MICROBIAL MEASUREMENTS AT VENTILATION SYSTEMS SUPPLY VENTS

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Eleanor Horn
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1 MICROBIAL MEASUREMENTS AT VENTILATION SYSTEMS SUPPLY VENTS M.Hinker * Allgemeine Unfallversicherungsanstalt, Wien, Österreich (General Workers Compensation Board, Vienna, Austria) ABSTRACT The number of cfu (colony forming units) in the air at outlets of ventilation systems has been compared to the incoming fresh air. In a first step 75 outlets of ventilation systems in 12 different companies were checked by taking 4 parallel samples with two different culture media, at the same time taking samples from the corresponding fresh air. At one of the 75 sampling places significantly elevated numbers of fungi were detected, with one penicillium species dominating. Consequently this sampling place was checked regularly for a period of 14 months to get information about fungal contamination over a longer period. In conclusion our results provide further evidence that microbial measurements of ventilation-air could be used as an indicator for the hygienic conditions of mechanical ventilation systems. INDEX TERMS HVAC systems, mechanical ventilation, microbial measurements, hygienic conditions, airborne microorganisms INTRODUCTION There is an ongoing discussion on the subject, how to find objective criteria for the hygienic conditions of mechanical ventilation systems. Guidelines like VDI 6022 in Germany give as a basic requirement for the supply air that its quality (related to dust, bacteria, mold and biological agents) must be better than the used fresh air. The guideline does not specify the detailed parameter, how to measure this quality. Several authors at the 8 th International Conference on Indoor Air Quality and Climate 1999 in Edinburgh (Indoor Air 1999) deal with microbial measurements in the air of HVAC-systems. The authors cover various aspects of microorganisms in ventilation systems, but there is no clear recommendation for using analysis of airborne microorganisms for routine-checks of HVAC-systems. We therefore wanted to try in practice, what results we could reach by using a relatively simple method for characterizing the hygienic conditions of ventilation systems at various workplaces and estimating the burden of airborne microorganisms for the employees compared to the fresh air. The offices and workplaces were randomly selected and were no complaint cases. METHODS 12 companies, which use HVAC-systems at their offices have been contacted and agreed to participate in our investigation. Altogether 476 measurements gave by parallel sampling 238 results which have been used for this work. * Contact author manfred.hinker@auva.sozvers.at 386

2 Air sampling was done with an impactor (Biotest RCS Plus) and two different media (TC - Total count and DG18 for fungi). At critical points (elevated results) a parallel sampling with a filtration system (Sartorius MD8 with gelatine filters) was used to confirm the results. Air volume was between 20 and 200 Liter, incubation temperature 25 C. The sampling spots were selected randomly and air-samples were always taken directly at outlets of supply air of the HVAC-system. Comparison samples, which represent the outside air, were taken as close as possible at those spots where fresh air was entered into the ventilation system. In a first phase (screening phase) 75 sampling spots in 12 companies have been analyzed and have been compared to the corresponding fresh air. In the second phase one sampling spot of the first phase, which had significantly elevated levels of fungi, has been measured 10 times over a period of 14 months. RESULTS Results are given in cfu/m 3 (colony forming units per cubicmeter air). Phase 1, Screening phase: The average number of 75 sampling spots is 338 cfu/m 3 for TC-agar and 70 cfu/m 3 for DG18- agar, compared to an average of the corresponding fresh air with 750 cfu/m 3 (TC-agar) and 446 cfu/m 3 (DG18-agar). Altogether 13 out of 150 measurements at ventilation outlets show higher burden of microorganisms than the corresponding fresh air. The following table summarizes these results. Table 1. Results of screening phase Fresh air (arithmetic mean value of 18 samples) Ventilation outlet (arithmetic mean value of 75 samples) Number of samples, where Ventilation air > fresh air TC-agar 750 cfu/m cfu/m 3 7 (out of 75) DG18-agar 446 cfu/m 3 70 cfu/m 3 6 (out of 75) The results prove that in most of the working places the impairment of the employees by microorganisms is lower than it would be in the fresh air. This is an indicator that the HVAC systems fulfill the requirement of guideline VDI 6022 to deliver at least better supply air than the corresponding fresh air. In figure 1 the number of fungi at the ventilation outlets are compared with the corresponding fresh air. 387

3 Fungi in HVAC-Air versus Fresh Air 3000 cfu/m Fresh Air Company 1-12 Figure 1. Comparison of fungi in supply air (75 sampling spots) versus fungi in the corresponding fresh air As we can see in the figure, company 10 had one sampling place with significantly elevated results in fungi. To confirm this result, additional sampling with a filtration system was done and gave similar numbers. There was a Penicillium genus clearly dominating. After finishing this screening phase it was agreed with company 10 to follow the measurements at this specific sampling place for a longer period. So phase 2 could be started over more than 14 months. Phase 2: Measurements started 3 months after the first measurement at that spot, where very high levels of fungi had been found. In the meantime Company 10 had restored parts of this office-room including the ceiling and the outlets of the ventilation system. During 14 months 10 times samples were taken, always accompanied with samples from the fresh air. Figure 2 summarizes these results. It became obvious that the numbers of fungi were far lower than the high level from the beginning of the screening phase. Only once in September the supply air was more contaminated than fresh air, but in that case the amount of fungi in fresh air was exceptionally low and seemed to be not representative for the whole day. 388

