Dive Computer Failure -- Ending the Dive

[Nemrod]

Last fall, our group of experienced divers in Coz would often begin a dive at or near 100 feet and over an hour later still be tooling along in the shallows around 20 feet. Long enough in some cases that the DMs started to whine. You just cannot do this type of multilevel diving, easily anyways, with the tables. On a square profile, that is a 25 minute dive.

However, one post in the thread does not understand that at least tech oriented divers still, largely, do not run computers so the OP is not the last "tables diver" at all or even close. There used to be a lot of controversy about riding a computer which seems to largely have gone away and since people are not getting bent in large numbers, well, it must be okay.


OP, consoles are so eighties. He may not be the last "tables diver" but he is close to being the last "console diver" .

N

 

[dfx]

Something is going over my head. Of course tables will be ultra conservative, especially if your max depth is a quick dip for perhaps 1/10 of the total dive time. I wouldn't take a 24hr break just because of the limitations of square profiles and tables.

The problem is that if you're deviating significantly from a square profile, the tables won't tell you how much your N2 exposure really was (when using them as if you were doing a square profile). All they will tell is that you went over the NDL ("you're bent!!!11"), and as such they will tell you to take a 24h break. It's not a matter of being ultra conservative, it's a matter of not taking the multi-level nature of a dive into account.

Or you can speculate that since your dive computer was still within the NDL when it failed, you obviously don't need a 24h break. Which is true, but then the tables are of no help. You still wouldn't know how much your N2 exposure really was, which is important for planning the next dive. The safe thing to do is to take a 24h break.

If you were actually doing a square profile, the tables should tell you something very similar to what the computer would have told you. In that case, the tables wouldn't tell you that you went over the NDL and a 24h break wouldn't be necessary.

In all of these cases, you would do what the tables tell you.

Of course you could take a time and try to model the dive by calculating each part separately, but it sounds like OP is just taking a square profile.

Sure, but doing that from memory after the fact is risking that you could get it wrong. I think I'd rather take a safe 24h break (unless, like you say, it actually was a square profile and the tables don't put you over the NDL).

 

[Lorenzoid]

Just what I was looking for.

Thanks!

You already knew the answer to your question. You clearly appear to have dive planning well in hand--much more so than Suunto expects their users to.

 

[AfterDark]

Here's my real world scenario: Dive 1 of 2 (planned) sometime during the dive PDC battery fails. Knowing the bot. time for the max depth I've hit so far I know I'm close to deco by the tables. I completed my dive did a 5min stop at 20fsw and a 10 min stop at 10fsw per tables, (I carry Navy air tables in a pocket) and surfaced. I called dive 2 because I was very tired from driving all night (14 hours) and didn't think the bottom time I had for dive 2 sans PDC was worth the effort.
I could have done a deco dive for dive 2, had the air but not the energy. So if you plan your dive with tables and PDC then execute the dive with a PDC you'll be ready to do either. I am very untrusting of electronic technology, testing it is what I do for a living. It isn't pretty.

 

[scubastingray]

The problem is that if you're deviating significantly from a square profile, the tables won't tell you how much your N2 exposure really was (when using them as if you were doing a square profile). All they will tell is that you went over the NDL ("you're bent!!!11"), and as such they will tell you to take a 24h break. It's not a matter of being ultra conservative, it's a matter of not taking the multi-level nature of a dive into account.

Or you can speculate that since your dive computer was still within the NDL when it failed, you obviously don't need a 24h break. Which is true, but then the tables are of no help. You still wouldn't know how much your N2 exposure really was, which is important for planning the next dive. The safe thing to do is to take a 24h break.

If you were actually doing a square profile, the tables should tell you something very similar to what the computer would have told you. In that case, the tables wouldn't tell you that you went over the NDL and a 24h break wouldn't be necessary.

In all of these cases, you would do what the tables tell you.


Sure, but doing that from memory after the fact is risking that you could get it wrong. I think I'd rather take a safe 24h break (unless, like you say, it actually was a square profile and the tables don't put you over the NDL).

Ah you misunderstood my question. I hadn't even gotten to the comp failure yet. I was trying to figure out if OP calls group dives because he tries to apply square profiles to multilevel diving. If that were the case he would quickly become a solo diver, because I and many I know would laugh at calling a dive for that reason. A dive with a deep spot at 80ft for 10 minutes followed by an hour in the shallows does not mean you are bent.

 

[dfx]

Ah you misunderstood my question. I hadn't even gotten to the comp failure yet. I was trying to figure out if OP calls dives because he tries to apply square profiles to multilevel diving. If that were the case he would quickly become a solo diver, because I and many I know would laugh at calling a dive for that reason. A dive with a deep spot at 80ft for 10 minutes followed by an hour in the shallows does not mean you are bent.

