Redundancy Required for Decompression Diving?

[Freewillow]

Of relevance to this thread it is worth pointing out that a single doesn't have enough gas to get into huge deco on a first dive in U.K. conditions,


Dives start simple and get more complicated with depth and time. You do not need the same gear to do a 28m 25 minute air dive as a 30m 30 minute dive or a 40m 40 minute dive. The risks are different and so the management of risk is different.

I agree.

Again, have the author correct me if I am wrong. Everything I said and understood was for a dive with a small TTS . This means a max of 5 minutes deco. We are in an advanced non tek dive forum.

 

[admikar]

Exactly. This is laughable. I do not understand why during a sport diving training, students are not pushed, with the right supervision, to go into a small one minute deco obligation. Just in order to find out how their computor would react and what indications are to be followed. This is much better than to have the same experience, on your own and have to try to figure out what your computor is telling you.

As I already said in another thread, during my AOW training, two of us were "forced" to do a dive to 40 m, to see how we react to narcosis. Two of us, among 8 other experienced divers,all in doubles, 3 of them instructors. We were told, and I think rightly so, that it is better to get narced in such a company, then to try it on our own.
Honestly, I do not know official procedures for deco dives, all I know that in my club, all 3* divers are diving doubles, and I was not allowed to do deco dive in a single-manifolded doubles and drysuit were mandatory to get me on that wagon.
Regarding mindset.....I was allowed to do training dives before I had enough dives for 2* card. When I asked to do some training dives for 3*(swim test and nav dive), I got resounding NO!, with explanation that I am not ready for 3*.

 

[Colliam7]

I do not understand why during a sport diving training, students are not pushed, with the right supervision, to go into a small one minute deco obligation. Just in order to find out how their computor would react and what indications are to be followed. This is much better than to have the same experience, on your own and have to try to figure out what your computor is telling you.

There is merit in this comment. I suspect the reason that such practices are not pursued is a matter of liability, as much as safety. I did this on one occasion, in a moment of 'enthusiasm', with 2 students completing a Deep Diver certification course. On Dive 4, we dove to 130 feet, and hovered above the bottom, letting our dive computers count down to '0' NDL. Then we stayed for a few additional seconds, and allowed the computers to display 1 minute of deco obligation. At that point, we initiated a normal ascent (30 ft/min). By the time we reached 75 feet, the calculated deco obligation has been eliminated, and we began accruing NDL as we continued to 35 feet. The goal was to demonstrate to the students that they should not 'panic' if their computers reached '0' NDL during a recreational dive, rather they should initiate a controlled, normal ascent. The context of the exercise was that a responsible recreational diver should not allow their computer to go to '0' NDL, or beyond, but that the diver should not create additional problems by a hurried or uncontrolled ascent in reaction to the computer screen display.

Afterward, I thought (long and hard) about that exercise and elected not to do it again - as part of the formal Deep Diver course. I concluded it was a violation of standards and, in the unlikely event that a problem developed, I would not have any support from my agency or my insurance company. I conducted that exercise in warm water, with excellent visibility, with divers that I had worked with in OW and again in AOW, and with whose skills I was familiar. But, while I felt comfortable with the exercise, I decided it was not a good idea, and that such a demonstration should be reserved fro dives other than formal training dives.

 

[KenGordon]

There is merit in this comment. I suspect the reason that such practices are not pursued is a matter of liability, as much as safety. I did this on one occasion, in a moment of 'enthusiasm', with 2 students completing a Deep Diver certification course. On Dive 4, we dove to 130 feet, and hovered above the bottom, letting our dive computers count down to '0' NDL. Then we stayed for a few additional seconds, and allowed the computers to display 1 minute of deco obligation. At that point, we initiated a normal ascent (30 ft/min). By the time we reached 75 feet, the calculated deco obligation has been eliminated, and we began accruing NDL as we continued to 35 feet. The goal was to demonstrate to the students that they should not 'panic' if their computers reached '0' NDL during a recreational dive, rather they should initiate a controlled, normal ascent. The context of the exercise was that a responsible recreational diver should not allow their computer to go to '0' NDL, or beyond, but that the diver should not create additional problems by a hurried or uncontrolled ascent in reaction to the computer screen display.

Afterward, I thought (long and hard) about that exercise and elected not to do it again - as part of the formal Deep Diver course. I concluded it was a violation of standards and, in the unlikely event that a problem developed, I would not have any support from my agency or my insurance company. I conducted that exercise in warm water, with excellent visibility, with divers that I had worked with in OW and again in AOW, and with whose skills I was familiar. But, while I felt comfortable with the exercise, I decided it was not a good idea, and that such a demonstration should be reserved fro dives other than formal training dives.

