DIVING

Appendix A. Breath-hold Incident Case Reports
Appendix A. Breath-Hold Incident Case Reports
Neal W. Pollock
Hypoxic Blackout
F - 10391
This 30-year-old male was freediving with friends in 10 m (30 ft). The group separated and he was diving alone for some
period of time. His friends subsequently found him floating motionless on the surface close to the boat. He was pulled
onto the boat and resuscitation initiated, albeit unsuccessfully. Autopsy records were not made available.
The details are limited in this unwitnessed event, but the diver’s decision to freedive without close supervision was a
critical problem. Apparently in good health, the most likely explanation was loss of consciousness resulting from hypoxia
of ascent. The victim’s weighting was appropriate for him to remain on the surface after ascent, but with no partner or
team providing close supervision and able to protect his airway, he succumbed.
F - 10401
This experienced and apparently healthy 31-year-old male was spearfishing with a group in approximately 100 fsw (30
msw) near a shipwreck. He descended to recover some equipment. Visual contact was not maintained by the group
on the surface. An unsuccessful search was initiated when the group recognized that he had been down too long. The
victim was subsequently recovered by police divers.
The unwitnessed events make interpretation speculative. Hypoxic blackout does seem to be the most likely issue. It is
possible that exertion at the bottom could have prompted loss of consciousness at that point, but it would be more likely
that blackout occurred during ascent, when oxygen levels fall rapidly through the combined effects of metabolic use and
decreasing ambient pressure. If the diver was not positively buoyant when consciousness was lost then he would sink to
the bottom. Maintaining visual contact could possibly have helped if loss of consciousness occurred later in the ascent,
when skilled divers might have been able to catch the victim and bring him to the surface more quickly.
NF - 10439
This 18-year-old male was spearfishing with a partner at a depth of approximately 65 fsw (20 msw). They began a relaxed
ascent and his buddy noticed the victim slow and then begin to sink. He was able to catch him and bring him to
the surface and to their boat where they were assisted by two other freedivers. The victim regained consciousness, was
transferred to EMS, and made a full recovery.
This case demonstrates how a life-threatening event can be quickly managed by effective close supervision. The aware
and capable partner was able to quickly effect a rescue, undoubtedly the lifesaving action. It was fortunate that the partner
had sufficient reserve to rescue the victim without getting into trouble himself. In this case, having both divers underwater
simultaneously was fortuitous. This is a good example of where a freediver recovery vest could have increased the
margin of safety. Even if the victim’s vest did not inflate immediately upon his loss of consciousness, his partner could
have established a secure hold on the victim and activated one of their vests to speed the ascent, reducing the risk of
a second blackout. It cannot be confirmed, but given the relaxed state of the victim immediately prior to the event, it is
likely that the victim employed excessive hyperventilation, delaying the urge to breathe long enough for hypoxic loss of
consciousness to develop with no warning. Limited hyperventilation is often used to reduce the carbon dioxide content of
the blood to delay the urge to breathe. The cost of this is a reduction in the time buffer between the urge to breathe and
a state of hypoxia that drives blackout. The erosion of the buffer time will not be noticed when all goes well. The problem
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