Noise-Induced Hearing Loss
The noise-induced hearing loss (NIHL) regulations apply in all workplaces where a person at work may be exposed to a noise level above 85 A-weighted decibels (dB[A]). Such a noise level is determined by evaluating the exposure over a period of eight hours. Therefore, if a person is exposed to high noise levels for short durations, the average exposure over eight hours may well be below the noise rating limit. The way in which such exposure is determined in practice is by means of a specific measurement by an approved inspection authority.
For details on approved inspection authorities who may perform noise measurements, visit http://www.labour.gov.za/DOL/downloads/documents/useful-documents/occupational-health-and-safety/aiapamphlet.pdf
The regulations require an employer to formally assess the workplace for potential exposure above the noise rating level of 85 dB(A) at least once every two years. Such an assessment should consider the potential sources of noise and the extent to which persons may be exposed. Other factors to include in the assessment would be the work processes and whether failure of noise control measures can be expected.
In terms of the diving environment, the following are common sources of loud noises:
- Compressor rooms are notorious for their high levels of noise and cylinder filling stations may likewise be noisy.
- Depending on the machinery used and the activities performed, workshops can be quite noisy.
- The air flow into hyperbaric chambers from high pressure gas banks have been measured as exceeding 100 dB(A).
- The peak noise levels that are measured in diver helmets (especially the free-flow type used for diving in contaminated waters) have been measured to exceed 110 dB(A).
- Commercial divers may be exposed to a range of noisy underwater tools where levels exceeding 170 dB have been measured.
- Boat engines may also cause noise exposure above the exposure limit.
Whenever the assessment by the employer determines that a person may be exposed above the noise rating limit, formal measurements and monitoring of noise exposure are required. The details of the noise monitoring required are described in the regulations, including references to the South African Bureau of Standards (SABS) documents that prescribe certain standards. The noise monitoring may only be performed by an approved inspection authority and this must also be performed every two years.
The records of assessments of potential exposure and of formal noise monitoring must be kept for a period of 40 years.
All areas with noise levels above the noise rating limit must be clearly demarcated with signs indicating that the area is a noise zone. No person may be allowed to enter such an area without wearing appropriate hearing protection. In addition, attempts should be made to reduce the noise levels by means of engineering or administrative control measures (e.g. the rotation of workers).
Persons who are exposed to noise levels above 85 dB(A) are required to take part in a medical surveillance programme, which will screen them for possible effects of exposure to noise. This would include the performance of a number of different audiogrammes (at baseline, followed by regular periodical audiogrammes as prescribed and exit audiogrammes). Not just any medical person may perform the medical surveillance – the regulations specifically state that it must be performed by someone with a qualification in occupational health; an ear, nose and throat (ENT) specialist; or an audiometrist. The records of the medical surveillance must also be kept for a period of 40 years.
All persons who are required to work in a noise zone are required to receive training on aspects related to the noisy work. The contents of the training (as listed in the regulations) include the contents of the regulations; the sources of noise exposure; the health effects and safety risks associated with noise; precautions to be taken by the workers (including how to wear and maintain hearing protective devices and the limitations to their use); the need for medical surveillance; and how to report problems. Additional aspects that form part of the training would be related to a number of duties and responsibilities the regulations place on workers.
Although noise exposure could be measured with relative ease both above and below water, the negative effects of underwater exposures are a bit more difficult to predict or model. Even exposures at levels exceeding 85 dB underwater may not always lead to hearing loss due to various dampening factors. This includes splinting of the tympanic membrane by water; the increased density of gas in the middle ear space (depending on the depth of the dive); and the gas mixture (i.e. gas mixtures other than air such as heliox or trimix used by recreational or commercial divers), all of which will have an effect on the auditory perception of the diver. These factors make it exceedingly difficult to model a noise dose-response curve in this environment. An additional complication is that occlusive earplugs are incompatible with diving, so that personal hearing protection strategies are not available to divers. This leaves engineering and administrative measures as the only practical options.
Notwithstanding the difficulty in modelling noise exposure of or providing personal hearing protection for divers, typical patterns of NIHL are frequently identified in divers (especially working divers). Accordingly, as we stated in the previous article in this series, some of them may qualify for compensation.
In conclusion, all diving operators and employers of divers should formally conduct a noise risk assessment as prescribed in the regulations and take further action (noise monitoring, medical surveillance, etc.) if noise exposure above the legislated limit is present.
- The Noise Induced Hearing Loss Regulations, published under section 43 of the Occupational Health and Safety Act, 1993.
- Goplen, F.K., Aasen, T., Grønning, M., Molvær, O.I. & Nordahl, S.H. Hearing loss in divers: a 6-year prospective study. Eur Arch Otorhinolaryngol; 2011 Jul; 268(7): p979-85.
- Skogstad, M., Haldorsen, T., Arnesen, A.R. & Kjuus, H. Hearing thresholds among young professional divers: a 6-year longitudinal study. Aviat Space Environ Med.; 2005 Apr; 76(4): p366-9.
- Skogstad, M., Eriksen, T. & Skare, Ø. A twelve-year longitudinal study of hearing thresholds among professional divers. Undersea Hyperb Med.; 2009 Jan-Feb; 36(1): p25-31.
- Talmi, Y.P. Barotrauma-induced hearing loss. Scand Audiol; 1991; 20(1): 1-9.
- Molvaer, O.I. & Lehmann, E.H. Hearing acuity in professional divers. Undersea Biomed Res.; 1985; 12(3): p333-349.
- Molvaer, O.I. & Albrektsen, G. Hearing deterioration in professional divers: an epidemiologic study. Undersea Biomed Res.; 1990 May; 17(3): p231-46.
- Curley, M.D. & Knafelc, M.E. Evaluation of noise within the MK 12 SSDS helmet and its effect on divers’ hearing. Undersea Biomed Res.; 1987 May; 14(3): p187-204.
- Summitt, J.K. & Reimers, S.D. Noise: A hazard to divers and hyperbaric chamber personnel. Aerosp Med.; 1971 Nov; 42(11): p1173-7.
- Ross, J.A., Macdiarmid, J.I., Dick, F.D. & Watt, S.J. Hearing symptoms and audiometry in professional divers and offshore workers. Occup Med (Lond).; 2010 Jan; 60(1): p36-42.
- Smith, P.F. Toward a standard for hearing conservation for underwater and hyperbaric environments. J Aud Res.; 1985 Oct; 25(4): p221-38.
- Molvaer, O.I. & Gjestland, T. Hearing damage risk to divers operating noisy tools underwater. Scand J Work Environ Health; 1981 Dec; 7(4): p263-70.
- Hughes, K.B. Sensorineural deafness due to compression chamber noise. J Laryngol Otol.; 1976 May 1; 90(8): p803-7.
Hi , I may have missed it as I was away in China until recently, Please let me know if there have been any similar as above studies relating to "Tinnitus" and it's potential affects to divers. I have a student diver with the symptoms but could not define any negative effect under water in confined water sessions so far, and intend continuing with open water qualification. His medical hearing tests have been normal. What now?