Noise Exposure in a Stamping Department
A metal-stamping department has 22 presses running two shifts. Full-shift dosimetry on 14 operators shows an 8-hour TWA of 91 dBA for the loudest group and 86 dBA for the rest. Peak readings at the press point of operation reach 118 dB. Workers report ringing ears at shift end and difficulty hearing conversation at home. The plant has issued foam earplugs with an NRR of 29 dB but has never fit-tested them; observation shows about half are inserted shallowly. Management proposes posting 'hearing protection required' signs and moving on, citing the earplugs' rating as sufficient. A capital request for enclosures and quieter tooling was deferred to next year.
1. Assess whether the current hearing conservation approach is adequate and explain the gap between the labeled NRR and real-world protection.
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The approach is inadequate on both exposure and program grounds.
Exposure. A TWA of 91 dBA exceeds the 85 dBA action level and the 90 dBA permissible limit. Peaks of 118 dB are impulsive and are poorly addressed by a single-number TWA; impulsive noise carries additional risk.
NRR reality. The 29 dB NRR is a laboratory value. Field performance is reduced by poor fit, movement, and insertion technique. Common derating approaches subtract a fixed amount or apply a percentage; either way, half the workforce inserting plugs shallowly is getting far less than the label suggests. At 91 dBA, a realistic field attenuation might leave workers near or above 85 dBA.
Program gaps. A hearing conservation program requires baseline and annual audiometry, training, fitting and verification, evaluation of attenuation, and recordkeeping. None appear to be in place.
Hierarchy. PPE is the last line. Enclosures and quieter tooling are engineering controls that reduce exposure for everyone and should not be deferred while relying on plugs.
Recommendation. Fit-test and train immediately, offer a variety of plug and muff options, add audiometry and tracking, and press the capital request with exposure and claims data.
2. A worker's annual audiogram shows a 15 dB shift at 4 kHz compared with baseline, and the worker denies off-job noise. What should happen next, and what does this finding imply for the program?
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A 15 dB shift at 4 kHz meets the threshold for a standard threshold shift under common criteria and triggers specific actions.
Immediate steps. Confirm with a retest after the worker has been away from noise for at least 14 hours. Review the audiogram for consistency and check for confounding causes such as infection or medication. Notify the worker in writing, refer for evaluation if indicated, and record the case.
Program implications. The shift is evidence that current protection is failing for at least some workers, which corroborates the fit observation. It should prompt a re-evaluation of attenuation, refitting, and a review of whether the worker's tasks differ from the dosimetry sample. It should also feed the case for engineering controls.
Do not blame the worker. The reflex to attribute the shift to off-job noise is common and often wrong. The professional response is to examine the exposure data and controls, not to close the file.
Follow-up. Track subsequent audiograms to detect progression, and verify that the worker's protection is effective in the actual task, not just in the fitting room.