SLEEPING ON THE JOB DURING NIGHT SHIFTS MAY BE ASSOCIATED WITH EXTENDED NIGHT SHIFTS AND OR VARIABLE NIGHT-SHIFT ONSET TIMES/

Continuous rotating shiftworkers temporarily working overtime slept at least once during the working hours of their night shifts. They worke d at an electric power distribution plant in Sao Paulo (Brazil). In or der to detect factors that could be associated with sleeping on the jo b, we compared those who slept (sleep group - S) with those who did no t sleep (non-sleep group NS) as to the number of night shifts, the ave rage length of night shifts, the variability in night shift onset and offset times and the length of sleep episodes at home between consecut ive night shifts. Data collection was based on dairies filled in by th e workers for 30 consecutive days. For both S and NS groups, the numbe r of night shifts for each worker varied from 5 to 9, no difference be ing found between groups. Individual means of night shifts length vari ed from 9.4 +/- 0.3 hr to 14.2 +/- 0.6 hr; they were significantly lon ger in the S than in the NS group. Night shift onset times were shown to be significantly more variable in the S than in the NS group, where as offset times did not differ significantly between groups. Length of sleep episodes at home was not significantly different between groups . Workers who slept on the job were those who had longer working bouts and / or more variable night shift onset times. Differences among wor kers may be due to individual strategies to cope with a situation in w hich the work schedule included night shifts that were much longer tha n the established 8 hours, and with many changes in onset times from o ne night shift to the next.