11. Air Movement Control Be11. Air Movement Control Between and Within Cleanroomtween and Within Cleanroom

ss

PurposesPurposes

• 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, h

oles and cracks in the walls, ceilings and other parts of the cleanroom fabric

Contamination can be pushed into tContamination can be pushed into the cleanroom athe 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 th

e cleanroom: electrical sockets and switches, and other types of services providers. Particularly difficult to foresee and control in a negatively pressurized containment room.

Methods of checking infiltrationMethods 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.

Containment leak testingContainment 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

Air Movement Control within a CleaAir Movement Control within a Cleanroomnroom

• 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 th

e 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.

Air movement visualizationAir 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.

Streamers

smoke or particle streamssmoke or particle streams

–oil smoke contamination

–Water vapour : from solid C02 (dry ice) or by nebulizing water

putter and smoke tube':putter and smoke tube':

• Titanium tetrachloride (TiCl4)produces acid corrodes some surfaces harmful to sensitive machinery or harm the operator's lungs.

Air Movement in turbulently Air Movement in turbulently ventilated rooms 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.

Air Movement in unidirectional flowAir Movement in unidirectional flow

• air moves in lines – Visualisation technique

s: smoke stream– Still picture

Air velocity and Direction Air velocity and Direction measurementmeasurement

• A permanent record: velocity and direction

Recovery Test MethodRecovery Test Method

• A quantitative approach • A burst of test particles introduced into t

he area to be tested mixed with their surroundingsthe 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.