To Dive Boat Captains, Dive Shops and the Diving Community – Seismic Survey Info

[njdiver1]

The New Jersey Council of Diving Clubs (NJCDC) tried to discover what would be a safe distance underwater for sport divers from the Marine Geophysical Survey’s or Seismic Survey’s operating area off Barnegat Inlet scheduled to occur from June to August 2015 and ran into some confusing information.

There is very limited research available regarding sport diver safety and distance from seismic testing. Most of the research we found suggested a safe Sound Pressure Level for sport divers of about 145 decibels (dB) referenced (re) to 1 microPascal (µPa). The NJCDC suggests sport divers add a safety factor and stay at this more conservative 145 dB re 1 µPa level at a distance of ~14 kilometers (8.6 miles, 7.5 nautical miles) from the boundaries of the survey area. The assumption is that all divers are wearing a wetsuit hood and a full dry or wetsuit (added safety).

Decibel level in water has a different measurement than in air! “Confusion arises because relative intensities in water are referenced to 1 microPascal whereas sound waves in air are referenced to 20 microPascals. Therefore, relative sound intensity given in dB in water are not the same as relative sound intensities given in dB in air.” For example, a dB level of 145 would not be safe in air while considered acceptable underwater. You can go to DOSITS: How does sound in air differ from sound in water? for a more complete explanation.

Columbia University, Office of Marine Operations, Lamont–Doherty Earth Observatory has been willing to work with the sport diving community and agrees with us and supports a safe level for sport divers at 145 dB re 1 µPa at a minimum distance of ~14 kilometers (8.6 miles, 7.5 nautical miles) from their survey area in their Final Environmental Assessment.

The coordinates we received for the survey area make a narrow rectangle that starts about 15 miles out of Barnegat Inlet to about 50 miles. We requested the coordinates be in DGPS (GPS) as all dive boats use GPS for navigation.

DGPS (GPS)
NW Corner SW Corner
39 43.12’ N, 73 41.00’ W 39 38.00’ N, 73 44.36’ W
NE Corner SE Corner
39 25.30’ N, 73 06.12’ W 39 20.06’ N, 73 10.06’ W

As reported by survey staff, the Lillian Wreck is within the survey area and should be avoided during their operations as the dB level would be dangerous. The NJCDC does not have reliable numbers on the Lillian. The South Ridge Wreck is approximately 12 kilometers (7.5 miles, 6.5 nautical miles) from the inshore edge of the survey area. The East Ridge Wreck is approximately 14 kilometers (8.6 miles, 7.5 nautical miles) and the Sea Hag (North Ridge Wreck) approximately 16 kilometers (10 miles, 8.8 nautical miles) based on our imperfect plotting. There is always the possibility that other dive boats Captains have dive sites that are closer to the survey area. Your plotter or GPS should be able to tell you the distance to the corners of the survey rectangle. Charts for the seismic survey area can be found in the Final Environmental Assessment on pages 4 and 35.

We have been informed that the survey is scheduled for ~36 days, is expected to start about June 1st and should complete by early July, barring unforeseen problems such as weather or mechanical issues with the vessel. Remember that the survey vessel travels at an average of 4.5 knots and could be at the far end of the survey area at the start of your dive and a lot closer later near the end of your dive. Disclaimer – the NJCDC does not claim to be an expert on this issue and is merely reporting what we were told and the results of our research. You will have to make the decision what is a safe distance! This is a first for this issue in our area and except for the help from Columbia University, no government or other agency has taken responsibility for warning divers or seemed to have any idea of a safe distance.


Here are excerpts and website URLs from our research:

Guidance

Recreational divers and swimmers

Frequency range 100 – 500 Hz 501 – 2500 Hz
SPL (dB re. 1 mPa) 145 155


Tolerance Levels

Summary of minimum SPL causing termination of (dive) underwater sound signals in bareheaded divers.

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 Auditory Threshold

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.


SPL = Sound Pressure Level
~ = Approximately
re = Referenced

http://www.dmac-diving.org/guidance/DMAC12.pdf
https://www.cagc.ca/resources/marine_seismic/seismic_vs_sonar.pdf
http://www.dtic.mil/dtic/tr/fulltext/u2/a220935.pdf
http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/2368/11732884.pdf?sequence=1
http://www.thecre.com/sefReports/wp-content/uploads/2012/12/Crum-L.A.-Mao-Y.-1996.-Acoustically.pdf
http://www.dfo-mpo.gc.ca/Library/319590.pdf
http://www.dosits.org/factsandmyths/ (#11)
http://www.nsf.gov/geo/oce/envcomp/...ntain-nj-margin-ea-final-26-may2015-final.pdf
http://www.subacoustech.com/wp-content/uploads/NPLDiverNoisePresentation.pdf

 

[Wookie]

Not all seismic guns are run the same. Pressures of the guns and frequency of the firing all play a role, but I've been in the water with air guns firing as few as 2 miles away, and you certainly feel it in your air spaces (ears and chest), but it isn't what I would consider painful, just remarkable. I have heard air guns going off at 20 miles also. They are barely feelable.

 

[njdiver1]

Not all seismic guns are run the same. Pressures of the guns and frequency of the firing all play a role, but I've been in the water with air guns firing as few as 2 miles away, and you certainly feel it in your air spaces (ears and chest), but it isn't what I would consider painful, just remarkable. I have heard air guns going off at 20 miles also. They are barely feelable.

This letter has been published with the participation and approval of the Columbia University, Office of Marine Operations, Lamont–Doherty Earth Observatory.

 

[lowviz]

...//... relative sound intensity given in dB in water are not the same as relative sound intensities given in dB in air.” For example, a dB level of 145 would not be safe in air while considered acceptable underwater. You can go to DOSITS: How does sound in air differ from sound in water? for a more complete explanation. ...//...

Yet again, sincere thanks for keeping us informed. I'm already booked to be in "the area" while this survey is being conducted.

Most interested in the findings. I'm assuming that it is taxpayer money funding it. Where can one find the results?

 

[njdiver1]

Yet again, sincere thanks for keeping us informed. I'm already booked to be in "the area" while this survey is being conducted.

Most interested in the findings. I'm assuming that it is taxpayer money funding it. Where can one find the results?

US NSF - GEO - OCE - environmental compliance

 

[Wookie]

It was an anecdotal story. I believe you said "very limited research available regarding sport diver safety and distance from seismic testing". Well, I haven't done any research except get in the water multiple multiple times with air guns going off in the vicinity, as well as put 34 passengers in the water also. With air guns firing as close as 2 miles, there were no injuries.

But I'm sure you have as much experience with seismic as I do. I've only worked seismic boats for a few years ad chief engineer, and as a chase boat for a few years more, and as a diver for other years. I'd love to hear your hands on anecdotal stories.