Incident due to battery change on dive computer

[Storker]

Actually, Storker, I believe you misread him. I believe he is correct.

He was talking about the OP and the specific second dive on that specific day. On that day the violated decompression limits, and he did not do the required decompression stop. Neither the tables nor his computer would have allowed a second dive. You are talking about a generic situation in which someone has not violated the limits. That's a different topic.

On second reading, you're right.

OTOH, since I'm a wuss, I dive with a Suunto set to minimum conservativeness (which is pretty close to the PADI RDP on square profiles, and IIRC not extremely different from V-Planner with +2 conservatism for most no-stop dives), so I'd probably be done for the day anyhow with a profile like the OP's. Because my computer would've told me I was in deco about five minutes before I started my ascent.

If I felt adventurous, knew my travel insurance coverage was good and I was fairly close to a chamber, I might do an extended SI and do a shallow, conservative dive later in the day even if my DC locked me out. My computer wouldn't be seriously bent, it'd only call for an extended safety stop of 5 minutes at 3m/10ft which I'd of course complete. I'd plan and dive on the PADI RDP, for the added conservatism on anything but a purely square dive. So even with the (purported) conservatism of Suuntos, I'd be able to do a second dive on tables if I really, really wanted to.

 

[lowviz]

-and that is my point. Here is an informed non-deco diver who is entirely capable of weighing the risk vs. benefits of a second dive.

 

[uncfnp]

Did you forget that we're talking about an OW diver, doing a Rec dive here? Or did you forget that I'm responding to posts saying that if the OP had known how to use and HAD tables, he wouldn't have had the issue that he did?

For an OW, Rec diver, it seems to me that there absolutely IS a practical difference between 87 feet and 93 feet. It's the difference of 5 minutes of bottom time. It is the difference of 1 pressure group of RNT, in many cases. It's the difference between 53 minutes of SI to get to the next pressure group versus 1 hour and 45 minutes.

Those seem like very practical differences to me.

It is fine for you experienced divers with DP training to say "there's not a significant difference between diving to 87 versus 93". It isn't very significant, to YOU. But, to an OW diver, doing Rec dives, who is attempting to save the day using tables after their DC died, it sure does seem significant to me.

BECAUSE I recognize my inexperience and lack of deco training, I would not fudge things by guesstimating and saying "anh, one pressure group either way doesn't matter. It's close enough."

Would you fault me for that?

As for having one or two computers, the OP's issue was not that he didn't understand the computer. It was that he knew enough to believe it was wrong. If he had had two computers, where one had a new battery and one was "known good" (so to speak), it seems pretty clear that after he recognized what was going on with his primary computer (which he did), he would have been able to switch to his backup and followed it because it would have been giving him good data that was ALSO inline with his own prior experience with that dive. IOW, for the OP a second DC would likely have gotten him through both dives that day without a deco obligation - much less a blown deco obligation.

---------- Post added April 13th, 2015 at 04:14 PM ----------

I'm starting to feel like some people here really think nobody should be allowed to dive until they've taken the Deco Procedures course.

Stuartv. I think you are sincerely interested in learning and I commend you for that. But that said, you need to be willing to listen. Question yes, but also LISTEN. And know that at your age (in diving years) things may seem very black or white but IRL its rarely that way.

As for different dive philosophies and approaches to risk, that's the beauty of this wonderfully diverse dive universe called SB. Yes, it is heavily skewed to professional divers but take advantage of that. Its a great opportunity for anyone willing to stay open minded and listen.

 

[dberry]

I'm thinking that there is more than one way to do things correctly and peaceful coexistence is entirely possible.

I'm thinking you're reading a different forum than I am.

 

[AfterDark]

What tables would an OW diver have that would have helped him do his second dive? According to the PADI RDP (I believe), he went into deco on his first dive.



Diving with two computers is the vastly better answer than telling him to learn how to use tables. In this specific scenario, the tables say he was in deco, so he was done for the day. If he'd had a second computer, that was setup correctly (meaning, as he intended it to be), presumably (because he said he did it before), he could have just done the second dive with his primary DC in gauge mode, and using his secondary DC for NDL info. IOW, tables? No second dive. Backup DC? Yes on a second dive.

It seems like a more common scenario would be that his primary computer actually died for some reason (versus being setup wrong). In that scenario, tables are, again, useless because he would be back on the surface after his first dive with no record of his BT or max depth. So, no way to use tables to work out a second dive. Unless you would suggest using the dive log from his buddy's DC... So, again we're back to tables wouldn't help but diving with two computers would.

