- Altitude diving
Altitude diving is scuba diving where the surface is 300 meters (1,000 feet) or more above
sea level(for example, a mountain lake). [cite book |title=Encyclopedia of Recreational Diving, 3rd edition |last=Brylske |first=A. |year=2006 |publisher= PADI|location=United States |isbn=1878663011 ] cite conference |first=M. |last=Murphey |title=Altitude Diving |booktitle=Advanced Diving: Technology and Techniques |publisher= NAUI|date=1991 |pages=150-56 |location=Montclair, CA ] The U.S. Navy tables recommend that no alteration be made for dives at altitudes lower than 91 meters (300 feet) and dives between 91 meters and 300 meters correction is required for dives over 44 meters sea water (145 feet sea water) (actual depth).cite book |title=US Navy Diving Manual, 6th revision |year=2006 |publisher=US Naval Sea Systems Command |location=United States |url=http://www.supsalv.org/00c3_publications.asp?destPage=00c3&pageID=3.9 |accessdate=2008-04-24 ] Altitude diving is significant in recreational divingbecause the depths and durations used for dives at altitude are different from those used for the same dive profileat sea level.cite journal |author=Morris R, Berthold R, and Cabrol N |title=Diving at Extreme Altitude: Dive Planning and Execution During the 2006 High Lakes Science Expedition |journal=In: NW Pollock and JM Godfrey (Eds.) The Diving for Science…2007 |volume=Proceedings of the American Academy of Underwater Sciences |issue=Twenty-sixth annual Scientific Diving Symposium |date=2007 |isbn=0-9800423-1-3 |url=http://archive.rubicon-foundation.org/7003 |accessdate=2008-06-14 ]
Measurement of Depth at Altitude
Special consideration must be given to measurement of depth given the effect of pressure on gauges.The use of bourdon tube, diaphragm, and digital depth gauges may require adjustment for use at altitude. Capillary gauges have been shown to be a conservative method for measurement of compensated depth at altitude. [cite journal |author=Mackay RS |title=Automatic compensation by capillary gauge for altitude decompression |journal=Undersea Biomed Res |volume=3 |issue=4 |pages=399–402 |year=1976 |issn=0093-5387 |oclc=2068005 |pmid=10897866 |url=http://archive.rubicon-foundation.org/2440 |accessdate=2008-04-24] Modern
dive computers detect changes in altitude and automatically adjust their calculation of a safe decompression regime for a dive at that altitude. If an altitude-aware computer is not used, altitude decompression tablesmust be used.
Decompression when diving at altitude
altitude, atmospheric pressure is lower than at sea level, so surfacing at the end of an altitude dive leads to a greater reduction in pressure and an increased riskof decompression sickness.cite book |title=Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. |last=Brubakk |first=A. O. |coauthors=T. S. Neuman |year=2003 |publisher=Saunders Ltd. |location=United States |isbn=0702025712 |pages=800 ] The dives are also typically carried out in freshwaterat altitude so it has a lower density than seawaterused for calculation of decompression tables. The amount of time the diver has spent at altitude is also of concern as divers with gas loadings near those of sea level may also be at an increased risk. The US Navy recommends waiting 12 hours following arrival at altitude before performing the first dive.
