CAUSES OF ACCIDENTS AND THE TIME OF DAY

The relationship between accidents and the time of day is not entirely clear. Although there is considerable evidence that performance is po orest in the early morning hours compared to at all other times, the d egree to which this is translated into accidents is not understood. In this study work-related fatal accidents were analysed to determine wh ether the causes of these accidents vary with time. The analysis used a classification and coding system devised to describe the wider circu mstances of the causes of fatalities. In terms of absolute numbers, fa talities were most common in the late morning or early afternoon. When these results were expressed in terms of the estimated number of work ers at work, the proportion of fatal accidents occurring at night was more than double chat occurring during the day. Behavioural factors we re the most common cause of fatalities at all times, but most common i n the early hours of the morning. Further analysis of the nature of th e behavioural involvement showed that errors in automatic processing ( skill-based errors) were the most common types of error and did not va ry much with time of day. Rule-based errors were most common during th e day whereas knowledge-based errors occurred mainly in the afternoon and night shifts. These results cast some doubt on the assumption that there is a direct relationship between the previously observed variat ions in performance across time and the ultimate safety outcome.