Lastly, I dive with 2 computers. And I would say that the chances of me diving with both of them having brand new batteries at the same time is about 1%. And that 1 percent is allowing for, either, diving in the pool to make sure they are both good, or a total fluke that both DCs happened to literally die at the same time. My DCs are not identical. Other than some tech divers with 2 Shearwaters (or similar), who dives with two identical computers?? Even if they were identical, I think it highly unlikely that both batteries would go at the same time. However, even if they both showed Low Battery at the same time, I would still change one first, then the other. Diving with 2 computers that have both just been serviced seems like not the best idea at all. There's always a chance the service could result in a problem, so it will always be better to dive one freshly serviced and one "known good".

So, again, it seems to me that, if you're going to use a DC at all, then there is really no NEED (for an OW Rec diver) to learn or use tables. For anyone who is concerned about missing out on some diving because their DC died, the best solution is to dive two DCs. The only way to even be close to as good, using tables, is if you use a DC and you also dive with a depth gauge that records max depth and a bottom timer. And that will still not give you nearly as much BT, on your second dive, as if you spent just a little more money and got a cheap DC as a backup, instead of the depth gauge and BT. Unless your first dive was totally a square profile. Then using tables might be somewhere close to as good. Maybe.

---------- Post added April 12th, 2015 at 01:04 PM ----------



So, if you had been his instructor, back 1000+ dives ago, he wouldn't have done what he did? Color me skeptical. People do stuff all the time that they were thoroughly and well instructed not to do. ESPECIALLY, when they've been engaging in whatever activity we're talking about for long enough to feel confident in their own skills.

stuartv I dive 2 computers on some dives. Other dives only one computer and sometime dives no computer. Among the items I always dive with is an analog depth gauge and a watch. Before EVERY dive I set my watch's bezel (that's the round thing on the outside of the watch with numbers on it) as for the max depth I usually know what it's going to be pre-dive, my depth gauge has a max depth indicator needle on it that records max depth. Knowing one's max depth and bottom time post dive is a responsibility every diver has to him/her self. IMO it is a poor and poorly equip diver that does not know that info post dive.

I also carry US Navy diving tables for air, not the standard PADI , NAUI......ect rec tables. The Navy tables allows a diver to plan and execute deco dives as well as NDL dives. Those tables along with the depth gauge and watch are my final backup or sometimes my primary system for diving time / depth. The tables were purchased on Ebay for $8.00.

Computers don't change the NDL times for a given depth. Computers only extend bottom time when doing multiple dives during a day or diving different depths during a dive(s). If a diver has a max depth of 90FSW for the entire dive the NDL time is the same computer or tables. The second dive to the same depth will be just as short with tables or computer. The more you know the safer you are!

 

[stuartv]

It isn't cut and dried. Was it 70' average or 93' for the calculations?

No he didn't do the time, but one could make a case...

My education on tables must not be as good as I thought. Because from what I know of how to use the tables (PADI RDP, NOAA, or USN), it IS cut and dried. If you went to a max of 93', then your NDL is 25 minutes (or close, depending on which table you actually use). I haven't yet learned about a table based on average depth. What agency teaches that in their OW class?

---------- Post added April 14th, 2015 at 12:45 AM ----------

Stuart, there is a difference between being taught how to use something, and understanding how it works.

Decompression status is a product of depth and time, and workload, and temperature, and individual factors we don't really understand. If you want to know why so many of us are scoffing at the difference between 87 and 93 feet, buy the GUE DVD, "The Mysterious Malady", and listen to the top researchers in this area talk about how little we know.

There are rules for the use of tables, and the tables are validated using those rules, and therefore, people using the tables and expecting to keep their DCS risk at the level accepted by the tables (which is not zero) should follow those rules. In one of the above posts, you are walked through the procedure for transitioning from a failed computer to tables -- my only caveat on that procedure in this example is that the OP did NOT do the indicated deco for his first dive, so assuming he is in pressure group Z at surfacing is simply a WAG. Had he appropriately decoed out, it would have been more reasonable.

You are right, that having a second computer is a relatively inexpensive and very rational approach to dealing with computer failure. Of course, the original post had nothing to do with a failed computer, but rather, with a computer doing exactly what it was supposed to do, and a diver second-guessing it. No number of redundant gauges will make up for someone who has a tool and misuses it.

Anyway, I really think that, with your level of curiosity and your apparent strong interest in diving, you ought to acquire a copy of Deco for Divers, at the very least, and read it. It will make the opinions of people who have studied this stuff for their own diving much easier to understand.

