11. Air Movement Control Between and Within Cleanrooms

1. 11. Air Movement Control Between and Within Cleanrooms

2. Purposes • To show that a cleanroom is working correctly, it is necessary to demonstrate that no contamination infiltrates into the cleanroom from dirtier adjacent areas. • Cleanroom Containment Leak Testing • Airborne contamination: doors and hatches, holes and cracks in the walls, ceilings and other parts of the cleanroom fabric

3. Contamination can be pushed into the cleanroom at • ceiling-to-wall interface • filter and lighting housings-to-ceiling interfaces • ceiling-to-column interface • the cladding of the ceiling support pillars • Service plenums and the entry of services into the cleanroom: electrical sockets and switches, and other types of services providers. Particularly difficult to foresee and control in a negatively pressurized containment room.

5. Methods of checking infiltration • Smoke test (dust test) • flow direction: open door, or through the cracks around a closed door, cracks at the walls, ceiling, floor and filter housings, service ducts or conduits. • Difficulty • where the containment originates from may be unknown, and it is often difficult to find the places to release test smoke.

6. Containment leak testing • Timing • handing it over to the user • major reconstruction work has been carried out • ISO 14644-2 lists the ‘containment leak’ test as an ‘optional’ test and suggest a re-testing interval of two years

7. Air Movement Control within a Cleanroom • sufficient air movement • dilute, or remove airborne contamination prevent a build-up of contamination • turbulently ventilated cleanroom: • good mixing, critical areas: where the product is exposed to the risk of contamination • unidirectional flow cleanroom • critical areas should be supplied with air coming directly from the high efficiency filters. However, problems may be encountered because of: • heat rising from the machinery and disrupting the airflow • obstructions preventing the supply air getting to the critical area • obstructions, or the machinery shape, turning the unidirectional flow into turbulent flow • contamination being entrained into the clean air.

8. Air movement visualization • Objective: sufficient clean air gets to the critical areas qualitative methods • Visualization: • Streamers • smoke or particle streams • Streamers (threads or tapes): • high surface-area-to-weight ratio, ex. recording tapes • A horizontal flow: 0.5 m/s (100 ft/min) streamer 45° to the horizontal • about 1m/s (200 ft/min) almost horizontal.

9. Streamers

10. smoke or particle streams • oil smoke  contamination • Water vapour : from solid C02 (dry ice) or by nebulizing water

11. putter and smoke tube': • Titanium tetrachloride (TiCl4)produces acid  corrodes some surfaces harmful to sensitive machinery or harm the operator's lungs.

12. Air Movement in turbulently ventilated rooms • working well: quickly dispersed • not working well Areas: not disperse quickly contamination build up  improved by adjusting the air supply diffuser blades, removing an obstruction, moving a machine.

13. Air Movement in unidirectional flow • air moves in lines • Visualisation techniques: smoke stream • Still picture

14. Air velocity and Direction measurement • A permanent record: velocity and direction

16. Recovery Test Method • A quantitative approach • A burst of test particles introduced into the area to be tested mixed with their surroundingsthe airborne particle count should be measured, • A useful endpoint is one-hundredth of the original concentration, and the time taken to reach there can be used as an index of efficiency.