Report on Decompression Illness, Diving Fatalities and Project Dive

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Section 6 - Breath-Holding IncidentsBehavioral Errors: The clearest example of behavioral errors duringbreath-hold diving is likely the presence of mind altering drugs.Alcohol ingestion preceded at least two of the fatal cases reported.The true impact of the alcohol cannot be determined, but it is possiblethat it contributed to decisions that ultimately contributed to theaccidents.A more elusive behavioral error involves the use of excessive hyperventilationprior to breath-hold. Hyperventilation can dramaticallydecrease the partial pressure of carbon dioxide in the blood. Sincecarbon dioxide is the primary trigger for inspiratory drive, the urgeto breathe is delayed until normal blood levels are restored. Thistranslates into longer breath-hold times. Hyperventilation, however,increases the body’s oxygen stores only slightly. The longerbreath-hold times will result in the oxygen partial pressure in theblood falling below normal (hypoxia). Problematically, hypoxia providesa surprisingly weak trigger for the inspiratory drive. A diverwho hyperventilates too much may fall unconscious due to hypoxiawithout ever being aware of an urge to breathe. This is known ashypoxic loss of consciousness (HLOC).A further complication of breath-hold diving to depth is that theincreased pressure with depth compresses the gas in the lung andeffectively increases the partial pressure of oxygen in the blood. Theproblem here is the reversal of the effect as the diver surfaces. Theoxygen partial pressure is reduced much faster than by consumptionalone as the ambient pressure is decreased. Unconsciousnesscan develop rapidly in the final part of the ascent, when the relativerate of pressure decrease is greatest. This phenomenon is referred toas shallow water blackout.Breath-hold divers who choose to use hyperventilation normallyexperiment to try and predict their personal safe limits. However, ifused too aggressively, even small increases in dive depth, exertionor breath-hold duration can produce a very hazardous situation.Excessive hyperventilation contributing to HLOC or shallow waterblackout may represent the underlying cause of death in many ofthe breath-hold fatalities with no other apparent explanation. This isvery difficult to document in most cases, but it is a risk that canclearly be reduced by conscious choice.The final behavioral error to be mentioned is the failure to ditch aweight belt when appropriate. There are several cases of fatality victimsbeing retrieved with weight belts still attached. It is difficult inmost to know if hypoxia impaired the ability to respond. At leastone case, though, highlights a lack of thought during a stressfulevent. One of the non-fatal cases involved an exhausted breath-holdDAN’s <strong>Report</strong> on Decompression Illness, Diving Fatalities and Project Dive Exploration: 2005 Edition 97
Section 6 - Breath-Holding Incidentsdiver who still was still wearing his weight belt when help arrivedat his surface position. The victim described his condition immediatelyprior to rescue as impending blackout. Ditching the belt at anypoint in the development of this incident would probably have beenan effective self-rescue.Equipment Problems: The records contain at least one case of adiver who became unconscious as he neared the surface duringascent from a breath-hold dive and quickly sank beyond the pointat which those on the surface could reach him. Weighting duringbreath-hold diving may be considered to optimize performance, butthe more important consideration of weighting is for safety. Abreath-hold diver should be slightly positively buoyant close to thesurface to minimize the risk of sinking should a problem develop inshallow water.Impaired Health and Fitness: The available records contain at leastthree fatal cases involving heart trouble, three involving seizure andat least one involving inadequate fitness that resulted in a doublefatality. The demands of breath-hold diving can be significant, particularlyin open water where rough water or currents may have tobe overcome. Inadequate fitness reserves may leave breath-holddivers unable to cope with normal challenges that can arise.6.4 SummaryWhile a small number of high profile fatality cases may be widelyreported, limited information is available for most breath-hold accidents.Non-fatal incidents are rarely reported. Data from both fataland non-fatal cases would provide valuable information to improveawareness, facilitate training and promote procedural evaluations.This is the first annual report to incorporate a review of breath-holdincident data. Breath-hold incident data reviews will be a standardcomponent of future annual reports.98DAN’s <strong>Report</strong> on Decompression Illness, Diving Fatalities and Project Dive Exploration: 2005 Edition
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1. INTRODUCTIONDivers Alert Network
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Section 1. Introduction1.3 Diving F
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2.2 PDE 2003This report includes da
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Section 2 - Project Dive Exploratio
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Figure 2.4-2 describes the breathin
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Figures 2.5-2 and 2.5-3 indicate th
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Towards the end of the series, PDE
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Case #2The diver was a 29-year-old
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3. Dive InjuriesSection 3 - Dive In
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Page 52 and 53: Section 3 - Dive Injuries3.3 Physic
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Page 68 and 69: 4. Dive FatalitiesDeath while divin
Page 70 and 71: Section 4 - Dive FatalitiesFigure 4
Page 74 and 75: Section 4 - Dive FatalitiesOur data
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Page 84 and 85: Section 4 - Dive FatalitiesConclusi
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Page 92 and 93: 6. Breath-HoldingIncidents6.1 Intro
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Page 134 and 135: Glossarymatical models to compute d
Page 136 and 137: GlossaryRepresentative SampleA grou
Page 138 and 139: 2004 Publications2004 PublicationsR
Page 140 and 141: NotesDAN’s Report</strong
Page 142: The only 24-hour, worldwide dive em
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