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

[Steve_C]

If you have looked at the tables ahead of time and know ballpark what the difference in NDL is for the mixes that you use that is good enough to get out safely given how conservative they are.

 

[Scared Silly]

@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.

BITD, I would use the rule of depth (in feet) + time = 100 for square profiles. Which what we primarily were diving.

 

[dmaziuk]

Interesting that there is no "official" recovery. In hindsight you'd think that a computer should be able to recalc in an emergency or run a dive plan with the data. Shearwater allows a dive plan to be done at depth so wouldn't think to be to hard make available. Could be a safety or cost vs use thing.

A 4-button 2"-screen interface would suck for it. You could do it in any decent dive planner, like subsurface, the only issue is how to take it down with you.

 

[rjack321]

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?

Couple of options. Although a bit surprised you were that close to deco? What GFs were you running? You can memorize any air table but really all you need to remember is the 60ft for 50mins and 100ft for 20mins and you can extrapolate from those setpoints. 15-20years ago the Navy tables had 60ft for 60mins and that's what we all planned around (with analog depth gauges)

30ft = indefinite
40 = 120
50 = 75
60 = 50 (another setpoint but in days of yore this was an hour)
70 = 35 (NAUI says 40 but its easier to just add 5mins for each 10ft shallower than 100ft)
80 = 30
90 = 25
100 = 20 (setpoint)
110 = 15mins (5mins less than at 100ft)

Deeper maybe skip the air NDLs.

 

[saridnour]

Thanks all. This is a lot of good conversation and information. Seems there is no real way but many options and possibilities. Please keep the ideas rolling!!

@rjack321 I run a 35/70 GF. I expect on many deeper dives to go into deco and plan for it. I count the deco as a part of my safety margin. I’d rather run true numbers vs guessing and padding things (diving ean but having air programed into computer or making extra longs safety stops as I feel should be done). I like the data to back my choices and to keep things consistent. Anyhow, that is why I knew I would hit deco in my case. Thank you for the calculation set points. I do need to reflect back on my old gauge days (certified in ‘91). Dive profile:

@KWS, I am not aware of any setting to revert gases. I could see this being an issue on EAN on multi dive days though. Even if able to be switched off, you’d have to remember to.

@HKGuns, @tbone1004, You could watch pp02 on air integration with current tech. There is no reason you would have to use the HP just as they do with CCR. BUT I do agree with tbone that it’s not practical as you would have to have multiple sensors to reconcile with one another and would be a larger fail point. Ratio computers do have a nitrox monitor cable to check and set air prior to dive. Cool feature but needs a dry side cable

@tbone1004, That’s was the issue. Yes, the safety and the conservatism I dive are to adjust and give me that padding. I was just trying to find a way to respect that padding in that type of situation just in case. FWW, one needs be careful using the surfGF numbers to identify if “safe” to surface. I did that last year. I had a conservative setting on my computer and went into deco on a boat dive. Since I was conservative, I looked at the surfGF and decided I could shave a min off my deco plan as it reported GF84 which I have been at a number of times. Yes, shaving time should never be done BUT since that was the first time I had dove with that conservative setting I made the choice to surface. I took a hit a few hours later. It’s why I keep to my plan and try to follow my plan as close as I possibly can and were and why I took the extras steps in this event. It is also why I wanted to see what “should” be done
As to a computer recalculating. I can really see how that could be an issue. However, I can also see it being beneficial in such a case. I could see it working in one of two ways.
1- There would be a menu option that labeled for an emergency error. The the gas could be changed with warning AND only down to a lessor O2% (anything greater is just conservatism and safe). Then it would recalc the dive with many warnings and prompts, etc etc.
2- Something like a dive planner that shearwater currently has. This though I could see could be useful “fun” in deco as well. If you had the option to run a dive plan with the current telemetry and adjust for GF and gases (allowing it to calc the gas changes as it does for ndl, it would allow one to see how a different gas choice or addition of a gases, etc would have effected their plan. This could be something to do while hanging on a line for information only.. BUT this too could be used in similar cases to estimate on air (or other gas options) and give you what the dive would look like with that gas to make choices from. Again informational only and would not change any of the actual dive or tissue calculations. Just the info on what would be the adjusted ndl, dec stops, etc.
I really think #2 could be a good tool for multiple uses and many do this through other tools post dive. Just was something that could be interesting to add to a computer.. also could allow to pull from the dive log for past dives telemetry to re-run surface side.


