Incident due to battery change on dive computer

[KeithG]

In her case, the charter captain shook his head but let her throw the computer overboard on the line and do the next dive.

I hope I never get stuck on a boat with this type of diver OR captain. Great potential to screw up my vacation week (and their life, not that I am too worried about them...)

I once iced my shoulder after a dive and the liveaboard crew was all over me. I was stupid and allowed the hang line to jerk my arm upwards when the boat crested a wave during my safety stop. The jerk aggravated an old injury. I spent at least 5 minutes calmly talking the situation over with several crew members (we went through all of the common DCS symptoms). I thanked them for their attention and concern and asked them to continue to challenge me regarding my condition over the rest of the week. Great crew!

 

[NAM001]

This is a funny thread. I say this because of all the threads on how tables no longer need to be taught, or needed. Reading the OP the first I thought was avg depth 70' & 46 minutes (70+46=116) and a already somewhat consevative 120 rule. I thought at most they may have exceeded NDL by a minute or so and how the deco times just didn't fit the situation.
This is what happens when tables are no longer taught. One must be able to trust the computer and you cant do that if you don't know if the computer is lying or not. If you don't understand the table basics along with a few memorized rules to verify correct data, then you should not trust the computer further than a data recorder. They did the same dive before and all was well. At least they recognized something was not right. What would have happened if the computer would have been aggressive instead of over conservative and the diver was afraid to come up because of the deco being called for, and then skipped the deco and came up. I have to agree with some posters ., Get a set of tables and plan with them. I doubt any one will have an issue with teaching them to any one. To the OP. get a table and look at the relation ship of (depth) plus (time at depth) for NDL's for various depths along with the deco required for crossing the line by a couple of minutes. You will find tha most sums is 110-120 and that the deco for crossing is just a couple of minutes total. As a note when you do cross unknowing ly that the optional safety stop now becomes a mandatory one and should cover the deco requirement.

One other thing that bothers me is that on prior dives you said that with the medium setting your bottom time was cut in half. Do you dive till a 2 minute warning goes off. It would seem that if you dove it before that you would have been curious why the dive is lasting so long if the old setting gave a NLD bottom time of 23 minutes. Why did you dive till 46 minutes? And what would have happened if your alarm did not go off to tell you to go up short on air in a real need of deco. This hits on plan the dive and dive the plan.

 

[modustollens]

When I learned SCUBA computers were only a rumour - I never saw one until many years later; hence I learned tables and keep a set in my dive log.

When I read that tables were not always taught anymore for the first time here on Scubaboard I furled my brow in disbelief.

After reading this thread I spent yesterday reviewing the computer manual for my computer to remind myself of how to interpret the data in case I go into deco. I have had that happen only twice though. The last time it happened I was on a course and my instructor rightly chewed me out. I did my first tech course with him a few days later - that demystified the procedures. He also gave me a copy of Powell's book to read as well and I have since bought my own copy. It is much better knowing than not; diving is less stressful and I would think less dangerous too. All this took an investment of both time and money; but I think a lot of new divers don't want to spend more of either than minimally necessary to simply get in the water.

Must have been pretty stressful to think that there might be time required for deco but not enough gas for it.

MT

 

[Mr Carcharodon]

Since the OP is using average depth, rather than max, it sound like he is already using something like the 120 rule. Planing with tables does not work well for multi vevel dives with short dips down to the max depth. The planning method employed was referring back to a previous dive's information and following the group. That does not seem terribly robust and having a check like the 120 rule seems like a good sanity check. Also the OP's computer was not locked out for the second dive it was in gauge mode. That's no problem at all if you have a way to plan.

 

[Jack Hammer]

This is a funny thread. I say this because of all the threads on how tables no longer need to be taught, or needed. Reading the OP the first I thought was avg depth 70' & 46 minutes (70+46=116) and a already somewhat consevative 120 rule. I thought at most they may have exceeded NDL by a minute or so and how the deco times just didn't fit the situation.
This is what happens when tables are no longer taught. One must be able to trust the computer and you cant do that if you don't know if the computer is lying or not. If you don't understand the table basics along with a few memorized rules to verify correct data, then you should not trust the computer further than a data recorder. They did the same dive before and all was well. At least they recognized something was not right. What would have happened if the computer would have been aggressive instead of over conservative and the diver was afraid to come up because of the deco being called for, and then skipped the deco and came up. I have to agree with some posters ., Get a set of tables and plan with them. I doubt any one will have an issue with teaching them to any one. To the OP. get a table and look at the relation ship of (depth) plus (time at depth) for NDL's for various depths along with the deco required for crossing the line by a couple of minutes. You will find tha most sums is 110-120 and that the deco for crossing is just a couple of minutes total. As a note when you do cross unknowing ly that the optional safety stop now becomes a mandatory one and should cover the deco requirement.

