Risk factors in heating, ventilating, and air-conditioning systems for occupant symptoms in US office buildings: the US EPA BASE study

Building-related symptoms in office workers worldwide are common, but of uncertain etiology. One cause may be contaminants related to characteristics of heating, ventilating, and air-conditioning (HVAC) systems. We analyzed data from 97 representative air-conditioned US office buildings in the Building Assessment and Survey Evaluation (BASE) study. Using logistic regression models with generalized estimating equations, we estimated odds ratios (OR) and 95% confidence intervals for associations between building-related symptom outcomes and HVAC characteristics. Outdoor air intakes less than 60 m above ground level were associated with significant increases in most symptoms: e.g. for upper respiratory symptoms, OR for intake heights 30 to 60 m, 0 to <30 m, and below ground level were 2.7, 2.0, and 2.1. Humidification systems with poor condition/maintenance were associated with significantly increased upper respiratory symptoms, eye symptoms, fatigue/difficulty concentrating, and skin symptoms, with OR = 1.5, 1.5, 1.7, and 1.6. Less frequent cleaning of cooling coils and drain pans was associated with significantly increased eye symptoms and headache, with OR = 1.7 and 1.6. Symptoms may be due to microbial exposures from poorly maintained ventilation systems and to greater levels of vehicular pollutants at air intakes nearer the ground level. Replication and explanation of these findings is needed.

PRACTICAL IMPLICATIONS

These findings support current beliefs that moisture-related HVAC components such as cooling coils and humidification systems, when poorly maintained, may be sources of contaminants that cause adverse health effects in occupants, even if we cannot yet identify or measure the causal exposures. While finding substantially elevated risks for poorly maintained humidification systems, relative to no humidification systems, the findings do not identify important (symptom) benefits from well-maintained humidification systems. Findings also provide an initial suggestion, needing corroboration, that outdoor air intakes lower than 18 stories in office buildings may be associated with substantial increases in many symptoms. If this is corroborated and linked to ground-level vehicle emissions, urban ventilation air intakes may need to be located as far above ground level as possible or to incorporate air cleaners that remove gaseous pollutants.

Potential effects of permeable and hygroscopic lightweight structures on thermal comfort and perceived IAQ in a cold climate

In this study, we simulated and measured the effect of permeable and hygroscopic lightweight structures on indoor air quality (IAQ) and thermal comfort in a cold climate. The potential effect of hygroscopic mass was assessed with the simulation of extreme cases, where permeable and hygroscopic lightweight structures with unfinished surfaces were compared with impermeable and non-hygroscopic ones. Measurements were conducted in 78 rooms of 46 newly built detached timber-framed houses and analyzed according to hygroscopic surface materials and envelope permeability. From the simulations, it was shown that permeable and hygroscopic structures considerably improved perceived air quality in summer, when a ventilation rate of 6 l/s pers. in the non-hygroscopic case corresponded roughly to 4 l/s pers. in the hygroscopic case. However, window airing and furnishing will reduce this difference in practice. Both simulated and measured results showed that permeable and hygroscopic structures significantly reduced peak indoor relative humidity levels and daily changes in relative humidity, but had no long-term effects. Measured results also indicated that completely non-hygroscopic houses did not exist in reality.

PRACTICAL IMPLICATIONS

Limited knowledge is available about building envelope and ventilation system interactions with consequent effects on indoor climate. To take such effects adequately into account in design and construction of buildings, solid scientific data explaining the significance of the phenomena studied are needed. We have demonstrated that moisture exchange has evidently enough importance to be taken into account in future building simulation tools.

