Hearing Health Risk in a Population of Flight Deck Personnel

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Hearing Health Risk in a Population of Flight
Deck Personnel

• CDR Glen Rovig,
  MSC, USN
• Navy Environmental
  Health Center
• Norfolk,
  Virginia
• International Military Noise Conference
• Baltimore, Maryland 25 April 2001

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• Study Questions
• What are typical unprotected ear-level noise
  exposures for flight deck personnel?
• Is there evidence of temporary threshold shifts
  in flight deck personnel?
• Are flight deck personnel at increased risk of
  NIHL compared to non-flight deck personnel on
  the same ship?

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Dosimetry

• Larson-Davis 705, shoulder level
• - 1 minute LEQ in dBA
• - Max dBA, 1 minute
• - Unweighted peak dB, 1 minute
• - 8-hr TWA, DoD criteria (85/3)

Mean TWA 109 (range 96.1-119.5) Mean mins
699 (range 203-1087)
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ABH3 1087 min TWA 116.3
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Methodology for TTS Study

• 77 flight deck personnel, Nimitz class carrier
• Max 10/day, audiogram a.m. before/ASAP after
  duty day
• TTS defined 10dB shift 2 or more freqs (1-6K,
  either ear)
• No special training/controls
• 
  

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Mean age 26.1 (19-49) Mean yrs svc 6.6 (1-30)
Mean yrs FD 5.8 (1-20) 73 males, 4
females HPDs 70 cranials (earmuffs) 7
double protection
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TTS RESULTS ON 77 FLIGHT DECK PERSONNEL

• 10 of 77 demonstrated TTS
• 1 of 10 wore double protection
• Major variables were TWA and time out of noise
• No control for time out of noise
• 4 of 10 were high risk for both TWA and time out
  of noise

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Mean TTS in 13 special cases. Each needed
double protection, was out of noise 30 min or
less before post-test, and wore single HPD. 30
(4) demonstrated TTS, compared to 13 for all
subjects. Cranials should have reduced effective
exposure lt85dBA.
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Subject 4 male ABE3, age 21, 2.5 years service
JBD Operator, bow catapults Cranials w/sound
powered phone Hx. tools/engines, frequent user
personal listening device Hx. 15-25dB permanent
shift _at_ 2-3K Hz both ears
C/O tinnitus, ? speech discrim TWA 119.5 (969
minutes) 14 mins. out of noise gt105dBA
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Subject 31 male AO3, age 22, 2 years service
Weapons Elev. Operator Double HPDs (cranials
foam) Recreational shooter Negative history PTS
No hearing complaints TWA 106.4 (467
minutes) 55 mins out of noise gt105dBA
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• INCREASED RISK OF NIHL?
• Identified 2 additional groups, similar length
  of service
• Compared baseline audio with last monitoring
  audio
• PTS 15dB drop _at_ 1,2,3 or 4K, or 10dB ave.
  drop 2,3,4K

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Three Comparison Groups, 77 each

• 1) Flight deck
• 2) Moderate exposure (Engineering spaces)
• (e.g. Enginemen, Hull Techs, Electricians Mates,
  Machinist Mates, plus a few assigned officers)
• 
  
• 3) Low exposure (Administrative spaces)
• (e.g. Disbursing Clerks, Postal Clerks, Yeomen,
  Personnelmen, and a few assigned Officers)

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Distribution by Length of Service
lt4 YRS 4 YRS 10 FD (76) 39 37
26 ENG (77) 34 43 28 ADMIN
(52) 14 38 27 Not part of analysis, for
clarification only
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PTS Prevalence by Group

• lt4YRS 4YRS ALL SUBJ
• FD 6/39 14/37 20/76
• 15 38 26
• ENG 6/34 10/43 16/77
• 18 23 21
• ADMIN 4/14 4/38 8/52
• 11 15
  

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Prevalence of HL gt20dB _at_1,2,3, or 4KHz
lt4 yrs 4yrs All Subj FD
2 / 39 (5) 14 / 37 (30) 13 / 76
(17) ENG 5 / 34 (15) 16 / 43 (37)
21 / 77 (27) ADMIN 0 / 14 2 /
38 (5) 2 / 52 (5)

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Pre-Existing Hearing Loss (
subjects each group having at least one
thresholdgt 20dB _at_ 1-4K Hz on baseline/entry
audiogram)

• FD 7 / 76 (9)
• ENG 11 / 77 (14)
• ADMIN 2 / 52 (4)
• Note 2/2 current ly impaired Admin Sailors had
  loss on entry
• 10 of 210 subjects had hearing impairment on
  entry, 18 now
• Overall, 55 of Sailors with current hearing
  impairment had a loss existing prior to entry

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SUMMARY and RECOMMENDATIONS
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1) Dosimetry revealed high environ noise levels.
(80 subjects needed double protection per
DoD) 2) 10 of 77 FD Sailors demonstrated TTS
(non-standardized post-exposure confounds
interpret.) 3) FD Sailors 25 more likely than
Engineers to experience PTS, almost twice as
likely as Admin 4) Engineers 60 more likely than
FD to have abnormal hearing, 6 times more likely
than Admin 5) Engineers were 60 more likely
than FD Sailors to have pre-existing HL upon
entry
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• RECOMMENDATIONS
• Enforce double hearing protection on FD
• Improved education for all hands
• More research on individual susceptibility
• Improved HPDs with enhanced communication
  capabilities
• Verify findings through large central database
  (DOEHRS-HC)

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CDR Glen Rovig, MSC, USN [phone]
rovigg_at_nehc.med.navy.mil