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Showing papers in "Indoor Air in 2004"


Journal ArticleDOI
TL;DR: The paper gives a practical overview of issues related to particulate matter indoors, as well as valuable information for understanding filtration and how particles contribute to adverse health effects.
Abstract: Airborne particulate matter is a diverse pollutant class whose excessive presence in indoor air contributes to an array of adverse health and material-damage effects. Particles are classified according to their diameter into three size modes: ultrafine (? 0.1 µm), accumulation (0.1-2 µm), and coarse (? 2 µm). These modes have largely distinct sources and composition, and they exhibit different dynamic behaviors. The concept of mass conservation or material balance provides a foundation for quantitative and mechanistically linking important outcome variables, such as concentrations and exposures, to the influencing input parameters. The factors governing indoor particle concentrations include direct emissions from indoor sources, ventilation supply from outdoor air, filtration, deposition onto indoor surfaces, and removal from indoor air by means of ventilation. In some circumstances, transport and transformation processes within indoor environments may also play an important role in influencing particle concentrations and consequences. Such processes include mixing, interzonal transport, resuspension, coagulation, and phase change.

557 citations


Journal ArticleDOI
TL;DR: In developed regions, good ventilation, getting rid of "dampness" problems, and adequate testing of new building materials would reduce morbidity and mortality, and in the developed world IAQ is a main cause of allergies, other hypersensitivity reactions, airway infections, and cancers.
Abstract: Man’s origin is in the tropical or near-tropical parts ofthe world. The spread into cold climates was possibleonly because of inventions such as clothing, housingand the use of fire (Sundell, 1994). However, in housesand shelters it is not only the thermal climate that haschanged. The climate shell also stops the free airmovement. The dilution of pollutants from close-to-man pollutant sources is diminished. The environmentwithin a shelter is always more polluted from indoorsources such as humans, open fires (still a major sourceof indoor air pollution in many developing regions)building materials, indoor activities, etc. than fromoutdoor air. This was and is the basis of the need forventilation and for discussions on indoor air quality(IAQ). Humans arrived in, e.g., southern Europe andChina a million years ago, but in America, northernEurope, Japan, etc. only some 10,000–40,000 yearsago, a period too short for major genetic changes. So ashumans we are still accustomed to a life outdoors in thewarm regions of Africa.As we spend most of our life indoors (in manyregions more than 90%), it is easy to understand thatthe most important environment in relation to ourhealth is the indoor environment (Sundell, 1999).During the breakthrough of modern hygiene, frommid 19th century, indoor environmental issues receivedmuch attention, as did the quality of drinking-waterand the treatment of sewage (e.g., linked to plaguessuch as cholera and tuberculosis).Ventilation comes from Latin ‘‘ventilare’’ meaning‘‘to expose to the wind’’. The main purpose ofbuildings is to create a climate more suitable forpersons and processes than the outdoor climate.Consequently, the main aim of ventilation in build-ings is to create an indoor air quality more suitablefor persons and processes than that naturally occur-ring in an unventilated building, and to reintroducethe positive effect of being ‘‘exposed to the wind’’,i.e. to dilute and remove the pollutants produced byman himself, his activities and the indoor surround-ings.Throughout history man has known that polluted airmay be detrimental to health. Greeks and Romanswere aware of the adverse effects of polluted air in,e.g., crowded cities and mines (Hippocrates, 460–377 BC).Abstract Indoor air is a dominant exposure for humans. More that half of thebody’s intake during a lifetime is air inhaled in the home. Thus, most illnessesrelated to environmental exposures stem from indoor air exposure. Indoor airwas believed to be a major environmental factor for more than a hundred years,from the start of the hygienic revolution, around 1850, until outdoor environ-mental issues entered the scene, and became dominant around 1960. Mainenvironmental issues today are outdoor air quality, energy use, and sustainablebuildings, but not indoor air quality (IAQ). But, there is mounting evidence thatexposure to IAQ is the cause of excessive morbidity and mortality. In developingregions indoor unvented burning of biomass for cooking is the cause of at least2,000,000 deaths a year (mainly women and children), and in the developedworld IAQ is a main cause of allergies, other hypersensitivity reactions, airwayinfections, and cancers. Cancer of the lungs is related to indoor radon and ETSexposure. Allergies, airway infections and sick building syndrome are associatedwith, e.g., ‘‘dampness’’, a low ventilation rate, and plasticizers. In the futuremore emphasis must be given to IAQ and health issues.

487 citations


Journal ArticleDOI
TL;DR: It is shown beyond reasonable doubt that poor indoor air quality in buildings can decrease productivity in addition to causing visitors to express dissatisfaction, and it is usually more energy-efficient to eliminate sources of pollution than to increase outdoor air supply rates.
Abstract: UNLABELLED The main justification for ventilation has historically been to create a healthy indoor environment. Ventilation removes air pollutants originating inside the building, including bio-effluents. The outdoor air supply rate that has been found by experience to provide subjectively acceptable indoor air quality and to prevent the accumulation of moisture in the building is generally sufficient to maintain the concentration of pollutants at healthily low levels. Until 5 years ago this would have been the justification for current ventilation practices, but in 1999 the first of a series of experiments was published, revealing new mechanisms by which raised levels of indoor air pollution may reduce productivity, either in addition to or instead of having negative effects on comfort and health. It was shown in realistic experimental exposures lasting up to 5 h that the performance of simulated office work could be significantly increased by removing common indoor sources of air pollution, such as floor-coverings, used supply air filters and personal computers, or by keeping them in place and increasing the rate at which clean outdoor air was supplied from 3 to 10 to 30 l s(-1) per person. These short-term effects were demonstrated repeatedly even at pollutant levels that had no measurable effects on the perception of air quality by the occupants themselves, although there were effects on subclinical SBS symptoms such as headache. Temperature and noise distraction have since been studied in directly comparable exposures. The prediction arising from these experiments, that the performance of real office work over time would be significantly and substantially affected by the changes in indoor environmental quality that take place in the course of normal building operation, have recently been validated in 8-week field intervention experiments carried out in call-centers in northern Europe and the Tropics. These findings have far-reaching implications for the efficient use of energy in buildings. PRACTICAL IMPLICATIONS It has now been shown beyond reasonable doubt that poor indoor air quality in buildings can decrease productivity in addition to causing visitors to express dissatisfaction. The size of the effect on most aspects of office work performance appears to be as high as 6-9%, the higher value being obtained in field validation studies. It is usually more energy-efficient to eliminate sources of pollution than to increase outdoor air supply rates. The experiments summarized in this article have documented and quantified relationships that can be used in making cost-benefit analyses of either solution for a given building. The high cost of labor per unit floor area ensures that payback times will usually be as low as 2 years.

