There is a risk of damage to divers' hearing due to underwater occupational noise exposure and there are no widely accepted noise exposure limits for underwater use. A new underwater hearing threshold hearing curve is established using 54 normally hearing sports divers. The results show that underwater hearing threshold is less sensitive in water than in air by 22 dB at 0 5 kHz and 60 dB at 4 kHz The results mean that the A-weighting scale, the well established decibel unit used to describe noise exposure limits in air, is not suitable for underwater use A "W-weighting" scale equivalent to the A-weighting scale is developed, and noise exposure limits are proposed for the prevention of occupational noise induced hearing loss underwater.
The hazards to hearing from occupational noise in the industrial situation are well recognised and described in National and European legislations Such hazards must be reduced by engineering noise control and/or personal hearing conservation programmes to below acceptable limits Unfortunately, there are currently no widely accepted noise exposure limits applicable for underwater use Professional divers are regularly exposed to intense noise which can reach sound pressure levels (SPL) above 200 dB (re 20 Val. Underwater noise may originate from equipment operated by the divers themselves such as jet cleaning tools, rock drills and stud guns or from transmitted sounds such as sonar
As in air, the effects of exposure to occupational noise underwater may result in temporary or permanent sensorineural hearing loss Additionally, high exposure levels may produce vertigo, nausea, and even vomiting Vertigo underwater may cause the diver to become disoriented, and swim downwards instead of towards the surface or he may panic and surface missing important decompression stops More seriously he may vomit into his mouth piece or mask, which can be fatal. Montague and Strickland (1961), Molvaer (1981), and Smith (1988) found that exposing divers to noise from modern underwater tools or tones of 130–190 dB SPL, cause temporary hearing threshold shifts of 10-40 dB, nausea and vertigo
The maximum permissible exposure to an equivalent continuous nolse level (Laeq) in air without using hearing protection is 90 dB(A) for 8 hours (IS0 1999, 1990) The current noise exposure limits are based upon the A-weighting sound level scale, which in turn is related to the threshold of hearing The most efficient approach to setting up noise exposure limits is the transposition of the current noise exposure limits from air to underwater This can be achieved with knowledge of hearing thresholds in the two media
Underwater hearing thresholds have been studied by Sivian (1943), Ide (1944), Reysenback de Haan (1956), Hamilton (1957), Wainwright (1958), Montague and Strickland (19611, Brandt and Hollien (1967), Hollien and Brandt (1969), Smith (1969), and others These studies report widely scattered values for underwater hearing thresholds and have been reviewed in detail by Al-Masn et al (1993)