Frequently asked questions

The usual causes fall into four groups: (1) clogged or wrong-spec filters that raise resistance; (2) fan or AHU faults such as a slack belt, dirty blades, reversed rotation or wrong VFD settings; (3) duct leakage, mis-set dampers or obstructions in the duct; (4) drifting pressure sensors, or a room layout change without rebalancing the air system.

Fix: check the pressure drop across the filters, check the fan and its settings, then rebalance the air before re-testing to ISO 14644-3 → Cleanroom testing

ISO 14644-3:2019 clause B.7.2.4 treats a reading above 0.01% of the upstream concentration as a leak (0.1% for filters with an MPPS efficiency from 99.95% up to less than 99.995%).

Leaks in the filter media, sealant or grid can be repaired by a method agreed between the customer and the tester, using materials that do not outgas; once the repair has cured, the spot must be rescanned (clause B.7.6). For a leak at the frame, check the gasket or gel seal and tighten the clamps evenly. If the filter is damaged or leaks in several places, replace it and leak-test it again after installation.

The humidity limit comes from the user’s specification, usually a set point with a tolerance such as 45±5% RH (an example given in the ASHRAE Design Guide for Cleanrooms, section 9.2). It is not a fixed value in ISO 14644.

Too humid: check that the cooling coil is cold enough to remove moisture, look for outside air leaking in and blocked or wet drain pans, or add a dehumidifier. Too dry: check the humidifier and whether too much dry outside air is being brought in.

Too warm: dirty coils, a refrigerant leak, a faulty expansion valve or compressor, or extra heat load from new equipment. Too cold: an unsuitable set point or deadband, a drifting sensor, a reheat that is not working, or a stuck chilled-water valve.

Calibrate the sensors first, then work through the cooling system. The temperature limit is the one the user specifies.

Check in this order: (1) HEPA leaks, with an installed filter leak test; (2) clogged or worn pre-filters; (3) room pressure lower than the next room, which lets air flow in from a dirtier area; (4) airflow or air changes below design; (5) gowning, movement and cleaning; (6) leaks in walls, ceilings, penetrations and door edges.

If the room passes at rest but fails in operation, look at people and activity in the room first.

PIC/S GMP Annex 1 in PE 009-16 (clause 53) recommends 10–15 Pa between rooms of different grades; PE 009-17 (clause 4.14) recommends at least 10 Pa. Both are guidance values. In Thailand, the 2026 MOPH notification keeps Annex 1 of PE 009-16 in force until 31 December 2029 → Thailand’s 2026 GMP notification

The failed tests must be repeated, and tests that the fix may affect should be repeated too. For example, after replacing a HEPA filter, repeat the leak test, airflow and particle count. QV TEST carries out re-tests and issues a new report → Request a quote

Full guide for every item → Cleanroom test failed? Causes and fixes