421 citations


Journal ArticleDOI
TL;DR: In this article, the association of student absence with measures of indoor minus outdoor carbon dioxide concentration (dCO(2) was explored, and the authors provided motivation for larger school studies to investigate associations of student attendance, and occupant health and student performance.
Abstract: UNLABELLED Student attendance in American public schools is a critical factor in securing limited operational funding. Student and teacher attendance influence academic performance. Limited data exist on indoor air and environmental quality (IEQ) in schools, and how IEQ affects attendance, health, or performance. This study explored the association of student absence with measures of indoor minus outdoor carbon dioxide concentration (dCO(2)). Absence and dCO(2) data were collected from 409 traditional and 25 portable classrooms from 22 schools located in six school districts in the states of Washington and Idaho. Study classrooms had individual heating, ventilation, and air conditioning (HVAC) systems, except two classrooms without mechanical ventilation. Classroom attributes, student attendance and school-level ethnicity, gender, and socioeconomic status (SES) were included in multivariate modeling. Forty-five percent of classrooms studied had short-term indoor CO(2) concentrations above 1000 p.p.m. A 1000 p.p.m. increase in dCO(2) was associated (P < 0.05) with a 0.5-0.9% decrease in annual average daily attendance (ADA), corresponding to a relative 10-20% increase in student absence. Annual ADA was 2% higher (P < 0.0001) in traditional than in portable classrooms. PRACTICAL IMPLICATIONS This study provides motivation for larger school studies to investigate associations of student attendance, and occupant health and student performance, with longer term indoor minus outdoor CO(2) concentrations and more accurately measured ventilation rates. If our findings are confirmed, improving classroom ventilation should be considered a practical means of reducing student absence. Adequate or enhanced ventilation may be achieved, for example, with educational training programs for teachers and facilities staff on ventilation system operation and maintenance. Also, technological interventions such as improved automated control systems could provide continuous ventilation during occupied times, regardless of occupant thermal comfort demands.

382 citations


Journal ArticleDOI
TL;DR: The phthalate and musk compounds load in a sample of apartments and kindergartens were low with a typical distribution pattern in air and household dust, but without a significant correlation between air and dust concentration.
Abstract: UNLABELLED In this study, the occurrence of persistent environmental contaminants room air samples from 59 apartments and 74 kindergartens in Berlin were tested in 2000 and 2001 for the presence of phthalates and musk fragrances (polycyclic musks in particular). These substances were also measured in household dust from 30 apartments. The aim of the study was to measure exposure levels in typical central borough apartments, kindergartens and estimate their effects on health. Of phthalates, dibutyl phthalate had the highest concentrations in room air, with median values of 1083 ng/m(3) in apartments and 1188 ng/m(3) in kindergartens. With around 80% of all values, the main phthalate in house dust was diethylhexyl phthalate, with median values of 703 mg/kg (range: 231-1763 mg/kg). No statistically significant correlation could be found between air and dust concentration. Musk compounds were detected in the indoor air of kindergartens with median values of 101 ng/m(3) [1,3,4,6,7,8-hexahydro-4,6,6,7,8,8- hexamethylcyclopenta-(g) 2-benzopyrane (HHCB)] and 44 ng/m(3) [7-acetyl-1,1,3,4,4,6-hexamethyl-tetraline (AHTN)] and maximum concentrations of up to 299 and 107 ng/m(3) respectively. In household dust HHCB and AHTN were detected in 63 and 83% of the samples with median values of 0.7 and 0.9 mg/kg (Maximum: 11.4 and 3.1 mg/kg) each. On comparing the above phthalate concentrations with presently acceptable tolerable daily intake values (TDI), we are talking about only a small average intake [di(2-ethylhexyl) phthalate and diethyl phthalate less than 1 and 8% of the TDI] by indoor air for children. The dominant intake path was the ingestion of foodstuffs. For certain subsets of the population, notably premature infants (through migration from soft polyvinyl chloride products), children and other patients undergoing medical treatment like dialysis, exchange transfusion, an important additional intake of phthalates must taken into account. PRACTICAL IMPLICATIONS The phthalate and musk compounds load in a sample of apartments and kindergartens were low with a typical distribution pattern in air and household dust, but without a significant correlation between air and dust concentration. The largest source of general population exposure to phthalates is dietary. For certain subsets of the general population non-dietary ingestion (medical and occupational) is important.

365 citations


Journal ArticleDOI
TL;DR: Perceived air quality, sick building syndrome symptoms and performance of office work were studied in a real office space at three levels of air temperature and humidity and two levels of ventilation rate and the previously observed impact ofTemperature and humidity on perceived air quality and the linear correlation between acceptability and enthalpy was confirmed.
Abstract: UNLABELLED Perceived air quality (PAQ), sick building syndrome (SBS) symptoms and performance of office work were studied in a real office space at three levels of air temperature and humidity and two levels of ventilation rate (20 degrees C/40%, 23 degrees C/50%, 26 degrees C/60% RH at 10 l s(-1) p(-1) outside air, and 20 degrees C/40% RH at 3.5 l s(-1) p(-1) outside air). Thirty female subjects participated in the experiment. They were exposed to each environmental condition for 280 min. Thermal comfort was maintained at different thermal environments by self-adjustment of clothing. The subjects performed simulated office work throughout each exposure and repeatedly marked a set of visual-analog scales to indicate their perception of environmental conditions and of the intensity of SBS symptoms at the time. The study confirmed the previously observed impact of temperature and humidity on perceived air quality and the linear correlation between acceptability and enthalpy. The impact on perceived air quality of decreasing the ventilation rate from 10 to 3.5 l s(-1) per person could be counteracted by a decrement of temperature and humidity from 23 degrees C/50% RH to 20 degrees C/40% RH. Performance of office work was not significantly affected by indoor air temperature and humidity. However, several SBS symptoms were alleviated when the subjects worked at low levels of air temperature and humidity, which implies that a longer term exposure to low indoor air temperature and humidity might help to improve the performance of office work. PRACTICAL IMPLICATIONS The findings of this study indicate the importance of indoor air temperature and humidity on perceived air quality and SBS symptoms. In practice, the required ventilation rate for comfort and health should no longer be independent of indoor air temperature and humidity.

