The Noise Exposure That Grew Quietly
A cabinet-making shop has 30 employees. A noise survey three years ago showed most work areas at 82-85 dBA, with the table saw and edge-bander areas at 88-90 dBA. At that time the shop implemented a hearing conservation program covering the table saw and edge-bander operators (8 people), including annual audiograms and hearing protection. Since then the shop added a second edge-bander and a CNC router, moved the assembly area closer to the saws, and increased production from one to two shifts. No new noise survey has been done. Two employees in the assembly area recently complained of ringing in the ears at the end of the shift. The shop's audiometric records show that one table saw operator has a 10 dB shift in the 4000 Hz range compared with the baseline from three years ago. Management says the program "covers the noisy jobs" and sees no need to re-survey.
1. Assess whether the current hearing conservation program still covers the right people, and explain the significance of the two complaints and the audiogram change.
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The program's coverage is almost certainly outdated. The original survey identified 8 people in two areas, but the shop has since added equipment (second edge-bander, CNC router), relocated assembly closer to the saws, and doubled shifts. Each of these can raise noise levels and expand the exposed population. The assembly workers who now complain of ringing were not in the original covered group. Ringing in the ears at end of shift is a symptom consistent with overexposure and warrants prompt action, not reassurance.
The audiogram change in the table saw operator is a 10 dB shift at 4000 Hz compared with baseline. A shift of this size at 4000 Hz is the classic early signature of noise-induced hearing change and should trigger review: confirm the audiogram's validity (test conditions, recent exposure before testing), compare with prior tests, and determine whether it represents a persistent shift. It should not be dismissed because the program "covers" that worker; coverage is not the same as effective control.
Conclusion: the program no longer demonstrably covers the exposed population, and the symptoms plus audiogram change indicate that current controls are not adequate.
2. Design a re-assessment plan and specify the decisions it should drive.
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Re-assessment plan:
- Noise survey: conduct a new survey covering all areas and both shifts, including the new equipment and the relocated assembly area. Use a calibrated sound level meter and dosimetry for workers who move between areas. Sample during representative production, including peak periods.
- Exposure grouping: use the survey to define similar exposure groups and identify everyone at or above the action level, not just the previously covered 8.
- Audiometric review: audit the table saw operator's records, confirm test conditions, and arrange follow-up testing. Review all audiograms for other shifts or trends.
- Symptom follow-up: interview the two assembly workers, document symptoms, and refer for evaluation as appropriate.
Decisions the assessment should drive:
- Who is enrolled in the hearing conservation program (expand as indicated).
- Whether engineering controls are needed (enclosure of the router, relocation of assembly, barriers, maintenance of bearings and blades).
- Whether hearing protection is required and which type, with fit and training.
- Whether the audiometric testing schedule and notification process need revision.
- Whether the program's written scope and responsible person need updating.
The plan should be scheduled with dates and owners, and the results should be used to revise the program, not filed and forgotten. Until the survey is complete, the precautionary step is to enroll the complaining assembly workers and provide protection and information.