Free CompEx Revision Questions — Practice Before Your Assessment

These free practice questions give you a taste of what to expect in the CompEx written assessment. They cover the most commonly tested topics — deficiency classification, equipment selection, gas groups, and IEC 60079 standards.

Sample Questions

Question 1 — Deficiency Classification

During a close inspection of an Ex d motor terminal box (Zone 1 IIB T4), you find that 2 of the 8 cover bolts are missing. What is the correct deficiency classification?

• A) Category B — note for records, monitor at next inspection
• B) Category A — rectify at next maintenance opportunity
• C) Category X — take out of service immediately ✓
• D) No deficiency — 6 bolts are sufficient for the flamepath

Answer: Category X. Missing bolts on Ex d equipment compromise the flamepath integrity. The equipment cannot contain an internal explosion with missing fasteners. Any missing bolt on an Ex d enclosure is Category X — the equipment must be taken out of service immediately regardless of how many bolts remain.

Question 2 — Cable Gland Selection

You are installing 4-core SWA cable into an Ex d junction box with an internal volume of 2.8 litres via a threaded M25 entry. What gland type is required?

• A) Non-barrier gland — threaded entry provides the flamepath
• B) Barrier gland — volume exceeds 2 litres, threaded entry ✓
• C) Non-barrier gland — threaded entries never require barrier glands
• D) Standard industrial gland — Ex d enclosures do not need certified glands

Answer: Barrier gland. The IEC 60079-1 volume rule requires a barrier gland for SWA cable in Ex d enclosures when the volume exceeds 2 litres (2000cm³) via a threaded entry. 2.8 litres exceeds the 2 litre threshold, so a barrier gland is required.

Question 3 — Gas Groups

Equipment marked Ex d IIB T4 Gb is installed in an area classified Zone 1 IIC. What action is required?

• A) No action — IIB equipment is acceptable in IIC areas
• B) Category B deficiency — note for records
• C) Category A deficiency — replace at next maintenance
• D) Category X deficiency — take out of service immediately ✓

Answer: Category X. IIB equipment in an IIC area is a serious non-compliance. IIC gas group has tighter flamepath requirements than IIB equipment is designed to meet. In an IIC area, every component must be IIC rated. This is a Category X deficiency — the equipment must be taken out of service immediately.