332 citations


Journal ArticleDOI
TL;DR: There is good evidence for a true association between dampness in buildings and health, but the causative factors behind this association are not known and the main focus in practical investigations should be on finding out and remediate the reasons for the humidity problem.
Abstract: The scientific literature on health effects from dampness in buildings, including mite exposure over the period 1998-2000 has been reviewed by a European group (EUROEXPO) of eight scientists in experience from medicine, epidemiology, toxicology and engineering. Forty studies deemed relevant have been the foundation for the conclusions. Dampness in buildings is a risk factor for health effects among atopics and non-atopics both in domestic and in public environments. However, the literature is not conclusive in respect of causative agents, e.g. mites, microbiological agents and organic chemicals from degraded building materials. There is a strong need for more multidisciplinary studies including expertise from all relevant areas. A general conclusion from the work was that there is a strong need for multidisciplinary reviews in scientific journals of articles dealing with associations between indoor environmental factors and health effects.

307 citations


Journal ArticleDOI
TL;DR: The Center for the Built Environment developed a Web-based survey and accompanying online reporting tools to quickly and inexpensively gather, process and present this information as mentioned in this paper, which can be used to assess the performance of a building, identify areas needing improvement, and provide useful feedback to designers and operators about specific aspects of building design features and operating strategies.
Abstract: Building occupants are a rich source of information about indoor environmental quality and its effect on comfort and productivity. The Center for the Built Environment has developed a Web-based survey and accompanying online reporting tools to quickly and inexpensively gather, process and present this information. The core questions assess occupant satisfaction with the foll- owing IEQ areas: office layout, office furnishings, thermal comfort, indoor air quality, lighting, acoustics, and building cleanliness and maintenance. The sur- vey can be used to assess the performance of a building, identify areas needing improvement, and provide useful feedback to designers and operators about specific aspects of building design features and operating strategies. The survey has been extensively tested and refined and has been conducted in more than 70 buildings, creating a rapidly growing database of standardized survey data that is used for benchmarking. We present three case studies that demonstrate dif- ferent applications of the survey: a pre/post analysis of occupants moving to a new building, a survey used in conjunction with physical measurements to determine how environmental factors affect occupants' perceived comfort and productivity levels, and a benchmarking example of using the survey to establish how new buildings are meeting a client's design objectives.

267 citations


Journal ArticleDOI
TL;DR: The review shows that ventilation has various positive impacts on health and productivity of building occupants, and reduces the prevalence of airborne infectious diseases and thus the number of sick leave days.
Abstract: The effects of ventilation on indoor air quality and health is a complex issue. It is known that ventilation is necessary to remove indoor generated pollutants from indoor air or dilute their concentration to acceptable levels. But, as the limit values of all pollutants are not known, the exact determination of required ventilation rates based on pollutant concentrations and associated risks is seldom possible. The selection of ventilation rates has to be based also on epidemiological research (e.g. Seppanen et al., 1999), laboratory and field experiments (e.g. CEN 1996, Wargocki et al., 2002a) and experience (e.g. ECA 2003). Ventilation may also have harmful effects on indoor air quality and climate if not properly designed, installed, maintained and operated as summarized by Seppdnen (2003). Ventilation may bring indoors harmful substances that deteriorate the indoor environment. Ventilation also affects air and moisture flow through the building envelope and may lead to moisture problems that deteriorate the structures of the building. Ventilation changes the pressure differences over the structures of building and may cause or prevent the infiltration of pollutants from structures or adjacent spaces. Ventilation is also in many cases used to control the thermal environment or humidity in buildings. Ventilation can be implemented with various methods which may also affect health (e.g. Seppdnen and Fisk, 2002, Wargocki et al., 2002a). In non residential buildings and hot climates, ventilation is often integrated with air-conditioning which makes the operation of ventilation system more complex. As ventilation is used for many purposes its health effects are also various and complex. This paper summarizes the current knowledge on positive and negative effects of ventilation on health and other human responses. The focus of the paper is on office-type working environment and residential buildings. In the industrial premises the problems of air quality are usually more complex and case specific. They are subject to occupational safety legislation and not discussed here.

252 citations


Journal ArticleDOI
TL;DR: Self-reported moisture-related problems in the building were strongly associated with asthma, allergic symptoms, and airway infections among children and adults, and the influence of selection bias in case-control studies has been studied, and questionnaires on self-reported symptoms and building characteristics have been validated.
Abstract: Dampness in buildings and health (DBH). Report from an on-going epidemiological investigation on the association between indoor environmental factors and health effects among children in Sweden

222 citations


Journal ArticleDOI
TL;DR: It is demonstrated that open office noise distraction, even at the realistic level of 55 dBA, increases fatigue and has many negative effects on the performance of office work, as does a moderately warm air temperature.
Abstract: UNLABELLED Three air temperatures (22/26/30 degrees C) and two acoustic conditions-quiet (35 dBA) or open-plan office noise (55 dBA)-were established in an office. Thirty subjects aged 18-29 years (16 male), clothed for thermal neutrality at 22 degrees C, performed simulated office work for 3 h under all six conditions. Many more (68% vs. 4%) were dissatisfied with noise in the noise condition (P < 0.01). Warmth decreased thermal acceptability (P < 0.001) and perceived air quality (P < 0.01) and increased odour intensity (P < 0.05) and stuffiness (P < 0.01). After 2 h, some forehead sweating was observed on 4, 36 and 76% of subjects (P < 0.001) at 22, 26 and 30 degrees C, while 0, 21 and 65% felt "warm" (P < 0.001). Raised temperature increased eye, nose and throat irritation (P < 0.05), headache intensity (P < 0.05), difficulty in thinking clearly (P < 0.01) and concentrating (P < 0.01), and decreased self-estimated performance (P < 0.001). Noise increased fatigue (P < 0.05) and difficulty in concentrating (P < 0.05) but did not interact with thermal effects on subjective perception. In an addition task, noise decreased workrate by 3% (P < 0.05), subjects who felt warm made 56% more errors (P < 0.05) and there was a noise-temperature interaction (P < 0.01): the effect of warmth on errors was less in the noise condition. Typing speed (P < 0.05) and reading speed (P < 0.05) were higher in noise. PRACTICAL IMPLICATIONS This paper demonstrates that open office noise distraction, even at the realistic level of 55 dBA, increases fatigue and has many negative effects on the performance of office work, as does a moderately warm air temperature. These findings may be used to provide economic justification for the provision of private offices and air temperature control in hot weather. The additional finding that noise distraction and heat stress can sometimes counteract each other in the short term is of academic interest only, as they both increase subjective distress and fatigue. In practice, neither should be deliberately introduced to counteract the other.

