Risk of sick leave associated with outdoor air supply rate, humidification, and occupant complaints

Posted by Siru Heiskanen on Feb 16, 2017

Authors: Milton, D. K., Glencross, P. M. and Walters, M. D.

Year of publication: 2000

Publication: Indoor air, 10(4), pp.212–221.

Keywords: indoor air quality, sick leave, ventilation, IEQ,

Link to publication

This study (2000) analyzed sick leave records for 3,720 hourly employees of a Massachusetts manufacturer in 40 buildings with 115 independently ventilated working areas. Building characteristics were identified, and IEQ (indoor environmental quality) complaints recorded.

Building features, such as low levels of outdoor air supply in mechanically ventilated buildings, have been associated with non-specific building related symptoms. They can be seen as short-term sick leave of employees. Sick leave as an indicator of poor IEQ is complex, however: there are several other factors that contribute to it. Sick leave analyses in this study were controlled for age, gender, seniority, hours of non-illness absence, shift, ethnicity, crowding, and type of job (office, technical, or manufacturing worker).

None of the buildings had elevated counts of bacteria, fungi, spores, endotoxins, or volatile organic compounds.

The study found consistent associations of increased sick leave with lower levels of air supply and IEQ complaints.

  • Among office workers, the relative risk for short-term sick leave was 1.53 with lower ventilation, and 1.52 in areas with IEQ complaints
  • Among those exposed to lower outdoor air supply rates, the risk of short-term sick leave was 35 % or 1.2 to 1.9 days of increased sick leave per person per year, depending on age and gender

The study also found, that using regular humidifiers were associated with sick leave. This might suggest, that they spread pathogens. If airborne spread of respiratory infections is an important cause of sick leave, then alternatives to ventilation may be effective for the control of this problem.

Based on these results, researchers counted that net savings of $400 per employee per year could be obtained with increased ventilation. At a national scale the lost of productivity could be as much as $22.8 billion per year. This estimate includes only the missing work caused by short-term sick leave, and doesn’t account for the loss of productivity caused by poor IEQ. Therefore the estimated financial saving could be much higher in reality.


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