For divers in the area of the operating airgun array:
UNDERWATER NOISE AND THE CONSERVATION OF DIVERS' HEARING: A REVIEW Volume I October 1989
In conclusion, the combined evidence of our work and these two other suprathreshold investigations
strongly suggest that the current underwater sound pressure level exposure limits are invalid and err on the unsafe side by significant amounts.
http://www.dtic.mil/dtic/tr/fulltext/u2/a220935.pdf
Limits for underwater noise exposure of human divers and swimmers Steve Parvin
Summary
Bio-effects of low frequency underwater sound (100 to 500 Hz)
SPL
dB re.1 μPa
| Effect
100 to 500 Hz
|
184 +
| Based on animal models liver haemorrhage and soft tissue damage are likely.
|
170+
| Tolerance limit for divers and swimmers. Sound causes lung and body vibration.
|
148 -157
| The loudness and vibration levels become increasingly aversive. Some divers will contemplate aborting an open water dive.
|
140 -148
| A small number of divers rate the sound as very severe.
|
136 -140
| The sound is clearly audible. The majority of divers tolerate the sound well with only Slight aversion.
|
130
| Divers and swimmers able to detect body vibration
|
80 -100
(SPL = Sound Pressue Level)
| Auditory Threshold
|
Guidance
Recreational divers and swimmers
Frequency range
| 100 500 Hz
| 501 2500 Hz
|
SPL (dB re. 1 mPa)
| 145
| 155
|
Parvin S J, Cudahy E A and Fothergill D M. Guidance for diver exposure to underwater sound in the frequency range from 500 to 2500 Hz. Proceedings of Undersea Defence Technology, La Spezia, Italy, 2002.
http://www.subacoustech.com/wp-content/uploads/NPLDiverNoisePresentation.pdf
Recreational scuba divers' aversion to low-frequency underwater sound
D. M. FOTHERG1LL, .1. R. SIMS, and M. D. CURLEY
Our data suggest that LFS exposures up to 145 dB re I µPa at frequencies between 100 and 500 Hz will have minimal impact on the recreational diver.
As a conservative measure, the consensus decision of scientists involved in the LFS program was that the maximal SPL intensity for the guidance should be set at 145 dB re 1 µPa (20).
Copyright C 2001 Undersea and 1 lyperbaric Medical Society, Inc.
(LFS= low-frequency underwater sound)
http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/2368/11732884.pdf?sequence=1
Safe Diving Distance from Seismic Surveying Operations
DMAC 12 Rev. 1 July 2011
Supersedes DMAC 12 which is now withdrawn
Background
Guidance Note DMAC 012 was issued in 1979 after consideration of the knowledge concerning the effects of seismic operations on divers in the water at that time. Over the last 30 years DMAC has discussed this guidance on a number of occasions and attempted to gain further knowledge from reports of diver/seismic operation interaction. Some of the few available reports have added to our knowledge.
1 Seismic airgun activity results in the transmission of acoustic waves through the water which the diver experiences as a noise analogous to a piling hammer. Multiple reflections of this acoustic wave from the sea surface, seabed and other structures may result in this sounding like a low frequency rumble.
2 The intensity of the sound experienced by the diver is principally dependent on the power of the seismic airgun array and the distance between the diver and the seismic airgun, but other factors may have important effects. These factors include the water depth at which the seismic activity takes place, the presence of thermoclines (layering due to changes in temperature), the depth of the diver versus the depth of the thermocline, bottom conditions, salinity and the sea state.
3 Not all seismic surveys are the same (e.g. ocean bottom cable surveys (OBC), streamer(s), vertical seismic profile surveys (VSP), site surveys, etc.) and there are differences in the types and purpose of source arrays used around the world, e.g. airguns, boomers, sparkers, etc.
4 The multiple factors involved make it difficult to determine a safe or tolerable distance, particularly in shallow water, without performing communication exercises between seismic and diving operations.
5 The duration of a divers exposure may limit tolerance.
Guidance
1 Where diving and seismic activity will occur within a distance of 10 kilometres, a joint risk assessment should be conducted, between the operators involved and the seismic and diving contractors in advance of any simultaneous operations.
2 Where possible, plans should be made to avoid overlapping seismic and diving activities. Where this is not possible, the activities should be prioritised and a simultaneous operations (SIMOPS) plan developed.
3 The parties should perform a communication exercise or test at the start of simultaneous operations to determine the acceptable safe distance for the local conditions. Starting at a distance of 10 kilometres, the seismic source array will be gradually ramped up, and the seismic vessel gradually moved closer to the diving operation, with constant communication between the diving supervisor and the seismic party manager. (Note: seismic source ramp ups are now the industry standard in all situations.)
4 The minimum safe distance, as determined from the testing outlined above, should not be compromised by either party.
5 There should be regular contact (at least daily) between the seismic vessel and diving vessel so that both are aware of each others work program for the day.
http://www.dmac-diving.org/guidance/DMAC12.pdf
10 kilometers = 6.21371192 miles = 5.39956803 nautical miles
Acoustically enhanced bubble growth at low frequencies and its implications for human diver and marine mammal safety
(Lawrence A. Crum and Yi Maoa)
In general, it was discovered that relatively large SPLs are required to induce rapid or significant ~and thus dangerous! gas bubble growth, unless the degree of dissolved gas supersaturation was quite large. Under normal conditions, enhanced diffusion produced by sonars and other high intensityacoustic projectors pose little risk to divers and marine mammals unless they are in the immediate vicinity of the source. However, the contraindications for their use are as follows:
(1) If the local SPL at the site of the diver or marine mammal is in excess of 210 dB ~re:1µPa!, gas bubble growth is predicted to occur within a period of a few seconds. Furthermore, bubble growth to sizes large enough to block capillaries and other small blood vessels is expected with its associated bioeffects.
(2) If a diver, breathing compressed gas, experiences rapid depth ascents such that the local body fluid is supersaturated with gas, considerably lower SPLs may result in conditions favorable for bubble growth.
http://www.thecre.com/sefReports/wp-content/uploads/2012/12/Crum-L.A.-Mao-Y.-1996.-Acoustically.pdf
Far-field Measurements of Seismic Airgun Array Pulses in the Nova Scotia Gully Marine Protected Area
CONCLUSIONS
From this study, several conclusions can be drawn:
The highest average sound pressure level (RMS) measured in the Gully MPA was 145 dB re 1μPa at 90 m depth, 50 km from the seismic array. This sound level was measured within the Gully Whale Sanctuary while the seismic vessel was surveying the western portion of the exploration block. It was estimated that sound levels in the Whale Sanctuary would have been higher, between approximately 153 and 157 dB, when the vessel was at its closest approach to the Gully in the eastern portion of the survey block. The worst case sound level at the Gully MPA boundary, i.e., 0.8 km from the source, can be estimated from the extrapolation of near-field measurements in Austin and Carr (2005) to be approximately 178 dB, 14 dB higher than predicted in Moulton et al. (2003).
http://www.dfo-mpo.gc.ca/Library/319590.pdf