Journal ArticleDOI
Susmita Dasgupta1, Mainul Huq, M. Khaliquzzaman1, Kiran Pandey1, David Wheeler1 
TL;DR: A detailed analysis of the implications for indoor air pollution (IAP) in Bangladesh, drawing on new 24-h monitoring data for respirable airborne particulates (PM10), suggests that poor families may not have to wait for clean fuels or clean stoves to enjoy significantly cleaner air.
Abstract: Poor households in Bangladesh depend heavily on wood, dung and other biomass fuels for cooking. This paper provides a detailed analysis of the implications for indoor air pollution (IAP), drawing on new 24-h monitoring data for respirable airborne particulates (PM10). A stratified sample of 236 households was selected in Dhaka and Narayanganj, with a particular focus on fuel use, cooking locations, structural materials, ventilation practices, and other potential determinants of exposure to IAP. At each household, PM10 concentrations in the kitchen and living room were monitored for a 24-h period during December, 2003-February, 2004. Concentrations of 300 microg/m3 or greater are common in our sample, implying widespread exposure to a serious health hazard. A regression analysis for these 236 households was then conducted to explore the relationships between PM10 concentrations, fuel choices and a large set of variables that describe household cooking and ventilation practices, structure characteristics and building materials. As expected, our econometric results indicate that fuel choice significantly affects indoor pollution levels: natural gas and kerosene are significantly cleaner than biomass fuels. However, household-specific factors apparently matter more than fuel choice in determining PM10 concentrations. In some biomass-burning households, concentrations are scarcely higher than in households that use natural gas. Our results suggest that cross-household variation is strongly affected by structural arrangements: cooking locations, construction materials, and ventilation practices. A large variation in PM10 was also found during the 24-h cycle within households. For example, within the 'dirtiest' firewood-using household in our sample, readings over the 24-h cycle vary from 68 to 4864 microg/m3. Such variation occurs because houses can recycle air very quickly in Bangladesh. After the midday meal, when ventilation is common, air quality in many houses goes from very dirty to reasonably clean within an hour. Rapid change also occurs within households: diffusion of pollution from kitchens to living areas is nearly instantaneous in many cases, regardless of internal space configuration, and living-area concentrations are almost always in the same range as kitchen concentrations. By implication, exposure to dangerous indoor pollution levels is not confined to cooking areas. To assess the broader implications for poor Bangladeshi households, we extrapolate our regression results to representative 600 household samples from rural, peri-urban and urban areas in six regions: Rangpur in the north-west, Sylhet in the north-east, Rajshahi and Jessore in the west, Faridpur in the center, and Cox's Bazar in the south-east. Our results indicate great geographic variation, even for households in the same per capita income group. This variation reflects local differences in fuel use and, more significantly, construction practices that affect ventilation. For households with per capita income

Journal ArticleDOI
TL;DR: Personalized ventilation can improve occupants' thermal comfort, perceived air quality and decrease the intensity of SBS symptoms compared to mixing ventilation and development of more efficient air terminal devices is recommended.
Abstract: UNLABELLED The response of 60 human subjects to a personalized ventilation system (PVS), providing control of positioning of the air terminal device and the airflow rate, was compared with the response to mixing ventilation (MV). Perceived air quality, thermal comfort, intensity of Sick Building Syndrome symptoms and performance of subjects were studied during 3 h 45 min exposures. In case of MV alone the room air temperature was 23 degrees C and 26 degrees C. The PVS supplied outdoor air at 23 degrees C or 20 degrees C or recirculated room air at 23 degrees C when the room temperature was 23 degrees C, and outdoor air at 20 degrees C when the room temperature was 26 degrees C. The PVS providing outdoor air improved perceived air quality and decreased SBS symptoms compared to MV alone and when the room air was re-circulated through the PVS. The percentage dissatisfied with air quality, 3 min after initial occupancy, decreased from 22% with MV to 7% with PVS; and from 49% to 20%, at room temperatures 23 degrees C and 26 degrees C, respectively. Over time, these differences in percentage dissatisfied decreased markedly. Headache and decreased ability to think clearly were reported as least intense when the PVS supplied outdoor air at 20 degrees C, while the most intense symptoms occurred with MV. PVS increased self-estimated performance. PRACTICAL IMPLICATIONS Personalized ventilation can improve occupants' thermal comfort, perceived air quality and decrease the intensity of SBS symptoms compared to mixing ventilation. Occupants will use the provided individual control of airflow rate and positioning of the air terminal device to obtain preferred microenvironment in rooms where the air temperature is within the range recommended by indoor climate standards. Development of more efficient air terminal devices is recommended.

Journal ArticleDOI
TL;DR: The fact that the chemicals identified in the office air and in the chamber experiments were insufficient to explain the adverse effects observed during human exposures illustrates the inadequacy of the analytical chemical methods commonly used in indoor air quality investigations.
Abstract: UNLABELLED In groups of six, 30 female subjects were exposed for 4.8 h in a low-polluting office to each of two conditions--the presence or absence of 3-month-old personal computers (PCs). These PCs were placed behind a screen so that they were not visible to the subjects. Throughout the exposure the outdoor air supply was maintained at 10 l/s per person. Under each of the two conditions the subjects performed simulated office work using old low-polluting PCs. They also evaluated the air quality and reported Sick Building Syndrome (SBS) symptoms. The PCs were found to be strong indoor pollution sources, even after they had been in service for 3 months. The sensory pollution load of each PC was 3.4 olf, more than three times the pollution of a standard person. The presence of PCs increased the percentage of people dissatisfied with the perceived air quality from 13 to 41% and increased by 9% the time required for text processing. Chemical analyses were performed to determine the pollutants emitted by the PCs. The most significant chemicals detected included phenol, toluene, 2-ethylhexanol, formaldehyde, and styrene. The identified compounds were, however, insufficient in concentration and kind to explain the observed adverse effects. This suggests that chemicals other than those detected, so-called 'stealth chemicals', may contribute to the negative effects. PRACTICAL IMPLICATIONS PCs are an important, but hitherto overlooked, source of pollution indoors. They can decrease the perceived air quality, increase SBS symptoms and decrease office productivity. The ventilation rate in an office with a 3-month-old PC would need to be increased several times to achieve the same perceived air quality as in a low-polluting office with the PC absent. Pollution from PCs has an important negative impact on the air quality, not only in offices but also in many other spaces, including homes. PCs may have played a role in previously published studies on SBS and perceived air quality, where PCs were overlooked as a possible pollution source in the indoor environment. The fact that the chemicals identified in the office air and in the chamber experiments were insufficient to explain the adverse effects observed during human exposures illustrates the inadequacy of the analytical chemical methods commonly used in indoor air quality investigations. For certain chemicals the human senses are much more sensitive than the chemical methods routinely used in indoor air quality investigations. The adverse effects of PC-generated air pollutants could be reduced by modifications in the manufacturing process, increased ventilation, localized PC exhaust, or personalized ventilation systems.

