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Calidad Del Aire Interior en Una Clínica de Odontología

    Science of the Total Environment 377 (2007) 349  – 365   www.elsevier.com/locate/scitotenv   Indoor air quality in a dentistry clinic   C.G. Helmis a,  , J. Tzoutzas  b , H.A. Flocas a , C.H. Halios a , O.I. Stathopoulou a , V.D. Assimakopoulos c , V. Panis  b , M. Apostolatou a , G. Sgouros a , E. Adam  b   a   Division of Applied Physics, Department of Physics, University of Athens, University Campus, Build.Phys-5, Athens 157 84, Greece  b  Department of Dentistry, University of Athens, Thivon 2, Goudi, 115 27, Athens, Greece   c   Institute for Environmental Research and Suitable Development, National Observatory of Athens, 15236, P. Penteli, Greece   Received 24 July 2006; received in revised form 25 January 2007; accepted 27 January 2007   Available online 16 April 2007    Abstract   The purpose of this work is to assess, both experimentally and theoretically the status of air quality in a dentistry clinic of the Athens University Dentistry Faculty with respect to chemical pollutants and identify the indoor sources associated with dental activities. Total VOCs, CO 2 , PM 10 , PM 2.5 , NO x  and SO 2  were measured over a period of approximately three months in a selected dentistry clinic. High pollution levels during the operation hours regarding CO 2 , total VOCs and Particulate Matter were found, while in the non-working periods lower levels were recorded. On the contrary, NO x  and SO 2  remained at low levels for the whole experimental period. These conditions were associated with the number of occupants, the nature of the dental clinical  procedures, the materials used and the ventilation schemes, which lead to high concentrations, far above the limits that are set by international organizations and concern human exposure.   The indoor environmental conditions were investigated using the Computational Fluid Dynamics (CFD) model PHOENICS for inert gases simulation. The results revealed diagonal temperature stratification and low air velocities leading to pollution stratification, accompanied by accumulation of inert gaseous species in certain areas of the room. Different schemes of natural ventilation were also applied in order to examine their effect on the indoor comfort conditions for the occupants, in terms of air renewal and double cross ventilation was found to be most effective. The relative contribution of the indoor sources, which are mainly associated with indoor activities, was assessed by application of the Multi Chamber Indoor Air Quality Model (MIAQ) to the experimental data. It was found that deposition onto indoor surfaces is an important removal mechanism while a great amount of particulate matter emitted in the Clinic burdened severely the indoor air quality. The natural ventilation of the room seemed to reduce the levels of the fine particles. The emission rates for the fine and coarse particulates were found to be almost equal, while the coarse particles were found susceptible to deposition onto indoor surfaces. © 2007 Elsevier B.V. All rights reserved.   Keywords: Dental clinics; Volatile organic compounds; Carbon dioxide; Particulate matter; Indoor air quality   1. Introduction  Recently the scientific community has become increasingly interested in the air quality of indoor   Corresponding author. Tel.: +30 2107276927; fax: +30 2107295285. E-mail address: chelmis@phys.uoa.gr  (C.G. Helmis). 0048-9697/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2007.01.100  areas of hospitals and healthcare facilities. Operating rooms, biochemical laboratories, infirmaries and private  practices have been examined where the mixture of  pollutants, chemical compounds, microorganisms and  biological infectious agents in the air form indoor con-ditions which are dangerous to health for both patients and health providers (Loizidou et al., 1992; San Jose-   350   C.G. Helmis et al. / Science of the Total Environment 377 (2007) 349  – 365  Alonso et al., 1999; Morawska, 2006). The comparison of such an environment within hospitals with different exposures to different risk factors, with or without air-conditioning, showed the positive effect of ventilation systems on the improvement of indoor air quality, as long as these systems are properly operated and well maintained (Holcatova et al., 2003)  when outdoor con-centrations are low. Indoor air quality in dental units has been also estimated and quantified with respect to microbial factors. Concentration measurements of microbial aerosols in general dental practices have been performed in order to carry out microbiological risk assessments (Bennett et al., 2000). The contamination levels have been analyzed by investigating the air, water and certain surfaces before, during and after dental treatments (Cellini et al., 2001; Monarca et al., 2002; Liguori et al., 2003). Other  researchers have compared the levels of  bacterial aerosols pollution between different dental environments as well as different positions within the same dental clinics (Grenier, 1995; Kedjarune et al., 2000).  Regarding dental offices, the investigation of the environmental pollution has been focused on the con-tamination from infectious diseases (tuberculosis, hep-atitis, upper respiratory infections, and other viral or  bacterial diseases) as produced by various dental pro-cedures (Micik et al., 1969; Mosley and White, 1975)  and the methods for reducing airborne contamination (Miller and Micik, 1978; Littner et al., 1983; Kohn et al., 2003; Harrel and Molinari, 2004).  