User Manual

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Siemens Building Technologies
Cerberus Division
01.2002
6.5 Operating mode of air handling systems
6.5.1 Continuous operation
Normally, clean room systems are continuously in operation, even outside working hours.
The flow control principle must be guaranteed at all times. However, it is often switched to
half power, e.g. with unidirectional airflow, at approx. 0.2m/s.
6.6 Air cleanliness classes
There are various national standards and guidelines with corresponding air cleanliness
classes for the assessment of the cleanliness of room air. The air cleanliness classes are
determined by measuring the particle concentration per volume unit for specific sizes of
particle. At present the ISO (International Organization for Standardisation) is working on a
harmonized standard which will supersede the following national standards:
U.S. Federal Standard 209
Internationally, this is the standard most complied with on this subject. Up to version 209D
the standard was based on British units of mass, i.e. particle concentrations were given in
the number of particles per cubic foot (ft
3
). The currently valid version 209E contains two
reference volumes, namely the cubic foot as before and the cubic metre in accordance with
the metric SI unit.
NFX44-101 (France)
Definition, classification of air cleanliness and other gases in relation to their dust content,
1981
BS 5295 Part 1: 1989 (Great Britain)
The cleanliness of the air in closed rooms. An introduction to and terminology for clean
rooms and clean room installations.
JIS B 9920 (Japan)
Measuring techniques for airborne particles in clean rooms and assessment criteria for air
cleanliness in clean rooms, 1989
JIS B 9922 (Japan)
Clean workplaces, 1992