Working towards healthy air in dwellings in Europe

Poor indoor air quality has been implicated in the increase in allergic and respiratory diseases seen in industrialized countries in recent decades. Although air pollution in the workplace is well studied, much less is known about the consequences of poor air quality in homes. In an attempt to halt or slow down the increase in allergic and respiratory diseases, the European Federation of Allergy and Airways Diseases Patients Associations (EFA) carried out the EU-funded project entitled 'Towards Healthy Air in Dwellings in Europe' (THADE). The aims were to: compile an overview of evidence-based data about exposure to indoor air pollution and its health effects, particularly in relation to allergies, asthma and other respiratory diseases such as chronic obstructive pulmonary disease; review cost-effective measures and technology to improve indoor air quality; review legislation and guidelines on indoor air pollution; produce maps of pollutants in dwellings; and recommend an integrated strategy that defines appropriate indoor air quality policies for implementation in Europe. This paper summarizes the information about air quality in dwellings and indoor environment-related diseases collected by expert consultants within the framework of THADE and terminates with recommendations for actions aimed at improving air quality in homes. The results of this project confirmed that air pollution in dwellings is a relevant health problem. It is a complex problem that must be addressed at European and international levels, and it involves the medical profession, scientific societies, patients' organizations, lawmakers, architects and the building industry. The complete THADE report is available at http://www.efanet.org/activities/documents/THADEReport.pdf.

Ventilation and performance in office work

Outdoor air ventilation rates vary considerably between and within buildings, and may be too low in some spaces. The purpose of this study was to evaluate the potential work performance benefits of increased ventilation. We analyzed the literature relating work performance with ventilation rate and employed statistical analyses with weighting factors to combine the results of different studies. The studies included in the review assessed performance of various tasks in laboratory experiments and measured performance at work in real buildings. Almost all studies found increases in performance with higher ventilation rates. The studies indicated typically a 1-3% improvement in average performance per 10 l/s-person increase in outdoor air ventilation rate. The performance increase per unit increase in ventilation was bigger with ventilation rates below 20 l/s-person and almost negligible with ventilation rates over 45 l/s-person. The performance increase was statistically significant with increased ventilation rates up to 15 l/s-person with 95% CI and up to 17 l/s-person with 90% CI. Practical Implications We have demonstrated a quantitative relationship between work performance and ventilation within a wide range of ventilation rates. The model shows a continuous increase in performance per unit increase in ventilation rate from 6.5 l/s-person to 65 l/s-person. The increase is statistically significant up to 15 l/s-person. This relationship has a high level of uncertainty; however, use of this relationship in ventilation design and feasibility studies may be preferable to the current practice, which ignores the relationship between ventilation and productivity.

Reduction potential of urban PM2.5 mortality risk using modern ventilation systems in buildings

Urban PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 microm) is associated with excess mortality and other health effects. Stationary sources are regulated and considerable effort is being put into developing low-pollution vehicles and environment-friendly transportation systems. While waiting for technological breakthroughs in emission controls, the current work assesses the exposure reductions achievable by a complementary means: efficient filtration of supply air in buildings. For this purpose infiltration factors for buildings of different ages are quantified using Exposures of Adult Urban Populations in Europe Study (EXPOLIS) measurements of indoor and outdoor concentrations in a population-based probability sample of residential and occupational buildings in Helsinki, Finland. These are entered as inputs into an evaluated simulation model to compare exposures in the current scenario with an alternative scenario, where the distribution of ambient PM2.5 infiltration factors in all residential and occupational buildings are assumed to be similar to the subset of existing occupational buildings using supply air filters. In the alternative scenario exposures to ambient PM2.5 were reduced by 27%. Compared with source controls, a significant additional benefit is that infiltration affects particles from all outdoor sources. The large fraction of time spent indoors makes the reduction larger than what probably can be achieved by local transport policies or other emission controls in the near future.

PRACTICAL IMPLICATIONS

It has been suggested that indoor concentrations of ambient particles and the associated health risks can be reduced by using mechanical ventilation systems with supply air filtering in buildings. The current work quantifies the effects of these concentration reductions on population exposures using population-based data from Helsinki and an exposure model. The estimated exposure reductions suggest that correctly defined building codes may reduce annual premature mortality by hundreds in Finland and by tens of thousands in the developed world altogether.

