OOA at 75'

[heinz57zuk]

New diver here. Let me start by saying that I love these discussions. They are truly educational and a must read. Being that I am a new diver, and freshly out of the classroom training, I have two separate schools of thougt on the issue of deep water safety stops:

Number one: As I understand, the more depth you descend to and the length of time at depth determines your saturation level based on recreational dive planners or dive computers. So, using common sense, which I have so little of, it would mean to me that your nitrogen saturation would only increase after a deep dive and getting to a more shallow dive profile while not exceeding your maximum ascent rate would be beneficial. Of course, your 3-5 minute safety stop at 12-20 ft. should always be mandatory if any possibility exists that this can be safely accomplished.

Number two: Since the saturation levels of nitrogen are directly affected by depth and time, and the off-gassing of nitrogen is also affected by the time and depth, it makes perfectly good sense to make safety stops at incremental depths to allow the slow and steady (and it would seem safer) off-gassing to occur.


Am I correct to make these theories?

 

[Scott L]

I'll read the article again, and maybe we can discuss it on a thread on Basic Scuba - but I am not going to stop doing them just because my computer is not set up to suggest them. I think they are a very good idea...!

I agree. How would your computer know the difference between a deep safety stop and a planned stop at that depth for any reason...

 

[Scott L]

New diver here. Let me start by saying that I love these discussions. They are truly educational and a must read. Being that I am a new diver, and freshly out of the classroom training, I have two separate schools of thougt on the issue of deep water safety stops:

Number one: As I understand, the more depth you descend to and the length of time at depth determines your saturation level based on recreational dive planners or dive computers. So, using common sense, which I have so little of, it would mean to me that your nitrogen saturation would only increase after a deep dive and getting to a more shallow dive profile while not exceeding your maximum ascent rate would be beneficial. Of course, your 3-5 minute safety stop at 12-20 ft. should always be mandatory if any possibility exists that this can be safely accomplished.

Number two: Since the saturation levels of nitrogen are directly affected by depth and time, and the off-gassing of nitrogen is also affected by the time and depth, it makes perfectly good sense to make safety stops at incremental depths to allow the slow and steady (and it would seem safer) off-gassing to occur.


Am I correct to make these theories?

Sounds good to me. You been reading GUE material?

 

[TSandM]

Heinz, your two theories are brief descriptions of the two approaches to decompression. The approach that considers only dissolved gas says that you offgas faster when the gradient of concentration between your blood and the gas you are breathing is greatest, and therefore, you should get as shallow as possible as quickly as possible, and stay there until you have offgassed enough to surface. This is often referred to as a "pure Buhlmann" approach.

The approach that thinks about bubble formation wants the diver to stay deeper, longer, and not to push the gradient, as that encourages bubble formation and enlargement. Bubble models results in deeper stops and a more gradual curve to the ascent profile.

Nobody really knows which is more "valid". There is not a whole lot of money in research on this, either. What we do know is that people use both approaches, and hybrids of them, every day, and most of those people don't get symptomatic DCS. In a terrible emergency, it is probably a very reasonable strategy to switch to a Buhlmann approach and get as shallow as you can, as quickly as is safe, as shallow is better for getting help and extends gas supplies. But it will probably increase your risk of DCS.

A different approach is to plan your gas reserves so that you can execute the ascent profile you prefer, no matter what happens underwater. That is a very conservative point of view, and one I prefer.

 

[dumpsterDiver]

Some good points, thanks.

I think the real life challenge is discussing all the minutae of solid dive team planning and execution with an insta-buddy who just wants to jump in the water. Especially when I turned out to be over-confident in his skill set. Remember, it was the MOST EXPERIENCED diver who went OOA of on this dive. Hmmm...

Many thanks, all.

VI

If the guy was very experienced and was over confident, attempting to discuss all the "minutae" of the dive would probably have accomplished nothing. He knows it all and has heard it before.

If I were depending on another guy to save my butt on a 100 ft night dive, I think I would be checking HIS air for ME. Of course, I don't dive that way. I rely upon a pony bottle, so if somebody does something really stupid, it will most likely be their ass on the line, more so than mine. I think the lesson should be, don't bet your life on another diver, regardless of the experience level, unless maybe you have to.

 

[dumpsterDiver]

Heinz, your two theories are brief descriptions of the two approaches to decompression. The approach that considers only dissolved gas says that you offgas faster when the gradient of concentration between your blood and the gas you are breathing is greatest, and therefore, you should get as shallow as possible as quickly as possible, and stay there until you have offgassed enough to surface. This is often referred to as a "pure Buhlmann" approach.

The approach that thinks about bubble formation wants the diver to stay deeper, longer, and not to push the gradient, as that encourages bubble formation and enlargement. Bubble models results in deeper stops and a more gradual curve to the ascent profile.