How about you take an extra computer, set as conservative as possible and for air? Then do a nitrox NDL dive but ascend when the conservative computer crosses the line. This dive will be no stop really (for some deco voodoo value of really) and so not a standards violation surely?

Unless of course the standards are designed to scare the students away from the NDL...

 

[Freewillow]

I like the 2 last posts. Great. I am not an instructor nor do I live in a world that carries such a huge liability burden. So your problems are really not mine

Loved to read that KenGordon got my message on where the NDL/Deco line is: quite variable when you see different computors/different algos/and different safety settings....................., especially for consecutive dives......

 

[dumpsterDiver]

There is merit in this comment. I suspect the reason that such practices are not pursued is a matter of liability, as much as safety. I did this on one occasion, in a moment of 'enthusiasm', with 2 students completing a Deep Diver certification course. On Dive 4, we dove to 130 feet, and hovered above the bottom, letting our dive computers count down to '0' NDL. Then we stayed for a few additional seconds, and allowed the computers to display 1 minute of deco obligation. At that point, we initiated a normal ascent (30 ft/min). By the time we reached 75 feet, the calculated deco obligation has been eliminated, and we began accruing NDL as we continued to 35 feet. The goal was to demonstrate to the students that they should not 'panic' if their computers reached '0' NDL during a recreational dive, rather they should initiate a controlled, normal ascent. The context of the exercise was that a responsible recreational diver should not allow their computer to go to '0' NDL, or beyond, but that the diver should not create additional problems by a hurried or uncontrolled ascent in reaction to the computer screen display.

Afterward, I thought (long and hard) about that exercise and elected not to do it again - as part of the formal Deep Diver course. I concluded it was a violation of standards and, in the unlikely event that a problem developed, I would not have any support from my agency or my insurance company. I conducted that exercise in warm water, with excellent visibility, with divers that I had worked with in OW and again in AOW, and with whose skills I was familiar. But, while I felt comfortable with the exercise, I decided it was not a good idea, and that such a demonstration should be reserved fro dives other than formal training dives.

I filmed an ascent which showed the computer approaching and then going into one minutes of deco and clearing the ceiling on ascent. I too have seen (and read about) so many people freaking out by going into deco. I think it is an important issue.

Depth: 95 ft, In Deco, 500 psi, No Buddy

 

[DevonDiver]

Exactly. This is laughable. I do not understand why during a sport diving training, students are not pushed, with the right supervision, to go into a small one minute deco obligation. Just in order to find out how their computor would react and what indications are to be followed. This is much better than to have the same experience, on your own and have to try to figure out what your computor is telling you.

Its pretty easy to teach that lesson without taking the risk of heavily saturating oneself.

Here's how I approach it:

1. If using a GF driven computer (i.e. Shearwater etc), pre-plan a conservative NDL for the dive. Track that NDL and surface well within it. Set GF to something ludicrous (like 10/30) so that significant staged deco is reached very quickly. I use this method for running 'simulated staged deco' training dives with tech students, whilst also keeping dive parameters very conservative during the learning (and mistake making) phase of training.

2. Conduct a dive using an appropriate EANx mix, but leave the computer set for air. Plan the EANx NDL and dive within it. The computer tracks as per air, so you can enter lite deco safe in the knowledge you're well insulated from DCS risk. I use this to teach recreational divers how their computers will respond/display to emergency deco situations.

For recreational divers, my message is simple:

DCS risk is a grey area, not black and white. Modern decompression algorithms and no-stop limits keep divers reasonably safe from risk, even accounting for other predisposing factors.

As you approach no-stop limits, there is less insulation against those risks.. so one has to be much more mindful of contributory risk factors like ascent speeds, safety stops, proper hydration, exertion, thermal protection, body composition, cardio-vascular fitness and personal physiological issues.

Exceeding no-stop limits makes dives less forgiving. Smaller predisposing or dive management factors now have a more immediate and profound impact. The medical consequences of those factors occuring become more severe.

As those no-stop limits are further exceeded, the DCS risk changes from reasonable to unreasonable. From unlikely to likely. From non-damaging, to injurious, to potentially fatal.

Those risks cannot be eliminated, but they can be mitigated. Risk mitigation is possible through appropriate and specific training and equipment... all of which is readily available across the globe.

To speak about small deco obligation as a "mortal sin" is, for me, stupid.

I don't recall seeing what you just quoted anywhere in this, or another, thread.

Who are you quoting exactly?!?

NDL is a "statistical evaluation" of a risk...

It is nonetheless representative of a real risk of injury. DCS isn't some hypothetical or fictional malady, nor is it restricted only to 'extreme' deco divers.

