Abstract
The information presented shows that it is not possible to ensure compliance with an absolute ceiling threshold limit for benzene. The ANSI standard can be slightly modified to provide practicable working criteria of 10 ppm time-weighted average and not more than 2% probability of exceeding 25 ppm. It would, however, be simpler for the hygienist to work to a daily exposure dose limit of 5000 ppm-minutes, which is proposed here. This criterion is tested against some typical log-normal distributions and is submitted to toxicologists for consideration.