Cornell University Ergonomics Web
Effects of Indoor Environmental Conditions on Computer Work Performance
By Alan Hedge & Daniel Gaygen
Indoor environmental conditions can affect measures of productivity. The
performance of simulated office tasks improves with an increase in the
ventilation rate from 3 to 30 l/s/p [1]. Call center operator performance
has been shown to improve with a high outdoor air supply and a new filter [2,3]
although not all studies have found this effect [4. When the temperature
is outside of a range from 21- 25°C there is an average 2% decrement in work
performance per degree C temperature rise [5]. It has been suggested that
providing workers with individual control over a +3°C range should produce ~3%
increase in cognitive and skilled manual performance and ~ 7% increase in typing
performance [6]. In experimental laboratory studies, computer task performance
has been shown to be impaired by polluted air from an old carpet [7,8] and by
emissions from old personal computers [9] . In field studies negative
associations have been found between self-reports of productivity and sick
building syndrome complaints [10] and positive associations with the use of
personal ventilation control [11].
The present study investigated the effects of environmental changes in the
office workstation microclimate on objectively measured changes in work output
at that workstation over an extended period in the offices of a participating
law firm housed in a 2 story air conditioned office building in Garden City, New
York, USA. Sixteen employees participated in the study. A web-based
software system (Prodyx-PDX) was being used to gather computer work performance data minute
by minute. Air temperature, relative humidity, carbon dioxide (CO2), respirable particulates at 10 microns (PM10) and total volatile organics (TVOC)
were used as measures of indoor environmental quality (IEQ). These measures also
were logged minute by minute by a custom-built unit. Air temperature and
relative humidity also were measured at some of the workstations for some of the
study period using portable data logger. All data were aggregated as means over
1 hour periods and these data were analyzed iteratively using the Mixed models
procedure to find the best solution. All data distributions were examined for
normality. Mean correct keystroke and error rates were log transformed (ln).
Data also were lagged in one-hour intervals.
Results show significant contemporaneous effects of mean CO2 had a significant
effect on mean mouseclicks/minute (p= 0.001) and air temperature affected the ln
mean correct keystrokes/minute (p= 0.031). At 19°C the average keying rate was
12 keystrokes/minute, at 20°C this rose to 25/minute, at 22°C is was 35/minute,
at 26°C is was 38/minute and at 28°C it was 40/minute. There was a 40% increase
in keying output when the temperature was 22°C rather than 20°C.
Results also showed significant lagged effects for the 1 hour lagged data for
mean CO2 (p = 0.05) and mean PM10 (p = 0.017) on ln mean error keystrokes/minute
(i.e. conditions experienced at one time affected work performance 1 hour
later). There were no effects for the 2 hours lagged data.
Findings from this study show that certain indoor environmental quality
variables (air temperature and carbon dioxide) have immediate effects on
objective measures of the quantity of computer work activity performed and that
indoor environmental quality variables (CO2 and respirable particulates) also
can have short-term lagged effects on the accuracy of computer work.
Acknowledgements
This research was
funded by the U.S. E.P.A. We also thank Jim Smith, Syracuse University, for help
with this work.
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