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Cleanroom Technology

HEPA Filters

HEPA filters are composed of a mat of randomly arranged fibres. The fibres are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting function are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibres is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibres cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles.:

HEPA filters, as defined by the DOE standard adopted by most American industries, remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter. The filter's minimal resistance to airflow, or pressure drop, is usually specified around 300 Pa at its nominal flow rate.

Lastly, it is important to note that HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds, chemical vapors, cigarette, pet, and/or flatulence odors call for the use of an activated carbon (charcoal) filter instead of or in addition to a HEPA filter.

ULPA Filters

 ULPA is an acronym for "Ultra Low Penetration Air (filter)" An ULPA filter can remove from the air at least 99.999% of dust, pollen, mold, bacteria and any airborne particles with a size of 100 nanometres (0.1 µm) or larger.

HEPA Fan Filter Unit (FFU)

A HEPA FFU is a type of air filtering equipment. It is used to supply purified air to cleanrooms or microenvironments by filtering out harmful airborne particles from recirculating air. The units are installed within the system's ceiling grid as part of a negative pressure plenum. They consist of their own pre-filter, HEPA filter and fan.

Pass Thru

Pass Thrus are used as a means of moving parts and/or materials from a non-controlled environment to a clean room environment. There are both wall mounted pass thru and floor mounted pass Floor mounted pass thrus are typically used for rolling carts. Pass thrus typically have mechanically interlocked doors to prevent particulates from entering the cleanroom when loading or unloading. Some pass thrus have their own HEPA FFU for additional cleanliness.

Cleanroom Classifications

Class 100 – less than 100 particles per cubic foot and 300-480 air changes per hour

Class 1000 – less then 1000 particles per cubic foot and 180 air changes per hour

Class 10000 – less then 10,000 particles per cubic foot 60 air changes per hour

Class 100000 – less than 100,000 particles per cubic foot 20 air changes per hour

Air Lock

Airlock is composed of two doors that are electrically interlocked in such a way that the two cannot be opened simultaneously. Airlocks are used in a variety of situations but in essence they are there to control the unwanted passage from one area to another.

Airlocks may be used to control the entry of personnel to a secure area such as a cleanroom, where dust or small particles may be a problem. Similarly if a constant temperature must be maintained then an airlock can be invaluable in reducing temperature fluctuations when doors are opened.

Sometimes gowning rooms are used as air locks without the interlocked doors. The purpose remains the same – prevent particulates or non controlled air to enter the cleanroom. However the gowning room relies on procedure or light indicators to make sure.

Magnahelic Gauge

In laminar air flow the air tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of air In laminar flow, the motion of the particles of the air is very orderly with all particles moving in straight lines.

Well designed cleanrooms use ceiling mounted HEPA fan filter units and low wall air returns to achieve laminar air flow from ceiling to floor. This means air borne particulates are driven downward away from critical process areas and out of cleanroom instead of moving around cleanroom in turbulent air flow. This type of cleanroom is more effective in removing particules.

Cleanroom Gowns

Workers typically wear non particulating cleanroom gowns and booties when working in cleanroom. They are either laundered by cleanroom laundry service or disposable. The level of gowning depends upon class of cleanroom and processes being performed. If facial hair is present than a beard/mustache guard is also worn. In lower class cleanroom (class 100k) sometimes just lab jacket, hair net and booties are worn.

Hardwall Cleanrooms

Hard wall cleanroom give advantages of softwall cleanrooms because

  • Most common type of cleanroom
  • Cleanable surfaces
  • Can control temperature and humidity
  • Can maintain positive air pressure
  • Can have gowning rooms, air lock
  • More durable

Softwall Cleanrooms

  • Lower cost
  • Utilizes existing air conditioning
  • Difficult to accommodate plumbing, gases, heat load, exhaust air
  • Limitation on how big
  • Cannot wipe down / clean
  • Often portable (if small size)
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