Risk of sick leave associated with outdoor air supply rate, humidification, and occupant complaints
Milton, D. K., Markglencross, P. and Walters, M. D.
2000 Indoor Air, 10(4): 212
Milton, D. K., Markglencross, P. and Walters, M. D., (2000), "Risk of sick leave associated with outdoor air supply rate, humidification, and occupant complaints", Indoor Air, 10(4): 212.
Abstract:
We analyzed 1994 sick leave for 3,720 hourly employees of a large Massachusetts manufacturer, in 40 buildings with 115 independently ventilated work areas. Corporate records identified building characteristics and IEQ complaints. We rated ventilation as moderate (25 cfm/person, 12 ls1) or high (50 cfm/person, 24 ls1) outdoor air supply based on knowledge of ventilation systems and CO2 measurements on a subset of work areas, and used Poisson regression to analyze sick leave controlled for age, gender, seniority, hours of non-illness absence, shift, ethnicity, crowding, and type of job (office, technical, or manufacturing worker). We found consistent associations of increased sick leave with lower levels of outdoor air supply and IEQ complaints. Among office workers, the relative risk for short-term sick leave was 1.53 (95% confidence 1.22-1.92) with lower ventilation, and 1.52 (1.18-1.97) in areas with IEQ complaints. The effect of ventilation was independent of IEQ complaints and among those exposed to lower outdoor air supply rates the attributable risk of short-term sick leave was 35%. The cost of sick leave attributable to ventilation at current recommended rates was estimated as $480 per employee per year at Polaroid. These findings suggest that net savings of $400 per employee per year may be obtained with increased ventilation. Thus, currently recommended levels of outdoor air supply may be associated with significant morbidity, and lost productivity on a national scale could be as much as $22.8 billion per year. Additional studies of IEQ impacts on productivity and sick leave, and the mechanisms underlying the apparent association are needed.
Practical Implications
This paper demonstrates an association between expert ratings of outdoor air supply rate and the presence of sick leave among 3,720 employees (and particularly among 600 office employees) of a large U.S. manufacturer. The paper shows that in this large sample the cost of providing additional ventilation may be more than offset by the savings that result from reduced sick leave. It is important to note that the range of ventilation rates compared [moderate with approximately 12, and high with approximately 24 l/s-person] are at the upper end of rates seen in these facilities. That indicates that benefits continue to accrue when ventilation is increased above 10 l/s-person, and that experimental studies to validate and to determine mechanisms for these observational findings should be a priority for indoor air research.