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greenturtle
06-23-2008, 03:25 PM
Thought this is good info to share, wasn't aware of the danger.......

WARNING: Shallow water blackout kills
Powered by CDNN - CYBER DIVER News Network
by DAVID WHITING
COSTA MESA, California(18 June 2008) — Free diver Gary Knap takes a series of big breaths, exhaling deeply each time.

Knap plans to try and swim 175 feet underwater in a pool without surfacing. Hyperventilating, many people believe, will allow a person to stay underwater longer.

He pushes off. By the middle of his third lap he notices things start to go black. But he feels OK and keeps swimming.

Seconds later, Knap is seen touching the wall. But his body slides to the bottom of the pool, unconscious. A friend swims down and saves him. Knap doesn't even remember finishing.

Fast forward several years. I'm snorkeling, free diving if you will, at Shaw's Cove in north Laguna Beach.

A sea lion stares at me, her brown eyes big enough to melt any human heart. She curves her body into a crescent, and with a flip she zooms off, leaving a trail of bubbles.

My lungs feel ready to burst. I head toward sky, breaking the surface gasping for air. I fill my lungs to join my new underwater friend, but before too long I have to head up again. I need oxygen, desperately.

Why could Knap swim far longer than I underwater? Why did he quietly slip into unconsciousness while my body's need for air literally forced me to the ocean's surface?

Part of it may be that Knap was in better shape. But the reasons likely have far more to do with the way our bodies function.

More importantly, the answers also may tell what happened on Saturday off Santa Catalina Island when a fit, certified scuba diver and strong swimmer died snorkeling, or free diving in 38 feet of water off his dad's boat.

Register writer Erika Ritchie reported Tim Hatch, 31, of Costa Mesa apparently died from something called shallow water blackout, "a loss of consciousness caused by cerebral hypoxia, or deprivation of oxygen to the brain."

Her report saddened me, and freaked me out. I'm a certified (elapsed) diver and have been snorkeling since I was 11. But I had no knowledge of this thing.

What causes shallow water blackout? Are we all at risk?

I talked to lifeguards, scuba instructors, researched online and interviewed Hatch's father, Bob.

His son was in terrific shape, Hatch told me on Monday. He recalled Tim riding his bike from Costa Mesa to Anaheim Hills for a family get-together, running 10 miles at a stretch twice a week, entering the O.C. Marathon in January, working out at the gym.

Father and son shared a true love of the sea, diving together nearly every weekend for years and visiting such scuba meccas as Cozumel, Aruba and St. Lucia. Hatch said he hoped others could learn from his son's death.


Tim Hatch and his fiancee, Michelle Oyler. Hatch died last weekend while diving at Catalina Island.

I discovered swimmers, surfers, divers, pretty much anyone hyperventilating while in water can drown from shallow water blackout.

It's worth taking a moment to understand:

1. Hyperventilating doesn't supersaturate your lungs or body with oxygen, as some believe. It can't. The body already is saturated with oxygen through normal breathing.

2. Hyperventilating does expel large amounts of carbon dioxide. This may sound good. But it's not. The urge to breathe, in fact, is triggered by high levels of carbon dioxide.

3. When you hyperventilate you can fool your body into thinking it doesn't need to breathe.

PADI, the international scuba diving certification organization based in Rancho Santa Margarita, puts it more bluntly in its textbook:

"Excessive hyperventilation – more than three or four breaths – can be dangerous because you can lower your carbon dioxide levels so far that your body runs out of oxygen before you get the urge to breathe.

"This can lead to sudden unconsciousness – without warning – and drowning. Don't hyperventilate excessively."

Knap knew about shallow water blackouts before he went into the pool that day. A friend of his had died from such a blackout.

But Knap, a chemical engineer who lives in San Clemente, wanted to find out more. He asked a buddy to swim over him while he conducted his experiment. Clearly, a risky move and something that no one should try.

"I always believed that you couldn't get into trouble free diving," Bob Hatch told me.

I had thought the same as Tim's father – until his son taught me a lesson.

shinek
06-23-2008, 03:43 PM
Good lesson for all. As divers, we should all have had some education as to the dangers of shallow water blackout, but how many of us really took it on board. When you're on a diving trip, do you like to snorkel between dives during a surface interval, lunch break or when you've finished diving for the day? A little hyperventilation and down we go to look at those critters there on the reef. Clearly, a little too much hyperventilation and you may stay down there with them for good.

Very sad for the family and friends of the Mr Hatch and they have my condolences, and perhaps we could all use this as a little reminder to avoid such tragedies in our own lives.

greenturtle
06-22-2010, 02:24 AM
Another article on the same subject....


http://news.smh.com.au/breaking-news-national/doctors-warn-of-underwater-blackout-risk-20100606-xmng.html

Doctors warn of underwater blackout risk
DANNY ROSE
June 6, 2010

Swimmers who deliberately hyperventilate before holding their breath underwater are placing their lives at risk, doctors have warned.

Karl Ng said over-breathing was known to suppress the body's natural reflexes and allow a swimmer to feel like they could hold their breath for longer.

It was dangerous, he said, as it carried the significant risk of falling unconscious underwater before a swimmer would feel any "severe urge to breathe".

"They may never get that sense of urgency ... a severe urge to breathe," said Dr Ng from the Department of Neurology at Sydney's Royal North Shore Hospital.

"I don't think any swimming event should be endorsing this practice.

"There is also a risk that people will do this in training when there is nobody around to rescue them."

Dr Ng said people competing in free-dive or other breath hold-type competitions, or recreational swimmers, may experiment with the practice without knowing the risks.

Hyperventilation was a period of rapid and deep breathing, and swimmers may do this deliberately thinking it improves their oxygen intake.

Dr Ng said it only resulted in a temporary lowering of carbon dioxide (CO2) in their blood.

The urge to breathe was triggered by a build-up of CO2, meaning those swimmers could black out from a lack of oxygen before they felt this reflex.

Dr Ng reported two recent Australian cases of such blackouts in a paper, co-written with Kishore Kumar, published in the Medical Journal of Australia.

Two Sydney-based medical students, fit young men who were experienced swimmers, dived into a pool to see who could swim the furthest underwater.

"Both students, having experience with this before, hyperventilated to try to beat each other," Dr Ng said.

"One went just over a pool length, the other went further and both blacked out and had to be rescued by their colleagues."

There were also cases overseas where the practice had resulted in brain injury and drowning, he said.