Key Elements of Contamination Control
We will look at several areas of concern to get a better idea of the overall picture of contamination control. These are the things that need to be considered when providing an effective contamination control program.
HEPA (High Efficiency Particulate Air Filter)
These filters are extremely important for maintaining contamination control. They filter particles as small as 0.3 microns with a 99.97% minimum particle collective efficiency.
CLEANROOM ARCHITECTURE
Clean rooms are designed to achieve and maintain an airflow in which essentially the entire body of air within a confined area moves with uniform velocity along parellel flow lines. This air flow is called laminar flow. The more restriction of air flow the more turbulence. Turbulence can cause particle movement
FILTRATION
In addition to the HEPA filters commonly used in clean rooms, there are a number of other filtration mechanisms used to remove particles from gases and liquids. These filters are essential for providing effective contamination control.
CLEANING
Cleaning is an essential element of contamination control. Decisions need to made about the details of clean room maintenance and cleaning. Applications and procedures need to be written and agreed upon by clean room management and contractors (if used). There are many problems associated with cleaning. Managers need to answer the following questions before proceeding with any clean room cleaning program:
1. What is clean?
2. How is clean measured?
3. What cleaning materials can be used in the clean room?
4. When can the clean room be cleaned?
5. How frequent does it need to be cleaned?
CLEANROOM GARMENTS
The requirements for clean room garments will vary from location to location. It is important to know the local garment requirements of the clean room management. Gloves, face masks and head covers are standard in nearly every clean room environment. Smocks are being used more and more. Jump suits are required in very clean environments.
HUMANS IN CLEANROOMS
There are both physical and psychological concerns when humans are present in clean rooms. Physical behavior like fast motion and horseplay can increase contamination. Psychological concerns like room temperature, humidity, claustrophobia, odors and workplace attitude are important. Below are several ways people produce contamination:
1. Body Regenerative Processes– Skin flakes, oils, perspiration and hair.
2. Behavior– Rate of movement, sneezing and coughing.
3. Attitude– Work habits and communication between workers.
COMMODITIES
Care is taken when selecting and using commodity items in clean rooms. Wipers, clean room paper and pens and other supplies that service the clean room should be carefully screened and selected. Review of the local clean room requirements for approving and taking these items into the clean room are essential. In fact, many clean room managers will have approval lists of these types of items.
COSMETICS
Many cosmetics contain sodium, magnesium, silicon, calcium, potassium or iron. These chemicals can create damaging particles. Clean room managers may ban or restrict cosmetics in the clean room. This is usually dependent upon the threat to the product being made in the clean room. A recent mirror on a space telescope was fogged up from the cologne that was present in the clean room.
MEASUREMENT AND INSTRUMENTATION
Some important measurements related to contamination control are particle count, air flow & velocity, humidity, temperature and surface cleanliness. Clean room managers usually have specific standards and/or instruments to measure these factors.
ELECTROSTATIC DISCHARGE (ESD)
When two surfaces rub together an electrical charge can be created. Moving air creates a charge. People touching surfaces or walking across the floor can create a triboelectric charge. Special care is taken to use ESD protective materials to prevent damage from ESD. Cleaning managers should work with their personnel to understand where these conditions may be present and how to prevent them.
