Testing air permeability
Our growing dependence on electronic equipment to help us, both in industry and in daily life, means more and more cleanrooms are needed by companies such as microchip manufacturers. Cleanroom air exchange requirements are particularly stringent, and as a result it is vital that their construction systems meet exacting air permeability criteria. Now, on behalf of industry, the air tightness of suspended ceiling structures has been investigated specifically with cleanrooms in mind for the first time. The suspended ceilings were fitted as per their standard requirements into a test box specifically designed for the purpose. Air permeability was tested with pressure differentials ranging from –5 Pa to –50 Pa and +5 Pa to +80 Pa, allowing researchers to calculate the air permeability based on the surface area and joints of the ceiling element being tested.
The evaluation was based on an existing system used to classify and evaluate the air tightness of doors and windows. This system distinguishes between four classes of air tightness; within each class, the boundaries are defined by the maximum permissible air permeability at a certain pressure given the surface area and length of the joints. In order to have a point of reference (to compare products, for example), the reference air permeability values for windows are based on a pressure differential of 100 Pa.
For the testing of the cleanroom ceilings, however, the reference air permeability taken as a practical point of comparison was based on a pressure differential of 30 Pa, reflecting the reality of cleanroom operations.