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 loss

Very high sound level eg > 140dB (c)

OtotoxicityExposure to chemicals containing ototoxins

Damage usually associated with combination of ototoxins and noise

Eg 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 high

frequency 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 PHL

1. 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 PHL

1. 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 deductions

4. 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 loss

SA 5%

WA 10% (Above baseline hearing loss previouslyassessed)

QLD 5%

TAS 5% binaural loss

NT 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 4510

Percentage 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 2002

Although 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)

Num

ber

of

claim

s per

hundre

d t

housa

nd e

mplo

yees

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 Matters

3 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