Journal ArticleDOI
TL;DR: The existing Climpaq-based procedure for simplified measurements of emissions of plasticizer from PVC and other plasticized materials was modified to generate quantitative and qualitative emission data on phthalates from different materials but the modified method did not create sufficient data for the calculation of emission rates.
Abstract: The main objective of this study was to generate quantitative and qualitative emission data on phthalates from different materials. To achieve this the existing (Chamber for Laboratory Investigations of Materials, Pollution and Air Quality) Climpaq-based procedure for simplified measurements of emissions of plasticizer from PVC and other plasticized materials was modified. It was applied to a range of products. Some of them were suspected of contributing to the indoor concentration of plasticizers. The emissions from PVC flooring, polyolefine flooring, a refrigerator list, two electric cables, PVC skirting and floor wax were studied in separate Climpaqs. The emission from the PVC flooring in the Climpaq was compared with results from the ultra-small chamber Field and Laboratory Emission Cell (FLEC). Sampling and analysis methods were optimized to measure plasticizers. Samples were taken in exhaust air from the chambers after 6, 35, 62, 105, and 150 days from the start of the experiment. PVC flooring was tested for an additional 100 days. Polyolefine covered with wax resulted in an air concentration of 22 microg/m3 of dibutylphthalate (DBP), which is two orders of magnitude larger than any other materials, but did not emit di(2-ethylhexyl)phthalate (DEHP). The other materials resulted in max concentration of approximately 1 microg/m3 of DEHP and low emissions of DBP. The concentration of DEHP in each chamber increased slowly to a rather stable level which was reached after 150 days. DBP concentrations in the chambers with PVC skirting, PVC flooring, polyolefine and floor wax reached their quasi-static equilibrium after 60 days. The modified method did not create sufficient data for the calculation of emission rates. Adsorption of emission on chamber surfaces made it impossible to use the first part of the experiment for emission rate calculation. When the concentration had stabilized, it was found to be almost identical and independent of chamber and ventilation rate. Emission rates were reduced at high concentrations probably because the concentration in the material was near equilibrium with the concentration in the chamber air.

Journal ArticleDOI
TL;DR: This paper focuses on significant research that has recently occurred in three subtopics: studies that have experimentally demonstrated the importance of hydroxyl radicals in indoor transformations, and the impact that the products of indoor chemistry can have on building occupants.
Abstract: UNLABELLED The mix of pollutants in indoor environments can be transformed as a consequence of chemical reactions, reducing the concentrations of the reacting species and increasing the concentrations of the products. Within this broad topic, the current paper focuses on significant research that has recently occurred in three subtopics: (1) Studies that have experimentally demonstrated the importance of hydroxyl radicals in indoor transformations. In the cases discussed, OH is a product of ozone/terpene reactions and goes on to react with other products, as well as the original terpene. The results demonstrate that the hydroxyl radical is responsible for a large fraction of the oxidized products, including certain products that cannot be made by ozone pathways alone. (2) Chemistry that occurs on indoor surfaces. Given the large surface-to-volume ratios indoors, such reactions may have a larger impact on indoor air quality than those that occur in the gas phase. In at least one case, ozone interacting with carpets, this has been demonstrated to be the case. (3) The impact that the products of indoor chemistry can have on building occupants. A major limitation in evaluating the impacts of indoor chemistry has been the inability to measure many of the reaction products. Sensory measurements are useful in detecting changes derived from indoor chemistry-changes missed by the analytical methods routinely used to evaluate indoor air. Sensitive physiological indicators of effects, such as eye blink rate, are also being investigated. Reactions among indoor pollutants are the principal source of short-lived, highly reactive compounds in the setting where humans spend the majority of their time-indoors. PRACTICAL IMPLICATIONS Indoor chemistry impacts indoor air quality. A better understanding of hydroxyl radical chemistry allows us to predict some of the compounds that humans are exposed to under certain situations, even if such species cannot be readily measured. Emissions from materials can be significantly altered by surface chemistry, and the products of such reactions often dominate a material's long-term emissions. Surface chemistry may help us better understand the reasons for complaints in "problem" buildings, especially damp buildings. A better understanding of the impact of indoor chemical reactions on human comfort and health would help prioritize efforts to improve indoor air quality.

Journal ArticleDOI
R de Dear1
TL;DR: In this paper, the authors discuss the methodological benefits and constraints of conventional climate chamber research in comparison to the field-based alternative, and give practical advice on evaluating and designing for thermal comfort.
Abstract: UNLABELLED Since the early twentieth century when air-conditioning began penetrating the market in a serious way, there has been a need for human factors research upon which HVAC engineering practice could be based. Now we have nearly a century of thermal comfort research from climate chambers and much has been learnt in that time. By stripping the research problem back to essential cause-and-effect variables, climate chamber methods have delivered results that are amenable to rigorous data analyses leading to unequivocal conclusions. However, in the minds of HVAC practitioners there are persistent doubts about the experiential realism of the chamber methodology, and the external validity of their findings, in particular, their relevance to building occupants going about their normal daily routines in fully-engineered indoor climatic environments. In response to this methodological concern in the 1990s, ASHRAE commissioned a series of thermal comfort studies aimed at field validating the findings of climate chamber research and the HVAC standards based upon them in a variety of climatic contexts around the world. This paper discusses the methodological benefits and constraints of conventional climate chamber research in comparison to the field-based alternative. In particular, issues such as sample size and demographics, research design, instrumentation and indoor climatic measurement procedures, questionnaires, clothing insulation and metabolic rate assessment techniques are analyzed. The discussion of methodology is then extended to the discipline of environmental psychology, which should have made a much more significant contribution to the topic of thermal comfort, and yet has remained relatively silent. The paper finishes by considering why engineers, most notably P.O. Fanger, have come to dominate a research topic that falls so clearly within the scope of psychology. HVAC engineering is the profession most directly occupied in the practice of thermal comfort, and therefore an engineer such as Fanger has been ideally qualified to design and conduct research, and even more important, presents its results in a way most directly useful to thermal comfort practitioners. PRACTICAL IMPLICATIONS The paper gives practical advice on evaluating and designing for thermal comfort.

