and reference tables during the exam.
  5. How long is the certificate valid? 5 years.
  6. What is the most common reason for failure? Incorrectly installing an Ex d (flameproof) cable gland—specifically the inner seal/shroud.
  7. Do I need to bring my own IEC standards? No, the training center will provide the necessary reference documents.
  8. Is there a difference between ATEX and CompEx? ATEX is the law/directive; CompEx is the certification that proves you are competent to work within that law.
  9. Can I take the exam online? No. Due to the practical assessment requirements, you must attend a licensed center.
  10. Is there a lot of math? Only basic calculations related to Ohms Law and IP ratings/temperature conversions.

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