Cleanroom Disciplines
Disciplines required within a cleanroom
Cleanroom personnel are a major source of particle and bacterial contamination. Particle contamination can cause product failure, and bacteria can be hazardous to patients. Almost all bacteria found in a cleanroom come from the people working within it as do many of the inert particles. It is therefore necessary to ensure that people working in a cleanroom generate the minimum of contamination. By observing certain rules within the cleanroom, the amount of contamination available to contaminate the product can be minimized.
CleanRooms asked Bill Whyte, a world-renowned expert on contamination control from the University of Glasgow and general secretary for the Scottish Society for Contamination Control, to provide guidance on proper disciplines that must be followed in a cleanroom. Here, Whyte outlines the do’s and don’ts of working in a cleanroom.
PEOPLE ALLOWED IN CLEANROOMS
People are a major source of contamination, with the average person producing, per minute, about 1,000,000 particles > 0.5u and several hundred bacteria-carrying particles. The more people, the higher contamination level within the cleanroom. Only essential personnel should therefore be allowed into cleanrooms and management should ensure this is so.
Because of the contamination problems that can be caused by ignorance, only people trained to work in a cleanroom should be allowed in. Personnel should therefore be formally trained in the various aspects of contamination control.
People who enter the cleanroom should not disperse significantly greater amounts of contamination than the normal population. Given below are examples of conditions that are likely to generate more contamination than normal and therefore may be unacceptable. Acceptability will depend on the contamination risk, e.g., whether bacteria are a hazard or not, and whether the product is highly susceptible to particle contamination or not. It will therefore be up to management to decide which of the following conditions are important:
- Skin conditions that will cause unusual amounts of skin to shed, e.g., dermatitis, sunburn or bad dandruff;
- Running noses, coughs and sneezes caused by colds, flue or chronic coughing;
- Allergic conditions that cause sneezing, itching and scratching, or a running nose;
- In a biocleanroom, high bacterial carriage. Examples are high levels of bacterial skin carriage and the carriage of food poisoning organisms in the intestine.
Depending on the contamination risk within the cleanroom, some, or all, of the following suggestions should be brought to the attention of the staff so that contamination within the room may be minimized:
- Personnel should have a good level of personal hygiene. They should shower regularly and keep dandruff at bay. They should wash their hair after a haircut and in case of dry skin they should use skin lotion to replace skin oils.
- Materials such as talcum powder, hair sprays, nail polish, or similar materials should not be allowed in many cleanrooms. Anything added on to the body should generally be considered a contaminant.
- Rings, watches and jewelry are often not allowed in a cleanroom. If jewelry is allowed it must be under the clothing and gloves. Rings can harbor contamination under them and puncture the gloves. Personnel may not wish to remove their wedding or engagement rings. It may be acceptable to ensure the skin under the rings as well as the rings are washed, and where the rings are not smooth, they should be taped over.
- Smokers produce more particles from their mouth than the normal population and offgas chemicals. It may be necessary to ensure that they have not smoked several hours before entering the cleanroom. It has been reported that taking a drink before entering the cleanroom reduces the number of particles given off form the mouth.
MATERIALS NOT ALLOWED INTO THE CLEANROOM
As a general rule, nothing should be allowed into the cleanroom that is not required for the production within the cleanroom. Anything that will give off contamination should generally be left outside the room. However, it will be up to the management of the cleanroom to decide what times could cause contamination of the product. This will be assessed in light of what is essential for production within the cleanroom. A checklist of items that are best left outside the cleanroom is given below:
Personal items:- Food, drink, sweets and chewing gum;
- Cans or bottles;
- Smoking materials;
- Radios, CD players, walkmans, cell phones, pagers, etc.;
- Newspapers, magazines, books and paper handkerchiefs;
- Wallets, purses and other similar items;
- Abrasives or powders;
- Aerosol-producing cans or bottles;
- Items made from wood, rubber, paper, leather, cotton and other natural occurring materials;
- Paper not manufactured for cleanrooms (if ordinary paper must be used then it should be sealed in plastic envelopes or laminated between plastic films);
- Pencils and erasers;
- Writing instruments that could scratch paper (such as fiber tipped pens) or contain ink that contains contaminating chemicals;
- Correcting fluid.
