Inspection Deficiency Categories — X A B C Explained
One of the most important — and most tested — areas of CompEx Ex03 and Ex04 is deficiency classification. IEC 60079-17 defines four categories: X, A, B, and C. Getting the category right is not just an exam requirement — it is a safety-critical decision that determines whether equipment stays in service or is immediately removed.
Category X — Immediate Danger
Category X means the protection mechanism of the equipment is compromised and there is an immediate risk of ignition. Equipment must be taken out of service immediately and not returned until rectified and re-inspected.
Examples of Category X deficiencies:
- Missing bolts on Ex d equipment — flamepath integrity compromised
- Open cable entries (no gland or stopping plug fitted)
- Flamepath gap exceeding IEC 60079-1 Table 1 limits
- IS equipment with damaged Zener barrier
- Ex e enclosure with damaged or missing IP gasket allowing moisture to reach live parts
- IIB rated equipment in IIC area
- Cable gland with insufficient thread engagement (<5 full turns for Ex d)
Category A — Rectify at Next Maintenance
Category A means protection is adequate for continued operation but a deficiency has been identified that must be rectified at the next scheduled maintenance opportunity. The deficiency is not immediately dangerous but will become so if not addressed.
Examples of Category A deficiencies:
- Paint on Ex d flamepath — gap still within limits but must be cleaned
- Loose cable gland locknut on Ex e entry
- Missing IP washer on Ex e threaded entry (gland still providing some sealing)
- More than 1mm bare conductor exposed in Ex e terminal
- Non-barrier gland in >2L Ex d enclosure with threaded entry
Category B — Monitor
Category B means a minor issue has been noted that should be monitored and rectified within an agreed timescale. It poses no immediate danger and the protection remains effective.
Examples of Category B deficiencies:
- Surface corrosion on external enclosure body (not affecting protection)
- Minor physical damage to enclosure body (no penetration)
- Faded or partially illegible warning label
Category C — Record Only
Category C is a note for records. No action is required but the observation is recorded so it can be monitored over time.
When classifying a deficiency, always ask: does this compromise the protection mechanism? If yes — Category X. If it will compromise it without intervention — Category A. If it could theoretically develop into a problem — Category B. If it is purely cosmetic with no safety significance — Category C.
Common Classification Mistakes
The most common mistakes in CompEx assessments are: classifying Category X deficiencies as Category A (most serious error), not knowing that IIB equipment in IIC area is Category X, and not recognising that a missing bolt is Category X regardless of how many bolts remain.
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