Computer dies, why can’t I continue to dive on tables?

[UCFKnightDiver]

Definitely and interesting question. I had something similar happen on a trip to Belize last year. I did the quick battery replacement and looong surface interval, followed by 18+ hours out of water. Now, this was based on the following information from my Wisdom 2 manual (see attached photo). No ill effects, hasn't happened again and definitely a lesson learned.

Anyone else's computer function this way?

Also, if this happens say, in the middle of the trip, could you not go back to dive 1 of the trip in your log book (hard copy) and calculate repetitive N2 loading with tables? This should give you a good idea of where you are. Should be more conservative than the real time capability of the dive computer...(flame suit on if I'm off here...)

If you happen to log your dives, sure.

 

[Puffer Fish]

Definitely and interesting question. I had something similar happen on a trip to Belize last year. I did the quick battery replacement and looong surface interval, followed by 18+ hours out of water. Now, this was based on the following information from my Wisdom 2 manual (see attached photo). No ill effects, hasn't happened again and definitely a lesson learned.

Anyone else's computer function this way?

Also, if this happens say, in the middle of the trip, could you not go back to dive 1 of the trip in your log book (hard copy) and calculate repetitive N2 loading with tables? This should give you a good idea of where you are. Should be more conservative than the real time capability of the dive computer...(flame suit on if I'm off here...)

Using a backup device, like a dive watch that logs dives will do the trick a lot easier and more accurately. You still need tables, but you have all the data. Done it several times. After several more days (with the computer back working).. the two sets of data merge again...

 

[Wookie]

I'll address this from the operator's point of view, and, yes, we do hear your computer beeping when you come up, and yes, we do read it over your shoulder when you give us your profile after a dive.

Your computer is as much life support equipment as your air is. Most if not all divers that own computers use them to keep track of their nitrogen loading, use them to maximize their bottom time, and do not use tables. If you used tables, you'd get a bottom timer and depth gauge, not a computer.

On a liveaboard where 5-9 dives per day are offered, your nitrogen exposure is bumping up against your NDL's, and your oxygen exposure is high, especially if you are diving nitrox. Most haven't really paid much attention to their computers, except to ensure it isn't in deco when you surface. Now, you forget to reset your O2 level on a dive. You "tox out" your computer at 20/50 feet, and continue to dive, because you don't hear that incessant caterwauling the computer is making. Or maybe you do notice it, and you surface, but the computer is locked. I defy anyone on this board to work a set of square profile tables any time after the first dive and still be on tables. It's next to impossible. I've seen it a hundred times, and only once have we been able to correlate the dive to tables, and that was for a true air hog making 20 minute runtimes in 45 feet.

Now, you might suggest I let you back in the water after your computer failure. But you are missing an essential piece of life support equipment. You have no real idea what your exposure to nitrogen or oxygen is, and 99% of divers don't have the knowledge to make a decision based on decompression theory/oxygen exposure/diving physiology to make the decision to get back in the water wisely. Those that do will almost always opt to sit out until they are "clean" and start over. That means a 24 hour rest.

A dive operator is expected to be (as a professional) more informed regarding decompression theory/oxygen exposure/diving physiology then the average open water diver. I still can't tell you what your profiles were, or what your oxygen exposure was nearly as well as that computer can. So I'll throw the question back at you a different way.

If your computer fails on you for whatever reason, is your desire to return to diving within 24 hours based on your own personal safety and desire to return from the dive trip safely, or is it based on monetary/vacation restrictions? Do you want to live to dive another day, or are you interested in instant gratification? Are you really wanting to rely on me to treat you properly for the signs and symptoms of decompression sickness rather than keeping safety first and foremost in your mind? Is "safe enough" safe enough?

I know which client I'd rather have on my boat.

 

[The Chairman]

You da man, Frank!!!

 

[Wookie]

You da man, Frank!!!

Thanks, Pete!

