Chronohygienic and chronosocial aspects of industrial accidents.

A series of 2,772 accidents has been analyzed in two plants. The following aspects were considered: 1) environmental circumstances, 2) accident causes as given by witnesses or victims, and 3) time of day. Activity of the plants or particular groups of workers was assessed by supervisors on a 10-point scale. A circadian rhythm of accidents has been shown. It was determined to be governed by the interrelationships between the following endogenous and exogenous rhythmic factors: human factors, such as fatigue and circadian fluctuation of biological functions; and multiple hygienic and social components, which either promote human performance or suppress it, e.g., high environmental temperature, overcrowding, and noise. The rate of accidents depends on the particular combinations of these factors, all of which change around the clock. In both plants, the circadian rhythm of accidents was approximately parallel to the circadian rhythm of activity of the plant as a whole rather than to the activity of shift workers only, with a peak around 1100 hr. The lowest number of accidents was noted during night shifts; some increase was observed after midnight, however, in spite of the lowest level of plant activity at that time.