Noise and Hearing Loss in the Metal Manufacturing Industry

David WelchGareth John

Alla GrynevychPeter Thorne

Day 1:

•Tour of facility

•Employees interviewed individually- Explanation of project- Interview- Disposable earplug assessment (Veri-Pro)

•Sound level meter measurements

Day 2:

•Hearing tests (otoscopy, tympanometry, and audiometry)

•Dosimetry

Research Protocol

Participants

• 27 Companies

• 160 Employees

• 155/160 Male

• 11/160 Clerical staff (including all 5 females)

Noise Levels

Noise Levels by Company Size(Production workers only)

There was no difference in mean noise level (F(2,135)=1.257, p=0.288)

Noisy Equipment Top Ten Rank Equipment name Mean Leq (dB(A))

1 Air gun 96.9

2 Angle grinder 93.2

3 Pedestal grinder 90.1

4 Saws 88.7

5 Roll former 85.2

6Steelworker -

punch and sheer83.2

7 Linisher 82.5

8 Electric drill 82.1

9 Air compressor 81.8

10 Guillotine 81.6

Impulse Noise Top TenRank Source of impulse noise Mean Lpeak (dB(C))

1Dropping sheet steel onto surface of an ArcWriter machine

141.5

2Sledge hammering a mild steel girder

139.6

3Dropping a steel bar onto a concrete floor from approx 0.5m

138.6

4Dropping a steel bar onto a concrete floor from approx 0.5m

137.5

5Sledge hammering a steel plate on a metal work surface

132.3

6Dropping sheet steel on top of other sheet steel from approximately 1m

131.8

7Hammering (ball-pein hammer) a galvanised steel sheet, on a metal work surface

129.3

8Rolling over a steel girder, on a metal stand

127.8

9 Centre punching a steel girder 125.3

10Dropping a large, hollow, aluminium tube onto concrete floor from approximately 1m

124.7

The mean age was approximately 40 years.

Age (years)

Age (years)

80604020

Number of Participants

25

20

15

10

5

0

Age

Lifetime Work Noise Exposure

Noise Exposure and Age

Hearing Thresholds by Age

0

5

10

15

20

25

30

35

40

45

1 2 3 4 6 8

Frequency (kHz)

Hearing Level (dB HL)

19-30

31-40

41-50

51+

Audiogram Notch

Criteria: 1. Poorer threshold at 4 or 6 kHz than at 2 kHz AND

2. Better threshold at 6 or 8 kHz than at 4 kHz AND/OR

3. Better threshold at 8 kHz than at 6 kHz AND

4. Notch depth >20 dB HL AND

5. Bilateral notches

Audiogram Notch

15 people had bilateral notches according to the criteria

– 0/40 (0%) 18-30 years– 4/39 (10%) 31-40 years– 6/54 (11%) 41-50 years– 5/27 (19%) 51 years or more

Hearing Threshold by Age and Notch

Hearing Threshold by Age and Notch

Hearing Threshold by Age and Notch

Hearing Disability vs Hearing LossAbility to hear in noisy backgrounds was impaired in 25% of participants

0

5

10

15

20

25

30

35

1 2 3 4 6 8

Frequency (kHz)

Hearing Level (dB HL)

Nodifficulty

Moderatedifficulty

Greatdifficulty

Tinnitus

Amount of tinnitus Number PercentPercent

(UK males ages 18-80)

Never 106 66 65

Up to 5 minutes 22 1428

Rarely 18 11

Half the time 1 1 1

Most of the time 5 3 2

All the time 8 5 4

Responses to the question: “In the last 12 months, when you are awake and it is quiet, have you experienced tinnitus . . .?”

Hearing Protection

• 160 workers interviewed• 86 (54%) used earmuffs• 75 (47%) used earplugs• 13 (8%) used either• 12 (8%) used neither

(Of these 12, 5 were production workers with Leq scores : 89.7, 86.6, 84.2, 81.9, and 71.6 dB(A). )

Lifetime Noise Exposure without HPE

(Overall, there was a correlation between age and years spent working in noise without HPE (r=0.480, p<0.001))

Poorly Fitted Earplugs

Older Workers Tended to Fit Earplugs Less Well

Poorly Fitted Earplugs = Poorer Hearing

Conclusions• High noise levels in metal manufacturing

• Half of production workers exposed >85dB(A)

• NIHL was not widespread (15/160 with measureable notch)

• Hearing disability was present in a quarter of workers – but not well linked with hearing loss

• HPE used by almost all production workers

• HPE used always by younger workers (up to approximately 40 years)

• Suggestive of greater awareness of the impact of noise in younger workers

• Poor fitting of foam earplugs was common

• Poor fitting of foam earplugs was associated with NIHL

Acknowledgements• Thanks to the many companies and individuals who gave their time to

participate in this research.

 

• Thanks to Dr John Wallaart, ACC Programme Manager, for his friendly advice and assistance.

• Thanks to John Skudder, ACC Workplace Safety Programme Manager, for his invaluable help in getting the research started and for sharing his knowledge along the way.

• Thanks to Zaneta Schumann, Department of Labour Service Manager, and the Auckland North Office of the Department of Labour for their kind help and interest in the research.

• Thanks to Sperian for the generous loan of the VeriPro system.