Doing damage by being over-cautious?

A simple method is presented for estimating a non-lethal level for inhalation toxicity studies. By reviewing 209 LC50 studies representing 96 chemicals that also reported a non-lethal level, it has been shown that taking 1/3 of the LC50 is a conservative estimate for a non-lethal exposure level. This approach was also compared to studies with LC01 and BMCL05 calculations. In the 38 studies that reported either of these values, again taking 1/3 of the LC50 provided a more conservation estimate for the non-lethal threshold. The studies included time intervals from 5 min out to 8 h and utilized multiple species such as the rat, mouse, hamster, guinea pig and dog. In all but 13 cases, taking 1/3 of the LC50 provided a more conservative estimate for a non-lethal exposure level compared to the experimentally observed value. In all but one of the 13 cases, the higher values were consequences of the selection of the exposure levels.