Edith Cowan University

Research Online Theses: Doctorates and Masters

2003

Emergency vehicle siren noise : a potential for hearing loss Douglas A. Riach Edith Cowan University

Recommended Citation Riach, D. A. (2003). Emergency vehicle siren noise : a potential for hearing loss. Retrieved from http://ro.ecu.edu.au/theses/1294

This Thesis is posted at Research Online. http://ro.ecu.edu.au/theses/1294

Theses

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Title

Emergency vehicle siren noise: A potential for hearing loss.

Name

Douglas A Riach

Student ID number 0975392

University

Edith Cowan University

Degree

Master in Health Science (Occupational Health and Safety)

Supervisors

Lorraine Gray Janis Mussett

Faculty

Communication, Health and Science School of Nursing and Public Health

Date

2003

Copyright and access declaration

This copy is the property of Edith Cowan University. However the literary rights of the author must also be respected. If any passage from this thesis is quoted or closely paraphrased in a paper or written work prepared by the user, the source of the passage must be acknowledged in the work. If the user desires to publish a paper or written work containing passages copied or closely paraphrased from this thesis, which passages would in total constitute an infringing copy for the purpose of the Copyright Act, he or she must first obtain the written permission of the author to do so.

2

ABSTRACT The purpose of this thesis was to critically investigate the noise produced by the sirens fitted to South Australian Police general patrol vehicles and calculate if this noise was of an intensity to cause noise induced hearing loss. Previous studies in Western Australia and in South Australia examined noise

emissions from emergency vehicle sirens for the purpose of selecting the most suitable siren for emergency vehicles, this being the siren emitting the greatest

intensity of sound. This study has researched emergency vehicle sirens from the perspective of employee exposure to siren noise. Noise levels were recorded from inside the police vehicles using a hand held digital sound level meter while the vehicle ••as driven under driving conditions of stationary, 60 kmlh, 80 kmlh and 100 km/h. Noise level readings were taken with the front windows closed and open. South Australian police sirens have three distinct settings with differing noise outputs. The change in vehicle speed was found to affect the noise intensity within the vehicle for all 3 siren types. The peak noise level recorded was with the windows open and the vehicle travelling at 100 kmlh ( 95, 94 and 97 dB(A)

for the three sirens respectively). Closing of the front windows when stationary and when driving at was found to reduce the noise intensity within the vehicle. The greatest reduction from closing the windows was recorded at 100 km/h. This reduction was 11, 9 and 7 dB(Al respectively for the three siren types. Siren type one was the siren normally used by the South Australian police, consequently the majority of exposure by South Australian police employees is to siren type one. These sirens produced a peak internal vehicle noise Intensity of 95 dB(A) at 100 kmlh with the windows open and 84 dB(A) at 100 kmlh with the windows closed. The reading of 95 dB(A) is greater that the 90 dB(A) eight hour continuouo exposure limit set by the South Australian Occupational Health Safety and

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Welfare Act of 1986. The maximum exposure time for unprotected ears using the 90 dB(A) eight hour equivalent continuous A weighted sound pressure level (la,., Bh) would be 2 hours and 30 minutes (150 minutes). The assumption of this study was that noise intensity levels in excess of 90 dB(A) La,. . .., will cause noise induced hearing loss. Therefore the noise intensity recorded from the vehicle siren tests at 100 km/h with the windows open hav6 the potential to cause hearing loss if the duration exceeds 150

minutes. The review of existing records of vehicle pursuits showed that between January i 1998 and December 31 2001, there were three instances where the exposure to siren noise exceeded the 150 minute exposure period. This study found the closing of the windows to reduce the noise intensity at all speeds and all sirens types to below the 90 dB(A) La,., ..,. it is therefore recommended that all police vehicles whilst using the sirens close all windows to reduce the noise intensity within the vehicle.

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DECLARATION

1certify that this thesis does not, to the best of my knowledge and belief:

(i)

incorporate without acknowledgement any material previously submitted for a degree or diploma in any institution of higher education:

(ii)

contain any material previously published or written by another person except where due reference is made in the text; or

(iii)

contain any defamatory material

Signed

~7 D. A. RIACH

I · '1 .

2.-ao

3

5

Acknowledgement The assistance of the South Australian Police, especially the members of the Police Driver Training Unit is acknowledged.