One other thing that bothers me is that on prior dives you said that with the medium setting your bottom time was cut in half. Do you dive till a 2 minute warning goes off. It would seem that if you dove it before that you would have been curious why the dive is lasting so long if the old setting gave a NLD bottom time of 23 minutes. Why did you dive till 46 minutes? And what would have happened if your alarm did not go off to tell you to go up short on air in a real need of deco. This hits on plan the dive and dive the plan.

The 120/130 rules only work if one applies average depth properly. We don't know if that 70' average was the actual average depth when the OP went into deco or if was what the computer showed the average to be after the dive including travel time, the 2 minute stop, the 5 minute safety, and however long to surface. I suspect the latter. The actual average depth could have likely been deeper and enough to incur a real deco obligation.[emoji2]

 

[Mr Carcharodon]

The 120/130 rules only work if one applies average depth properly. We don't know if that 70' average was the actual average depth when the OP went into deco or if was what the computer showed the average to be after the dive including travel time, the 2 minute stop, the 5 minute safety, and however long to surface. I suspect the latter. The actual average depth could have likely been deeper and enough to incur a real deco obligation.[emoji2]

See post #26. I'd call that 75, meh.

 

[KevinNM]

Must have been pretty stressful to think that there might be time required for deco but not enough gas for it.

What is PJ's line? "When the gas is done, the deco is done!"

 

[lowviz]

... having a check like the 120 rule seems like a good sanity check. ...

Sanity checks are a good thing. But the 120 rule is little more than just a rough sanity check. That rule is a linear approximation to a curve. It can only be good over a range of values. It was designed to be good between 50' and 100'. Way off at either extreme.

Tables and Rules are funny. Look at the USN Dive Table #3. Give me a break, look at the numbers, somebody skewed and rounded that bigtime. It is aggressive in the shallow working end and very conservative at the deep end. Go figure why that is...

I dive a very conservative algorithm that gets me into trouble when I voice it, but I also want to know where the radicals draw the line as to where you have entered real deco, as in no foolin'. Couldn't get a consistent answer for that. Came up with my own. Type six 2's into your calculator, divide by depth and divide that result by depth again. That is what I use for my first real hard stop. If you can't do the long division on your Wetnotes before your time is up, you are out of your range.

Ran some V-Planner to back me up. No prior nitrogen load, first dive, sanity check results below:

 

[Storker]

My gf has a Suunto D4 and it doesn't reset the nitrox mix.

I last dove my Vytec in Truk three weeks ago. I just turned it on now and it's still set for 28%.

Weird. Although I prefer that my PDC resets to 21% after a period of non-use, I'd accept more or less any practice as long as it was consistent across the different models of the same brand. Here, it appears as if different Suuntos behave differently since the Stinger, the Zoop and the Cobra all automatically reset the O2%.

My Stinger resets itself to 21% after 2 hours if I don't dive, or at midnight.

According to the user's manual it's not at midnight. It's after the no-fly time has passed.

From the Stinger user's manual (p.45):

In the EAN mode, the default setting is for standard air (21% O2). It remains in this setting until the O2% is adjusted to any other percentage of oxygen (22%-50%).

If a dive is started within two hours Stinger retains this value until the dive series is finished. If unused, the computer will retain the manually entered value for the selected oxygen percentage for about two hours, after which it will revert to the default setting of 21% O2.

From the Zoop user's manual (p. 44):

NOTE! The Nitrox settings will revert to default settings 21% (air) and PO2 1.4 bar after approximately 2 hours.

From the Cobra user's manual(p.70):

If unused, the computer will retain the manually entered value for the selected oxygen percentage for about two hours, after which it will revert to the default setting of 21% O2.

I use a Cobra, and my son uses a Zoop. We dived 32% last monday, and yesterday, when I checked, they had both reverted to 21%. I'd guess that they follow the same practice as the Stinger, i.e. that the percentage is retained until the no-fly time is over, and that they revert to 21% after that.

 

[NAM001]

lovis

you are right about the extreems when using the 120 rule, however he was with in the window to use it as a sanity check. From his post I got that he appeared to use a time probably around 30 min for an ndl because of his conservative setting in the past. It seams that when you hit 40 min one should say hey Ive been down here for a long time.
Then to find your computer is now calling for that much deco after 46 min. I also suspect that 70 ft may have been the center of his dive depth window and not time corrected. Even though if not time corrected, being down 10 or nmore minutes olonger than normal should be a flag. If the 70 ft is time corrected then the 120 rule should have been looked at to validate what the computer said. Especially since he knew he had done a battery change and perameter change.