Hi TSandM, I completely understand that deco calculations are not an exact science. I also understand why you think the difference between 87 and 93 feet is little to worry about. The issue here is that you are completely missing my point.

A number of you have responded to the OP with some version of "he should have learned how to use tables during his OW training and then actually used them after his first dive." As if that knowledge and process would have made his second dive both doable and safer.

And my point is that all we know about the OP's training (I think) is that he is OW certified. Thus, even if he was trained on using tables, you are unreasonable and unjustified in putting it on him to make any decisions based on decompression theory instead of strictly following the tables (or his DC).

I'm not saying people wouldn't be helped by learning deco theory. I have been shopping for Deco for Divers. It's not available in Kindle format and they don't have it at my LDS, and I haven't anted up to order it from Amazon yet, but I will have it and read it soon. However, do you really think you are safer by knowing and using deco theory? It seems to me that diving strictly by the tables is probably safer, isn't it? But I digress...

To finish my point, the OP did a dive to a max of 93' for 46 minutes. People responded with "he should have used tables!" And the point I've been making is that, when you assume you are talking to someone with no more training than OW certification, that response is useless. If you follow the rules OW divers are trained by, tables would have him sitting out the rest of the day after the first dive. Period. And if you go further and say, "well, he should have followed the tables for his first dive, too", then he may as well have not even had a computer and he would have had to miss almost half his first dive just to be allowed to do a second dive.

I'm illustrating that the "learn tables. Use tables" mantra is not the silver bullet that some people seem to think it is. And chanting it is, sometimes, like this particular case, just useless. "Learn deco theory. Use deco theory." Sure! That's a much better mantra. I can get behind that. But it seems a bit unreasonable to expect an OW diver to (or tell them that they should) know deco theory and be able to make judgment calls about how they can use deco theory to "massage" the use of an NDL table (as in, for example, using the SI and NDL for 87' instead of the one for 93').

Sure, encourage people to learn it, but you have to give the guy an answer that is appropriate for HIS level of training, not yours.

 

[Storker]

you have to give the guy an answer that is appropriate for HIS level of training, not yours.

That's been done several times in this thread already: if you don't know squat about deco theory you should never get in the water with a bent computer. No matter the DC's conservatism settings. Case closed, thread over.

If you, however, know some basic principles of deco theory, it IS possible to do a second dive on tables with a computer locked in gauge mode.



--
Sent from my Android phone
Typos are a feature, not a bug

 

[lowviz]

My education on tables must not be as good as I thought. Because from what I know of how to use the tables (PADI RDP, NOAA, or USN), it IS cut and dried. If you went to a max of 93', then your NDL is 25 minutes (or close, depending on which table you actually use). I haven't yet learned about a table based on average depth. What agency teaches that in their OW class?

Your understanding of tables is correct. However, I did say "calculations". Tables aren't the only way, ask GUE. The problem with this discussion is that it crosses over the NDL and that is inappropriate for the OP. Many of us are trying to offer insights without selling deco. I feel this way because there is an undeniable push (by many) to find the most aggressive DC that will give you the most bottom time. That is fine, but when you start living on the line you may find that you want more information about the other side.

Many posters, myself included, are not overly concerned with crossing this line, you just use your training. A deco table gives you a letter group (if you clear deco) just like the NDL table. I'm pretty much done as this thread is straying a bit too far. Use your two DC's, shut one up and put it into a pocket or clip it onto your BC. You will be fine. And I don't mean this the least bit sarcastically, that sort of redundancy is to be commended. IJS that there are other options.

Cheers

 

[delmolino]

I got my Deco for Divers from BookDepository.com (i believe it is a UK website) and it arrived in NYC in 5 days. I usually like kindle versions as well but for my diving books I am liking more the printed versions.
Deco for Divers: A Diver's Guide to Decompression Theory and Physiology : Mark Powell : 9781905492299

PS - I am not related to this website, but I was extremely pleased with their service, though price of the book is not exactly cheap...

 

[rhwestfall]

Tables, second PDC, math, etc. They are all possible tools to implement. The big issue is the OP really approached (or likely crossed) a very potentially deadly line and DID NONE OF THE ABOVE!!!!!

The take away for anyone reading this is to (as they always taught) - PLAN A DIVE, DIVE A PLAN (and the plan can have contingencies). Even a simple dive should have some checks and balances that easily would have prevented this or identified it very early on.

The OP, as I said before, needs to re-visit the dive planning portion of his education.