Fungal spore transport through a building structure

The study carried out laboratory measurements with a full-scale timber frame structure to determine penetration of inert particles with size distribution from 0.6 to 4 microm and spores of Penicillium and Cladosporium through the structure. Pressure difference over and air leakage through the structure were varied. Measurements at moderate pressure differences resulted in the penetration factors within the range of 0.05-0.2 for inert particles, and indicated also the penetration of fungal spores through the structure. The measurements showed that the penetration was highly dependent on pressure difference over the structure but not on holes in surface boards of the structure. The results show that surface contacts between the frames and mineral wool may have a significant effect on penetration. The penetration was approximately constant within particle size rage of 0.6-2.5 microm, but particles with diameter of 4.0 microm did not penetrate through the structure at all even at a higher-pressure difference of 20 Pa, except in the case of direct flow-path through the structure. Results have important consequences for practical design showing that penetration of fungal spores through the building envelope is difficult to prevent by sealing. The only effective way to prevent penetration seems to be balancing or pressurizing the building. In cold climates, moisture condensation risk should be taken into account if pressure is higher indoors than outdoors. Determined penetration factors were highly dependent on the pressure difference. Mechanical exhaust ventilation needs a special consideration as de-pressurizing the building may cause health risk if there is hazardous contamination in the building envelope exists.

Microbial contamination of indoor air due to leakages from crawl space: a field study

Mechanical exhaust ventilation system is typical in apartment buildings in Finland. In most buildings the base floor between the first floor apartments and crawl space is not air tight. As the apartments have lower pressure than the crawl space due to ventilation, contaminated air may flow from the crawl space to the apartments. The object of this study was to find out whether a potential air flow from crawl space has an influence on the indoor air quality. The results show that in most cases the concentration of fungal spores was clearly higher in the crawl space than inside the building. The size distribution of fungal spores depended on the fungal species. Correlation between the fungal spores in the crawl space and indoors varied with microbial species. Some species have sources inside the building, which confounds the possible relation between crawl pace and indoor concentrations. Some species, such as Acremonium, do not normally have a source indoors, but its concentration in the crawl space was elevated; our measurements showed also elevated concentrations of Acremonium in the air of the apartments. This consistent finding shows a clear linkage between fungal spores in the indoor air and crawl space. We conclude that a building with a crawl space and pressure difference over the base floor could be a potential risk for indoor air quality in the first floor apartments.

Effectiveness of duct cleaning methods on newly installed duct surfaces

Two kinds of air duct cleaning methods, mechanical brushing with different brushes and compressed air cleaning, were compared in the laboratory and in newly built buildings. The ducts were contaminated either with test dust or with dust originated from a construction site. The amount of dust on the duct surface was measured with the vacuum test method and estimated visually before and after the cleaning. In addition, the cleaning times of the different techniques were compared and the amount of residual oil in the ducts was measured in the laboratory test. The brushing methods were more efficient in metal ducts, and compressed air cleaning was more efficient in plastic ducts. After the duct cleaning the mean amount of residual dust on the surface of the ducts was <or=0.1 g/m2 in the laboratory test with ducts contaminated at construction site and <or=0.3 g/m2 after cleaning in the field. The decrease in the dust deposits on the surface ranged from 86 to 99% and from 75 to 94% in the ducts cleaned in the laboratory or in the building site, respectively. The oil residues and the dust stuck onto the oil were difficult to scrape off and remove, and none of the cleaning methods were capable of cleaning the oily duct surfaces efficiently enough. Thus new installations should consist only of oil-free ducts.

