An intensive standardisation process is currently in progress within t
he air cleaning field, During the past few years new test methods and
classification systems have been developed for all types of filters, f
rom coarse filters to absolute and ULPA filters. CEN (Comite Europeen
de Normalisation) is working to establish common standards throughout
Europe, while Eurovent is leading the development of new and modern te
st methods that can meet today's requirements for ventilating air filt
er installations in indoor environments and other areas, In the United
States, ASHRAE is launching a new test method to determine the fracti
onal efficiency of filters using a new concept for test methods and cl
assification. The Institute of Environmental Sciences has introduced a
number of test methods, ranging from flat sheet tests of filter mater
ials to tests of filter installations, that have to meet very stringen
t performance requirements.