DISCIPLINES WITHIN THE CLEANROOM
To ensure that contamination is kept to a minimum, rules of conduct are required within a cleanroom. The following disciplines should be considered when drawing up a list of procedures that should be used within the cleanroom.
To ensure that air is not transferred from an area of higher contamination to one of lower contamination, the following disciplines should be adhered to:
- Doors should not be left open. If they are, air will be transferred by general turbulence of the air within the rooms, or by the temperature difference between two areas;
- Doors should not be opened and closed quickly, or air will be pumped from the less clean to to the cleaner side;
- Doors should be fitted with door-closing devices to ensure that the doors are kept closed and that the doors will shut slowly and hence reduce the air transfer;
- When passing through a set of doors in an airlock, personnel should wait until the first door is closed before going through the next one. Interlocks between entry and exit doors often achieve this but care must be taken to ensure that there is no danger in case of fire. Indicator lights, which show if the doors are shut, are also used.
The following suggestions should be considered to ensure that personnel do not contribute to the contamination with the room:
- Silly behavior is not allowed. The generation of contamination is proportional to activity. A motionless person generates about 500,000 particles >0,.5u/min. A person with head, arms and body moving generates about 1,000,000 particles >0.5u/min. A person walking at 2 mph generates about 5,000,000 particles >0.5u/min;
- Personnel should be positioned correctly with respect to the product so that contamination does not land on the product. An example of this is personnel getting between the air supply filters and the product in a unidirectional flow system;
- Consideration must be given to how products are to be moved or manipulated. “No-touch” techniques should be devised to prevent contamination getting from the gloved hand onto the product. Examples of this are the use of a vacuum “wand” to handle wafers in semiconductor areas and the use of forceps to manipulate vials in pharmaceutical cleanrooms;
- Personnel should not support material against their bodies. Although they will be wearing cleanroom clothing, which is much cleaner than indoor or factory clothing, it is not contamination free;
- Personnel should not talk when working over the product or spittle from the mouth will pass round the imperfect seal between the mask and the skin, or through the mask. Masks should always be worn over the nose;
- Personnel should not allow anything to trail over the product;
- Personnel should not touch cleanroom surfaces and then the product. A cleanroom although much cleaner than a normal factory environment, is not free from contamination;
- Personal handkerchiefs should not be brought into cleanrooms. These are clearly a major source of contamination and will transfer particles into the air and onto the gloves. Noises should not be blown inside a cleanroom. The change area may be an acceptable alternative.
- Cleanroom wipes that have a low concentration of contamination should be used; the exact type of wipe to be used will depend on economics and what is being produced in the cleanroom. It will also be necessary to decide how often a wipe should be used before being discarded;
- It is usual to find that great care has been taken to ensure that a product is not contaminated during it’s manipulation stages. However it may be left out in the cleanroom between manipulation stages and hence be contaminated by particles depositing from the cleanroom air. Products to be sorted or left standing in a cleanroom should therefore be kept in closed cabinets, containers or in unidirectional flow benches;
- Waste material should be collected frequently into easily identified containers;
- Cleanrooms should be correctly cleaned (and disinfected if required). This is a major topic not discussed within this paper.
- And finally: The cleanroom must be kept neat and tidy. If it is not tidy, it cannot be kept clean.
Acknowledgement: This article is based on the information given in a set of procedures written by the author for the Scottish Society for Contamination Control. Their assistance is acknowledged. Thanks to Ms. Lynn Morrison, S3C2 who posed for the photographs demonstrating incorrect procedures.
Bill Whyte is a Research Fellow in the Mechanical Engineering Department at Glasgow University in Scotland. He has been involved with cleanrooms for over 30 years and has published over 100 papers and reports on this subject, as well as editing the book “Cleanroom Design,” published by J Wiley & Sons. He is founder, former chairman and now secretary of the Scottish Society for Contamination Control. He has extensive experience as an industrial consultant.
