we are scheduled to do one no decomp dive (salt cay) then fly back to grand turk 4 to 5 hours later on a 5 minute flight ( 9 miles) with a ceiling of 1000ft. data per DAN all refer to flights of 2000 -8000 ft. owner of salt cay dive shop said "no problem" because of low ceiling (i am going to ask her if others have done this dive plan before); have email in to DAN for their opinion as well. would appreciate your learned opinion. thanks
flying ( ceiling of 1000ft) after one no de comp dive
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bleeb
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One source of guidance is the NOAA Ascent to Altitude table. You have to use the letter pressure groups found on the NOAA dive tables on the same page. From my quick look, you might be on the edge, depending on exact profiles, gasses, prior dives, etc. Need a bit more information (depth and dive time).
One risk to be considered is if the chances that the pilot might unexpectedly have to go a bit higher. Flying with someone knowledgeable about divers might reduce some of this risk. The shortness of the flight may also reduce the chances of getting all that high.
One risk to be considered is if the chances that the pilot might unexpectedly have to go a bit higher. Flying with someone knowledgeable about divers might reduce some of this risk. The shortness of the flight may also reduce the chances of getting all that high.
I think THIS article is a very good one.
Remember that the DCS risk for a single dive isn't zero, even if you don't fly. The DCS risk for flying after diving is clearly increased -- by how much, given a combination of your particular profile and your particular flight, is not known. You have to make a decision about how much risk you are willing to incur. Having an understanding of the theory behind nitrogen dynamics in the body helps -- a single, short, deep dive loads primarily fast compartments that unload quickly; a shallower dive to the NDLs will mean more loading in slower tissues, which might be more problematic with ascent.
The NOAA tables cited would indicate that a pressure group N diver could get into trouble with a flight in five hours; I don't have the NOAA tables to find out what combination of depth and time would result in that pressure group, but for the RDP (which tends to be more conservative on first dives) you could do that with a 50 foot dive within NDLs.
As the DAN article says, if you want to be perfectly safe, don't dive at all; beyond that, you have to gather the data you can (none of which is going to answer your specific question) and make a risk assessment.
Remember that the DCS risk for a single dive isn't zero, even if you don't fly. The DCS risk for flying after diving is clearly increased -- by how much, given a combination of your particular profile and your particular flight, is not known. You have to make a decision about how much risk you are willing to incur. Having an understanding of the theory behind nitrogen dynamics in the body helps -- a single, short, deep dive loads primarily fast compartments that unload quickly; a shallower dive to the NDLs will mean more loading in slower tissues, which might be more problematic with ascent.
The NOAA tables cited would indicate that a pressure group N diver could get into trouble with a flight in five hours; I don't have the NOAA tables to find out what combination of depth and time would result in that pressure group, but for the RDP (which tends to be more conservative on first dives) you could do that with a 50 foot dive within NDLs.
As the DAN article says, if you want to be perfectly safe, don't dive at all; beyond that, you have to gather the data you can (none of which is going to answer your specific question) and make a risk assessment.
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DAN has done a study on divers on Saba, where after the dive you have to ascent to your hotel, and quite a few fly back to St. Maarten, and found no increase in DCS incidents.
gert7to3
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Would the risk be reduced breathing nitrox?
Also, some dive buddies were pondering this issue here in Chicago. Lake Michigan's altitude is just over 500 Ft above sea level. We have a few buildings here with observation decks around 1000 ft above the ground. It's conceivable that some one could complete a dive then go up another thousand feet in a building. Of course building security might be alerted if you showed up in a dripping wet suit..........
Also, some dive buddies were pondering this issue here in Chicago. Lake Michigan's altitude is just over 500 Ft above sea level. We have a few buildings here with observation decks around 1000 ft above the ground. It's conceivable that some one could complete a dive then go up another thousand feet in a building. Of course building security might be alerted if you showed up in a dripping wet suit..........
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In an ideal world, best to wait the recommended time by your training agency or until your computer's "time to fly" zeroes out. If you can't wait longer, try to mitigate the risks as much as you can.
