An instructor question that is bugging me

[jonnythan]

OK, so the dangerous thing *was* doing a deep bounce dive after a long dive.

Yes that is extremely dangerous.

 

[seadoggirl]

You've got to watch that bouncing. It is a common thing here on the gulf coast. MOst of the divers that do it are very advanced divers. Sometimes they are the ones who forget the rules. It is even scarier when they have new divers on the boat.

 

[TheRedHead]

It's not an "advanced" thing to do and as jonnythan said, dangerous.

 

[Rick Murchison]

Rick
I understand the practice of bounce diving while fishing I’ve done it a many times with not much bottom time before hand. Am I understanding you correctly even with the extended bottom time we all had, a quick bounce afterwards would have little effect on the diver because of the time factor involved? ( Yes he was on the bottom before hand with us)

Nope... if he was on the ten minute dive then he's playing with fire with a bounce shortly after it.

The problem is that after such a borderline NDL dive, there will be bubbles in the blood.. but they're in the venous system and get effectively filtered out by the lungs.
Doing a bounce dive can compress the bubbles and allow them to pass the lungs, so that you suddenly have bubbles in your arteries when you're coming back up... and this can bend you pretty badly.

The only change I'd make to what Jonnythan posted is to replace "will be" with "may be" in the first sentence. The first dive is within the doppler NDL. If a 30 fpm ROA and a 3 minute safety stop were done the asymptomatic bubbles of concern are probably not there (that's the whole point of using the doppler vice the old Navy tables). Now had you stayed for 15 minutes and made a 60 fpm ascent without a safety stop - the NDL for 115 on the Navy table - then your likelihood of having asymptomatic bubbling that a bounce dive can pass through becomes statistically significant.
Rick

 

[jonnythan]

http://gue.com/Projects/WKPP/Decompression/nobounce.html

Here's a good article to read concerning it.

 

[tom wicker]

You've got to watch that bouncing. It is a common thing here on the gulf coast. MOst of the divers that do it are very advanced divers. Sometimes they are the ones who forget the rules. It is even scarier when they have new divers on the boat.

I do understand it is a no no but as Rick said it is mostly done by the spear fisherman on small private sites usually two will drop on a site and check it for fish than they move on to the next where another two will take a turn. I would also like to say I have never seen a beginner on a boat doing this. My concern was the bounce was done immediately after a deep long dive

Nope... if he was on the ten minute dive then he's playing with fire with a bounce shortly after it.

Rick thanks for taking the time to clear this up for me.

http://gue.com/Projects/WKPP/Decompression/nobounce.html

Here's a good article to read concerning it.

Jonny thanks for the read