4 Company 10: Fungi HVAC- versus Fresh Air cfu/m Fresh Air Ventilation Outlet Dez 99 Mär 00 Apr 00 Apr 00 Mai 00 Mai 00 Jun 00 Sep 00 Okt 00 Jän 01 Feb 01 Date Figure 2. Fungi in HVAC-Air over a period of 14 months compared to the corresponding fresh air It should also be mentioned that the spectrum of species of fungi was not identified in detail, but a rough visual inspection did not reveal any predominating species in the supply air. DISCUSSION We have tried to use a simple bioaerosol sampling method for checking HVAC systems with regard to its hygienic condition and the microbiological quality of the supply air which it produces. Visual inspections can only give superficial information and many parts of the ductsystem are not accessible. Therefore a method, which analyses the final air at the outlets could give us a valuable tool for controlling the whole system. Since the method includes cultivation on certain media, one medium and one cultivation temperature will hardly cover all possible microorganisms. It is also probable that growing microorganisms in any HVAC system will not release spores or cells permanently. This means that even with existing growth the results by air sampling could be negative. Bearing those restrictions in mind, regular measurements of bacteria and fungi at the outlets of ventilation systems could be one of the tools for a better control of the maintenance of HVAC systems. CONCLUSION AND IMPLICATIONS Guidelines like the VDI 6022 demand general requirements for supply air of HVAC systems. One of those demands states that the microbiological quality of the supply air has to be better than or at least equal to the corresponding fresh air. The guideline does not specify, how to 389

5 measure this quality or which parameters should be used. In this investigation one method with air-sampling and cultivation was used and tested. Further investigations should gather more experience and informations about the optimal way of testing the compliance to this standard, as e.g. to find the optimal equipment, media, cultivation temperature and sampling strategy. REFERENCES Ahlen C, Haugen E.N., Frydenlund F, Kristiansen O, Lysne HN Composting in ventilation filters? - A possible key to altered thermotolerance in microbial flora of indoor air. Air 1999, Vol 2, pp Edinburgh: Indoor Buttner M P, Cruz-Perez P, Garett P J, Stetzenbach L D Dispersal of Spores from fungalcontaminated duct material. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 2, pp Edinburgh: Indoor Hake W, Neumeister-Kemp H G, Kemp P C, Martiny H Reduction of Microorganisms by HVAC system filters and analysis of the microorganisms passing through the filters. Air 1999, Vol 4, pp Edinburgh: Indoor Halonen R, Reimann M, Seuri M et al Transport of Microbes via supply ventilation ducts. Air 1999, Vol 2, pp Edinburgh: Indoor Kemp P C, Carlsson T, Nickelmann A, Neumeister-Kemp H G Comparisons of Microorganism loading from two air filter materials during the first eight weeks of service life. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 4, pp Edinburgh: Indoor Keune A Hygiene requirements of air conditioning systems from the technical point of view. VDI-Berichte Nr. 1603, 2001, pp (German) Kim Yong Hup, Kim guang Yong, Sim Il Chol Features of microbial contamination in HVAC system. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 2, pp Edinburgh: Lysne H N, Ahlen C, Stang J et al Hygienic conditions in ventilation systems and the possible impact on indoor air microbial flora. Proceedings of the 8 th international Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 2, pp Edinburgh: Indoor Neumeister-Kemp H G, Esposito W., Kemp P C, Kircheis U Fungi genera throughout the HVAC system in a well maintained New York building: the worth of high cleanliness standards. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 2, pp Edinburgh: Indoor Parat S, Perdrix A, Maitre A Airborne Microorganisms in Buildings: Influence of technical, environmental and climatic factors. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 4, pp Edinburgh: Indoor Thomann W R, Tulis J J The relative contribution of the HVAC system to the total glass fiber and fungal spore levels in indoor spaces. Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air 1999, Vol 4, pp Edinburgh: Indoor VDI (VEREIN DEUTSCHER INGENIEURE) Hygienic aspects for the planning, design, operation and maintenance of air-conditioning systems. VDI 6022 (German) 390

Test record CFU measurement. Test ID Site/Clinic Spijkenisse

Test record CFU measurement. Test ID Site/Clinic Spijkenisse Test record CFU measurement Test ID 1130036 Site/Clinic Spijkenisse Objective of the test: To verify that there are < 10 CFU/m3 in the clean air flow area. Type of test: CFU test, Microbial precipitation