«Health and Productivity Gains from Better Indoor Environments and Their Implications for the U.S. Department of Energy William J. Fisk1 Staff ...»
thus, results could have been biased by the subjects’ expectations.
Because viral respiratory infections will often exacerbate asthma symptoms, a third approach for reducing asthma symptoms is to modify buildings in a manner that reduce viral respiratory infections among occupants, as discussed previously.
With the available data, the magnitude of the potential reduction in allergy and asthma symptoms is quite uncertain, but some reduction is clearly possible using practical measures. The subsequent estimate is based on two considerations: 1) the degree to which indoor allergen concentrations and concentrations of irritating chemicals can be reduced, and 2) the strength of the reported associations between symptoms and changeable building and IEQ factors.
Regarding the first consideration, significant reductions in allergy and asthma symptoms would not be expected unless it was possible to substantially reduce indoor concentrations of the associated allergens and irritants. From engineering considerations, it is clear that concentrations of many allergens could be reduced very substantially. Filtration systems, appropriately sized, should be capable of reducing concentrations of the smaller airborne allergens by approximately 75%.
Some of the source control measures, such as elimination of water leaks, control of indoor humidities, reduction or elimination of indoor smoking and pets, and improved cleaning and maintenance are likely to result in much larger reductions in the pollutants that contribute to allergies and asthma.
As discussed above, several cross-sectional or case-control studies have found that building-related risk factors, such as moisture problems and mold or environmental tobacco smoke, are associated with 20% to 100% increases in allergy and asthma symptoms, implying that 16% to 50% reductions in symptoms are possible by eliminating these risk factors. However, the complete elimination of these risk factors is improbable. Assuming that it is feasible and practical to reduce these risks by a factor of two, leads to a 8% to 25% estimate of the potential reduction in allergy and asthma symptoms. With this estimate, the annual savings would be ~$1 to ~$4 billion. Control measures can be targeted at the homes or offices of susceptible individuals, reducing the societal cost.
Sick Building Syndrome Symptoms
Linkage. Characteristics of buildings and indoor environments have been linked to the prevalence of acute building-related health symptoms, often called sickbuilding syndrome (SBS) symptoms, experienced by building occupants. SBS symptoms include irritation of eyes, nose, and skin, headache, fatigue, and difficulty breathing. Although psychosocial factors such as job stress influence SBS symptoms, many building factors are also known or suspected to influence these symptoms including: type of ventilation system; rate of outside air ventilation; level of chemical and microbiological pollution; and indoor temperature and humidity (Mendell 1993; Sundell 1994; Menzies and Bourbeau 1997, Seppanen et al. 1999). In the review by Seppanen et al. (1999), 21 of 27 assessments meeting study quality criteria found lower ventilation rates to be significantly associated with an increase in at least one SBS symptom (Figure 4).
Extrapolating from one of the largest studies, a 5 L s-1 increase in ventilation rates in US office buildings would reduce the proportion of office workers with frequent upper respiratory symptoms from 26% to 16%. For eye symptoms, the corresponding reduction would be from 22% to 14%. In a set of problem buildings studied by (Sieber et al. 1996), SBS symptoms were associated with evidence of poorer ventilation system maintenance or cleanliness. For example, debris inside the air intake and poor drainage from coil drain pans were associated with a factor of three increase in lower respiratory symptoms.19 In the same study, daily vacuuming was associated with a 50% decrease in lower respiratory symptoms.20 In some, but not all, controlled experiments, SBS symptoms have been reduced through practical changes in the environment such as increased ventilation, decreased temperature, and improved cleaning of floors and chairs (Mendell 1993, Menzies and Bourbeau 1997, Seppanen et al. 1999).
Therefore, SBS symptoms are clearly linked to features of buildings and indoor environments.
Population Affected and Cost of SBS Symptoms. SBS symptoms are most commonly reported by office workers and teachers that make up about 50% of the total workforce (64 million workers21). In a modest fraction of buildings, often referred to as “sick buildings”, symptoms become severe or widespread, prompting investigations and remedial actions. The term “sick building ________________
19For debris in air intake, relative risk = 3.1 and 95% CI = 1.8 to 5.2 For poor or no drainage from drain pans, relative risk = 3.0 and 95% CI = 1.7 to 5.2 20Relative risk = 0.5, 95% CI = 0.3 to 0.9 21Based on statistical data of employed civilians by occupation (US Department of Commerce 1997), there are approximately 63 million civilian office workers plus teachers (49.6% of the civilian workforce). Assuming that 50% of the 1.06 million active duty military personnel are also office workers, the total is approximately 63.5 million.
Figure 4—Ventilation Rates per Person and SBS Symptoms syndrome” is widely used in reference to the health problems in these buildings.
However, the syndrome appears to be the visible portion of a broader phenomenon. These same symptoms are experienced by a significant fraction of workers in “normal” office buildings that have no history of widespread complaints or investigations (e.g., Fisk et al. 1993; Nelson et al. 1995, Brightman et al. 1997), although symptom prevalences vary widely among buildings. The most representative data from US buildings, obtained in a 56-building survey (that excluded buildings with prior SBS investigations) found that 23% of office workers reported two or more frequent symptoms that improved when they were away from the workplace. (HS Brightman, Harvard School of Public Health, Personal Communication). Applying this percentage to the estimated number of U.S. office workers and teachers (64 million), the number of workers frequently affected by at least two SBS symptoms is 15 million.
SBS symptoms are a hindrance to work and are associated with absences from work (Preller et al. 1990) and visits to doctors. When SBS symptoms are particularly disruptive, investigations and maintenance may be required. There are financial costs to support the investigations and considerable effort is typically expended by building management staff, by health and safety personnel and by building engineers. Responses to SBS have included costly changes in the building, such as replacement of carpeting or removal of wall coverings to remove molds, and changes in the building ventilation systems.