The most common of the modifications to decompression tables at altitude are the "Cross Corrections" which use a ratio of atmospheric pressure and sea level to that of the altitude to provide a conservative equivalent sea level depth. [cite journal |last=Cross |first=E. R. |title=Decompression for high-altitude diving |journal=Skin Diver |volume=16 |issue=12 |date=1967 |pages=60 ] [cite journal |last=Cross |first=E. R. |title=Technifacts: high altitude decompression |journal=Skin Diver |volume=19 |issue=11 |date=1970 |pages=17–18, 59 ] The Cross Corrections were later looked at by Bassett and by Bell and Borgwardt. [cite conference |first=B. E. |last=Bassett |title=And yet another approach to the problems of Altitude Diving and Flying After Diving. |booktitle=Decompression in Depth Symposia |publisher=Diving Science & Technology Corp. |date=1979 |pages=38-48 |location=Santa Ana, California |url=http://archive.rubicon-foundation.org/4230 |accessdate=2008-04-24 ] [cite journal |first=B. E. |last=Bassett |title=Decompression Procedures for Flying After Diving, and Diving at Altitudes above Sea Level |journal=US Air Force Technical Report |volume=SAM-TR-82-47 |date=1982 |url=http://archive.rubicon-foundation.org/4531 |accessdate=2008-04-24 ] [cite conference |first=R. |last=Bell |coauthors=Thompson A.; Borowari R. |title=The theoretical structure and testing of high altitude diving tables |booktitle=Decompression in Depth Symposia |publisher=Diving Science & Technology Corp. |date=1979 |pages=49-79 |location=Santa Ana, California |url=http://archive.rubicon-foundation.org/4230 |accessdate=2008-04-24 ] [cite journal |author=Bell RL, Borgwardt RE |title=The theory of high-altitide corrections to the U.S. Navy standard decompression tables. The cross corrections |journal=Undersea Biomed Res |volume=3 |issue=1 |pages=1–23 |year=1976 |pmid=1273981 |issn=0093-5387 |oclc=2068005 |url=http://archive.rubicon-foundation.org/2748 |accessdate=2008-04-24]
Hennessy formulated that is was possible to convert standard air decompression tables for no-stop diving at altitude or from a habitat based on
phase equilibration theory. [cite journal |author=Hennessy T. R. |title=Converting standard air decompression tables for no-stop diving from altitude or habitat |journal=Undersea Biomed Res |volume=4 |issue=1 |pages=39–53 |year=1977 |issn=0093-5387 |oclc=2068005 |pmid=857357 |url=http://archive.rubicon-foundation.org/2784 |accessdate=2008-04-24]
Bühlmann recognized the problem [cite journal |author=Bühlmann AA |title= [Decompression problems in diving in mountain lakes] |language=French |journal=Schweiz Z Sportmed |volume=37 |issue=2 |pages=80–3; discussion 99–102 |year=1989 |pmid=2799365 ] [cite journal |author=Bühlmann AA |title= [Decompression during lowered air pressure] |language=German |journal=Schweiz Med Wochenschr |volume=114 |issue=26 |pages=942–7 |year=1984 |pmid=6087447 ] [cite journal |author=Bühlmann AA, Schibli R, Gehring H |title= [Experimental studies on decompression following diving in mountain lakes at reduced air pressure] |language=German |journal=Schweiz Med Wochenschr |volume=103 |issue=10 |pages=378–83 |year=1973 |month=March |pmid=4144210 ] and proposed a method which calculated maximum nitrogen loading in the tissues at a particular ambient pressure. [cite journal |author=Böni M., Schibli R., Nussberger P., Bühlmann A. A. |title=Diving at diminished atmospheric pressure: air decompression tables for different altitudes |journal=Undersea Biomed Res |volume=3 |issue=3 |pages=189–204 |year=1976 |issn=0093-5387 |oclc=2068005 |pmid=969023 |url=http://archive.rubicon-foundation.org/2750 |accessdate=2008-04-24] [cite book |title=Decompression-Decompression Sickness |last=Bühlmann |first=A. A. |year=1984 |publisher=Springer-Verlag |location=Berlin New York |isbn=0387133089 ]
Wienke proposed guidelines for decompression diving at altitude in 1993. [cite book |title=Diving above sea level |last=Wienke |first=B. R. |year=1993 |publisher=Best Publishing |location=Flagstaff, AZ |isbn=0941332306 ]
Egi and Brubakk reviewed various models for preparing tables for diving at altitude. [cite journal |author=Egi S. M., Brubakk A. O. |title=Diving at altitude: a review of decompression strategies |journal=Undersea Hyperb Med |volume=22 |issue=3 |pages=281–300 |year=1995 |issn=1066-2936 |oclc=26915585 |pmid=7580768 |url=http://archive.rubicon-foundation.org/2194 |accessdate=2008-04-24]
Repetitive dives should be conducted in the same manner as other dives including "Cross Corrections" for altitude. The US Navy does not allow repetitive diving for surface-supplied helium-oxygen diving and a 12 hour surface interval is required. An 18 hour surface interval is required if the dive requires decompression.
* [http://www.8thelementdiving.com/scuba_math/altitude.php Altitude Diving: Understanding the Tables] - Todd Stedl, PhD and
* [http://faculty.washington.edu/ekay/altitude.html Altitude Exposure after Diving] - Edmond Kay, MD
* [http://www.scuba-doc.com/divealt.html Diving At Altitude] - John Ware, PhD
* [http://www.mindspring.com/~divegeek/altitude.htm At-Altitude Arithmetic] - Larry "Harris" Taylor, PhD
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