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 particlecollective efficiency.
CLEANROOM ARCHITECTURE- Cleanrooms 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 cleanrooms, 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 cleanroom maintenance and cleaning. Applications and procedures need to be written and agreed upon by cleanroom management and contractors (if used). There are many problems associated with cleaning. Managers need to answer the following questions before proceeding with any cleanroom cleaning program: 1. What is clean? 2. How is clean measured? 3. What cleaning materials can be used in the cleanroom? 4. When can the cleanroom be cleaned? 5. How frequent does it need to be cleaned?
CLEANROOM GARMENTS- The requirements for cleanroom garments will vary from location to location. It is important to know the local garment requirements of the cleanroom management. Gloves, face masks and head covers are standard in nearly every cleanroom 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 cleanrooms. 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 communciation between workers.
COMMODITIES- Care is taken when selecting and using commodity items in cleanrooms. Wipers, cleanroom paper and pens and other supplies that service the cleanroom should be carefully screened and selected. Review of the local cleanroom requirements for approving and taking these items into the cleanroom are essential. In fact, many cleanroom 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. Cleanroom managers may ban or restrict cosmetics in the cleanroom. This is usually dependent upon the threat to the product being made in the cleanroom. A recent mirror on a space telescope was fogged up from the cologne that was present in the cleanroom.
MEASUREMENT AND INSTRUMENTATION- Some important measurements related to contamination control are particle count, air flow & velocity, humidity, temperature and surface cleanliness. Cleanroom 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.