40% O2 mix at the safety stop

[Thalassamania]

Yep you got it. Most DCS hits on rec. profiles I think are a direct result of wicked ascent rates. Don't quote me but I think that's the main issue. Especially when some agencies are still teaching 60 fpm ascent rates

There's nothing wrong with a 60 fpm ascent rate, per se ... the real reason for changing it was that most recrational divers were doing more like 120 (and that's scary, given tables designed for 60).

I always practiced 30 fpm and started stopping or slowing down earlier in my profiles. Like 30, 20, 10 and real slow from 10 ft. to the surface. Adding in a deep stop is not a bad idea either on a deep recreational dive. Have to be carefull there so you don't ongas by stopping too long. But if you're diving a computer it'll compensate just as it would for a multi-level dive. And if you are diving a multi-level dive then you don't need a deep stop as you've covered it with the profile anyway, or should have.

Generally slow is good, but you really need to "shape" the curve a little. I use rather fast ascent rates (comensurate with low work level and CO2 production) for up to my deep stop fsw, I use 60 fpm from my deep stop to 20 where I wait for at least 3 min. When needed (and possible) we hang 100% O2 at 15 feet, with long hoses. From 20 we surface very slowly.

If you're contemplating NEEDING O2 at your stop then you may be pushing NDL's (and gas reserves) and it would be a good time to think about more training. If you're diving doubles (or a big single) and pushing it then you can really get in trouble and need to RUN to a DECO course

Or get a good mentor.

... Do not mess with 100% 02 unless you have the proper training and have demonstrated the proper skills to be able to use it safely. Any cavalier advice about using it for any other reason is handing people bullets for a gun and not providing the training necessary to safely handle that gun. As far as references to what divers were doing 10 years ago compared to now, 02 for decompression has been around a lot longer than that. Do some research and you will find that studies on breathing 02 will go back further than most peoples birthdates on SB.

Sound advice. I'd only change to, "Do not mess with 100% 02 unless you and your team have the proper training and have demonstrated the proper skills to be able to use it safely."

It seems like there has been a trend for many people want to adapt techniques developed and used in technical diving for every day recreational diving. While those on the frontier of any sport who consistently push the boundaries of knowledge and training will constantly set the bar for those that follow, many of these techniques and skills are not for beginner divers. That is one of the reasons we have training and certification levels. Simply put, while any new diver can benefit from learning to back kick, some of these techniques, like accelerated 02 decompression require seriously higher skill levels to be done safely. The problem as I see it is that their are many who do not seem to understand the different levels of risk associated with various technical diving skills. The downside to a bad back kick is next to negligible, the downside to using hi pp02' is death. If you want to use the skills and techniques from technical diving, for god's sake, take the training necessary to use them safely. Don't just take anecdotal advice from anyone on the bloody internet! Would you take flying lesson's online? How about skydiving lessons? Find a good instructor and learn to do it safely and enjoy the benefits.

rant over..........

Again, Find a good instructor (or even better a good mentor).

 

[hypertech]

Personally I think no stop open water diving should not require hang bottles. Gas management people; plan your dive and dive your plan.

I have seen a boat on Oahu that hangs regs (or used to). That was because their questionable guide/instructors were taking noob/tourist divers on dives way above their skill level, but the captain was one of the 500psi nazi's (return with 500psi or you don't get to do the second dive). The guides would bring the heaviest breather back to the hang bar with 500psi and then put them on the hang reg.

In recreational no stop single tank diving, which is in my opinion the basic scuba that we discuss in this forum, hanging regs or tanks are just there so you can break the rules you should have learned in your OW training!

I must be having a bad day as I really feel like being a devils advocate.

I have read plenty of threads lately questioning some dive ops practices so I definately understand where you are coming from. I'm specifically thinking about the threads related to the blue hole and how it is beyond the abilities of many of the people who go there.

But, then again, we do lots of things that are not strictly required in order to increase safety. Things like choosing to use 1.4 ppo2 or always taking a safety stop even if the dive table doesn't require it. So, why then would it necessarily be a sign of a bad operator to have the rich gas at the safety stop? Couldn't it be a premium offering in some cases to increase your safety margin even further?

 

[Thalassamania]

I must be having a bad day as I really feel like being a devils advocate.

I have read plenty of threads lately questioning some dive ops practices so I definately understand where you are coming from. I'm specifically thinking about the threads related to the blue hole and how it is beyond the abilities of many of the people who go there.

But, then again, we do lots of things that are not strictly required in order to increase safety. Things like choosing to use 1.4 ppo2 or always taking a safety stop even if the dive table doesn't require it. So, why then would it necessarily be a sign of a bad operator to have the rich gas at the safety stop? Couldn't it be a premium offering in some cases to increase your safety margin even further?

The problem is that a rec diver who's been skip-breathing the entire dive, has a sicked headache, and comes up to a tank of 100% oxygen with a long hose, switches to that tank and sinks to the depth of the hose (now at almost 30 fsw). This diver is has a buddy that is nowhere to be found and is incapable, anyway, of dealing with a diver that is having a seizure. Get the picture?

 

[OldNSalty]

Even if one did go ahead and start bringing a bottle of O2, held a good stop etc. and pulled it off I don't think its a good idea.