Journal ArticleDOI
TL;DR: It is shown that the determination of SVOC-emissions from materials is important because after a few weeks the emission rates for SVOCs might be higher than for VOCs and with the knowledge of this "emission potential" it is possible to estimate also the release of SV OCs into the (indoor) environment.
Abstract: area (loading about 0.4 m 2 /m 3 ) with about 100 g/m 2 (primer), 1000 g/m 2 /mm (screed) and 300-600 g/m 2 (adhesive) making them an important possible source for VOC/SVOC-emissions, additionally to those from the floor covering. Within the research project ''Environmental and health quality of composite building products'' which Abstract Emissions of volatile organic compounds (VOC) and semivolatile organic compounds (SVOC) from materials for flooring installation (primer, screed, adhesive, floor covering) were measured by means of emission test chambers and cells over a time period of at least 28 days at 23 � C, 50% relative humidity and an area specific air flow rate of q ¼ 1.25 m 3 /m 2 h. Single com- ponents were tested in comparison to three complete structures (same concrete, primer, screed, adhesive) with different types of floor covering (PVC, carpet, linoleum). Sorption into concrete/screed and different permeability of flooring materials affected the emissions from the complete structures. The complete structures with linoleum and PVC showed the same types of emission and emission rates as the individual floor coverings themselves. Emissions from the carpet-covered structure resulted also from the lower layers. In all cases emis- sions from the complete structures were lower than the sum of emissions from the single components. For two adhesives the formation of secondary emissions (aldehydes and organic acids) was observed starting after the standard testing time of 28 days.

Journal ArticleDOI
TL;DR: This presentation will focus on the development of standards for the indoor thermal environment and indoor air quality (ventilation) and an overview of existing methods is presented, and areas where revision of present standards or thedevelopment of new standards are needed.
Abstract: UNLABELLED On the international level, International Organization for Standardization (ISO), European Committee for Standardization (CEN) and American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) are writing and reviewing standards relating to the indoor environment on a regular basis. This presentation will focus on the development of standards for the indoor thermal environment and indoor air quality (ventilation). In the future, recommendations for acceptable indoor environments will be specified as classes. This allows for national differences in the requirements as well as for designing buildings for different quality levels. Several of these standards have been developed mainly by experts from Europe, North America and Japan. Are there, however, special considerations relating to South-East Asia (lifestyle, outdoor climate, economy) that are not dealt with in these standards and that will require the revision of existing standards? Critical issues are: adaptation, the effect of increased air velocity, humidity, type of indoor pollutant sources, etc. This paper will present an overview of existing methods, and discuss areas where revision of present standards or the development of new standards, are needed. PRACTICAL IMPLICATIONS The international standards for the indoor environment provide the designer with criteria, which are internationally recognized, for the design of buildings and systems.

Journal ArticleDOI
TL;DR: Factors influencing the human perception of air movement are summarized and attempts to specify in general terms when air movement is desirable and when it is not.
Abstract: UNLABELLED Air movement--good or bad? The question can only be answered by those who are exposed when they are exposed. Human perception of air movement depends on environmental factors including air velocity, air velocity fluctuations, air temperature, and personal factors such as overall thermal sensation and activity level. Even for the same individual, sensitivity to air movement may change from day to day as a result of, e.g., different levels of fatigue. Based on existing literature, the current paper summarizes factors influencing the human perception of air movement and attempts to specify in general terms when air movement is desirable and when it is not. At temperatures up to 22-23 degrees C, at sedentary activity and with occupants feeling neutral or cooler there is a risk of air movement being perceived as unacceptable, even at low velocities. In particular, a cool overall thermal sensation negatively influences the subjective perception of air movement. With occupants feeling warmer than neutral, at temperatures above 23 degrees C or at raised activity levels, humans generally do not feel draught at air velocities typical for indoor environments (up to around 0.4 m/s). In the higher temperature range, very high air velocities up to around 1.6 m/s have been found to be acceptable at air temperatures around 30 degrees C. However, at such high air velocities, the pressure on the skin and the general disturbance induced by the air movement may cause the air movement to be undesirable. PRACTICAL IMPLICATIONS Based on existing literature, the paper summarizes factors influencing the human perception of air movement and attempts to specify in general terms when air movement is desirable and when it is not.

Journal ArticleDOI
Peter Nielsen1
TL;DR: The paper discusses the quality level of Computational Fluid Dynamics and the involved schemes (first, second and third order schemes) by the use of the Smith and Hutton problem on the mass fraction transport equation.
Abstract: UNLABELLED Computational Fluid Dynamics (CFD) and new developments of CFD in the indoor environment as well as quality considerations are important elements in the study of energy consumption, thermal comfort and indoor air quality in buildings. The paper discusses the quality level of Computational Fluid Dynamics and the involved schemes (first, second and third order schemes) by the use of the Smith and Hutton problem on the mass fraction transport equation. The importance of "false" or numerical diffusion is also addressed in connection with the simple description of a supply opening. The different aspects of boundary conditions in the indoor environment as, e.g., the simulation of Air Terminal Devices and the simulation of furnishings and occupants are discussed. The prediction of the flow in a room with a three-dimensional wall jet by the use of different turbulence models such as the k-epsilon model, the V2-f model and the Reynolds Stress model is addressed in the last chapter of the paper. PRACTICAL IMPLICATIONS The use of computational Fluid Dynamics as a practical design method for room air distribution is widespread. It is important to consider the quality of the predictions in order to obtain a sufficient level of accuracy. It is also important to work with a practical description of supply openings as well as with the right level of details in the occupied zone and the right turbulence model. All these aspects are addressed in the article.

