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• 1. What is noise?
• 2. Responsibilities
• 3. Noise assessments
• 4. How should noise be managed?
• 5. What are noise control measures?
  • 5.1 Elimination - new plant and workplaces
  • 5.2 Engineering controls - existing plant and workplaces
  • 5.3 Administrative noise control measures
  • 5.4 Personal hearing protectors
• 6. Audiometric testing
• Appendix 1 - extract from the Workplace Health and Safety Regulation 1997
• Appendix 2 – Obligations under the Workplace Health and Safety Act 1995
• Appendix 3 – Noise hazard identification checklist
• Appendix 4 – Instruments for assessing noise levels
• Appendix 5 – Guidance material
• Appendix 6 – Ototoxins
• Appendix 7 – Acoustic shock
• Appendix 8 – Dictionary

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Appendix 7 – Acoustic shock

Introduction
Acoustic shock symptoms
Sources of acoustic incidents
Factors influencing likelihood of acoustic shock
Reducing the risk and severity of acoustic shock
Managing acoustic incidents

Introduction

7.1 Acoustic shock is a term used to describe the physiological and psychological symptoms a person may experience after hearing a sudden, unexpected, loud sound (referred to as an acoustic incident), via a telephone headset or handset.

7.2 It is not the same as Acoustic trauma, which is caused by very high (greater than 140 dB(C)) peak noise levels. Acoustic shock does not usually result in hearing loss. It can be triggered by sounds with peak noise levels well below those in the National Standard or those currently required by telecommunications regulators.

7.3 Call/contact centre telephone operators are thought to be the type of workers most at risk.²⁹

7.4 Though many acoustic incidents are reported from call centres throughout Australia, only a small proportion result in acoustic shock symptoms. Data from one telecommunications corporation indicates that only about 11% of those who reported an acoustic incident showed any symptoms and only 1.5% developed long-term symptoms.³⁰

7.5 The effect on individuals can vary greatly for the same increase in sound level. Why this is so is not known with certainty and is still being researched. One theory (Patuzzi³¹ suggests that an acoustic incident induces a startle reflex in one of the middle ear muscles and that the sound threshold of this reflex is lowered when the person is under stress. So it is likely that acoustic shock is not due to one single factor, such as the level of sound experienced, but to a combination of physical and psychological stressors in the workplace.

Acoustic shock symptoms

7.6 A person may experience some or all of a number of symptoms that have been grouped into the following three categories:

1. Primary (immediate) symptoms – include but are not limited to:
• a feeling of fullness in the ear;
• burning sensations/sharp pain around/in the ear;
• numbness/tingling/soreness down side of face/neck/shoulder;
• nausea/vomiting;
• dizziness;
• tinnitus and other head noises such as ‘fluttering’;
• hearing loss (in a very few cases); and
• falling to the floor (in extremely rare cases).
2. Secondary symptoms– include but are not limited to:
   • headaches;
   • fatigue; and
   • anxiety.
3. Tertiary symptoms– include but are not limited to:
• sensitivity to previously tolerated sounds (hypersensitivity);
• hyper vigilance; and
• anxiety concerning return to telephone work.

People experiencing such symptoms will respond in different ways. As with other workplace injuries and ill health, some may experience further effects including anger, social isolation, depression and other psychological problems.

Sources of acoustic incidents

7.7 Sources that may cause acoustic incidents include:

1. tones from misdirected facsimiles or modems;
2. transmission faults within the network;
3. faulty customer equipment;
4. faulty telephone or headset equipment;
5. feedback oscillation from some cordless phones;
6. mobile phones when flip cover is closed;
7. customers yelling, blowing whistles, slamming down phones etc.

Factors influencing likelihood of acoustic shock

7.8 The factors influencing the likelihood of an individual receiving an acoustic shock have been suggested by the Australian Communication Industry Forum³² to include the following:

1. number of calls made or received by a person in a working day – increases chance of receiving an acoustic incident;
2. background noise level – operators increase volume control in high background noise;
3. loudness of the received sound – severity may increase with increasing loudness;
4. suddenness of the increase in sound level – may induce startle;
5. duration of the increase in sound level – affects perceived loudness;
6. frequency of sound – 1 kHz to 4 kHz more likely to cause startle;
7. nature and unexpectedness of the sound – may affect perceived loudness;
8. operator’s pre-existing health condition – e.g. middle ear inflammation or previous baro-trauma, from diving or flight depressurisation increases risk;
9. operator’s tiredness, anxiety or stress – stress levels have been shown to have a significant influence;
10. number of previous acoustic incidents – more likely to react if experienced previous acoustic incidents;
11. severity of any previous acoustic shock – may increase the reaction to a new acoustic incident;
12. time since last acoustic incident – greater time less reaction; and
13. whether a handset or headset is used – headset cannot be removed as quickly.

Reducing the risk and severity of acoustic shock

7.9 Possible risk control measures are:

1. using acoustic shock protection devices
   (Note: It is not possible to simply limit the volume of a telephone to a level that simultaneously provides complete protection from acoustic shock while maintaining high intelligibility in all listening situations.);
   
2. reducing the background noise levels in the room by, for example:
• reducing amount of external and building service noise entering the room;
• reducing reverberation (reflections) within the room by use of sound absorbing materials;
• placing acoustic barriers around/between workstations;
• locating photocopiers, printers and fax machines away from workstations;
• training operators to control voice levels;
• encouraging staff not to hold discussions near operators;
3. implementing a procedure for prompt repair of faulty telephone and network equipment;
4. preventing mobile phones from being used in or near call centre areas;
5. training operators in the proper fitting and use of headsets to reduce feedback;
6. improving the work environment and procedures to reduce stress;
7. developing and implementing procedures for managing acoustic incidents and acoustic shocks;
8. providing information and training to operators and supervisors so that they can understand and identify acoustic incidents and acoustic shock symptoms.

Managing acoustic incidents

7.10 A procedure for managing an acoustic incident should at least include the following:

1. the operator should:
• remove the headset immediately;
• move to the ‘timeout’ area;
• report the incident and any symptoms to management; and
• discuss with management the ability to continue work or, where appropriate, relocation to another workstation or referral for medical and/or audiological assessment.
2. management should:
• record and log the incident including possible source;
• check headset and other equipment for faults;
• discuss the incident, any symptoms and ability to continue working with the operator;
• when symptoms persist or are severe, refer the operator for medical and/or audiological assessment and record this referral;
• review the adequacy of noise and stress control measures;
• provide the operator with assistance in rehabilitation and return to work (i.e. an injury management program).

²⁹ and ³⁰ ITU-T Recommendation p.10 (12/98): Vocabulary of terms on telephone transmission quality and telephone sets, Geneva, 1998.

³¹ Patuzzi, R, Acute Trauma in users of Telephone Headsets and Handsets, Proceedings of Risking Acoustic Shock Seminar, Fremantle, 2001.

³² ACIF, DR ACIF G616:2003, Draft guideline: Acoustic safety for telephone equipment, Sydney, 2003.

Last updated 21 August 2008

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