Surely no one carries a pony bottle with pure O2 in it?!? That just sounds like you are looking for problems. I do plan on eventually getting a pony as a back-up air source but I think good old air will be fine in it.

 

[Thalassamania]

Surely no one carries a pony bottle with pure O2 in it?!? That just sounds like you are looking for problems. I do plan on eventually getting a pony as a back-up air source but I think good old air will be fine in it.

I've carried a pony with pure oxygen in case we missed the hang bottle on the way back up. But you are right, usually it should be filled with air or EAN.

 

[String]

You need a card anyway to get your bottles cleaned,

Not in most parts of the world.

labelled and filled, get on boats (well tech dives).

Not in most parts of the world.

I mean what if one uses a "pony" with O2 and someone else grabs it?

Proper labelling with name and MOD.

 

[Bismark]

I agree with what you said, but I can't let a good rant go by

I'm a pilot and I don't see any reason why a person couldn't learn from book and the internet how to do flight planning. I wouldn't want to go throw them into a cockpit and expect them to manage task loading and execute a landing in one piece, but as far as the information processing that goes on during preflight - I don't see a problem.

Unless I grossely misunderstand the task here, I think we are deciding at what depth and what mix one would need to change a regulator/mix to be safe, then actually performing the task requires very little special training. What we are talking about is properly understanding the parameters and limitations of a dive profile. If that's the case, then learning by book or internet certainly seems reasonable. You just need to make sure your source is sound. I wouldn't trust a web forum as my sole source of info, but a lot of this probably could be self taught with the proper resources.

No offense, you are right, you grossely (sic) misunderstand the task here. You have got it backwards: understanding the parameters of 02 tox etc, can be done by study; learning to maintain 20' maximum floor while handling a multitude of tasks (eg: the gas switch for starters....) is not something you can learn from a book. I have yet to see a new diver be able to hold a 20' stop (not 25' not 15' and definitely not 30'...) for longer than it takes to pass through it. This may seem like a rudimentary skill, but for those who haven't mastered it, it is far from as easy as falling off a chair. (speaking from experience here) A diver with a minimum of experience will be incredibly task loaded just trying to maintain position in the water column (in Cold water, it is much, much more difficult) and adding any task effectively uses up a good portion of the bandwidth available to a new diver they were using to maintain their position. Now lets make the penalty for failing to maintain this depth and maintain an awareness of where they are in the water column an 02 hit, convulsions, and most likely drowning. That is the reality of the downside of the lack of skill we are playing with here. There are several reasons why any good tech instructor teaches the critical components of a dive (gas switch definitely being one of them) in shallow water: one of the most important is that maintaining buoyancy control in in the first 2 ATA's if more difficult than in depths below that. Mistakes in buoyancy control are rapidly amplified and your ascent or descent takes on a geometric progression: IE, your descent or ascent accelerates, further accelerating....etc. A friend was teaching two students to do valve drills and when asked if they were comfortable holding buoyancy in 20' of water, they said yes. They were beside a 80' wall and they started their valve drills at 20'. My friend finally grabbed them and told them to cut the drill as they were descending past 60'..... the point being that they were so task loaded that they lost track of their buoyancy for a few seconds and things rapidly escalated. These two students were experienced divers new to tech. Now imagine if that had been a gas switch to 02..........what do you suppose would have happened by the time they hit 60'...or deeper? 02 hit? Don't know for 100% but if I was a betting man...........

As far as the flying thing goes, speaking as someone with several hundred hours in F-18's, I am really damn glad I didn't just learn a lot of that from books......

 

[String]

Surely no one carries a pony bottle with pure O2 in it?!?

Why wouldn't they? I do it regularly when i know im going to be deep or long and run up some stops. Although i could deco out on backgas i use the pony with 100% to give me a nice safety margin at 6m.

Just treat it as a small stage.

 

[Thalassamania]

I agree with what you said, but I can't let a good rant go by

I'm a pilot and I don't see any reason why a person couldn't learn from book and the internet how to do flight planning. I wouldn't want to go throw them into a cockpit and expect them to manage task loading and execute a landing in one piece, but as far as the information processing that goes on during preflight - I don't see a problem.

Unless I grossely misunderstand the task here, I think we are deciding at what depth and what mix one would need to change a regulator/mix to be safe, then actually performing the task requires very little special training. What we are talking about is properly understanding the parameters and limitations of a dive profile. If that's the case, then learning by book or internet certainly seems reasonable. You just need to make sure your source is sound. I wouldn't trust a web forum as my sole source of info, but a lot of this probably could be self taught with the proper resources.

Some people are quite capable of learning even very complex physical tasks from a book, but others are not. We live in a culture that tends to reduce everything to the least common denominator, e.g. link.

 

[Blackwood]

Even if one did go ahead and start bringing a bottle of O2, held a good stop etc. and pulled it off I don't think its a good idea. I mean what if one uses a "pony" with O2 and someone else grabs it?

Then they better hope I'm not too miffed about them taking my bottle to skip the time extension implied by the loss of my deco gas (i.e. to rescue them)

To me, a proper bottle includes MOD marking, but to someone who doesn't know what he's looking at, that won't matter. Fortunately, my proper procedure includes turning the bottle off, and someone who nonchalantly grabs it probably won't think to turn it on.