Nitrox would lessen the nitrogen load, especially if you use air NDLs or dive computer set for air. Regardless of how you do it, don't push any NDLs. Hydrate well. Have the pilot make a slow ascent if air traffic and conditions permit, and try not to get above 1000' as planned. NOAA/US Navy have procedures/tables for this, but their acceptable risk may not be compatible with yours. Incidentally, BSAC tables take flying after diving into consideration, but they are more laborious to use than what most people stateside are used to.
Agree wholeheartedly with TSandM. The risk of DCS after a dive is never zero. I've seen/treated a good number of cases of altitude related DCS, some with diving beforehand and others from very high altitude exposure alone.
Nitrox would lessen the nitrogen load, especially if you use air NDLs or dive computer set for air. Regardless of how you do it, don't push any NDLs. Hydrate well. Have the pilot make a slow ascent if air traffic and conditions permit, and try not to get above 1000' as planned. NOAA/US Navy have procedures/tables for this, but their acceptable risk may not be compatible with yours. Incidentally, BSAC tables take flying after diving into consideration, but they are more laborious to use than what most people stateside are used to.
Agree wholeheartedly with TSandM. The risk of DCS after a dive is never zero. I've seen/treated a good number of cases of altitude related DCS, some with diving beforehand and others from very high altitude exposure alone.
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If it were a sort relatively deep dive I'd have not problem with the flight. If it were a shallow dive out to the no-D limit I'd be more worried. I'd dive the richest nitrox I could and then breath as much oxygen, in water at a stop if possible, on the deck if need be. Two hours of surface Oxygen will take you from Navy Group N to Group A ... OK to fly.
Agree with AFdivedoc in that the conservative way to go is to follow what your training organization told you and wait 12 hours before you fly. However, given the extremely low altitude, you may want to refer to Revision 6 of the U.S. Navy Diving Manual, available for download here. It has a table for flying after diving that's based on your RGD and predicted altitude. See table 9-6 on page 9-61. Note that these are U.S. Navy RGDs based on Navy decompression tables so you'll have to turn your dive into a square-profile dive and use the no-stop and repet tables located on p. 9-62 and 9-63. Remember that these tables are validated on relatively young Navy divers who are in good physical condition.
Also, with the caveat that I've never taken that flight, I'm not sure I'd bank on the altitude being 1000 feet or lower. Are you 100% sure that the aircraft won't go any higher than that? The airport at Grand Turk is all of 13 feet MSL so I suppose it's possible but it seems a bit low for a commercial flight.
Best regards,
DDM
The article Lynn cited above was from a 1995 DAN article. If you do a search on the DAN site for "Flying," it is the first article you get. The second one details the results of their later study and the 2002 workshop consensus results. You have to be a DAN member to download the PDF summary of that workshop. FOr the purposes of this thread, the important paragraph is found on pages 12-13:
Finally, a minimum threshold altitude below which guidelines were unnecessary was
discussed. Although no data were available that specifically addressed the question, a
previous publication had suggested that restrictions were unnecessary below a threshold
altitude of 2,300 feet (701 meters) (15). The U.S. Navy Diving Manual had followed this
recommendation without apparent problem until introduction of the 1999 procedures that
reduced the threshold to 1,000 feet (305 meters) for internal consistency (5). The
workshop participants agreed that 2,000 feet (610 meters) was a reasonable, if uncertain,
threshold, as no problems with 2,300 feet were cited.
discussed. Although no data were available that specifically addressed the question, a
previous publication had suggested that restrictions were unnecessary below a threshold
altitude of 2,300 feet (701 meters) (15). The U.S. Navy Diving Manual had followed this
recommendation without apparent problem until introduction of the 1999 procedures that
reduced the threshold to 1,000 feet (305 meters) for internal consistency (5). The
workshop participants agreed that 2,000 feet (610 meters) was a reasonable, if uncertain,
threshold, as no problems with 2,300 feet were cited.
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