The effects of moderate heat stress and open-plan office noise distraction on SBS symptom intensity and the performance of office work

Thomas Witterseh

The effects of moderate heat stress and open-plan office noise distraction were studied in a normal office. In the office six workstations with computers were installed. Behind a screen extending across the office, concealed equipment was installed to provide an outdoor air supply rate of 15 L/s/person and to control the air temperature and humidity in the office. Digital audio tape (DAT) playback equipment was similarly placed behind the screen. Six experimental conditions were established in a 3x2 design: air temperatures of 22, 26 and 30(C with a constant absolute humidity of 0.0074 kg/kg dry air, corresponding to 45, 35 and 28 %RH respectively; and two noise distraction conditions: 1) a quiet office condition (35 dBA unoccupied) and 2) an open-plan office noise condition (55 dBA unoccupied, with clearly audible conversations, movement, office machinery and telephones ringing intermittently). 30 subjects occupied the office in groups of 6 at a time (Fig. 1) and performed simulated office work for 3 hours under all 6 conditions, reporting intensity of SBS symptoms and environmental acceptability on questionnaires. Subjects wore their own clothes, selected and adjusted to provide thermal neutrality at 22(C. No changes were permitted at the higher temperatures.


Figure 1. Subjects during exposure in the office

Only 4% were dissatisfied with the noise in the quiet condition, while 68% were dissatisfied in the open-plan office condition (P<0.01). Increasing air temperature significantly decreased the subjective acceptability of the thermal environment (P<0.001) and air quality (P<0.01), while significantly increasing odour intensity (P<0.05), and air stuffiness (P<0.01). Increased air temperature significantly increased eye, nose and throat irritation (P<0.05), headache intensity (P<0.05), difficulty in thinking clearly (P<0.01) and in concentrating (P<0.01), and decreased self-estimated performance (P<0.001). Noise significantly increased fatigue (P<0.05) and difficulty in concentrating (P<0.05). Noise did not interact significantly with any thermal effects on subjective perception. Acceptability of the overall indoor environment in the office (Fig. 2) was found to be significantly deteriorated both by noise (P<0.05) and increased air temperature (P<0.001).


Figure 2. Indoor environment acceptability

In an addition task, noise decreased the rate of performance by 3% (P<0.05) (Fig. 3), subjects who felt too warm made 56% more errors (P<0.05) and a noise-temperature interaction was observed (P<0.01): noise removed the effect of warmth on errors (Fig. 4). Noise distraction tended to decrease the performance of an open-ended creative thinking task, but significantly increased typing speed (P<0.05) and reading speed in a proof-reading task (P<0.05). While subjects during a relatively short experiment may exert some conscious effort to counteract heat stress and noise distraction, becoming more fatigued as a result, office work will generally be performed considerably less well in open-plan offices than in enclosed offices, and at air temperatures that are subjectively found to be too warm.


Figure 3. Addition speed


Figure 4. Addition error rate