Description
Emergency situations in a properly designed, constructed and operated clean room phenomenon is quite rare, but completely eliminate their occurrence, unfortunately, almost impossible.
In case of sudden pollution of a clean room due to a malfunction of the ventilation system or from internal sources, you should know the time during which a clean room or clean zone is able to restore the specified cleanliness class during normal operation of all systems.
How to measure the recovery time of the cleanliness class
Evaluation of the recovery time of a cleanliness class is usually carried out in small clean rooms of high cleanliness classes.
In this case, particles generated by an aerosol generator are fed into the room air. Depending on the specific conditions, testing using two approaches is allowed:
direct measurement of the recovery time of a given purity class with an initial increase in the concentration of particles a hundred times compared with the permissible level;
measuring the time to reduce the concentration of particles a hundred times from a certain, artificially created level and calculating the recovery time of the required class.
This value is also directly related to the parameter of a clean room, as the rate of air exchange. Comparison of data on the measured frequency of air exchange and the recovery time of the cleanliness class can help identify some problems that are not obvious at first glance, for example, the presence of stagnant zones in a clean room.
The choice of approach depends on the class of cleanliness of the room, its volume, as well as on what level of air pollution of a particular room during testing is considered acceptable.
For clean rooms with a unidirectional flow, this test is not carried out, since the recovery time of the cleanliness class in a laminar flow depends solely on the speed of this flow.
The results of measuring the recovery time class clean
The protocols and test report on clean rooms include data on the measurement method used, measured and estimated values of the recovery time, and conclusions on the compliance of the specified requirements.
