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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants
compensation in national service, as do all NRC committee members. This report presents the subcommittee's evaluations, conclusions, and recommendations.
DESCRIPTION OF THE LATRA MODEL
The LATRA model is designed to estimate the probabilities of mild and serious health effects from exposing specified human subpopulations to estimated concentrations of specific rocket emissions. For each emission, exposure-response functions (ERFs) were developed to relate estimated exposure concentrations to expected health effects. At present, separate ERFs are derived for "sensitive" and "normal" segments of the general population. An ERF is specified by two points: a lower concentration assumed to be associated with a 1% incidence of a particular effect, and an upper concentration assumed to be associated with a 99% incidence of a particular effect. An ERF is fit to the two concentration versus-incidence points using a log-probit model (equivalent to assuming a lognormal distribution of the probability of effect). The resulting curve is then used to calculate the expected health effects and the risk profile for each population subgroup. A different procedure would be used to establish ERFs for carcinogenic emissions; however, the ERFs currently included in LATRA are not for substances known or suspected to be carcinogenic.
To set the 1% effect levels for sensitive populations, the Air Force considered the National Research Council's short-term public emergency guidance levels (SPEGLs) and other published exposure concentrations estimated to be safe for exposures of the general public. In establishing the 1% effect levels for normal populations, the Air Force considered exposure concentrations independently estimated to be safe for workers. The 99% effect levels were set 5-fold higher than the 1% effect levels for sensitive populations and 10-fold higher than the 1% effect levels for normal populations to reflect the assumed greater range in sensitivity among members of the normal population.
The subgroups considered sensitive to the rocket emissions modeled by LATRA are children (less than 15 years of age), the elderly (more than 64 years of age), and all persons with bronchitis, asthma, or other physiological stress, especially upper-respiratory ailments. The remainder of the population is considered normal.