Oh yes of course. No argument there, I was just making a case for why the 24h break after a dive computer failure is a decent suggestion. Once you take a dive computer failure into account, let's say right at the end of such a dive that you describe, and if all you have to go by is your max depth and the time, checking that against tables puts you way past the NDL. Without any other information available, the only safe thing to do would be to take a 24h break, and this is where the recommendation in the manual comes from. I'd say a square profile is the exception for most recreational divers.

 

[AfterDark]

Oh yes of course. No argument there, I was just making a case for why the 24h break after a dive computer failure is a decent suggestion. Once you take a dive computer failure into account, let's say right at the end of such a dive that you describe, and if all you have to go by is your max depth and the time, checking that against tables puts you way past the NDL. Without any other information available, the only safe thing to do would be to take a 24h break, and this is where the recommendation in the manual comes from. I'd say a square profile is the exception for most recreational divers.

If I may interject here the above is why I carry Navy air tables the only other factor is having the air to complete any deco required by the tables. The information is out there, it isn't "sanctioned" by any agency and unconventional by decompression standards in sport diving today but it doesn't mean Navy air tables don't work or are dangerous. Air only deco takes longer and requires more air but it is doable, and IMO safer than guessing. More time can be added to each stop. I see this as safer than divers experimenting with deep stops at least navy air tables are proven, not flawless; but what is in this sport?

 

[scubastingray]

If I may interject here the above is why I carry Navy air tables the only other factor is having the air to complete any deco required by the tables. The information is out there, it isn't "sanctioned" by any agency and unconventional by decompression standards in sport diving today but it doesn't mean Navy air tables don't work or are dangerous. Air only deco takes longer and requires more air but it is doable, and IMO safer than guessing. More time can be added to each stop. I see this as safer than divers experimenting with deep stops at least navy air tables are proven, not flawless; but what is in this sport?

He's saying if your computer fails you cannot know how close you were to the NDL. If you only have two points of data (duration and max depth), you cannot reliably estimate your current nitrogen loading. This has nothing to do with proprietary navy tables, etc.

 

[KeithG]

In reading the Zoop manual the procedure for correcting a computer failure is as follows: Ascend to 60ft, slow ascent to 30ft per minute, hold at 10-20ft for as long as air will allow, surface and discontinue diving for 24hrs minimum.

Hang on. This does not pass the sniff test. Are you sure this is what the manual says?
on a recreational dive, you have no deco obligation and can go directly to the surface. Since you are ending your dive early, you WILL have lots of air, so feel free to make a 3-5 minute safety stop @15 feet. But holding at 10-20 as long as air will allow? Nope. Not doing that. That could be an hour or more....

P.s. if you are computer diving, the only viable backup to a computer failure is a backup computer.

 

[NAM001]

I agree with you, the manual's recovery protocol is made under the assumption that you only have one computer and have no other method of backup. You appear to be plenty familiar with bt and tables so I would switch to that and continue the dive. This example you conveyed is all too familiar in many topics here on SB. The solutions given being based on assumptions that do not apply. Did my heart good to read this thanks. BTW keep on using the computer, its a good log keeper if you ever need a chamber ride or other medical attention.

Until recently I have always been a BT and Tables diver and always planned my own dive even when diving with a group charter. In fact I have turned down computers on rental equipment dives and thumbed more than one dive when my time was up based on the profile planned and actual dive executed regardless of what the DM or guides computer said the 'groups' NDL was because that was how I planned the dive (side note: I recommend trying this, the look from a new diver after giving the 'instructor finger waggle' to a DM is worth the cost in bottom time alone).

I'm not out to set a bottom time records and enjoy conservatively planned dives even at the loss of bottom time or depth. I'm not looking to enter a discussion about the merits of comp vs. BT; I just dive tame profiles and BT/Table is how I was trained (read: what I am comfortable with).

I finally purchased my first DC (Suunto Zoop). My choice to dive a computer is more one of redundancy than expediency. I will still dive my full SPG console with depth gauge and carry a bottom timer. I will still monitor both in the fashion I always have during a dive along with the added computer check. In reading the Zoop manual the procedure for correcting a computer failure is as follows: Ascend to 60ft, slow ascent to 30ft per minute, hold at 10-20ft for as long as air will allow, surface and discontinue diving for 24hrs minimum.