The effect of cleanliness control during installation work on the amount of accumulated dust in ducts of new HVAC installations

The aim of this study was to evaluate the amount of dust in supply air ducts in recently installed ventilation systems. The samples for the determination of dust accumulation were collected from supply air ducts in 18 new buildings that have been constructed according to two different cleanliness control levels classified as category P1 (low oil residues and protected against contaminations) and category P2, as defined in the Classification of Indoor Climate, Construction and Building Materials. In the ducts installed according to the requirements of cleanliness category P1 the mean amount of accumulated dust was 0.9 g/m2 (0.4-2.9 g/m2), and in the ducts installed according to the cleanliness category P2 it was 2.3 g/m2 (1.2-4.9 g/m2). A significant difference was found in the mean amounts of dust between ducts of categories P1 and P2 (P < 0.008). The cleanliness control procedure in category P1 proved to be a useful and effective tool for preventing dust accumulation in new air ducts during the construction process. Additionally, the ducts without residual oil had lower amounts of accumulated dust indicating that the demand for oil free components in the cleanliness classification is reasonable.

Ventilation and health in non-industrial indoor environments: report from a European multidisciplinary scientific consensus meeting (EUROVEN)

Scientific literature on the effects of ventilation on health, comfort, and productivity in non-industrial indoor environments (offices, schools, homes, etc.) has been reviewed by a multidisciplinary group of European scientists, called EUROVEN, with expertise in medicine, epidemiology, toxicology, and engineering. The group reviewed 105 papers published in peer-reviewed scientific journals and judged 30 as conclusive, providing sufficient information on ventilation, health effects, data processing, and reporting, 14 as providing relevant background information on the issue, 43 as relevant but non-informative or inconclusive, and 18 as irrelevant for the issue discussed. Based on the data in papers judged conclusive, the group agreed that ventilation is strongly associated with comfort (perceived air quality) and health [Sick Building Syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave], and that an association between ventilation and productivity (performance of office work) is indicated. The group also concluded that increasing outdoor air supply rates in non-industrial environments improves perceived air quality; that outdoor air supply rates below 25 l/s per person increase the risk of SBS symptoms, increase short-term sick leave, and decrease productivity among occupants of office buildings; and that ventilation rates above 0.5 air changes per hour (h-1) in homes reduce infestation of house dust mites in Nordic countries. The group concluded additionally that the literature indicates that in buildings with air-conditioning systems there may be an increased risk of SBS symptoms compared with naturally or mechanically ventilated buildings, and that improper maintenance, design, and functioning of air-conditioning systems contributes to increased prevalence of SBS symptoms.

Association of ventilation system type with SBS symptoms in office workers

This paper provides a synthesis of current knowledge about the associations of ventilation system types in office buildings with sick building syndrome (SBS) symptoms and discusses potential explanations for the associations. Most studies completed to date indicate that relative to natural ventilation, air conditioning, with or without humidification, was consistently associated with a statistically significant increase in the prevalence of one or more SBS symptoms, by approximately 30 to 200%. In two of three analyses from a single study (assessments), symptom prevalences were also significantly higher in air-conditioned buildings than in buildings with simple mechanical ventilation and no humidification. The available data also suggest, with less consistency, an increase in risk of symptoms with simple mechanical ventilation relative to natural ventilation. Insufficient information was available for conclusions about the potential increased risk of SBS symptoms with humidification or recirculation of return air. The statistically significant associations of mechanical ventilation and air conditioning with SBS symptoms are much more frequent than expected from chance and also not likely to be a consequence of confounding by several potential personal, job, or building-related confounders. Multiple deficiencies in HVAC system design, construction, operation, or maintenance, including some which cause pollutant emissions from HVAC systems, may contribute to the increases in symptom prevalences but other possible reasons remain unclear.