Journal ArticleDOI
TL;DR: It is indicated that increasing outdoor air supply rate and replacing filters can have positive effects on health, comfort and performance and some SBS symptoms and environmental perceptions are recorded.
Abstract: UNLABELLED A 2 x 2 replicated field intervention experiment was conducted in a call-center providing a telephone directory service: outdoor air supply rate was adjusted to be 8% or 80% of the total airflow of 430 l/s (3.5 /h) and the supply air filters were either new or had been in place for 6 months. One of these independent variables was changed each week for 8 weeks. The interventions did not affect room temperature, relative humidity or noise level. The 26 operators were blind to conditions and each week returned questionnaires recording their environmental perceptions and Sick Building Syndrome (SBS) symptoms. Their performance was continuously monitored by recording the average talk-time every 30 min. Replacing a used filter with a clean filter reduced talk-time by about 10% at the high ventilation rate but had no significant effect at the low rate. Increasing the outdoor air supply rate reduced talk-time by 6% with a new filter in place but increased talk-time by 8% with a used filter in place. The interventions also had significant effects on some SBS symptoms and environmental perceptions. The present results indicate that increasing outdoor air supply rate and replacing filters can have positive effects on health, comfort and performance. PRACTICAL IMPLICATIONS Supply air filters should be changed frequently not just because their airflow resistance increases progressively but because they degrade air quality with negative consequences for health, comfort and the performance of office work, all of which are factors that affect office productivity (profitability). Increasing outdoor air supply rates may only be beneficial when new filters are installed. Unwanted negative effects may be produced when used filters are in place. Filter condition (used or new) should always be recorded to make it possible to draw sound conclusions in studies of the effects of outdoor air supply rates on building occupants.

Journal ArticleDOI
TL;DR: The observed relationship between indoor minus outdoor CO(2) concentrations and mucous membrane and lower respiratory symptoms suggests that air contaminants are implicated in the etiology of building related symptoms.
Abstract: Indoor air pollutants are a potential cause of building related symp- toms and can be reduced by increasing ventilation rates. Indoor carbon dioxide (CO2) concentration is an approximate surrogate for concentrations of occu- pant-generated pollutants and for ventilation rate per occupant. Using the US EPA 100 office-building BASE Study dataset, we conducted multivariate logistic regression analyses to quantify the relationship between indoor CO2 concen- trations (dCO2) and mucous membrane (MM) and lower respiratory system (LResp) building related symptoms, adjusting for age, sex, smoking status, presence of carpet in workspace, thermal exposure, relative humidity, and a marker for entrained automobile exhaust. In addition, we tested the hypothesis that certain environmentally mediated health conditions (e.g., allergies and asthma) confer increased susceptibility to building related symptoms. Adjusted odds ratios (ORs) for statistically significant, dose-dependent associations ( P< 0.05) for combined mucous membrane, dry eyes, sore throat, nose/sinus congestion, sneeze, and wheeze symptoms with 100 p.p.m. increases in dCO2 ranged from 1.1 to 1.2. Building occupants with certain environmentally medi- ated health conditions were more likely to report that they experience building related symptoms than those without these conditions (statistically significant ORs ranged from 1.5 to 11.1, P < 0.05).

Journal ArticleDOI
TL;DR: It is found that relatively new apartment buildings, single-family homes with crawl space/concrete slab foundation, elevated indoor humidity, and reported wintertime windowpane condensation were associated with recurrent wheezing in infants, and improvements of the building quality may have potential to prevent infant wheazing.
Abstract: This study was conducted to examine the impact of building characteristics and indoor air quality on recurrent wheezing in infants. We followed a birth cohort (BAMSE) comprising 4089 children, born in predefined areas of Stockholm, during their first 2 years of life. Information on exposures was obtained from parental questionnaires when the children were 2 months and on symptoms and diseases when the children were 1 and 2 years old. Children with recurrent wheezing, and two age-matched controls per case, were identified and enrolled in a nested case-control study. The homes were investigated and ventilation rate, humidity, temperature and NO2 measured. We found that living in an apartment erected after 1939, or in a private home with crawl space/concrete slab foundation were associated with an increased risk of recurrent wheezing, odds ratio (OR) 2.5 (1.3-4.8) and 2.5 (1.1-5.4), respectively. The same was true for living in homes with absolute indoor humidity >5.8 g/kg, OR 1.7 (1.0-2.9) and in homes where windowpane condensation was consistently reported over several years, OR 2.2 (1.1-4.5). However, air change rate and type of ventilation system did not seem to affect the risk. In conclusion, relatively new apartment buildings, single-family homes with crawl space/concrete slab foundation, elevated indoor humidity, and reported wintertime windowpane condensation were associated with recurrent wheezing in infants. Thus, improvements of the building quality may have potential to prevent infant wheezing.

Journal ArticleDOI
TL;DR: The results may help to explain the high prevalence of respiratory disorders among smokers, and they may also draw attention to a hitherto unknown or neglected risk factor of ETS.
Abstract: We used a mass spectrometry-based assay for identifying the endotoxin (lipopolysaccharide, LPS) marker (R)-3-hydroxytetradecanoic acid in cigarette smoke particles and found that smoking involved inhalation of 17.4 pmol of endotoxin per each smoked cigarette. Indoor exposure to environmental tobacco smoke (ETS) entailed inhalation of 12.1 pmol of LPS/m3 air, an amount that was 120 times higher than the levels found in smoke-free indoor air. Endotoxin is one of the most potent inflammatory agents known, hence our results may help to explain the high prevalence of respiratory disorders among smokers, and they may also draw attention to a hitherto unknown or neglected risk factor of ETS.

