Is it permissible for an employee to work with an environment with noise exposure of 97 dBA for 1 hour, then 100 dBA for one-half hour, then 90 dBA for 4 hours?

The correct choice indicates that it is not permissible for the employee to work in this noise exposure scenario as specified. According to OSHA's noise standard, the permissible noise exposure limits are defined by both the duration and the intensity of the sound.

The standard specifies a maximum allowable exposure level of 90 dBA for an 8-hour workday. For noise levels above 90 dBA, specifically at 97 dBA or 100 dBA, the permissible exposure time decreases significantly. For instance, at 100 dBA, the maximum exposure time allowed is around 2 hours, significantly less than the total exposure in the given scenario.

When plus the exposures altogether, the combination of loud noises at 97 dBA and 100 dBA, even for the shorter durations, contributes to an exceedance of permissible noise exposure limits, leading to an increased risk of hearing loss without appropriate hearing conservation measures. Therefore, the overall time spent in an environment with such high noise levels is not compliant with OSHA regulations, justifying the conclusion that it is not permissible for the employee to work under these conditions.