 

[redacted]

OTOH, these are dives I have done many times before and I am not surfacing with a screaming computer or one locked out due to a violation. I know I was within NDL when the computer died and I know I did not continue the dive and chance unknowingly going into deco. I know from experience that with a 2 to 2.5 hour SI I have safely returned to the water and conducted another dive with a familiar profile. So, while 24 hours will clear all loading, I also know that is excessive based on past experience. I'm going to want to return to diving after a 2.5 hr SI and dive conservatively base on tables (which we know are more conservative than my computer would have been which was why6 we could not reconstruct computer dive without going into deco). Logically, the risk of DCS should be reduced by switching to tables since we agree they are more conservative than the computer would have been. The very reason why you were not able to reconstruct computer dives on tables is why this procedure should not result in any increased risk as compared to what would have occurred had the computer not failed while still within NDLs.

I'll address this from the operator's point of view, and, yes, we do hear your computer beeping when you come up, and yes, we do read it over your shoulder when you give us your profile after a dive.

Your computer is as much life support equipment as your air is. Most if not all divers that own computers use them to keep track of their nitrogen loading, use them to maximize their bottom time, and do not use tables. If you used tables, you'd get a bottom timer and depth gauge, not a computer.

On a liveaboard where 5-9 dives per day are offered, your nitrogen exposure is bumping up against your NDL's, and your oxygen exposure is high, especially if you are diving nitrox. Most haven't really paid much attention to their computers, except to ensure it isn't in deco when you surface. Now, you forget to reset your O2 level on a dive. You "tox out" your computer at 20/50 feet, and continue to dive, because you don't hear that incessant caterwauling the computer is making. Or maybe you do notice it, and you surface, but the computer is locked. I defy anyone on this board to work a set of square profile tables any time after the first dive and still be on tables. It's next to impossible. I've seen it a hundred times, and only once have we been able to correlate the dive to tables, and that was for a true air hog making 20 minute runtimes in 45 feet.

Now, you might suggest I let you back in the water after your computer failure. But you are missing an essential piece of life support equipment. You have no real idea what your exposure to nitrogen or oxygen is, and 99% of divers don't have the knowledge to make a decision based on decompression theory/oxygen exposure/diving physiology to make the decision to get back in the water wisely. Those that do will almost always opt to sit out until they are "clean" and start over. That means a 24 hour rest.

A dive operator is expected to be (as a professional) more informed regarding decompression theory/oxygen exposure/diving physiology then the average open water diver. I still can't tell you what your profiles were, or what your oxygen exposure was nearly as well as that computer can. So I'll throw the question back at you a different way.

If your computer fails on you for whatever reason, is your desire to return to diving within 24 hours based on your own personal safety and desire to return from the dive trip safely, or is it based on monetary/vacation restrictions? Do you want to live to dive another day, or are you interested in instant gratification? Are you really wanting to rely on me to treat you properly for the signs and symptoms of decompression sickness rather than keeping safety first and foremost in your mind? Is "safe enough" safe enough?

I know which client I'd rather have on my boat.

 

[dumpsterDiver]

People keep indicating that you would have to re-evaluate all your previous dives and work the tables. I don't think that is necessary at all.

Why would you not simply pick the max NDL for your last dive depth and work from there? As long as you know you never went into deco, the prior dives are inconsequential.

Except of course from an oxygen exposure standpoint, but I typically run less than 1.4 ATM of Oxygen for most of my dives and i have never violated my computer wrt oxygen exposure when taking resonable surface intervals, so oxygen exposure would not be a huge concern.

 

[Mr Carcharodon]

People keep indicating that you would have to re-evaluate all your previous dives and work the tables. I don't think that is necessary at all.

Why would you not simply pick the max NDL for your last dive depth and work from there? As long as you know you never went into deco, the prior dives are inconsequential.

Except of course from an oxygen exposure standpoint, but I typically run less than 1.4 ATM of Oxygen for most of my dives and i have never violated my computer wrt oxygen exposure when taking resonable surface intervals, so oxygen exposure would not be a huge concern.

The problem is that it depends on what the previous dives have been. Repetitive dives closely spaced, or deep dives, make it tricky. Usually fast compartments will control, but not always. And if mid compartments are controlling you could end up with spinal cord bends which could be pretty nasty. Sitting it out for 24 hours maybe unduly conservative in most cases, but sitting it out for just over an hour in the face of repetitive dives may not be.

