In dive, manage having EAN programed into computer while diving air?

[saridnour]

I am an advanced diver but pulled a noob mistake, I usually only use EAN for tech dives or deco. I dive at least weekly and got into a grab and go for rec diving. I'm posting this question as I am sure it has happened but could not find much info on what one should do in water. I figure it may be a good thing that people read and think about this through my embarrassment of making this mistake. The first thing I'd think one should do is look to their buddy's comp if diving the same profile, but this was not applicable in this instance.

The situation:
99% of my rec dives are just on air. This was also a shore dive. Unfortunately I did not reset my teric or perdix back to air post prior dive AND I forgot to check the setting (was in a hurry to hit the water) pre dive. These are all on my checklist now but at the time, happened. I dove 30% programmed into the computers while I was only carrying air. I dove to 70ft and varied my bottom time on an obstacle from the 40 to 70ft range over a 55min dive. I pushed close to the NDL but did not exceed it. I also do recall thinking I must have been shallower longer than I had thought due to NDL time (this should have been where I noticed it). My buddies peeled off earlier, but that was the plan (they knew I had the gas and do dive solo often as was doing some photography). While headding to do my 5min safety stop, I noticed my error. My computer was calculating the dives NDL based on nitrox 30%. I knew since I was close to my NDL on 30% that I would be in deco if it could recalculate on air. So what is the correct way to handle this issue? Since I was not on a tech dive I did not pre plan the slate or bring tables. How would one calculate the correct deco/safety stop with margin for this dive while in water?

What I did:
In my case I was diving sidemount so had an extra cylinder of air. I reset my computers to air ASAP. I looked at my surf GF to see where it thought I should be. I started and stretched my safety stops to start at 25' and moved up to 10' over 25min. I baked in a lot of extra time just to be as safe as I could but was using the force (experience) to determine what I needed, but was still a guess. Post dive I was able to recalculate the entire dive in subsurface from my telemetry calculating air with my computers GF. It showed I needed a 6min 10' deco stop and was well within the safety margin I did at the time. I keep going back to what if.. what if I pushed this closer to my max air volume, what if the dive was deeper, what if I was diving 40%, etc.

Question:
What is the proper safety method to handle and or calculate what should have been done here in real numbers and in real time?
I know I could have brought or planned a lot prior to dive, that's not the feedback I am after. We have all just jumped in for easy dives like this before. It happens all the time without issue. In hindsight we could do a lot differently. But what I am looking for is the correct safety procedure to handle this as I am sure it happens a lot, but probably just not noticed. I'm curious if and how to calculate the stop needed for gas estimates as close to actual as possible.

And one last note..
The 3min or 5min safety stops are done for a reason. This example shows where that 5m stop could have made a difference on getting bent if I had not noticed my error at all. Just my 2cents for anyone reading this as a take away. Don't blow off your Safety Stops!!

Thanks in advance!!
Andy

 

[saxman242]

I'll own to having done this once. I fortunately was with others diving on air, so I made sure to stay above them, didn't go anywhere near my NDLs, and did about a 10 minute safety stop. And felt incredibly stupid the entire time.

To add insult to injury, I normally wear a backup computer and didn't have it with me on that dive either.

 

[tbone1004]

@saridnour
You can use the rough "rule of 130", i.e. depth+time=130, only good for first dive of the day, and it's a fairly aggressive profile, but it's a good rule of thumb to keep in mind for air diving.

You can try to figure out a rough GF adjustment to deal with air vs. EAN30. I.e. if you're GF is normally 60/80, and you did a 32min dive to 70ft, you have a 2min stop at 10ft which is basically NDL since that will clear by the time you get up. That's on air. To get the same 2min stop at 10ft on EAN30, you have to drop GF-hi to 60.
Run a couple of plans based on your chosen GF's in whatever software you like, and then learn to drop the GF accordingly. Keep that rough table in your wet notes, or just plan on dropping it down to say 60 and padding the stop by a couple of minutes and you'll be more than close enough.

Otherwise, stay in the water at shallow depth until you get bored, cold, or run out of gas. Cold being particularly important since your offgas rates go to hell in a handbasket when you get cold

 

[Protondecay123]

I'm not sure that other than memorizing or having a good recollection of a dive table there is anything else you could really do.

 

[tursiops]

You can use the rough "rule of 130", i.e. depth+time=130, only good for first dive of the day, and it's a fairly aggressive profile, but it's a good rule of thumb to keep in mind for air diving.

Don't you mean 120, not 130? 120 would be old Navy tables on air, but 130 would be more like 32%.

 

[tbone1004]

Don't you mean 120, not 130? 120 would be old Navy tables on air, but 130 would be more like 32%.

depends on the specific depth. They tend to alternate between 120-130 depending on the specific combination. Once you hit 100ft they basically go to 130, and anything before gives you a "mandatory" safety stop, so I just use 130.

 

[tursiops]

depends on the specific depth. They tend to alternate between 120-130 depending on the specific combination. Once you hit 100ft they basically go to 130, and anything before gives you a "mandatory" safety stop, so I just use 130.

Sorry, that makes no sense to me. 120 is safer, not 130.

 

[tbone1004]

Sorry, that makes no sense to me. 120 is safer, not 130.

hence my statement about being a pretty aggressive profile. I do 130 with a 5 minute safety stop. That said, if my computer still works, then I would just drop my GF Hi down a bunch.

 

[tursiops]

hence my statement about being a pretty aggressive profile. I do 130 with a 5 minute safety stop. That said, if my computer still works, then I would just drop my GF Hi down a bunch.

Place of dive tables in modern diving

 

[NAM001]

Don't you mean 120, not 130? 120 would be old Navy tables on air, but 130 would be more like 32%.

120 rule falls apart below 60 ft, the more as you get shallower the more off it gets. I would use 130 also to determine how much past NDL i was. If the majority of the dive was below 60 ft then 120 would probably be the most appropriate to use. If < 60 then 130. the shallower the less problem.