According to study author Kenneth N. Forston, a Ph.D. candidate in the Department of Economics at Princeton University, "the injury hazard is substantially higher late at night than during regular daytime work hours." He points to the incidents at Three Mile Island, which occurred shortly after 4 a.m. on March 28, 1979, and at Chernobyl, which occurred at 1:23 a.m. on April 26, 1986, as indicators that night-time shift work can be more hazardous than daytime work hours.
Forston used data from workers' compensation claims in Texas to estimate the empirical distribution of injuries. His results show that the injury rate is high during off-hours late at night and low during the regular 9-to-5 shift. which is when most white-collar workers are employed. Blue-collar workers whose jobs tend to be inherently more dangerous work more late-night shifts.
"There are inherent physiological implications of late-night work that make off-hours jobs more hazardous than daytime jobs. This is an important distinction," said Forston, "because it suggests that in scheduling work hours, firms should consider shift time in addition to such factors as shift length, which is merely correlated with late-night work and contributes to a higher injury rate, but is not unique to night work."