Abstract
Self recorded data for 28 days of day and night sleep were analysed in 33 experienced, permanent night workers employed as night guards in a security company. They worked either ten 16 hr shifts (group SG10, n=22) or fourteen 12 hr shifts (group SG14, n=6), during 4 weeks, or eighteen 9 hr shifts of beat patrols (group BP18, n=5). The mean day sleep after each shift of group SG10 lasted 3.6 hr, but the sum of day and night sleeps on the same day amounted to 12.9 hr. Group SG14 subjects worked blocks of 2-3 consecutive shift, day sleep between shifts being 6.5 hr and longer than that after the last shifts of 5.2 hr. For subjects in group BP18 who worked blocks of 2-4 consecutive shifts, day sleep between shifts was 7.1 hr, longer than day sleep after the last shifts of 6.4 hr. The cumulated day and night sleep after the last shifts of the latter two groups amounted to 14.5 hr. When working blocks of 3-4 consecutive night shifts, the data indicated the possibility of accumulation of sleep deficit on days between shifts. The length of day sleep after the last shift increased significantly in the order of group SG 1 O; SG 14, and BP 18, parallel to the increase in the number of consecutive night shifts. This supports the assumption that temporary sleep deficits accumulate in shift systems using blocks of more than 2-3 consecutive night shifts.
