History behind Dive computer error mode

[sharkbaitDAN]

Extrapolate data beyond what was verified safe by navy divers & do its best to get me to the surface, regardless of how many violations I did. After I surface it can lock up all it wants.

Locking mid dive is like having a car refuse to drive because you are a mile over the annual mileage limit for your service interval.

Speaking to many divers over the years, I think there are quite a few who would say that the Navy tables are already "beyond safe" for recreational dives. For the type of scenario you are talking about, I believe the Navy procedure would be to surface and get in a chamber. Someone please correct me if I'm wrong. In this scenario, the safest course of action may be getting to the surface, and then getting unbent.

Dive computer algorithms are models, and they do a terrible job of modeling the actual physiology of diving. The are good enough to work most of the time when certain assumptions can be made, but if you start to go beyond those assumptions, the entire model will break down. It may continue to give numbers that are safe, or it may not, and you have no way to know the whether the decompression schedule is still safe. In all likelihood, the people who wrote the model wouldn't know the answer either. Your options are to use a different model, which takes different parameters into account, or to follow the recommendations of the people who wrote the model you are using.

I see the Suunto lock-out mode as more akin to the limp home mode that most modern cars have. If there is a sensor failure, or certain types of mechanical failures, the car's computer will limit engine performance until someone who knows what they are doing can diagnose, and fix the problem. The car's computer doesn't know what is actually wrong, just that some data is outside normal parameters, and it will give you just enough to get you home. A Suunto locks you out because certain parameters are outside what the programmers considered. It does not know why, or how, but the model may no longer be accurate.

---------- Post added July 26th, 2014 at 02:34 PM ----------

No disagreement from me about having at least one deco gas for such a dive; I would think two would be better. But the idea that helium is "best practices" at 50m is simply false. Just one example of several is below.

Wow. Ok. All I know is that air would be extremely narcotic at those depths. TDI, IANTD, GUE and UTD all teach the use of helium for dives to 50m.

 

[rongoodman]

No disagreement from me about having at least one deco gas for such a dive; I would think two would be better. But the idea that helium is "best practices" at 50m is simply false. Just one example of several is below.

People might defend deep air in a particular case because of the cost or availability of He or unusually benign dive conditions, but that doesn't alter the fact that it's not ideal. Bringing PSAI into it won't be helping your case, unless you want to spend the next 50 posts defending "PSAI Narcosis Management". (Although PSAI actually does have a trimix course covering similar depths.)

 

[Akimbo]

... For the type of scenario you are talking about, I believe the Navy procedure would be to surface and get in a chamber. Someone please correct me if I'm wrong. In this scenario, the safest course of action may be getting to the surface, and then getting unbent…

Not exactly. I believe you are referring to Sur-D-O2 (Surface Decompression using Oxygen). See Page 9-1, US Navy Diving Manual Rev. 6 with Change A

Divers don’t get bent on Sur-D-O2 tables because the they are asymptomatic during the water stops (if any) and short surface interval — 5 minutes from leave last stop to full depth in the chamber on O2. The procedure changes to a treatment if symptoms present.

9-1 INTRODUCTION
9-1.1 Purpose. This chapter discusses the decompression requirements for air diving operations.

9-1.2 Scope. The decompression procedures contained in this Chapter are new. They replace the air decompression procedures that have been in use by the Navy for more than fifty years. These new procedures are safer, more flexible, and provide more operational capability than the older procedures. The primary improvement in safety results from the use of oxygen during decompression to accelerate elimination of excess nitrogen from the body. All but the shortest decompressions are performed either with oxygen breathing in the water or with surface decompression on oxygen.

As you can see, Sur-D-O2 is now the preferred method of decompression in the US Navy, as it has been for commercial surface diving operations for decades. The diver is warm, safe, and under the watchful eye of a diving supervisor.

…Wow. Ok. All I know is that air would be extremely narcotic at those depths...

That is a gross overstatement if by “those depths” you mean 50 M or 165'. Your statement might be accurate for a small minority of inexperienced deep air divers but is not universally true.

Experienced working divers routinely perform complex tasks around the world on air to the 65-75M or 215'-250' range — and have been for more than a half century.

 

[Dr. Lecter]

People might defend deep air in a particular case because of the cost or availability of He or unusually benign dive conditions, but that doesn't alter the fact that it's not ideal. Bringing PSAI into it won't be helping your case, unless you want to spend the next 50 posts defending "PSAI Narcosis Management". (Although PSAI actually does have a trimix course covering similar depths.)

We're not discussing deep air, Narcosis Management, or what your opinion of "ideal" is; we're discussing 50m on OC and whether TMX is "best practice" for that shallow depth. It's not. Some agencies teach TMX as an option for 50m, some teach it as mandatory, and neither is "best practice."

Wow. Ok. All I know is that air would be extremely narcotic at those depths. TDI, IANTD, GUE and UTD all teach the use of helium for dives to 50m.

You're wrong about IANTD:

[h=2]Technical Diver (OC Only)[/h][h=4]Purpose:[/h]1. This Program is designed to train divers to conduct dives to depths between 100 fsw (30 msw) and, at the instructors option, up to 170 fsw (51 msw) using custom blend breathing gas mixtures; and to provide greater understanding of custom blend breathing gas mixtures, a complete knowledge of the limits of any EANx mixture, and the use of EANx and oxygen for decompression.
2. The knowledge and skills taught in this program are more than adequate to qualify divers to perform dives outside of training up to 180 fsw (54 msw).

