THE INFLUENCE OF VARIOUS AIR EXCHANGE-RATES ON AIRBORNE PARTICLES ANDMICROORGANISMS IN CONVENTIONALLY VENTILATED OPERATING-ROOMS

Concentrations of airborne particles and microorganisms were assessed as a function of the air exchange rate in two operating theatres equip ped with conventional air ventilation systems. The measurements were m ade with and without human activity (surgery). Under conditions withou t human activity the effect of the air exchange rate on viable (=micro organisms) and non-viable airborne particles was measured. Under condi tions with human activity an investigation was made to determine wheth er the air exchange rate has a significant influence on airborne parti cle and bacteria concentrations. In addition, the influence of the num ber of persons in the operating theatres and the various operating act ivities were calculated. Statistical differences were found for airbor ne particle and airborne bacteria concentrations in supply and room ai r with and without human activity. From the point of view of hygiene, these differences must be considered irrelevant because of the slight margin (less than one logarithmic step) between the values. A comparis on of all air exchange rates clearly shows that the number of personne l present in the operating theatre exerts the strongest influence on a irborne particle concentration variance in room air. As regards airbor ne bacteria concentrations in room air, explanation of variance by the parameters air exchange rate, number of persons and operating activit y is negligible. Summarizing the low (7.5 and 10/h) and high (15 and 2 0/h) air exchange rates did not increase the explanation of variance f or airborne particle and bacteria concentrations although the differen ces were significant.