nearly 4,000 persons participated in a study to evaluate three odorant systems in four test modes and at 24 different test sites participants included trained panels, untrained erda employees, and several thousand untrained volunteer evaluators. the classical testing technique and three modified test modes were used to represent a spectrum of conditions that would define the effect of environmental familiarity and mental distractions upon olfactory responses to lp-gas. significant efforts were directed toward determination of odorant levels that not only can be detected but also will be detected. the study showed that in addition to defects of the nasal anatomy, psychological factors also affect olfactory responses, and that unfamiliarity with a given environment as well as anxieties or mental distractions can produce reduced awareness to odorants intended to warn individuals of the presence of lp-gas. a second part of the study involved a laboratory determination of equilibrium k-values for both ethyl mercaptan and thiophane at three temperatures. novel sample handling and gas chromatographic techniques provided reproducible results which were in close agreement with theoretical predictions. (28 tables, 29 tables). (era citation 03:005983)