Some cases of SBS lead to protracted and expensive litigation. Moving employees imposes additional costs and disruptions. Clearly, these responses to SBS impose a significant societal cost, but information is not available to quantify this cost.
Calculations indicate that the costs of small decreases in productivity from SBS symptoms are likely to dominate the total SBS cost. Limited information is available in the literature that provides an indication of the influence of SBS symptoms on worker productivity. In a New England Survey, described in EPA’s 1989 report to Congress (U.S. Environmental Protection Agency, 1989), the average self-reported productivity loss due to poor indoor air quality was 3%.
Woods et al. (1987) completed a telephone survey of 600 U.S. office workers and 20% of the workers reported that their performance was hampered by indoor air quality, but the study provided no indication of the magnitude of the productivity decrement. In a study of 4373 office workers in the U.K. by Raw et al. (1990), workers who reported higher numbers of SBS symptoms during the past year also indicated that physical conditions at work had an adverse influence on their productivity. Based on the data from this study, the average self-reported productivity decrement for all workers, including those without SBS symptoms, was about 4%.22 In an experimental study (Menzies et al. 1997b), workers provided with individually-controlled ventilation systems reported fewer SBS symptoms and also reported that indoor air quality at their workstation improved productivity by 11% relative to a 4% decrease in productivity for the control population of workers.23 ________________
22The data indicate a linear relationship between the number of SBS symptoms reported and the self-reported influence of physical conditions on productivity. A unit increase in the number of symptoms (above two symptoms) was associated with approximately a 2% decrease in productivity.
Approximately 50% of the workers reported that physical conditions caused a productivity decrease of 10% or greater; 25% of workers reported a productivity decrease of 20% or more. Based on the reported distribution of productivity decrement (and productivity increase) caused by physical conditions at work, the average self-reported productivity decrement is about 4%.
23P 0.05 for the reduction in SBS symptoms and p 0.001 for the self-reported change in productivity.
In addition to these self-reported productivity decrements, measured data on the relationship between SBS symptoms and worker performance are provided by Nunes et al. (1993). Workers who reported any SBS symptoms took 7% longer to respond in a computerized neurobehavioral test24 and error rates in this test decreased non-significantly (the18% decrease was not significant). In a second computerized neurobehavioral test, workers with symptoms had a 30% higher error rate 25 but response times were unchanged. Averaging the percent changes from the four performance outcomes yields a 14% decrement in performance among those with SBS symptoms. Multiplying by the estimated 23% of office workers with 2 or more frequent symptoms yields a 3% average decrease in performance.
Other objective findings were obtained in a study of 35 Norwegian classrooms.
Higher concentrations of carbon dioxide, which indicate a lower rate of ventilation, were associated with increases in SBS symptoms and also with poorer performance in a computerized test of reaction time26 (Myhrvold et al.
1996); however, the percentage change in performance was not specified.
Renovations of classrooms with initially poor indoor environments, relative to classrooms without renovations, were associated with reduced SBS symptoms and with improved performance by 5.3% in the reaction time tests27 (Myhrvold and Olsen 1997).
Investigations by Wargocki et al. (1999, 2000, 2000a) and Lagercrantz et al. (2000) provide additional objective evidence that SBS symptoms reduce productivity. In a series of laboratory-based, blinded, controlled, randomized experimental studies, the health symptoms and satisfaction with of IEQ of workers were
monitored along with the workers’ performance of work-related tasks including:
typing, addition, proof reading, and creative thinking. The laboratory had the appearance of a normal office but enabled precise control of all environmental parameters. Some experiments were performed with and without a pollutant source (a 20 year old carpet) placed in the laboratory behind a visual screen.
Other experiments varied the outside air ventilation rate with the carpet present.
The study design controlled for the effects on performance of learning when tasks were repeated. These studies have shown that removing the pollutant ________________
24p 0.001 25p = 0.07 26Correlation coefficient = 0.11 and P value = 0.009 for performance versus carbon dioxide.
Correlation coefficient = 0.20 and P value = 0.000 for performance versus a score for headache, heavy headed, tiredness, difficulty concentrating, and unpleasant odor. Correlation coefficient = 0.11 and P value = 0.008 for performance versus a score for throat irritation, nose irritation, runny nose, fit of coughing, short winded, runny eyes. Correlation coefficients are controlled for age.
27Measures of statistical significance are not included in paper.
source (carpet) or increasing ventilation rates with the pollutant source present were associated with increased satisfaction with indoor air quality,28 decreases in some SBS symptoms,29 and increases in performance in text typing, proof reading, and addition. 30 Considering these three work tasks, these studies suggest that doubling of the ventilation rates increase overall performance by 1.9% (Wargocki et al. 2000a). Subsequent analyses indicated that the work performance improved only when the intensity of SBS symptoms diminished and identified a 7% improvement in the score on a creative thinking test31 as the ventilation rates increased from 3 to 10 L s-1 per person (Wargocki et al. 2000b).
The estimate of the productivity loss from SBS symptoms must be based on the limited information available. The self-reports discussed above suggest a productivity decrease, averaged over the entire work population, of approximately 4% due to poor indoor air quality and physical conditions at work. Although SBS symptoms seem to be the most common work-related health concern of office workers, some of this self-reported productivity decrement may be a consequence of factors other than SBS symptoms. Also, dissatisfied workers may have provided exaggerated estimates of productivity decreases. The objective data reviewed above suggest that SBS symptoms are associated with decrements on the order of 2% to 3%. Based on these data, we assume a productivity decrease caused by SBS equal to 2%, recognizing that this estimate is highly uncertain. This 2% estimate is the basis for subsequent economic calculations.