Journal ArticleDOI
TL;DR: For moderately complex office work which involves manipulation dexterity such as a call center operation where call operators interact with computer-based information systems, tropically acclimatized workers' performance could be improved by increasing the outdoor air supply rate from 5 l/s/p to 10 l/S/p if the temperature is to be maintained at the higher band of the thermal comfort range.
Abstract: UNLABELLED A study was performed in a call center that provides billing inquiry services using a 2 x 2 balanced experimental plan for nine consecutive weeks. Two independent variables, temperature and outdoor air supply rate, were combined and introduced to the occupants in a blind intervention approach. The temperature set-points were fixed at 22.5 degrees C and 24.5 degrees C, and outdoor air supply rate at 5 l /s/p and 10 l/s/p. Temperature and outdoor air supply rate had significant interaction effects on worker's talk time (P < 0.001), which means that the effects of temperature on talk time performance were not independent of the effects of outdoor air supply rate or the opposite. Talk time was reduced significantly when the outdoor air supply rate was increased from 5 l /s/p to 10 l/s/p at 24.5 degrees C (P < 0.01); this may be associated with the significant reduction in a principal component factor which includes intensity of dryness, aching eyes and nose-related symptoms (P < 0.01). Decreasing the temperature from 24.5 degrees C to 22.5 degrees C at 10 l /s/p significantly increased talk time (P < 0.01). Analysis of the principal component factor based on the neurobehavioral symptoms also revealed that temperature reduction led to an increased mean factor score of these symptoms (P < 0.04). PRACTICAL IMPLICATIONS For moderately complex office work which involves manipulation dexterity such as a call center operation where call operators interact with computer-based information systems, tropically acclimatized workers' performance could be improved by increasing the outdoor air supply rate from 5 l/s/p to 10 l/s/p if the temperature is to be maintained at the higher band of the thermal comfort range, around 24.5 degrees C. At a low ventilation rate (5 l/s/p), decreasing the temperature from 24.5 degrees C to 22.5 degrees C (which is a commonly adopted set-point in tropical office buildings) also leads to improvement of talk time performance. The magnitude of talk time improvement was greater by more than four times when the strategy to increase the outdoor air supply rate was implemented at a lower range of outdoor air supply rate (5-10 l /s/p) as compared to the higher range (9.8-22.7 l/s/p).

Journal ArticleDOI
Shuzo Murakami1
TL;DR: The CFD (Computational Fluid Dynamics) method presented will be a valuable and powerful tool for analysis and design of healthy indoor environments and dry eye syndrome.
Abstract: UNLABELLED This paper reviewed the CFD (Computational Fluid Dynamics) study conducted by our group on analyzing and designing the microclimate surrounding the human body. First, it describes the analysis results of flow and temperature fields around the human body. Next, it refers to the analysis and design of the quality of air inhaled and exhaled by the human body. Lastly, it describes the CFD and experimental study on the microclimate around the eyes, focusing on dry eye syndrome. PRACTICAL IMPLICATIONS The CFD method presented will be a valuable and powerful tool for analysis and design of healthy indoor environments.

Journal ArticleDOI
TL;DR: The results of this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.
Abstract: The combined effects of noise and temperature on environmental perception and acceptability were studied on 18 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. Three homogeneous climatic conditions were chosen (air temperature at 18, 24 or 30 degrees C, air velocity =0.1 m/s). For each of them, three different noise levels were continuously maintained (35, 60, 75 dBA, recorded fan noise). The 18 subjects were divided into three groups and each group experienced only one single thermal condition, at each level of noise, during three different experimental sessions. Subjective answers about perception and comfort were obtained at t = 30 and 120 min. Main results indicate that acoustic perception decreases when thermal environment is far from thermoneutrality. Although the combined effects of noise and temperature did not influence the physiological data, our results show that whatever the ambient temperature, thermal unpleasantness is higher when noise level increases. Finally, equivalence between acoustic and thermal sensations is proposed for short-term exposure (1 degree C = 2.6 dBA) and for steady state (1 degrees C = 2.9 dBA). In conclusion, this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.

Journal ArticleDOI
TL;DR: This study demonstrates that semi-quantitative dampness/mold exposure indices, based solely on visual and olfactory observation and weighted by time spent in specific rooms, can predict existence of excessive building-related respiratory symptoms and diseases.
Abstract: Using a semi-quantitative mold exposure index, the National Institute for Occupational Safety and Health (NIOSH) investigated 13 college buildings to examine whether building-related respiratory symptoms among employees are associated with environmental exposure to mold and dampness in buildings. We collected data on upper and lower respiratory symptoms and their building- relatedness, and time spent in specific rooms with a self-administered question- naires. Trained NIOSH industrial hygienists classified rooms for water stains, visible mold, mold odor, and moisture using semi-quantitative scales and then estimated individual exposure indices weighted by the time spent in specific rooms. The semi-quantitative exposure indices significantly predicted building- related respiratory symptoms, including wheeze (odds ratio (OR) ¼ 2.3; 95% confidence interval (CI) ¼ 1.1-4.5), chest tightness (OR ¼ 2.2; 95% CI ¼ 1.1- 4.6), shortness of breath (OR ¼ 2.7; 95% CI ¼ 1.2-6.1), nasal (OR ¼ 2.5; 95% CI ¼ 1.3-4.7) and sinus (OR ¼ 2.2; 95% CI ¼ 1.2-4.1) symptoms, with expo- sure-response relationships. We found that conditions suggestive of indoor mold exposure at work were associated with building-related respiratory symptoms. Our findings suggest that observational semi-quantitative indices of exposure to dampness and mold can support action to prevent building-related respiratory diseases.

Journal ArticleDOI
TL;DR: Five of eight building-related symptoms were significantly and positively associated with the concentration of colony forming units of molds in floor dust: eye irritation, throat irritation, headache, concentration problems, and dizziness, and in none of the analyses was mold exposure the strongest covariate, being secondary to either asthma, hay fever, recent airway infection, or psychosocial factors.
Abstract: This stratified cross-sectional epidemiological study included 1053 school children aged 13-17 years. All pupils filled in a questionnaire on building-related symptoms and other relevant health aspects. The following exposure measurements were carried out: room temperature, CO2 level, and relative humidity; building characteristics including mold infestation were assessed, and dust was collected from floors, air, and ventilation ducts during a working day. Dust was examined for endotoxin level, and cultivated for viable molds. We did not find a positive association between building-related symptoms and extent of moisture and mold growth in the school buildings. Five of eight building-related symptoms were significantly and positively associated with the concentration of colony forming units of molds in floor dust: eye irritation, throat irritation, headache, concentration problems, and dizziness. After adjusting for different potentially confounding factors in separate analyses of each symptom, the above-mentioned associations between molds in dust and symptoms were still present, except for concentration problems. However, in none of the analyses was mold exposure the strongest covariate, being secondary to either asthma, hay fever, recent airway infection, or psychosocial factors.