CompEx Ex03 is the unit covering the inspection of electrical equipment in explosive atmospheres for gas groups IIA and IIB. It is one of the most commonly held CompEx units and is required for anyone who carries out periodic inspection of Ex equipment on petrochemical sites, offshore platforms, oil refineries, and any Zone 1 or Zone 2 area where propane, methane, ethylene, or similar gases may be present.
What Does Ex03 Cover?
The Ex03 unit is based primarily on IEC 60079-17 — the standard for inspection and maintenance of Ex equipment. The knowledge required includes:
- Zone classification — Zone 0, 1, and 2 for gas atmospheres
- Equipment Protection Level (EPL) — Ga, Gb, Gc
- Gas groups IIA and IIB — common gases, MESG values
- Temperature classes T1 to T6 and auto-ignition temperatures
- All protection types — Ex d, Ex e, Ex i, Ex p, Ex n, Ex ec
- IEC 60079-17 inspection grades — Visual, Close, Detailed
- Deficiency classification — Category X, A, B, C
- Cable gland selection and inspection — barrier vs non-barrier, thread engagement
- Earthing and bonding requirements
- Documentation and inspection records
Ex03 covers IIA and IIB gas groups — the majority of industrial sites. Ex04 additionally covers IIC gas group (hydrogen, acetylene) which requires additional knowledge of the higher-risk IIC equipment requirements. Many offshore workers hold both Ex03 and Ex04.
IEC 60079-17 Inspection Grades
The three inspection grades in IEC 60079-17 define what checks are carried out and under what circumstances:
Visual Inspection
A visual inspection is carried out without the use of tools and without opening or disturbing equipment. It checks for obvious defects visible from outside — damaged enclosures, missing warning labels, paint on flamepaths, corrosion of earth tags, blocked ventilation, and obvious physical damage.
Close Inspection
A close inspection includes all visual checks plus checks that require opening or disturbing equipment — such as checking cable gland thread engagement, examining terminal connections, measuring flamepath gaps, and verifying stopping plug thread turns. This is the grade most commonly required for periodic inspection of process equipment.
Detailed Inspection
A detailed inspection includes all close inspection checks plus a full strip-down using tools and test equipment. It is carried out less frequently and typically involves measurement of clearances, testing of interlocks, and verification of internal wiring.
Deficiency Classification — Category X, A, B, C
Every deficiency found during inspection must be classified under IEC 60079-17:
| Category | Action Required | Examples |
|---|---|---|
| X | Take out of service immediately — danger of ignition | Missing bolts on Ex d, flamepath damaged, cable entry open |
| A | Rectify at next scheduled maintenance opportunity | Paint on flamepath (not affecting gap), loose gland |
| B | Monitor — rectify within agreed period | Surface corrosion on enclosure, minor damage to label |
| C | Note in records — no action required immediately | Minor cosmetic damage, slight discolouration |
Category X deficiencies require immediate removal from service. The most commonly tested scenarios involve missing or damaged bolts on Ex d equipment, open cable entries, flamepath damage, and insufficient thread engagement. Candidates must know not just that these are Category X, but why — the specific IEC 60079 clause and the safety principle at risk.
Preparing for the Ex03 Written Assessment
The written assessment tests your ability to apply the IEC 60079 standards to specific scenarios. You will be expected to identify the correct protection type for a given zone and gas group, classify deficiencies found during inspection, and explain the reasoning behind your decisions.
EX Academy's 15 inspection simulations are built specifically around the Ex03/Ex04 assessment format — each one presents a real work order, equipment data, and a series of questions that mirror exactly what the CompEx written and practical assessments test.