Investigations concerning the standardisation of control-investigations of supply-air in air-conditioning systems in hospitals.

In the following investigation, air-germ measurements were conducted--using the Reuter-Centrifugal-Sampler (RCS) and the Sartorius-Sampler MD 3 (SAR), and using standardized nutrient-substratum and breeding conditions--in order to detect differences in the measuring process itself. The aim of the study was to find a standard for routine-measurements in hospitals. A special "Supply-Air-Box" was developed because of the known turbulences during the emission of air from the channel; in order to cut off the interference-factor during the measurements caused by the blending with the room-air. The results of the air-germ measurements showed a sufficient reproducability and a good representation of the results in differing measuring positions with both devices during repeated measurements. A marked difference between the two measuring-devices are the markedly higher CFU-numbers in the measurements using the RCS-device and the resulting higher variability of the single-values. The measurements using the supply-air-box show that--with the usual measuring position immediately in front of the supply-air grille screen or without grille screen at the channel end--a considerable part of room-air is also registered during the determination of the CFU-number because of the existing turbulences. Because of the markedly lower CFU-numbers with this procedure, new recommendations were suggested for the maximal mean CFU-number in the supply-air. Accordingly, not more than 5 CFU/m3 of air should be found with three-step-filtered supply-air in well-maintained installations for the inrestricted utilization of the rooms, and not more than a mean value of 30 CFU/m3 of air with two-step-filtered supply-air.