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Disturbances of wound healing 281 18.8 Spondylitis 23 1.5 Out of a total of 1,492 operations 304 20.3 operating room for some years. This is told to illustrate that it is necessary to check many points in solving hygienic problems. How- ever, air conditioning is only one of the factors in contamination. Special Problems Air pollution means pollution by solid, liquid, or gaseous particles (Strauss 1977). In general it is technically easy to filter liquid and certain gaseous particles suspended in the air. But it is much more difficult to free the air from solid particles, especially those of a diameter of less than 5 ~tm. The concentration of solid particles dif- fers considerably, and depends on the urbanization and the weather. Amazingly, there are strict relations between size of particles and grade of pollution (Fig. 1). The higher the pollution the larger the number of particles. Filtration of solid particles depends on the sedimentation, the inertia of particles, their thermic movement, electrostatic effects, and the size and shape of the particles. Even if they are irregularly shaped, solid particles are classified by diameter, as proposed by Stokes in 1969. Filters can be classified in different ways (Strauss 1977). Most widely used is a classification based on the precipitation or filtration rate of filters. Roughing filters clean the air from the major particles, fine-fibred filters retain the majority of even fine dust particles, microorganisms, and germs of a size of more than 1 ~tm. HEPA- The degree of cleanliness is related to the concentration of par- ticles in the air (Strauss 1977). In general, particles are of a diameter of more than 0.5 ~m/m z. There exist different rules in different countries. Operating rooms belong to the class of rooms for which the highest requirements are necessary. One can differentiate two relative frequency of p articles B A C 10-2 ........ ;6" ........ ;00 ........ 'i07 m diameter of particles Fig. 2. Distribution of the particles of proofing aerosols according to German Industrial norm (DIN 24 184). A Paraffin oil, B natural aerosol with radioactive particle, G Quartz-dust Table 2. Emission of Particles in Relation to Movement According to P. R. Austin and S. W. Timmerman Kind of movement Number of particles/min Standing or sitting without moving 100,000 Sitting, slight movements 500,000 Moderate movements 1,000,000 Standing up and moving 2,500,000 Slow going 5,000,000 Gymnastics, sport 15,000,000 to 30,000,000 Every 1,000-10,000 particles I germ or 1 germ-carrier! classes of operation theatres; one in which operations on bones, im- plantations of organs, or cardiac operations are performed; another in which abdominal operations or operations on the urinary tract are carried out. In general, the more sensitive a tissue is to infection and the longer and the more difficult an operation, the higher is the necessity for a true clean room technique.
Rules of the different governments for this technique take into account the cleaners, the room class, the filter, the number of filtrations, the ventilation rate, room temperature, and humidity. The ventilation rate is especially important. The number of germs depends on the rate of ventilation (Russenberger and Wanner 1974). Using natural ventilation during operation up to 700 germs/m 3 can be observed. Conventional air conditioning systems with a 12-fold ventilation rate/hour show 300 germs/hour, with a 20-fold ventilation rate 60 germs/hour. With a laminar flow technique with a 600-fold ventilation rate the room is germ-free (Russenberger and Wanner Table 3. Ventilation Rate in Relation to the Used Technique Times/hour Conventional technique 20-40 Supporting jet stream technique 15-30 Laminar flow technique 400-700 1974). These data illustrate how expensive it is to make a room germ-free. In order to have an idea of the requirements of operation theatres you must know that in the air of a big city nearly 50 millions of particles/m a are dispersed. The air of a clean room should not contain more than 3.5 particles larger than 0.5 ,m diameter/litre and no particles of more than 5 !am diameter/litre, as recommended by the Federal Standard in U.S.A. and the German industrial norm (DIN), Laminar flow demands a high ventilation rate (Table 3). In order to get a unidirectional or uniform flow--that is the correct expression, but laminar flow has become more popular since the first publica- tions-an air-flow-velocity of 0.45 +_0.1 m/second is necessary (Strauss 1977). This means that the ventilation rate and the expense depend on the size of the room. Therefore different technical solutions have been elaborated by the industry, each respecting the high standard. In general a total room technique, a cabin or tunnel technique (i.e., a room in the room), and a local technique (i.e. working place or working field) are distinguished. The admission of air can be turbulent, pseudolaminar, or laminar. Conventional air conditioning systems cannot fulfil the requirements of clean rooms, even if the ventilation rate is increased. Their air flow is always turbulent, and the turbulence of the air flow (Schicht 1972) is responsible for a high amount of contamination with germs. Under conditions of an operation 3.5 millions of particles >- 0.5 gm/m a are soon demonstrable. Using the laminar flow technique the airflow can be arranged as a cross- or a down-flow (Figs. 3 and 4). Total room or cabin tech- nique raise questions of expense and costs, because airflow conditions are the same. In cabin or tunnel technique the clean room is much smaller. The supporting jet stream technique (Allander and Abel Fig. 6, Local technique: upward flow in the operation field according to Nouri ..\\\\ Fig, 7. Helmet technique according to Weber 1968, Skiba 1975, Schicht and Steiner 1972) (Fig. 5) allows a pseudo- laminar flow over the operation table while at the borders turbulences arise. The jet stream has the function of bringing the air in line. The working place technique is only possible in laboratories or factories.