Lack of effects of carbon monoxide on human vigilance

Previous publications on the effects of low levels of carbon monoxide (CO) on human vigilance performance have found conflicting results. While several studies have found statistically reliable effects, none have gone unchallenged. This article presents a critical review of the literature and the results of a study employing 52 human male subjects performing a numeric monitoring task. CO levels were 0, 100, and 200 ppm which produced mean carboxyhemoglobin levels 0.01, 4.61 and 12.62 percent respectively. No CO-exposure levels produced any effect on vigilance performance. The power of the statistical test for CO effects was shown to be quite high, even for fairly trivial possible decrements of performance.