On the other hand, very few attempts have been made to assess the air quality status of dental offices from the chemical point of view. Girdler and Sterling (1998) tested whether the exposure of dental staff to nitrous oxide during inhalational sedation with nitrous oxide/oxygen complied with specified occupational exposure standards while they assessed and determined the factors affecting the levels of nitrous oxide pollution. More recently, Godwin et al. (2003) measured the concentration levels of   respirable particulate matter, CO 2  and VOCs in dental clinics and estimated emission rates of indoor sources. The objective of the present study was to evaluate the indoor environment of a selected clinic in the Dentistry Faculty of Athens University with respect to CO 2 , TVOCs, PM 10 , PM 2.5 , SO 2  and NO x  and to identify  possible sources and relations between specific dental activities and pollution levels. Furthermore, the mechan-isms in the airflow and temperature fields associated with the formation of the pollution levels were examined with the application of the Computational Fluid Dynamics (CFD) model PHOENICS and the relative contribution of the indoor sources of particulate matter to the indoor air quality status was assessed with the aid of the Multi Chamber Indoor Air Quality Model (MIAQ).   2. Experimental site, methodology and instrumentation The study took place in the Dentistry Faculty of Athens University, which consists of two individual 5 floor buildings (the Undergraduate Studies Building and the Postgraduate Studies Building) connected by in-ternal corridors.  Before the main experiment, preliminary measure-ments of TVOCs, CO 2  and particulate matter concentra-tions were performed in several areas of the Dentistry   Fig. 1. Ground plan of clinic, location of instruments for the pollutants measurements and measurement points of the airflow characteristics ( ● : location of DANTEC instruments, : dentistry chairs, |: bulkheads) (not in scale).    C.G. Helmis et al. / Science of the Total Environment 377 (2007) 349  – 365   351   Faculty. From the results obtained, the Total Treatment Clinic, on the third floor of the Undergraduate Studies Building, was selected according to its characteristics and high pollution levels. The Clinic has an area of 290 m 2  and operates in two shifts (08:00  – 12:30 and 13:00  – 17:00) with 70  – 100 occupants in every shift. It is naturally (not mechanically) ventilated. Heating is achieved by central heating radiators and air conditioners (A/Cs), which were rarely used. In Fig. 1, the ground plan of the Clinic is presented, along with the position of the instruments used for the pollutant measurements. In this room, the pollutants TVOCs, PM 10 , PM 2.5 ,  NO, NO 2 , SO 2  and CO 2  were monitored during the  period from the 3rd December 2004 to the 3rd March 2005, during both working days and weekends, using the following instrumentation:  ã   Portable instrumentation  –  two indoor air quality monitors (IAQRAE and ppbRAE of RAE systems) for TVOCs measurements (resolution: 10 ppb and   1 ppb respectively, accuracy: 10%) and one monitor (IAQRAE of RAE systems) for CO 2  measurements  –  were employed. The TVOCs and CO 2  concentrations refer to 1-hour mean values, derived from 1-min continuous measurements. The measured values of    TVOCs are isobutylene equivalent and conversion from ppb to μ g m −   3  has been done by multiplying the measured value with the factor 2.3, according to Alevantis and Xenaki-Petreas (1996). The IAQRAE  system provides also measurements of temperature and relative humidity, as one hour mean values.  ã   Automated Horiba analyzers measuring NO, NO 2 , SO 2 , interfaced to a data logger giving 10-min average values. The NO x  analyser uses a semicon-ductor sensor and the SO 2  analyser an optical system. The  principle of operation is the chemiluminescence and UV fluorescence for the NO x  and SO 2  analyzers respectively. The lowest detection limits (LDL) were 0.98, 0.61 and 1.31 μ g m −   3,  respectively.   ã   Particle samplers measuring PM 10  and PM 2.5 , giv-ing mean concentrations calculated gravimetrically (weighing instrument KERN 770, accuracy 0.01 mg) from pre-set sampling periods (24 h, 10 h, 14 h) (Model 200 Personal Environmental Monitors (PEM)   and SKC Universal DELUXE sampling air pumps of 2 L min −   1 ).   ã   Outdoor concentrations of PM 10  and meteorological data were collected from the air pollution monitoring station operated by the Ministry of Environment (Goudi). The station was located at a distance of 50 m to the south of the Dentistry Faculty. From the meteorological data collected from the station, it was   evident that during 52% of the total experimental time the Dentistry Faculty was downwind of the station, and 48% upwind. During the whole experimental period a logbook was kept recording all the activities taking place in the clinic, including the number, the location and the duration of the open windows, the number of students and personnel occupying the room and the nature of their work, the materials used, as well as the cleaning  processes and hours.  In order to quantify the ventilation prevailing in the clinic, the air change rates (ACH) were calculated following the methodology presented by Bartlett et al. (2004). ACH, measured in h −   1 , is the rate at which outside air replaces indoor air in a given space. The methodology involves the solution of the mass-balance equation for the CO 2  concentrations, considering indoor homogeneity and negligible deposition. Outdoor CO 2  concentrations were frequently monitored during the experiment and ranged on average at 1170 mg m −   3 . Indoor emission rate of CO 2  was considered mainly due to human respiration and was taken to be 589 mg min −   1  CO 2  per person (Godwin et al., 2003; Bartlett et al.,  2004). The number of people in the clinic was estimated  according to the logbook records.  