My question is why? The Zoop's failure outline makes sense if you have no redundancy, no idea what your bottom time is, no idea what you depth is and no plan other than 'trust the comp'. But, if I maintain contingency plan based on where the RDP places my PG, know the elapsed BT and maximum depth, why could I not just transfer the dive back to a BT/Table dive and proceed as planned. Once topside any subsequent dives that day (and probably trip) would be planned off of the RDP. I have to believe the RDP is more conservative than even the most conservative DC algorithm particularly when diving a square max depth profile and not using a eRDPML. Ignore any scenarios where the RDP puts me past an NDL, these are leisure dives that should remain well inside of any deco obligation.

I'll provide two examples:

1. Dive 1 of a day. Planned profile is 60ft for 35 minutes. Computer fails 10 minutes in. I don't know exactly when the comp failed but I know I am 10 minutes into a 35 minute dive via my BT. Why do I need to ascend? Why can't I continue the dive based on the planned profile and exit the water in PG 'N' per the RDP; conduct a surface interval and proceed to dive 2?
2. Dive 2 of a day (different day not related to example 1). Post SI, RDP says I would be an 'E' if you calculate a square profile using the table. Planned profile is 50ft for 45minutes. Comp fails 40 minutes in, thumb the dive and proceed to boat. Why could I not use the RDP to figure out I am a PG 'T' then proceed as planned later that day to dive using data from log and RDP for both of the previous two dives?

Curious how the SB community views this. I don't need to know that I am doing redundant math if I plan dives in this fashion, I know that and I'm happy to self identify as a math nerd. Besides, the point of redundancy is to be able to safely mitigate any critical equipment failure. Thanks!

---------- Post added July 12th, 2014 at 11:02 PM ----------

I agree with you, teh manual recovery protocol is made under the assumption that you only have one computer and have no other method of backup. You appear to be plenty familiar with bt and tables so i would switch to that and continue the dive. This example you conveyed is all too familiar in many topics here on SB. The solutions given being based on assumptions that do not apply. And then provided as a one solution fits all manor. Did my heart good to read this thanks. BTW keep on using the computer, its a good log keeper if ou ever need a chamber ride or other medical attention.

Until recently I have always been a BT and Tables diver and always planned my own dive even when diving with a group charter. In fact I have turned down computers on rental equipment dives and thumbed more than one dive when my time was up based on the profile planned and actual dive executed regardless of what the DM or guides computer said the 'groups' NDL was because that was how I planned the dive (side note: I recommend trying this, the look from a new diver after giving the 'instructor finger waggle' to a DM is worth the cost in bottom time alone).

I'm not out to set a bottom time records and enjoy conservatively planned dives even at the loss of bottom time or depth. I'm not looking to enter a discussion about the merits of comp vs. BT; I just dive tame profiles and BT/Table is how I was trained (read: what I am comfortable with).

I finally purchased my first DC (Suunto Zoop). My choice to dive a computer is more one of redundancy than expediency. I will still dive my full SPG console with depth gauge and carry a bottom timer. I will still monitor both in the fashion I always have during a dive along with the added computer check. In reading the Zoop manual the procedure for correcting a computer failure is as follows: Ascend to 60ft, slow ascent to 30ft per minute, hold at 10-20ft for as long as air will allow, surface and discontinue diving for 24hrs minimum.

My question is why? The Zoop's failure outline makes sense if you have no redundancy, no idea what your bottom time is, no idea what you depth is and no plan other than 'trust the comp'. But, if I maintain contingency plan based on where the RDP places my PG, know the elapsed BT and maximum depth, why could I not just transfer the dive back to a BT/Table dive and proceed as planned. Once topside any subsequent dives that day (and probably trip) would be planned off of the RDP. I have to believe the RDP is more conservative than even the most conservative DC algorithm particularly when diving a square max depth profile and not using a eRDPML. Ignore any scenarios where the RDP puts me past an NDL, these are leisure dives that should remain well inside of any deco obligation.

I'll provide two examples:

1. Dive 1 of a day. Planned profile is 60ft for 35 minutes. Computer fails 10 minutes in. I don't know exactly when the comp failed but I know I am 10 minutes into a 35 minute dive via my BT. Why do I need to ascend? Why can't I continue the dive based on the planned profile and exit the water in PG 'N' per the RDP; conduct a surface interval and proceed to dive 2?
2. Dive 2 of a day (different day not related to example 1). Post SI, RDP says I would be an 'E' if you calculate a square profile using the table. Planned profile is 50ft for 45minutes. Comp fails 40 minutes in, thumb the dive and proceed to boat. Why could I not use the RDP to figure out I am a PG 'T' then proceed as planned later that day to dive using data from log and RDP for both of the previous two dives?

Curious how the SB community views this. I don't need to know that I am doing redundant math if I plan dives in this fashion, I know that and I'm happy to self identify as a math nerd. Besides, the point of redundancy is to be able to safely mitigate any critical equipment failure. Thanks!