A question commonly asked is "What is a clean room?" Generally speaking, a "Clean Room" is an enclosed room that has equipment which controls the amount of particulate matter in the air by using air pressure and filters. To meet the requirements of a "Clean Room" as defined by Federal Standard 209E and newer ISO standards, all Clean Rooms must not exceed a particulate count as specified in the air cleanliness class.
What are the room classes?
Standards have changed in the last few years. Federal Standard 209E classified rooms in numbers: Class 1, Class 10, Class 100, Class 1,000 Class 10,000 and Class 100,000. This method is simple, the number assigned to the class is the classification that the room must be designed to. Class 1 was the cleanest. The new ISO 14644-1 (or British Standard BS5295) has changed these numbers to simple classes: Class 3, Class 4, Class 5, Class 6, Class 7 and Class 8. Class 3 is the cleanest.
The difference? Generally speaking, federal standards are measured in cubic feet and the ISO standards are measured in cubic meters.
What is measured in the air? Class 3, 4 and 5 are based on the maximum number of 0.1 and 0.5 micron particles that are permitted in a cubic foot of air approaching any work operation within the room. Class 6, 7 and 8 are based on the number .5 micron particles.
What is a micron? To give you an idea of what is being measured, one micron is one-hundredth the width of a human hair. The smallest particle seen with the naked eye is a 10 micron particle. Clean rooms can control .01 and .05 particles!
Where do these particles come from? The clean room is under positive pressure, keeping out new particles from coming in. So where do they come from? Micro-organisms come from people in the room and other particulates from the processes in the room. Microbes come from skin cells of humans. We shed our outermost layer of skin every 24 hours, that is 1 billion flakes every 24 hours! One flake is about 35 microns.
Class limits (amount of particles allowed)
Federal 209B Standards:
* Class 100,000: Particle count not to exceed a total of 100,000 particles per cubic foot of a size 0.5 micron and larger or 700 particles per cubic foot of a size 5.0 micron and larger.
* Class 10.000: Particle count not to exceed a total or 10,000 particles per cubic foot of a size 0.5 micron and larger or 65 particles per cubic foot of a size 5.0 micron and larger.
* Class 1,000: Particle count not to exceed a total of 1000 particles per cubic foot of a size 0.5 micron and larger or 10 particles per cubic foot of a size 5.0 micron and larger.
* Class 100: Particle count not to exceed a total of 100 particles per cubic foot of a size 0.5 micron and larger.
ISO or BS 5295 Standards:
* Class 1: The particle counts shall not exceed a total of 3000 particles/m3 of a size of 0.5 micron or greater. The greatest particle present in any sample shall not exceed 5 micron.
* Class 2: The particle count shall not exceed a total of 300,000 particles/ m3 of a size 0.5 micron or greater: 2000 particles/m3 of a size 5 micron or greater: 30 particles of a size 10 micron or greater.
* Class 3: The particle count shall not exceed 1,000,000 particles of a size of 1 micron or greater: 20,000 particles/m3 of a size 5 micron or greater: 4000 particles/m3 of a size 10 micron or greater; 300 particles/m3 of a size 25 micron or greater.
* Class 4: The particle count shall not exceed a total of 200,000 particles/m3 of a size 5 micron or greater: 40,000 particles/m3 of a size 10 micron or greater: 4000 particles/m3 of a size 25 micron or greater.
A properly designed clean room must have a high rate of air changes to scrub the room of particulates. A Class 5 room can have an air change rate of 400 to 600 times per hour while a Class 7 room can change at 50 to 60 changes per hour.
Testing and certification
Once the room is completed, most specifications call for testing and certification. Some requirements state that the room should be test annually also. Testing is usually conducted by an independent testing agency using the ISO Standards. It is also imperative for the owner to purchase a clean room monitor in order to determine the daily status of the room.