Air sampling in the assessment of continuous exposures to acutely-toxic chemicals. Part I--Strategy.

This paper describes the conceptual basis for assessing the hazard of continuous exposures to acutely toxic chemicals. It is stressed that the variability of workers' short-term exposures to airborne chemicals must be considered in establishing strategic criteria which define an acceptable (or unacceptable) environment. The argument is developed that the traditional strategy of an absolute ceiling limit is unworkable since any set of exposures can be declared out of compliance if a sufficiently large number of samples is collected. It is proposed that acute-exposure limits be defined instead as air concentrations that can be exceeded by an explicit fraction of the population of exposures. An "exceedance" rate of 5% is suggested provided that exposure limits incorporate appropriate safety factors which are relatively large for potent acute toxins and small for irritants. The implications of this strategy are analyzed with some existing ceiling limits proposed by NIOSH.