AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects, or an impaired ability to escape.
AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.
Airborne concentrations below the AEGL-1 represent exposure levels that could produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects. With increasing airborne concentrations above each AEGL, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL. Although the AEGLs represent threshold levels for the general public, including susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses, it is recognized that individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL.
Propylene oxide is an extremely flammable, highly volatile, colorless liquid. Its odor has been described as sweet and alcoholic, and it has reported odor thresholds ranging from 10 to 200 ppm (Jacobson et al. 1956; Hellman and Small 1974; Amoore and Hautala 1983). The primary industrial uses of propylene oxide include in the production of polyurethane foams and resins, propylene glycol, functional fluids (such as hydraulic fluids, heat transfer fluids, and lubricants), and propylene oxide–based surfactants. It is also used as a food fumigant, soil sterilizer, and acid scavenger.
Data addressing inhalation toxicity of propylene oxide in humans were limited to one case report, general environmental work surveys, and molecular biomonitoring studies. Studies addressing lethal and nonlethal inhalation toxicity of propylene oxide in animals were available in monkeys, dogs, rats, mice, and guinea pigs. General signs of toxicity after acute exposure to propylene oxide vapor included nasal discharge, lacrimation, salivation, gasping, lethargy and hypoactivity, weakness, and incoordination. Repeated exposures resulted in similar but generally reversible signs of toxicity. Much of the toxicologic evidence suggests that propylene oxide reacts at the site of entry. Therefore, inhalation of propylene oxide results in respiratory tract irritation, eventually leading to death. Possible neurotoxic effects have also been observed in rodents and dogs after inhalation exposure to higher concentrations of propylene oxide.
Propylene oxide is a direct alkylating agent that covalently binds to DNA and proteins. Consequently, it has tested positive in a number of in vitro tests but has produced equivocal results in in vivo test systems. Data addressing the po-