In order to further investigate the mechanisms associated with the indoor environmental conditions of the clinic, a detailed examination both experimentally and numerically of the air quality was conducted. Intensive TVOCs and PM measurements were per-formed, at two different locations of the room, in the central part (location K) and in the northern part (location B) simultaneously, during the period of 17  –  25 February 2005 (Fig. 1). The indoor environmental conditions were examined by applying the CFD model PHOENICS for the 19th, 23rd, 24th and 25th February 2005 and the indoor production of Particulate Matter was assessed by employ-ing the indoor air quality model MIAQ for the 23rd February. The necessary experimental data for the application of the previous models are spot mean air velocity, temperature and turbulence intensity measure-ments at several indoor locations of the clinic, CO 2  measurements at a fixed indoor position, all under different ventilation and occupational conditions, as well as surface temperature measurements of the indoor materials. The data were taken using the following instruments:   ã   DANTEC Flow Masters (type 54N60) for spot mean   air velocity, temperature and turbulence intensity measurements of 1-min sets (accuracy 0.1 cm s −   1 ,    352   C.G. Helmis et al. / Science of the Total Environment 377 (2007) 349  – 365   Table 1   Average concentration values of CO 2 , TVOCs, NO x  and SO 2 , ranges of measured PM 10  and PM 2.5 , temperature and relative humidity, as well as discomfort index, for the experimental period   Parameters measured   Average background   Average working hours Daily maximum   Daily values   Average   Limit values   value   value   range   range   value   CO 2  (mg m −   3 )   TVOCs ( μ g m −   3 )    NO ( μ g m −   3 )    NO 2  ( μ g m −   3 )   SO 2  ( μ g m −   3 )    b Temperature (°C)    b Relative humidity (%) Discomfort index   DI Thom (°C) PM 10  indoor ( μ g m −   3 ) PM 2.5  indoor ( μ g m −   3 ) −   −   1250   2200   1500  – 4600   1600   a 1800   950   1900   2000  – 5500   1300    b1 300,  b2 500   50   65   10  – 650   55    –   35   55   40  – 150   45   c 250 (1 h)   4   6.5   5  – 30   5   350 (1 h)   22.2   25.7   23.7  – 29.4   23.7   e 20  – 24   26.7   25.6   24  – 41.7   26.1   30  – 60%   19.1   21.1   19.8  – 22.7   19.9   g b 21   33  – 326   138   h 50 (24 h)   23  – 229   75   i 65 (24 h)   4  – 40   14   140   The corresponding limit values are also shown.   a ASHRAE Standard 62-2001 rev. (2003).   b (1) Molhave, 1995; Seifert, 1990; European Concerted Action, 1992. (2) Building Standard —  State of Washington. c Directive 1999/30/EC.  d Directive 1999/30/EC.  e ASHRAE Standard 55 (2004), for winter.  f  ASHRAE Standard 55 (2004).  g b 21: normal conditions, 21  – 24: less than 50% of occupants feel discomfort, 24  – 27: more than 50% of occupants feel discomfort, 27  – 29: the   majority of the occupants feel discomfort, 29  – 32: all the occupants feel discomfort, N 32: need for medical treatment.   h Directive 1999/30/EC.  i USEPA (US Environment Protection Agency, 1997). 0.1 °C and 1%, for velocity, temperature and turbu-lence intensity, respectively).  ã   Infrared thermometer (Cole-Palmer, 08406) for surface temperature measurements of the indoor materials.   ã   IAQRAE for CO 2  measurements.   Regarding MIAQ, the indoor environment was consi-dered as a single zone occupying a volume of 820.7 m 3 , with a total of 885 m 2  surfaces (ceiling, floor and 4 walls). The ventilation of the room with open doors and windows was measured to be 1.75 m 3  s −   1 , for the 23rd February, by use of the instrument Dantec.  CO indoor concentrations were continuously moni-tored with the IAQRAE during the experiment, but the levels were very low, below the limit of detection of the instrument and thus are not presented. Ozone concen-trations could not be measured in this study due to malfunction of the ozone analyzers.  3. General indoor air quality characteristics  In Table 1, the average hourly values of TVOCs, CO 2 , NO x  and SO 2  during the working hours, the non-working hours and the whole experimental period are  presented, along with the range of the maximum hourly values. Table 1 also presents the average daily values of PM 10  and PM 2.5  during the working days along with the range of the daily values, as well as the corresponding threshold limit values. It should be noted that the term “  background concentrations ” will be used hereafter for    the values recorded during the weekends and non-working hours, when the clinic was not occupied. According to Table 1, the relative humidity in the clinic ranged at low levels during the experimental period. The thermal comfort is studied with the aid of Thom dis-comfort Index DI (Thom, 1959), which reflects the  proportionate contribution of air temperature (T) and relative humidity (RH) to the human thermal comfort. From Table 1 can be seen that the daily maximum value of the index ranges between 19.8 and 22.7 °C, suggesting that acceptable thermal comfort conditions prevail in the clinic, while there are periods that a small percentage (less than 50%) of occupants feel discomfort. 3.1. CO 2  Indoor CO 2  concentrations are associated with human presence, since CO 2  is metabolic, as well as 
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