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Causes of Cleanroom Contamination

There are three major categories of cleanroom contaminants – airborne, fluid and transfer contaminants. Once these come into contact with an object, some of the contaminants can immediately cause problems. Hard particles are capable of damaging the surface of a component through a grinding action or by becoming embedded in the surface. Softer particles may not cause surface damage but may still interfere with the operation of a device. Other contaminants cause no harm until another process takes place, pushing them across the contamination threshold. Oxygen, sulphur dioxide and trioxide, for example, can produce oxides or salts of the metal base. These salts can then grow in size by a process known as nucleation – the absorption of water vapour – until their size becomes a problem. Also, pressure and/or heat may cause the particles to penetrate into the surface of the component, where they form an alloy or compound, resulting in a serious loss of structural strength.

Cleanroom personnel can be a source of contamination

People working in the cleanroom are a prime source of contamination. They shed skin and hair, give off perspiration and dandruff and emit oral and nasal emissions, which can produce from 100,000 particles per minute (ppm) to three million of 0.5 microns and larger. In fact, particles of 0.3 microns or larger are emitted from each person per minute unless properly garbed.

Cleanroom controls contamination

A cleanroom deals with contamination in three ways:

  • By filtering the air entering the room, preventing the entry of particulate matter.
  • The air-handling system changes the air in the room, effectively purging the air of particulate matter generated within the room.
  • It also provides an area for cleaning parts and personnel, and specifies special clothing made of “limited linting” fibre, as well as floors chosen for resistance to particulate generation.

Step to keep cleanroom clean

Aside from efficient construction and a set of good quality HEPA filters, keeping a conventional cleanroom clean is dependent on employee awareness. Employees must be trained not only about contamination entering the room, but also to limit contamination generated within the room. Psychology can be helpful in maintaining a cleanroom environment. It is important that employees be made constantly aware of the job they are performing, are instructed to maintain as strict a discipline as possible and are constantly reminded of the nature of the work they are accomplishing. This can be done by constant repetition and by establishing a group identity & a sense of group unity and by uniting all the workers in a single purpose – the maintenance of a clean environment.

The ideal cleanroom workers should be motivated to achieve and maintain cleanliness. They have to be aware of contamination control principles and the consequences of each action or inaction. They should be willing to keep their hands, fingernails and face clean, and refrain from combing their hair in the room, or wearing fingernail polish or jewellery. Most importantly, they must be willing to assume responsibility for cleaning up their assigned work station at periodic intervals.

Personnel awareness & responsibilities in conventional cleanroom

The first step is to train employees in personal hygiene. All personnel should be examined to ascertain that there is no profuse nasal discharge, or skin condition that can result in above-normal skin shedding. Examinations should also include the possibility of the existence of dandruff, skin flaking or high amounts of acid found in the moisture of hands or severe nervous conditions such as itching, scratching or claustrophobia.

In addition, all personnel should receive periodic re-indoctrination. They should be encouraged to bathe frequently and shampoo weekly to discourage dandruff, wear clean clothes and avoid scratching their body parts. The wearing of gloves is advocated and daily shaving (or utilisation of masks) should be encouraged. Should long hair be prevalent, the usage of caps or hoods should be encouraged.

In addition, the following instructions should be adapted to achieve the maximum potential from a cleanroom facility. It is not intended that these instructions be utilized in all cleanrooms under all circumstances. We suggest that they be utilised as a guide in total or in part, as required to achieve the end results of individual cleanroom specifications.

  • The cleanroom shall be considered a restricted area. Only authorised personnel will be allowed to enter. Visitors must be approved by the cleanroom supervisor.
  • All entry and egress will be via air locks and air showers except in an emergency.
  • Cleanroom garments will be worn by all personnel and visitors in the cleanroom.
  • Cleanroom garments will be discarded when leaving the cleanroom at the end of the shifts, lunch periods, etc. New cleanroom garments will be utilised when returning to work.
  • No smoking will be permitted within any room in the cleanroom facility.
  • No paper products will be allowed in the cleanroom unless they are suitably sealed in plastic containers. This includes books, manuals, paper pads, towels, etc.
  • All writing will be done with ball point pens; no pencils or erasers will be allowed.
  • Personnel tool boxes will not be allowed in the cleanroom.
  • Clothing that will produce lint shall be avoided, even if covered with cleanroom garments.
  • Operations which will contaminate the cleanroom – grinding, sawing, filing, etc. – will be prohibited unless they are done within an approved exhaust device.
  • The use of abrasive sandpaper or emery cloth will be prohibited unless they are used within an approved exhaust device.
  • Personnel with excessive skin disorder, sunburn or rash will use approved lanolin based skin lotions to control viable particle contamination.
  • No cosmetics will be worn in the cleanroom.
  • Waste baskets must be covered at all times. They shall be emptied daily and vacuumed.
  • No flaking or corrosive materials will be allowed in the cleanroom.
  • All material parts and containers will be cleaned prior to transfer to the cleanroom.
  • Personnel shall have clean hands and fingernails.
  • Personnel shall be clean-shaven and their hair shall not be excessively long.
  • Personnel with dandruff problems shall wash their hair at least once a week, utilizing suitable lotions to control this problem.
  • Personnel with head colds or other ailments which will cause excessive excretions from coughing or sneezing shall be given work in an area that does not require contamination control.
Cathy Albano, Liberty Industries, Inc., USA
www.liberty-ind.com

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