NOISE INDUCED HEARING LOSS (NIHL)SISA PRESENTATION DECEMBER 2007
BY JASON SPARNON, AUDIOLOGIST & JAN MACHOTKA, AUDIOLOGIST
Based on The Australian Safety and Compensation Council (ASCC) WORK-RELATED NOISE INDUCED HEARING LOSS IN AUSTRALIA (APRIL 2006)
Introduction to NIHL
NIHL is entirely preventable but once acquired it is irreversible
NIHL is defined by National Code of Practice (2004) as hearing impairment arising from exposure to excessivenoise at work, and is also commonly known as industrial deafness.
Most recent data (2006) suggests that the number of NIHL represents 19% of all of all disease-relatedclaims made and 3.2% of the total disease and injury related claims.
Causes of NIHL Continuous Noise exposure
The extent of hearing loss increases with time of exposure, and also increases with increasing the intensity of sound levels to which an employee is exposed
National Occupational Health and Safety Commission (NOHSC) standard identifies a continuous exposure level of 85dB(A) over 8 hrs and a maximum peak exposure level 140 dB(C)
Greatest amount damage occurs in the first 10-15 years
Most scientific evidence suggests that the hearing loss does not progress once exposure to noise has discontinued
Causes of NIHL Impulsive Noise
Eg Explosions and Gunfire
Can result in asymmetrical lossVery high sound level eg > 140dB (c)
OtotoxicityExposure to chemicals containing ototoxins
Damage usually associated with combination of ototoxins and noiseEg butanol, toluene, carbon monoxide, solvent mixtures and certain types of medications eg cancer therapy drugs and asprins
Causes of NIHL Compounding factors
Non-work related
Role of co-factors remains poorly understood
Eg Congenital factors and recreational noise
Eg cardiovascular disease, diabetes, and neurodegenerative diseases
Interpreting Audiograms
Audiograms represent the softest sound a person can hear.
Conductive loss–outer or middle ear. Sensorineural loss –inner ear or neural pathway.
Permanent. Often age or noise related. Liability usually based upon sensorineural only
X = left ear. O = Right ear[ or ] denotes bone conduction
Effect of NIHL
NIHLs commonly appear as a sloping loss that is most prominent in the higher frequencies (4k)
Effects speech perception by reducing perception of consonant sounds (p,b,k,s,z etc) needed for speech clarity.
Vowels usually remain intact as there is often good residual hearing throughout the lower frequencies.
Result = clients report that they can hear people speaking but not understand them – the vowels come through clearly but the important consonants are distorted.
Progression of NIHL ( 0 – 5 years)
Normal Hearing= 0%
Mild high frequency loss= 4.6% (40yo), 0% (70yo)
Progression of NIHL (10 – 20 years)
Moderate to severe highfrequency loss= 23.8% (40yo), 18.9 (70yo)
Moderate highfrequency loss= 16.8% (40yo), 11.9 (70yo)
Moderate to Profound highfrequency loss= 67.4% (40yo), 62.5% (70yo)
Progression of NIHL (25 + years)
Calculation of percentage hearing loss (PHL)
Procedure for determine PHL1. Establish hearing threshold levels at defined frequencies: 500Hz, 1000hz, 1500Hz, 2000Hz, 3000Hz, 4000Hz
3. Add up all the percentage hearing losses to give an overall figure
2. Go to look up tables (NAL Report No 118) for each of the frequencies to determine percentage hearing loss (PLH) for each frequency (PLH500, PLH1000…..);
5. This % hearing loss (PLH) determined is used for compensation claims.
4. Appropriate deductions (if any) made
Calculation of percentage hearing loss (PHL)
Deductions from PHL1. Asymmetrical hearing loss
Noise Ordinarily effects bothEars equally.
? – shooter - tumor
= 21.2% = 16.8% (using L levels for R)
2. Non-sensorineural hearing loss
Deductions from PHL (cont’d)Calculation of percentage hearing loss (PHL)
= 61.7 % = 16.9%
3. Age related hearing loss (presbyacusis)
Deductions from PHL (cont’d)
= 23.8% (40yo), = 18.9 (70yo)
Other possible deductions4. Pre-employment hearing loss and Congenital hearing loss
5. Non-work related medical conditions eg diabetes
6. Recreational noise exposure
7. Evidence suggests that noise exposure alone does not usually produce a loss greater than 75 dBHL at high frequencies, and 40 dBHL at lower frequencies.
Statistics of NHIL claims
Jurisdiction Industrial deafness threshold, i.e. when a claim can be made
Comcare 5%.Seacare 10%VIC 10%NSW 6% binaural lossSA 5%WA 10% (Above baseline hearing loss previously
assessed)QLD 5%TAS 5% binaural lossNT 5% whole person impairment (percentage of loss of whole body)
ACT A worker is not entitled to compensation if the totalhearing loss is less than 6%
Table 1. Comparison of Comparison of Workers’ Compensation Arrangements.
Statistics of NHIL claims
1998-99 1999-2000 2000-2001 2001-2002
Claims for NIHL 5755 5280 5185 4510Percentage of Total Disease
Claims
24 22 21 19
Percentage of Total Disease and
Injury Claims
3.8 3.5 3.5 3.2
Table 2. Number of Claims for NIHL
*most recent data available (2006)
Claims in SA decreased from 370 in 1999 to 190 in 2002Although the number of NIHL claims has been reduced, it does not mean that noise induced deafness in Australia has been reduced
Statistics of NHIL claims Figure 1. NIHL Claims per Exposed Employees (2001/2)
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400
600
800
1000
1200
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The highest number of claims are made by: Labourers and related workers, 33% Tradespersons and related workers, 30% Intermediate production & transport workers (plant or machine operators or transport drivers),25%
Statistics of NHIL claims The average cost of workers compensation claims for NIHL in 2001/2 was calculated to be $6711.
Therefore, for Australia, the direct cost of NIHL claims for 2001/2 is calculated to be $6711 x 4510 claims i.e. just over $30 million.
This figure does not include Hearing Aid fittings
Prevention NIHL
Noise Control and Hearing Loss Prevention Program
Establishing a noise control policy and program
Actions to reduce noise exposure eg. Noise insulation, ear protection
Actions to monitor the health of employees eg, annual hearing screening programs
noise control policy and program will enable a systematicapproach to hearing conservation in a company eg purchasing policy on equipment noise levels, mandatory ear protection, training programs for employees
Services provided by Hearing MattersDetermination of NIHL percentage and diagnostic reports.
Referrals to ENT specialists when appropriate
Hearing aid fittings and tinnitus treatment when appropriate
Noise protection equipment
Who is Hearing Matters3 audiologists – Jan, Tara, Jason
Only independent clinic owned by its audiologists
NOT aligned by any hearing aid manufacturer
NOT solely a hearing aid clinic – also diagnostic clinic
Hearing Aids CIC: Mild – Moderate
ITC: Moderate
BTE: Moderate-Severe
Open-Fit: Mild – Severe