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Comparison of Damage Risk Criteria Using the Albuquerque Blast Overpressure Walkup Study Data

Comparison of Damage Risk Criteria Using the Albuquerque Blast Overpressure Walkup Study Data . William J. Murphy Amir Khan Peter B. Shaw Hearing Loss Prevention Section Division of Applied Research and Technology National Institute for Occupational Safety and Health.

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Comparison of Damage Risk Criteria Using the Albuquerque Blast Overpressure Walkup Study Data

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  1. Comparison of Damage Risk Criteria Using the Albuquerque Blast Overpressure Walkup Study Data William J. Murphy Amir Khan Peter B. Shaw Hearing Loss Prevention Section Division of Applied Research and Technology National Institute for Occupational Safety and Health The results reported in this paper represent the opinions of the authors and are not representative of the policies of the National Institute for Occupational Safety and Health.

  2. Blast Overpressure Studies

  3. Outline • Blast Overpressure Exposure Evaluations • MilStd 1474D • LAeq8hr Protected & Unprotected • AHAAH Warned & Unwarned • Statistical model for effects threshold • Population Averaged Model • Audiometric Failures • Audiometric and Conditional Failures • Dose Response Curves

  4. Outline continued • Exposure Assessment Comparisons • Threshold Estimates from BOP Study • Fitting Performance • Damage Risk Criteria Implications • MilStd 1474D: 177 dB Limit • LAeq8hr: 85 dBA Limit • AHAAH: 500 Auditory Hazard Unit (AHU) limit

  5. MilStd 1474D Free-Field Exposure

  6. Statistical Analysis of BOP Data • Obtained the waveforms from Data Archive from USAARL-MRMC and USARL – HRED • MILSTD 1474D – B duration (also computed A & C durations) • LAeq8hr – Protected and Unprotected • AHAAH model – Protected Warned and Unwarned • Checked against Chan et al. 2001, Ahroon & Patterson 2005, Price (2005), Jokel (2007) • Obtained the injury data from USAARL-MRMC • Checked the injury data against 1999 Contractor report DAMD17-96-6007

  7. Statistical Analysis of BOP Data • Applied a General Estimating Equations to evaluate the Population Averaged effects using xtgee in Stata. • Represents the response pattern of the population as a whole • Makes no assumptions regarding propagation of failure through to other exposure levels • Tells us nothing about the chances of an individual subject failing within the exposure. • Tells us about the chance of having a failure in the population.

  8. Mil STD 1474 D 185 dB 193 dB

  9. LAeq8hr Unprotected Levels 124 dB 115 dB

  10. LAeq8hr Protected Levels 101 dB 109 dB

  11. AHAAH Unwarned Model 10109 AHU 3053 AHU

  12. AHAAH Warned Model 2480 AHU 718 AHU

  13. 5% Failure Thresholds L(95,95)

  14. Five Exposure Assessments Compared QIC: Lower value indicates a better fit QIC = Quasi Likelihood under the independence model Information Criterion

  15. Mil-Std Observations • Mil-Std 1474D • L(95,95) with No Presumed Auditory Failures • Chan : L(95,95) = 193 dB • NIOSH : L(95,95) = 193 dB • Chan’s analysis: Presumed Auditory Failures • Add 9 dB for threshold of L(95,95) = 186 dB • NIOSH analysis (Auditory & Conditional Failures) • L(95,95) = 185 dB. • Add 8 dB for Population Average threshold for the L(95,95) lower confidence bound.

  16. LAeq8hr Observations • LAeq8hr Protected versus Unprotected • French Weapon Noise Criteria: • LAeq8hr < 85 dB Unprotected • Chan’s analysis without presumed failures • LAeq8hr < 100 dB Protected (assumed 15 dB for protectors) • Unprotected limit 124 dB without presumed failures • NIOSH analysis without presumed failures • 14 dB HPD effect for Protection • Unprotected limit: 124 dB Audiometric Failures • Unprotected limit: 115 dB Aud. & Cond. Failures • Protected limit: 101 dB Aud. & Cond. Failures

  17. AHAAH Observations • NIOSH Analysis L(95,95) Audiometric failures (no presumed failures) • Unwarned Threshold = 10109 AHU • Warned Threshold = 2480 AHU • NIOSH Analysis L(95,95) Audiometric and Conditional Failures (no presumed failures) • Unwarned Threshold = 3053 AHU • Warned Threshold = 718 AHU • AHAAH Model proposes a 500 AHU Limit which is more conservative than the data suggest

  18. Concerns for AHAAH Model • Predictions of Hazard at Levels 3 & 4 not really tested in BOP study. • Experiments can be designed to test this.

  19. Concerns for AHAAH Model • Justification for 500 AHU as a threshold limit • Warned limit • 718 or 2480 AHU – Population Average, L(95, 95) • Unwarned Limit • 3053 or 10109 AHU – Population Average, L(95, 95) • Validation of the Warned/Unwarned middle ear • No consideration given for adaptation/fatigue • Model turns Warned condition ON but not OFF

  20. Questions? William Murphy 4676 Columbia Parkway, MS C-27 Cincinnati, OH 45226-1998 wjm4@cdc.gov 513-533-8125

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