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  • 9. Cleanroom Testing and Monitoring

  • Purposes for initial test:

    Fulfill the design

    working correctly and achieving the contamination standards

    Bench-mark:

    establish the initial performance of the room to compare the results of routine check or contamination problem in the future.

    Training the staff: (most important)

    initial testing is to familiarize and train the staff.

    Only opportunity to understand how their cleanroom works and learn the methods used to test.

  • initial test

    Time

    been built/ going to hand over/ reopen

    Tested standards

    ISO 14644-1.

    Monitoring

    to regularly check the room at the time intervals set by ISO 14644-2

  • Principles of Cleanroom Testing

    Quantity:

    Turbulently: dilute--air volume (supply and extract)

    Unidirectional: remove air velocity

    Direction (flow direction):

    from clean area less-clean areas to minimise the movement of contaminated air.

    Quality:

    the air will not add significantly to the contamination within the room

    Distribution inside cleanroom

    the air movement has no areas with high concentrations of contamination.

  • Cleanroom Tests

  • Air supply and extract quantities

    turbulently ventilated cleanrooms the air supply and extract volumes

    unidirectional airflow air velocity.

    Air movement control between areas: direction

    The pressure differences between areas are correct.

    The air direction through doorways, hatches, etc. is from clean to less-clean.

  • Filter installation leak test

    a damaged filter

    between the filter and its housing or

    any other part of the filter installation.

    Containment leak testing

    Contamination is not entering the cleanroom through its construction materials.

  • Air movement control within the room

    turbulently ventilated : check that there are no areas within the room with insufficient air movement.

    unidirectional airflow : check that the air velocity and direction throughout the room is that specified in the design.

    Airborne particles and microbial concentrations

    final measurements of the concentration of particles and micro-organisms

  • Additional tests

    temperature

    relative humidity

    heating and cooling capabilities of the room

    sound levels

    lighting levels

    vibration levels.

  • requirements

    Guides provided by

    the American Society Heating Refrigeration and Airconditioning Engineers (ASHRAE) in the USA, and

    the Chartered Institute of Building Services Engineers (CIBSE) in the UK.

  • Testing in Relation to Room Type and Occupation State

    The type of tests to be carried out in a cleanroom depends on whether the room is unidirectional, turbulent or mixed airflow:

    as-built ---in the empty room,

    at rest --- the room fitted with machinery but no personnel present or

    fully operational---these occupancy states are discussed more fully in Section 3.4 of this book.

  • Re-testing to Demonstrate Compliance

    The cleanroom checked intervals, these intervals being more frequent in higher specified rooms: ISO 14644-2

  • Monitoring of Cleanrooms

    Use risk assessment to decide what monitoring tests should be done and how often. The variables that are most likely to be monitored are:

    air pressure difference

    This might be necessary in high quality cleanrooms such as ISO Class 4, and better.

    airborne particle count

    This might be necessary in high quality cleanrooms such as ISO Class 4, and better.

    where appropriate, microbiological counts.

  • 10. Measurement of Air Quantities and Pressure Differences

  • Purpose

    A cleanroom must have sufficient clean air supplied to dilute and remove the airborne contamination generated within the room.Air Cleanliness:

    Turbulently ventilated cleanroom

    air supply; the more air supplied in a given time, the cleaner the room.

    unidirectional cleanroom

    air supply velocity

    Test:

    Initial testing of the design

    Regular intervals check

  • Air Quantities

    Instruments:

    Hoods: air supply volumes

    Anemometers: air velocities

    Turbulently ventilated rooms

    measured within the air conditioning ducts Pitot-static tube

  • Measuring air quantities from within a cleanroom

    Air air filter (no diffuser) anemometer at the filter face average velocity air volume

    Difficulty: the non-uniformity of the air velocity inaccurate measurement

    Air air diffusers unevenness of air velocities incorrect air volumeHood: air supply volume average velocity measured at the exit of the hood air volume

  • Anemometers

    Anemometers: away from the filter of about 30cm (12 inches) Vane Anemometer

    Principle: Air supply turning a vane frequency velocity

    Accuracy: velocity is less than about 0.2 m/s (40 ft/min), the mechanical friction affects the turning of the vane

  • Vane Anemometer

  • Thermal Anemometers

    Principle: Air passing through the head of the instrument cooling effect the air velocity: Fig.10.3 : a bead thermistor ()Low velocities can be measured with this type of apparatus

  • Differential Pressure Tests

    The units:

    Pascals, inch water gauge are used (12Pa = 0.05 inch water gauge).

    Pressure difference: 10 or 15 Pa between clean areas

    15 Pa is commonly used between a cleanroom and an unclassified room,

    10 Pa between two cleanrooms.

  • Large openings:

    problems can occur when trying to achieve a pressure difference between areas connected by large openings, such as a supply tunnel. To achieve the suggested pressure drop :

    Very large air quantities through the tunnel

    To accept a lower pressure difference

  • Apparatus for measuring pressure differences

    Manometer:

    range of pressure difference of 0-60 Pa (0-0.25 inch water)

    inclined manometer; magnehelic gauge; electronic manometer

  • Inclined manometer

    works by pressure pushing a liquid up an inclined tube.

    small pressure changes in the inclined tube up to a pressure of about 60 Pa.

    After that pressure, the tube moves round to the vertical measuring pressure differences can be in the 100 to 500 Pa range.

  • Methods of checking pressure differences

    pressure differences between areas

    adjusting the pressure differences :

    extract be reduced to increase the pressure, and increased to decrease it.

    If manometers are not permanently installed, a tube from a pressure gauge is passed under the door, or through an open by-pass grille or damper into the adjacent area.In some ventilation systems, the pressures within rooms are measured with respect to one reference point. When this type of system is being checked, the pressure difference across a doorway can be calculated by subtracting the two readings of the adjoining spaces.

  • 11. Air Movement Control Between and Within Cleanrooms

  • 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

  • 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 pillarsService 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.

  • 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.

  • 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

  • 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.

  • Air movement visualization

    Objective: sufficient clean air gets to the critical areas qualitative methodsVisualization:

    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