Twenty-four healthy male clerical workers (50-59 years of age) in an automobile manufacturing plant performed as accurately as they could a calculating task consisting of the addition or subtraction of two 2-digit numbers at five grades of task load for 5 min each. The workers' work capacities were inferior in speed but not in precision to those of male students determined previously. The resting levels of occipital midline beta-2 (OZβ2) amplitude were significantly lower for the workers than for the students. The workers' mental workloads were objectively shown to be lighter than the students' based on a significant difference between the percent increases in OZβ2 amplitude over resting levels. The workers' subjective mental workloads assessed by subjective rating of task difficulty (SRTD) were lighter than the students' at higher task loads. From the trend that there was no undue rise in either SRTD or percent increase in OZβ2 amplitude, it was judged that no task load could induce excessive mental workload on workers.
Two kinds of respirator canisters, an organic vapor (OV) canister containing activated carbon and a methyl bromide (MB) canister containing activated carbon impregnated with triethylenediamine were investigated for their filtration efficiency of MB gas under various conditions of MB concentration, humidity and temperature. At lower MB concentrations, the breakthrough time of the OV canister was shorter than that of the MB canister. It also decreased with an increase in temperature, whereas the breakthrough time of the MB canister did not change with temperature. Humidity affected the breakthrough times of the OV canister as much as those of the MB canister. The desorption and the remaining filtration efficiency of MB gas were examined in both canisters which had been used for fumigation in plant quarantine. More than 5 ppm of MB gas leaked from 11 out of 18 used OV canisters, whereas less than 0.1 ppm MB leaked out from each of the used MB canisters. The mean remaining breakthrough time of the used OV canisters was 9.3 min, whereas that of the used MB canisters was 74.4 min. From the present study, it was shown that the gas masks with the OV canisters were not suitable for fumigating with MB gas.