[The necessity for alternative methods of hygienic testing of air technical designs for operating rooms]

The performance assessment of technical systems for the supply of clean air is fraught with problems which are caused by the present assessment procedures and norms. Until now the distribution of germs in a clean room has been considered as stationary and has been tested as though it was independent of the measuring time. Accordingly the quality of clean air rooms has to date been determined by measurements of particle or germ concentrations (Federal Standard 209; European Standard 209-WG-1; VDI 2083/1). By contrast different methods demonstrate that the contaminations introduced into a clean air room as particles or as particle-bound bacteria are eliminated according to an exponential function in a time-dependent manner. Therefore the measurements of single concentrations without the consideration of the time-dependence of concentration changes must needs lead to extremely faulty results. Furthermore the influence of disturbing factors (test persons, properties of different air supply ceilings, measuring instruments). As a consequence of the poor reliability and lacking validity of presently valid assessment methods, there is a discrepancy between the seemingly high performance of the clean air supply systems under laboratory conditions (DIN 4799) on the one hand, and the frequently unsatisfactory functioning of the same systems under practical conditions. This discrepancy has caused a significant loss of confidence towards the whole clean air technique, especially among the users. Therefore critical test and evaluation methods should be immediately set up for comprehensive testing of technical clean air systems, methods which include the time-dependence of particle or germ elimination as well as test-dependent disturbing factors.