Hearing Protector Attenuation Measurement on the End-User:
A Case Study

Kevin Michael, Ph.D. Cindy Bloyer
Michael & Associates, Inc. U.S. Healthworks

Steel Industry Study

  • 389 workers individually fit-tested as part of annual audiometric testing
  • Workers selected HPDs
  • 192 wearing flanged reusable HPD, NRR = 27 dB
  • 85 wearing urethane foam HPD, NRR = 33 dB
  • Others wearing variety of types

Individual Attenuation Measurements- Retest

105 of the insert-type HPD wearers were re-tested for attenuation in December of 1998. These individuals were selected because the overall attenuation measured during the initial test was relatively low (< 8 dB).

Observations

Questionable policies:
--"All HPDs for this plant must be NRR > 25 dB"
--Derate the NRR by x % to estimate field performance

Solution: Perform field monitoring of HPD performance and compare to workplace exposure

Conclusions

  • Assumed protection based on NRR can be wildly inaccurate
  • Actual protection may be zero or may exceed manufacturers attenuation data
  • The missing step: verify protection provided to the end user
  • Field monitoring of insert-type HPD effectiveness practical to integrate into annual audiometric evaluation
  • Retraining / refitting / retesting with field monitoring system resulted in 14 dB average improvement in attenuation


Email: kevin@michaelassociates.com

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