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Table of Content

Page Title page Copyright and access declaration Abstract Declaration of originality Acknowledgement Table of contents

1 2 3 5 6 7

Chapter 1 -Introduction 1.1 History of vehicle sirens 1.2 Problem. 1.3 Significance of study 1.4 Purpose of study 1.5 Study design 1.6 Study limitations 1.7 Research questions 1.8 Thesis assumption 1.9 Definitions and Terms 1.9.1 Noise 1.9.2 Intensity 1.9.3 lmmission 1.9.4 Emission 1.9.5 Decibel scale ... 1.9.6 dB(A} 1.9.7 Eight Hour equivalent Continuous A Weighted (La,..ah} Levels 1.9.8 Tinnitus 1.9.9 Presbycusis 1.9.10 Noise induced hearing loss 1.9.11 Acoustic trauma 1.9.12 Temporary threshold shift 1.9.13 Permanent threshold shift

11 11 12 12 12 13 13 14 14 14 14 15 15 16 16 16 17 17 17 17 17

Chapter 2 - Literature review 2.1 2.2 2.3 2.4 2.5 2.6 2.7

Introduction Structure of the human ear Hearing mechanism of the human ear How noise is transmitted Noise induced hearing loss Significance of noise induced hearing loss Noise measurement

18 18 21 22 23 24 25 7

2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2:19 2.20

Standards and legislation Noise trauma Temporary threshold shift Permanent threshold shift Structural damage Audible noise Ultrasonic and infrasonic sound Sound levels responsible for hearing loss Overseas occupational studies Australian occupational studies Overseas emergency services studies Australian emergency services studies Literature summary

26 26 27 27 27 28 29 30 31 32 32 33 35

Chapter 3- Methodology 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14

Research design overview Validity Reliability Ethical considerations Study setting Vehicles Sirens Vehicle selection Equipment and apparatus noise recording equipment Noise level recording position Noise level testing Tesling protocol Hearing protection Collection of 1998 and 1999 exposure data

37 37 38 38 38 39 40 42 43 44 44 46 46 46

Chapter 4 - Results 4.1 4.2 4.3

Vehicle siren noise levels prior to activation of sirens Noise levels produced by sirens 1998 to 2001 exposure data

48 48 49

Chapter 5- Discussion and findings 5.1 5.2

Research question one Research queslion two 5.2.1 Siren one windows closed 5.2.2 Siren one windows open 5.2.3 Siren two windows closed 5.2.4 Siren two windows open 5.2.5 Siren three windows closed 5.2.6 Siren three windows open

51 51 51 52 52 53 53 53 8

5.3

5.4 5.5 5.6 5.7 5.8

5.9 5.10 5.11 5.12 5.13 5.14 5.15

Research question 3 5.3.1 Siren one 5.3.2 Siren two 5.3.3 Siren three Research question four Research question five Generalisation Transferability Limitations 5.8.1 Traffic noise 5.8.2 Road noise 5.8.3 Vehicle suspension 5.8.4 Wind 5.8.5 Vehicle condition 5.8.6 Soulh Australian Police data Problems with noise standards Presbycusis Tinnitus Extraneous noise Extra auditory effect Suggested further studies Recommendations 5.15.1 Pre employment hearing tests 5.15.2 Exit tests 5.15.3 Hearing tesls

54 54 54 55 55 56 57 57 57 58 58 58 58 59 59 61 61

62 62 62

63 63 63 63

Chapter 6 - Conclusions 6.13 Conclusion

References

65

66

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List of Tables 1 2 3 4 5

Decibel scale Table of test conditions Vehicle noise level dB(A) sirens not operating Siren noise levels Exposure to siren noise recorded from vehicle pursuit data 1998 to 2001 6 Decrease in peak noise pressure dB(A) recorded when retested with the windows closed compared with windows open

15 46 48 49 50 55

List of Figures

1 2 3 4 5 6 7

Structure of the human outer ear Structure of the human middle ear Structure of the human inner ear Police general duties patrol vehicle Astra electronic siren control panel Police vehicle with twin mounted speakers Noise monitor

19 20 21

40 41

42 44

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Chapter 1

INTRODUCTION

Emergency vehicles have sirens, which produce noise. In this introduction the problems of producing excessive noise in the work environment will be identified. The significance of work related, noise induced hearing loss will be stated and the common terminology explained. 1.1 History of vehicle sirens Even before the use of motor vehicles by the South Australian emergency services, warning devises were used to warn people and road users of the approaching emergency vehicle. Prior to the introduction of motor vehicles, horse drawn fire engines were fitted with a bell, which was vigorously rung by a fireman when attending a fire. The South Australian police introduced sirens on police motor vehicles in the 1950's. In the early 1970's sirens were replaced with under the bonnetmounted twin alternating horns, which produced the distinctive "Hee Haw" noises. Although technically a combination of two horns, these devices were commonly referred to as sirens. In early 1980's there was a gradual replacement of the alternating horns with electronic sirens. Presently all South Australian police patrol vehicles and most other emergency services' vehicles are fitted with electronic sirens and roof mounted speakers. 1.2 Problem The Police Service and the other emergency services use sirens on their vehicles to warn road users of the presence of emergency vehicles and to assist with negotiating traffic in urgent situations. The selection of siren types has obviously been related to noise output with an emphasis on warning other drivers of the emergency vehicle approach. At the time of commencing this 11

study the magnitude and the effect of exposure to the siren noise on the oc