Incident due to battery change on dive computer

[lowviz]

USN Dive Table 5, Ratio Deco, Deco on the Fly, or an informed estimate of your nitrogen load and a conservative dive.

 

[Storker]

The OP said he went to a max of 93' and had a dive time of 46 minutes. What table are you using that would allow him to get back in the water for his second dive that day?

The OP went beyond his DC's NDL, didn't really know what he was doing and didn't have a plan B. That's another issue than just having your DC die on you during the dive, which is what we were discussing at this point.

If you want to ride the NDLs, especially the liberal ones, you'd better be prepared to skip a dive or two if SHTF, and you'd also better have good medical & travel insurance coverage. Because there's a risk you'll see the inside of a chamber sooner or later, and that might be a mite expensive. And, of course, both a bit tedious and somewhat uncomfortable.

 

[RJP]

Oh?

The OP said he went to a max of 93' and had a dive time of 46 minutes. What table are you using that would allow him to get back in the water for his second dive that day?

Any one that you can generate yourself using V-Planner or any one of a dozen different dive planning apps.

By about dive 100 you'll learn that not all "tables" are plastic and cost $24.99 at your friendly neighborhood dive shop.

 

[stuartv]

If you think there's a practical difference between 87ft max depth and 93ft you're simply not paying attention to the reality of decompression models.

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.

 

[lowviz]

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

 

[Storker]

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.

Like whom? I know that at least one of the "people here" who disagree with you has never taken any deco class, and also has no plans whatsoever of taking one.

 

[TSandM]

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.

 

[RJP]

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.

See, there's your problem right there...

Deco "theory" is "theoretical" not "practical." Nitrogen bubbles don't give a s**t about pressure groups on your neatly printed table.

As someone mentioned above, you're measuring with a laser... but deco theory is cutting with an axe.

Perhaps this is why so many hits are "undeserved" in the minds of the diver in the chamber. "But I can't be bent... I did a 53 minute surface interval, and only went to 87ft for exactly 48 minutes!"

---------- Post added April 13th, 2015 at 04:38 PM ----------

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

 

[boulderjohn]

Using tables wouldn't have helped the OP to be able to do a second dive that day.

Here's where you're totally, patently, indisputably wrong.

You're a rec diver, so you should never incur a deco obligation that can't be cleared by a nice, slow ascent and a three to five minutes' SS at 5m. Assume worst case, i.e. you assume that when you surface you are in pressure group Z.

Oh?

The OP said he went to a max of 93' and had a dive time of 46 minutes. What table are you using that would allow him to get back in the water for his second dive that day?

The OP went beyond his DC's NDL, didn't really know what he was doing and didn't have a plan B. That's another issue than just having your DC die on you during the dive, which is what we were discussing at this point.

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.

 

[lowviz]

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.

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...