Did you ever get bent, or be on a dive with someone how got bent?

Real experience with DCS tends to eliminate any gung-ho bravado or delusions of invincibility. It tends to sober people towards a conservative approach to diving...especially when you become cognizant of the small factors that can make the difference between healthy and harmful results.

Even avoiding 'scare stories' about paralysis and death, the results of DCS injury and treatment can have profound long-term consequences for the diver.

Rehabilitation from DCS injury, even if treated, can be prolonged and life impacting. Even with a full recovery (no nerve or tissue damage), it's likely that the victim might be restricted from further diving for some time.

So... when pushing that 'grey area' is the benefit of a pathetic few extra minutes even worth the risk of being medically prohibited from further diving for months afterwards? Or missing a flight home from vacation? Or a significant medical bill that may not be fully covered by your insurance? Or the trauma and upset you cause to friends, family and fellow divers by subjecting yourself to emergency medical care?

Are those few extra minutes really worth the risk of pushing yourself further into a grey zone where DCS likelihood and increased severity of injury becomes more significant?

The reason technical diving training exists is to mitigate those increased risks. It provides a significantly higher standard of dedicated training, along with a proven (accident analysis driven) equipment and techniques blueprint for preserving a high degree of safety and risk insulation. In short, it balances risk appropriately.

I really don't understand the lemming-like obsession to push one's tolerances into potentially injurious and unforgiving dive parameters. To push dives up to, or beyond no-stop limits.... to show scorn for conservatism... For what? A few pathetic extra minutes at depth?

If someone was that desperate and carefree for a few extra minutes underwater, then they'd probably benefit from diving more frequently... rather than diving more aggressively.

Or if they truly needed the capacity to dive deeper or longer than reasonable no-stop limits permit, then they can take advantage of the readily available training and equipment that empowers extended diving with a high degree of risk mitigation.

 

[Diver-Drex]

I learned deco procedures as KenGordon described and DD alluded to.
During the dive your backup computer was set to your actual gas. Your primary computer was set to air and you followed the ascent it prescribed. We did all of the gas planning using planned depth as a square profile as well as multiple iterations of "cut" tables to understand what bottom times and ascents should look like.
Doing this serves two purposes. First, we would plan the air bottom time to be equal or less than the actual gas NDL. This we would never actually incur a deco obligation. So we could learn and become proficient with low risk.
Second, as proficiency was gained bottom times could be planned that were beyond the NDL for the actual gas. Making the dive as if it were on air provided conservatism.
The backup computer set to the actual gas made sure that O2 was tracked and provided accurate data if there was an accident if some sort.
This was taught to me in a club environment, although by guys who were instructors. Doubles and backup mask, light, smb and spool were required.

 

[Edward3c]

I learned deco provedutes as KenGordon described and DD alluded to.
During the dive your backup computer was set to your actual gas. Your primary computer was set to air and you followed the ascent it prescribed. We did all of the gas planning using planned depth as a square profile as well as multiple iterations of "cut" tables to understand what bottom times and ascents should look like.
Doing this serves two purposes. First, we would plan the air bottom time to be equal or less than the actual gas NDL. This we would never actually incur a deco obligation. So we could learn and become proficient with low risk.
Second, as proficiency was gained bottom times could be planned that were beyond the NDL for the actual gas. Making the dive as if it were on air provided conservatism.
The backup computer set to the actual gas made sure that O2 was tracked and provided accurate data if there was an accident if some sort.
This was taught to me in a club environment, although by guys who were instructors. Doubles and backup mask, light, smb and spool were required.

What I don't see here (or in most of the other posts) is the gas planning that is required for any dive planned deco or not.

 

[Patoux01]

Are those few extra minutes really worth the risk of pushing yourself further into a grey zone where DCS likelihood and increased severity of injury becomes more significant?

The reason technical diving training exists is to mitigate those increased risks. It provides a significantly higher standard of dedicated training, along with a proven (accident analysis driven) equipment and techniques blueprint for preserving a high degree of safety and risk insulation. In short, it balances risk appropriately..

See, the problem with most of your statements, is that many of us read "train with me or you're gonna die" in it.

If I take any "5 minutes close to NDL dives", I can find a set of tables/computer settings that would have called for deco on it, hence we should all require "technical" training (such a garbage name btw, diving in its nature is a technical activity).

If you can hold a safety stop, you have the capabilities of doing 5 minutes of (obviously) backgas deco, and for such a short time, I'd not be too fussed about doing it on a single tank with a good buddy. Longer than that and I start diving with redundancy, which I usually do anyway, simply for the sake of longer bottom time (more often gas limited than NDL limited)