Textile wall materials and sick building syndrome

We studied the relation between the amount of textile and other soft fiber wall materials used in the office and the symptoms related to sick building syndrome in two identical, mechanically ventilated, eight-story office buildings. The study population consisted of 400 workers (85% of the source population): 264 males (66%) and 136 females (34%). A self-administered questionnaire inquired about the occurrence of symptoms and related personal and environmental determinants. The office environment was assessed concurrently. Exposure was defined as the surface area of textile or other soft wall material (SWM) in the office. The outcomes were formed using the 7-d prevalences of individual symptoms, including mucosal irritation score (eye irritation, nasal dryness, nasal congestion, pharyngeal irritation); allergic reaction score (eye irritation, nasal congestion, nasal excretion, sneezing); asthma reaction score (wheezing, breathlessness, cough); skin reaction score (dryness, itch, or irritation, rash); and general symptom score (headache, lethargy). In the logistic regression controlling for potential confounders, the adjusted odds ratio for the symptoms of mucosal irritation was 1.82 (95% confidence interval [95% CI] = 1.14, 2.90) in the low-exposure group, compared with the unexposed reference group; and 2.46 (95% CI = 1.15, 5.28) in the high-exposure group, compared with the reference group. Corresponding odds ratios for the symptoms of allergic reaction were 1.82 (95% CI = 1.14, 2.90) and 3.16 (95% CI = 1.41, 7.09). No difference was found in the risk for asthmatic or skin reactions or general symptoms. The results support a hypothesis that textile and other soft-fiber wall materials used in the office environment are possible determinants of sick building syndrome.

Air recirculation and sick building syndrome: a blinded crossover trial

OBJECTIVE

This study tested the hypothesis that recirculated air in mechanically ventilated buildings causes symptoms commonly referred to as the sick building syndrome and perceptions of poor indoor air quality.

METHODS

A blinded, four-period crossover trial was carried out in two identical buildings, contrasting 70% return air (index phase) with 0% of return air (reference phase). Each period lasted 1 work-week. The study population comprised 75 workers who had reported symptoms related to the work environment or perceptions of poor indoor air quality. Participants reported their ratings of symptoms, their perceptions, and related information in a daily diary. The outcome criteria included aggregative symptom scores for mucosal irritation, skin reaction, allergic reaction, and general symptoms formed of ratings of component symptoms. Perceptions of unpleasant odor, stuffiness, or dustiness were additional outcome criteria.

RESULTS

All 75 participants returned their diaries. For no symptoms did the scores differ between the two phases more than could be expected by chance. Mean rating of unpleasant odor was significantly smaller during the index phase, but mean ratings of dustiness and stuffiness did not differ materially between the two phases.

CONCLUSIONS

Our results suggest that 70% recirculated air, when accompanied by an adequate intake of outdoor air, can be used without causing adverse effects.

The effect of air humidification on symptoms and perception of indoor air quality in office workers: a six-period cross-over trial

The objective of this study was to evaluate the effect of air humidification on (a) the dryness of the skin and mucosa, (b) allergic and asthmatic reactions, and (c) the perception of indoor air quality. A total of 290 office workers at the Pasila Office Center were included in a six-period cross-over trial. One wing of the building was operated with 30-40% humidification, and the other wing operated under conditions of no air humidification (relative humidity from natural conditions was 20-30%). The length of each study period was 1 work wk. The workers were instructed to keep a structured daily diary of their symptoms, their perception of the indoor air, and potential determinants of the symptoms. A total of 211 (72.6%) workers who returned at least two weekly diaries, and who had experienced both humidified and nonhumidified conditions, were included in the analyses. The primary outcome--dryness symptom score--was characterized by dryness, irritation or itching of the skin and eyes, dryness or irritation of the throat, and nasal dryness. Means of the daily symptom scores and perception ratings during the humidified and nonhumidified periods were calculated for each participant, and intraindividual differences in the means were used to assess the effect of air humidification. The dryness symptom score was significantly smaller during the humidified phase than during the reference phase (paired t test; p less than .05). Allergic symptoms that were considered as a separate outcome, a sensation of dryness, and draft were also significantly less frequent during the humidification phase (p less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)