A U.S. Navy SEAL hopeful and his friend, an off-duty lifeguard, were barreling through underwater drills in a pool just 3.5 feet (1 meter) deep. No one realized anything was wrong until their limp, unconscious bodies were noticed beneath the surface.
This summer, nearly four years after those deaths in a Staten Island pool raised alarms about a little known hazard called shallow-water blackout or hypoxic blackout, New York City is putting up warning signs at all public pools prohibiting prolonged breath holding.
It is part of a movement to raise awareness of the peril that has killed accomplished swimmers and to stop it by banning lengthy breath holding in the nation’s estimated 300,000 public pools.
Shallow-water blackout occurs when a person tries to swim underwater for an extraordinarily long time, typically to build endurance. Swimmers often start by taking multiple deep breaths to go a longer distance underwater, causing their blood levels of carbon dioxide to plunge. Once underwater, carbon dioxide levels fail to rise quickly enough to signal the brain to breathe, oxygen levels fall rapidly, and the swimmer faints underwater and drowns.
“Because the swimmer has a low oxygen level at the time of the fainting, brain damage occurs within a couple of minutes, and death is very likely,” a doctor warns in a recent public service announcement. Afterward, Olympic Gold Medalist Michael Phelps urges coaches to end the risky swim team tradition of marathon breath-holding workouts.
New York City and Santa Barbara, California are among the first U.S. cities to outlaw long breath holding in public pools.