Moreover, TDI teaches air to 45m. That extra 5m is really what you're going to hang your hat on? If we were talking about air below 187'--or we were discussing CC instead of OC--you might have a narcosis argument to make - we're not, and you don't.

 

[Akimbo]

People might defend deep air in a particular case because of the cost or availability of He or unusually benign dive conditions, but that doesn't alter the fact that it's not ideal…

You probably don’t want to go there. If ideal is the criteria, then mixed gas diving without a chamber onboard constitutes unsafe and illegal working conditions in many parts of the world. Mixed gas and a bell-chamber system are required below 50 Meters in the North Sea, which effectively dictates Saturation Diving.

Trimix is the poor-man’s solution for mixed gas diving, or mixed gas on the cheap. HeO2 is the norm in commercial diving, who are under insurance and government restrictions to conduct safe diving operations.

 

[sharkbaitDAN]

We're not discussing deep air, Narcosis Management, or what your opinion of "ideal" is; we're discussing 50m on OC and whether TMX is "best practice" for that shallow depth. It's not. Some agencies teach TMX as an option for 50m, some teach it as mandatory, and neither is "best practice."



You're wrong about IANTD:
[/FONT][/COLOR]
Moreover, TDI teaches air to 45m. That extra 5m is really what you're going to hang your hat on? If we were talking about air below 187'--or we were discussing CC instead of OC--you might have a narcosis argument to make - we're not, and you don't.

Ok, are you saying that all other things being equal, including cost, you would dive to 50m on air instead of TMX?

Second, from IANTD:

[h=2]Normoxic Trimix Diver (OC, SCR, CCR)[/h][h=4]Purpose:[/h]1. This Program is designed to train those who wish to dive to depths between 130 fsw (39 msw) and 200 fsw (60 msw), but who do not wish to breathe air below 130 fsw (39 msw). Trimix affords a means of reducing narcosis on dives to such depths.

Third, TDI has the helitrox course which seems to be similar to the IANTD Normoxic TMX course.

Both of these agencies seem to find value in using TMX at 50m, no? Maybe best practices was the wrong phrase because I didn't include commercial diving or CCR practices.

So far, I have not been shown any evidence that air is better than TMX at 50m. It sort of seems like wanting to get from point A to point B, and you have a choice of drunk or sober. You'll probably make it if drunk, but isn't being sober safer? Given an easy method of reducing narcosis, which has been implicated in many deaths of deep air divers, why not use it, assuming helium is available?

 

[Akimbo]

Ok, are you saying that all other things being equal, including cost, you would dive to 50m on air instead of TMX?...

As for me, yes. I have used air to 50 meters for decades with minimal discernible performance compromise. I have switched between air and HeO2 many times and have not been able to tell the difference beyond the effects on my voice and thermal conductivity. The reliability of air decompression algorithms and tables are much more evolved and proven over thousands of times more dives than on Trimix and HeO2 combined.

 

[BRT]

My Oceanic computers say that any dive with a first decompression stop much below 70 feet will lock you out. The computer simply doesn't have a viable solution.

 

[ballastbelly]

thats pretty much like what i have in my manual (though i have not seen it happen in action while underwater, nor do i wish to)


http://ns.suunto.com/Manuals/Zoop/Userguides/Suunto_Zoop_UserGuide_EN.pdf

The Error Mode results from omitted decompression, i.e. when you stay above the
ceiling for more than three minutes. During this three-minute period the Er warning is
shown and the audible alarm beeps. After this, the dive computer will enter a permanent
Error Mode

is there a dive computer review website where they do the type of depth test i mentioned before?
http://www.youtube.com/watch?v=UAbjXS9afxI

 

[Dr. Lecter]

Ok, are you saying that all other things being equal, including cost, you would dive to 50m on air instead of TMX?

Second, from IANTD: [/FONT][/COLOR]
Third, TDI has the helitrox course which seems to be similar to the IANTD Normoxic TMX course.

Both of these agencies seem to find value in using TMX at 50m, no? Maybe best practices was the wrong phrase because I didn't include commercial diving or CCR practices.

So far, I have not been shown any evidence that air is better than TMX at 50m. It sort of seems like wanting to get from point A to point B, and you have a choice of drunk or sober. You'll probably make it if drunk, but isn't being sober safer? Given an easy method of reducing narcosis, which has been implicated in many deaths of deep air divers, why not use it, assuming helium is available?

So you're claiming these agencies, which teach both TMX and air for 50m dives…are offering a class in something other than "best practice"? If you want to claim TMX at 50m reduces narcosis, nobody's going to bat an eye. When you start trying to dictate what's safe/best practice/what everyone should be doing…you'd better not be spewing BS, and in this case you most assuredly are.

Yes, all else being equal, I'd dive air for a 50m dive. HE carries with it its own complications and risk factors, and outside CCR there's no reason to dive it for such a shallow dive.

And you're pretending it's a binary choice between "drunk" and "sober"; once again, you're objectively wrong. Impairment is subjective: one diver may well be less impaired on air at 50m than another diver on a common TMX blend at the same depth. Moreover, TMX reduces narcosis, to some non-quantifiable degree, but hardly eliminates it--the idea that you're automagically sober at 50m so long as you're on TMX is both false and dangerous.