The purpose of this study was to investigate the medical records of 900 maintenance personnel employed in an aircraft manufacturing plant, and determine if the accident rate followed a Poisson distribution as well as the extent to which it did. It was assumed that the closer the data conformed to the Poisson curve, the more likely it would be that the variance in accident rates was due to "pure chance factors." The investigation of data in this study was expected to reveal information concerning the relative importance of the various injury sources, the conditions, processes or activities that produce injuries, extent of recurrence of each kind of injury or accident in each type of activity or operation, repeaters, which could be utilized in preventing recurrence.