Altitude diving
Encyclopedia
Altitude diving is scuba diving
where the surface is 300 meters (1,000 feet) or more above sea level
(for example, a mountain lake). 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). Altitude diving is significant in recreational diving
because the depths and durations used for dives at altitude are different from those used for the same dive profile
at sea level.
.
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. Modern dive computer
s 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 tables must be used.
, 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 risk
of decompression sickness
. The dives are also typically carried out in freshwater
at altitude so it has a lower density than seawater
used 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.
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.
Albert A. Bühlmann
recognized the problem and proposed a method
which calculated maximum nitrogen loading in the tissues at a particular ambient pressure.
Wienke proposed guidelines for decompression diving at altitude in 1993.
Egi and Brubakk reviewed various models for preparing tables for diving at altitude.
Paulev and Zubieta have created a new conversion factor in order to make any sea level dive table usable during high altitude diving in 2007.
helium-oxygen
diving and a 12 hour surface interval is required. An 18 hour surface interval is required if the dive requires decompression.
in 1982 in Lago Licancabur
.
The deepest known staged decompression altitude dive was conducted by Nuno Gomes
at Boesmansgat
(Bushman's hole) in South Africa. Conducted at an altitude of approximately 5000 feet (1,524 m), Gomes dived to a depth of 927 feet (282.5 m). Gomes's decompression schedule was calculated as being equivalent for a dive to 1112 feet (338.9 m) if it had been conducted at sea level.
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
where the surface is 300 meters (1,000 feet) or more above sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
(for example, a mountain lake). 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). Altitude diving is significant in recreational diving
Recreational diving
Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...
because the depths and durations used for dives at altitude are different from those used for the same dive profile
Dive profile
A dive profile is a two dimensional graphical representation of a dive showing depth and time.It is useful as an indication of the risks of decompression sickness and oxygen toxicity and also the volume of open-circuit breathing gas needed for a planned dive as these depend in part upon the depth...
at sea level.
Measurement of depth at altitude
Special consideration must be given to measurement of depth given the effect of pressure on gaugesPressure measurement
Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called pressure gauges or vacuum 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. Modern dive computer
Dive computer
A dive computer or decompression meter is a device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.- Purpose :...
s 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 tables must be used.
Decompression when diving at altitude
At altitudeAltitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
, atmospheric
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
pressure is lower than at sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, so surfacing at the end of an altitude dive leads to a greater reduction in pressure and an increased risk
Risk
Risk is the potential that a chosen action or activity will lead to a loss . The notion implies that a choice having an influence on the outcome exists . Potential losses themselves may also be called "risks"...
of decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
. The dives are also typically carried out in freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
at altitude so it has a lower density than seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
used 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.
Decompression tables
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. The Cross Corrections were later looked at by Bassett and by Bell and Borgwardt.Hennessy formulated that is was possible to convert standard air decompression tables for no-stop diving at altitude or from a habitat
Underwater habitat
Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping...
based on phase equilibration theory.
Albert A. Bühlmann
Albert A. Bühlmann
Professor Albert A. Bühlmann was a Swiss physician who was principally responsible for a number of important contributions to decompression science at the Laboratory of Hyperbaric Physiology at the University Hospital in Zürich, Switzerland. His impact on diving ranged from complex commercial and...
recognized the problem and proposed a method
Bühlmann tables
The Bühlmann decompression algorithm is a mathematical model of the way in which inert gases enter and leave the body as the ambient pressure changes. It is used to create Bühlmann tables. These are decompression tables which allow divers to plan the depth and duration for dives and show...
which calculated maximum nitrogen loading in the tissues at a particular ambient pressure.
Wienke proposed guidelines for decompression diving at altitude in 1993.
Egi and Brubakk reviewed various models for preparing tables for diving at altitude.
Paulev and Zubieta have created a new conversion factor in order to make any sea level dive table usable during high altitude diving in 2007.
Repetitive diving
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-suppliedSurface supplied diving
Surface supplied diving refers to divers using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel sometimes indirectly via a diving bell...
helium-oxygen
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...
diving and a 12 hour surface interval is required. An 18 hour surface interval is required if the dive requires decompression.
Pre and Post Dive Ascents
In addition to making depth adjustments using the Cross Conversions, dives at altitude often require pre and post dive altitude ascents which must be taken into consideration. Several methods for performing post dive ascents are used. One is to adjust the dive times needed for an altitude ascent. Another is to use surface intervals to allow for an ascent.Extreme altitude diving
Although no official records are recognized, the highest recorded altitude at which a scuba dive has been conducted was 19300 feet (5,882.6 m), by a team led by Dr Charles Brush and Dr. Johan ReinhardJohan Reinhard
Dr. Johan Reinhard is an Explorer-in-Residence at the National Geographic Society. He is also a Senior Research Fellow at The Mountain Institute, West Virginia, a Visiting Professor at Catholic University, Salta, Argentina, and an Honorary Professor of Catholic University, Arequipa, Peru...
in 1982 in Lago Licancabur
Lago Licancabur
Lago Licancabur is a crater lake in Chile located in the Licancabur volcano in the Antofagasta region, of the Región de Antofagasta, Province of El Loa and close to San Pedro de Atacama as well as very close to the border of Chile with Bolivia...
.
The deepest known staged decompression altitude dive was conducted by Nuno Gomes
Nuno Gomes (diver)
Nuno Gomes is a South African SCUBA diver who holds the official current world record deep dive . He used self contained underwater breathing apparatus to dive to a depth of 1,044 feet...
at Boesmansgat
Boesmansgat
Boesmansgat, also known in English as "Bushman's Hole", is believed to be the third-deepest submerged freshwater cave in the world, approximately 270 metres deep...
(Bushman's hole) in South Africa. Conducted at an altitude of approximately 5000 feet (1,524 m), Gomes dived to a depth of 927 feet (282.5 m). Gomes's decompression schedule was calculated as being equivalent for a dive to 1112 feet (338.9 m) if it had been conducted at sea level.
External links
- Altitude Diving: Understanding the Tables - Todd Stedl, PhD and PADIPadiPadi or PADI may refer to:* Padi, Chennai, India* Padi , a musical group* Paddy field, a type of cultivated land * Professional Association of Diving Instructors, a scuba organization...
Instructor - Altitude Exposure after Diving - Edmond Kay, MD
- Diving At Altitude - John Ware, PhD
- At-Altitude Arithmetic - Larry "Harris" Taylor, PhD