Evaluation of the Increased Accident Risk From Workplace Noise

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Evaluation of the Increased Accident Risk From
Workplace Noise

• Esko Toppila(1), Rauno Pääkkönen(1), Ilmari
  Pyykkö(2)
• 1Finnish Instutute of Occupational Health
• 2University of Tampere

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Noise directive
Individual susceptibility
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Specific accident risk related statements

1. The indirect effects on workers' health and
   safety resulting from interactions between noise
   and warning signals or other sounds have to be
   observed in order to reduce the risk of accidents
2. In exceptional situations where, because of the
   nature of the work, the full and proper use of
   individual hearing protectors would be likely to
   cause greater risk to health or safety than not
   using such protectors

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What we know about noise and accidents ?

• Risk factors in a shipyard (Moll van Charante,
  Mulder, 1990)
• Noise gt 82 dB
• Noise and hearing loss in 43 of accidents
• Accident reports in Finland
• Railroad worker with hearing handicap died
  because of not hearing an approaching train (2)
• Similar event with 4 deads in United Kingdom
• Radio equipped hearing protectors and ice hockey
  game (2)
• Morata al, 2005
• Hearing warning signals and loosing direction
  information is complained by workers with hearing
  handicap or using HPE
• Germany
• Traffic noise and limitations for attenuation of
  HPD

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Girard al, 81346 workers, five year follow-up
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Origin of interaction between noise and accident
risk

• Noise
• Reduced speech intelligibility
• Possibility of hearing warning sounds
• Reduced capacity to localize the sounds
• Hearing handicap
• Increases the risk
• Hearing protectors
• cause on artificial hearing loss -gt possible
  increase of accident risk

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How to proceed ?
Risk assessment
Evaluation of the characteristic of hearing
handicap
Corrective actions
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Risk assessment

• Sound direction
• Moving vehicles?
• Possibility to collide ?
• Yes -gt sound location must be evaluated
• Speech intelligibility
• Accidents possible due to missunderstanding
• Yes -gt Evaluate speech intelligibility
• Warning signals present
• Evaluate the audibility of warning signas using
  ISO 7731
• Correct with hearing loss and attenuation of HPDs
• Loss of concentration
• Consequences of wrong manoeuvring ?

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Why correct the audibility of warning signals?
Speech consonants
Speech Consonant
Hearing loss
Normal plug/muffs
Musicians HPD
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Evaluation of Speech intelligibility using ANSI
S3.5
Frequency (Hz) Speech level Noise level Hearing loss HPD atten
250 70.9 70 16
500 86.5 65 16
1000 82.4 45 25
2000 79.4 25 35
4000 65.8 1 45
8000 28.7 -15 50
SII 0.652958
SII depends on speech intelligibility
requirements Easy speech SII gt0.3 Complicated
speech SII gt0.7
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Comparison of audiogram (mean of 0.5- 2 kHz) and
self-evaluated hearing

Normal hearing Mild hearing
Moderate loss
hearing loss
Not enough if elevated accident risk
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Practical example railway yard
Average noise level 85 dB -gt use of HPD mandatory
Noise source Noise characteristics Max level (dB)
Locomotive breaks high frequency noise gt2.5 kHz over 115 dB
Wheel noise in turnings high frequency noise gt2.5 kHz over 115 dB
Typhoons high freq. 0.8 and 1.6 kHz over 115 dB
Typhoons low freq 0. 5 kHz over 115 dB
Pressured air 4 -8 kHz 115 dB
Accident risk caused by moving trains
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Requirement for hearing in railway yard work
Railway Medical Services recommendation
Condition 1 kHz 2 kHz 3 kHz 4 kHz
When work starts 20 20 20 25
When working 25 25
or hears whisper from 5 m with both ears or
hears conversation from 5 m with both ears
Finnish railway requirements
Condition speech freqs. (0.5- 2kHz 3-4 kHz
When entering to work 2o 40
When working 40 60
Speech must be understood from 2-4 m distance
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Problems and solution

• Normal hearing inspection rate is every 3 years
• What to do with those whose hearing is near to
  the limit ?
• Increase the inspection rate -gt expensive
• HPDs increase the effect of hearing loss -gt what
  should be the requirement for hearing when
  wearing HPDs
• Solution Use of level dependent HPDs

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Advantages of the solution

• The sound exposure of railroad yard men could be
  reduced below 85 dB without compromising the
  safety of workers
• No more discomfort due to the high noise levels
• When using hearing protectors, the hearing level
  was always better than without protectors. Thus
  the requirement of hearing was always fulfilled
  at work and very frequent hearing tests were not
  anymore mandatory
• The overall costs of the solution are lower than
  the cost of the previous solution The price of
  electronic muffs was lower than the cost of
  frequent visits to otologists

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Conclusions

• Noise causes an increased accident risk
• The risk is elevated for those with hearing
  handicap
• HPDs may still increase the risk
• Electronic hearing provide a good mean for
  reducing the accident risk for workers with
  hearing handicap
• Evaluation of increased accident risk is
  difficult
• Hearing handicap and working conditions must be
  analyzed in parallel