 

[Thalassamania]

This question has been answered several times in the past, so here it is, one more time:

The AAUS Dive Computer workshop recommends 18 hours out of the water.

At the same workshop Emmerman and Sharkey presented ways of accurately getting onto tables if you'd kept good records, that they had independently worked out (references are to the Navy tables that were in use at the time, but the same approach will work with other tables:

Record the time of day, put the computer in dive planning mode, record all the Depth/Adjusted NOD limit pairs as they scrolled by on the computer (e.g., 60 ft would permit a 22 minute NOD dive, 50 feet would permit a 31 minute … etc). Each Adjusted NOD limit would be subtracted from the NOD limit for a new diver at that depth (e.g., for 60 ft: 60 min – 22 min = 38 min. For 50 ft: 100 min – 31 min = 69 min … etc.) that yields a number that represents how long you would have had to dive to that depth to have the amount of nitrogen you now have in you. Then you take each Depth/Time of Theoretical Dive back to the Repetitive Group Designation Table and grab a Group Designator (e.g., for 60 ft and 38 min: Group G. For 50 feet and 69 min: Group I … etc.) Then you take the “worst possible case” that is to say the highest letter (e.g., “I” in the example we are running).

So you'd call yourself a Group I diver at the time you originally recorded, and thus be able to use the tables. The only way to get back onto a computer, however, is to follow standard computer failure protocols (which was agreed at that workshop to be no diving for 18 hours).

Not simple, but potentially useful, the full write-ups can be found in the proceedings at the RUBICON site (free, but send them money anyway, it's for the best possible cause, the advancement of human knowledge).

Other thoughts if you can't sit out for 18 hours:

Two hours of surface breathing oxygen will take you from U.S. Navy Group N to Group A.

A couple of hours with a pure oxygen rebreather (or an oxygen stage) at 15 feet would set you up even better.

 

[Puffer Fish]

This question has been answered several times in the past, so here it is, one more time:

The AAUS Dive Computer workshop recommends 18 hours out of the water.

At the same workshop Emmerman and Sharkey presented ways of accurately getting onto tables if you'd kept good records, that they had independently worked out (references are to the Navy tables that were in use at the time, but the same approach will work with other tables:

Record the time of day, put the computer in dive planning mode, record all the Depth/Adjusted NOD limit pairs as they scrolled by on the computer (e.g., 60 ft would permit a 22 minute NOD dive, 50 feet would permit a 31 minute … etc). Each Adjusted NOD limit would be subtracted from the NOD limit for a new diver at that depth (e.g., for 60 ft: 60 min – 22 min = 38 min. For 50 ft: 100 min – 31 min = 69 min … etc.) that yields a number that represents how long you would have had to dive to that depth to have the amount of nitrogen you now have in you. Then you take each Depth/Time of Theoretical Dive back to the Repetitive Group Designation Table and grab a Group Designator (e.g., for 60 ft and 38 min: Group G. For 50 feet and 69 min: Group I … etc.) Then you take the “worst possible case” that is to say the highest letter (e.g., “I” in the example we are running).

So you'd call yourself a Group I diver at the time you originally recorded, and thus be able to use the tables. The only way to get back onto a computer, however, is to follow standard computer failure protocols (which was agreed at that workshop to be no diving for 18 hours).

Not simple, but potentially useful, the full write-ups can be found in the proceedings at the RUBICON site (free, but send them money anyway, it's for the best possible cause, the advancement of human knowledge).

Other thoughts if you can't sit out for 18 hours:

Two hours of surface breathing oxygen will take you from U.S. Navy Group N to Group A.

A couple of hours with a pure oxygen rebreather (or an oxygen stage) at 15 feet would set you up even better.

As it takes a bit of time to do the reconstruction and it is always more conservative than using the computer, doing so would get one back into the water fairly quickly (would most likely involve missing at least one dive, but not a day.)

Anyone that has been on trips and has their data can easily try this out and see what they get versus the computer.

Obviously if you assume you don't know anything... and were completely dependent on the computer, you should sit down for a while.. but not sure why Live aboards don't know or understand this.