Nobody really knows which is more "valid". There is not a whole lot of money in research on this, either. What we do know is that people use both approaches, and hybrids of them, every day, and most of those people don't get symptomatic DCS. In a terrible emergency, it is probably a very reasonable strategy to switch to a Buhlmann approach and get as shallow as you can, as quickly as is safe, as shallow is better for getting help and extends gas supplies. But it will probably increase your risk of DCS.
A different approach is to plan your gas reserves so that you can execute the ascent profile you prefer, no matter what happens underwater. That is a very conservative point of view, and one I prefer.

I agree with all of this, I would have hauled butt (maybe 60 feet per minutes) to around 35 feet, then STOP. I know that I can haul a neutrally bouyant diver from 35 feet to the surface with zero air (while exhaling one big breath if I am calm).

I would stop at around 35 feet, check my air supply and try to determine if we could safely and calmly hang at that depth for a couple of minutes. If there were coordination issues, bouyancy issues, an overly stressed diver, then I would just make a direct and hopefully slow ascent.

 

[Edward3c]

Comments/thoughts.

Some thoughts:

buddy checks - are for buddies. I neglected to do a buddy check with MY buddies. This could have caused confusion with a panicking diver unfamiliar with long hoses. Although Diver B claims they did a "quick" buddy check and SPGs read 3000psi I question this. A more thorough buddy check would have been explicit in revealing my nitrox mix and MOD of 103'.

If I’m diving in a three, which I hate, the buddy check is between all three not just two and a add-on.

complacency - although a 100' cold water night dive is not "routine," it is not something I stress about. I should have been more inquisitive with this experienced diver in a new drysuit. I let my familiarity with the person stand in for familiarity with his skills as a diver which I, in retrospect, didn't really have.

Unless a site has been dived during daylight hours your adding to the task loading by including darkness.

complacency - we had a dive plan and my buddy was blowing it hard. The onus was on me to correct that. He of course was burning through MY air reserve and I was not cognizant of that.

Did the dive plan include the gas level for leaving your max depth, you planed a square profile?

long hose - despite the lack of pre-dive brief on usage, the use of a 7' primary hose and bungied backup was facile and made easy a potentially stressful situation. I can "real-life" recommend it's usage.

I still don’t see the great advantage of this configuration as it isn’t taught by most ‘recreational’ agencies. Its another factor to cause confusion.

lack of procedures - at the safety stop I became task loaded with managing depth, time, navigation to the exit point (desirable to avoid nearby overhead docks/boats), my light, 2 buddies, and then my given-back-to-me long hose. I lost my buoyancy and blew a minute of my safety stop. Not a huge deal for me, but probably a bigger deal for diver A who was deeper for longer, on air, and 20 years older. Practice of skills would enhance the ability to multi-task, and a pre-dive brief of procedures to follow in an OOA beyond the usual "take my long hose, we ascend" to include delegation of tasks such as navigation, depth, time.

As others have stated once you’ve donated why take it back, DCI can be treated, drowning can’t. When was the last time you checked your buoyancy on a near empty cylinder. To many weight themselves for the start of the dive not the end.

Regards

Edward

 

[TSandM]

I still don’t see the great advantage of this configuration as it isn’t taught by most ‘recreational’ agencies. Its another factor to cause confusion.

There's no confusion. The person WEARING the long hose knows how to donate and deploy it; the recipient just receives it. Having some length of hose makes it possible to swim side by side, if you need, for example, to get closer to shore and away from boat traffic before you ascent. It also makes a calm ascent MUCH easier.

Just because most recreational agencies don't teach the use of a long hose, doesn't mean there is anything wrong with it.

 

[USCScubaboy]

There's no confusion. The person WEARING the long hose knows how to donate and deploy it; the recipient just receives it. Having some length of hose makes it possible to swim side by side, if you need, for example, to get closer to shore and away from boat traffic before you ascent. It also makes a calm ascent MUCH easier.

Just because most recreational agencies don't teach the use of a long hose, doesn't mean there is anything wrong with it.

I started a thread a bit ago regarding this. Since then, I have switched to a 5' hose for my primary. My buddy and I were practicing our OW skills in Laguna last week and it was much easier for my to share air with my buddy on the 5' hose than for him to share his air with me on his 40" octo. All it takes to clear the air of all the confusion is a proper buddy check in the beginning to establish that in case of an OOA situation, you will be handing your primary to your buddy.

 

[T. Bix]

Not sure where to begin...

so it means doing a couple of gauge checks during the dive (I usually do 2...well 3 if you count on the surface - one about 5 minutes in... and one just over what you expect to be around half the dive). .

I must be way too anal, I would bet if you asked any one of my regular dive buddies they would say I check everybody's air at least every five to seven minutes. It is just something that stuck with us from day 1. nobody had an octo, guages failed, and computers didn't exist. We just planned (plan) and dove the Navy Dive tables and double check(ed) everything....... My guess is TSandM (Lynne) and I would get along fine.....