Thanks,
Andy

 

[NAM001]

Not average depth......you need to use maximum depth. Tables, and the "rule," use maximum depth.

Yes table use max depth Is that not an area of large error just like square profiles. I dont see how that could be accurate if you were at 100 for 5 minutes and 40 ft for 30 minutes. those aspects is what creates gross errors that result in gross conservatism in the results. The computer was supposed to be the great white savior to resolve that preticular problem. And in the OPs example his computer was still working so he should be able to just do a rough EAD calc to get him in ball park. Now another thing in a post. Can a shearwater use dive planning mode while submerged/ or other words is dive planning mode a surface access function only. Ive never attempted to do that. Never had the need. If one had the tables with them they could split the dive into 2 dives with the min SI between them and then be perhaps a bit closer than just using avg depth. Other than that you have no other allternative than to just goto the shallowest depth the GF value will let you go to and sit it out as long as the air will last. One other option maybe. Use the tissue saturation display and stay till it gets below perhaps 70%. The GF value may be the same thing. One could also stay at SS depth until surf GF gets below say 50 and that may be good enough. Either way it is better than doing nothing and with the shearwater you have an actual calculating tool with viewable GF data that is far superior to a dive table as inherent errors in design and use goes.

 

[tbone1004]

@saridnour even on the LP side, you're talking ppO2 starting at 2.0 ish at the surface for air, and only goes up from there. The sensors we have are simply not capable of handling that. 2.0 at the surface, close to 3.0 at depth, just for air. Double that for EAN40. Simply not something the sensor technology can handle. Since the ppO2 is a function of IP, and no regulator is perfectly balanced to tank pressure, that sensor would also have to have a pressure sensor in it to normalize it.

The issue with changing the gas mid-dive, even if in an emergency, is what kind of liability that manufacturer is going to take if you hit a wrong gas mix. If the diver couldn't be trusted to put the right mix in before the dive, what makes them think that they'd pick the right mix now?

As @cerich says, this is an equipment solution to a skills problem. Add into your predive checks, and your descent checks, to validate that you're diving the right gas. Alternatively, keep a set of tables in your pocket. The Shearwater will give you the average depth and max depth you've already seen, so keep a table of your choice in your pocket/wetnotes, and you can always revert to that.

 

[wstorms]

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.

regarding depth; a higher O2 mix in your computer would probably have worked in your favor in this case. If you think you are using EAN / following your computer that thinks so, the computer will most likely give you an alert when your max depth / ppO2 is "reached". The richer the gas, the shallower the MOD. So having a richer gas in your computer compared to what you are actually breathing gives you a shallower dive (if you do follow your computer). On the other hand, this would also "allow" for a longer bottom time, so it isn't perfect.

Some preventative tips:
- check your gas before the dive, both in the cylinder and in the computer (duh, captain obvious, I know)
- set your computer to default back to air after X hours at the surface
- copy air rec tables to wetnotes, make it a habit to always carry them
- make some default air deco tables for realistic WSHTF scenario's, put them in wetnotes. Do include rock bottom gas needs
- play with an planner app to plan a lot of dives in the range you usually dive, study the results so you have a rough idea of what a dive "should" look like

When it does go wrong, assume you are in deco, recover from there. Some options in order from relatively conservative to hail Marry:
- check your wetnotes, follow the next deeper / longer matching table (based on deepest point) up

- check your wetnotes, follow the next deeper / longer matching table (based on average depth) up

- (upfront) study ratio deco and apply principles for air

- guesstimate and padd as much as gas allows.
a) The PADI EAN32 table gives you approximately 1.6 x longer bottom times compared to the PADI RDP (air) table. Roughly. Give or take. Sort a.... So if you are close to your EAN NDL, you are close to exceeding your air NDL by 2/3.
b) running over by 2/3 is quite a lot so you will need a serious decompression. If you assume at least a 1:1 ratio over even a 1:1.5 ratio it sort a, kind a, seems to, roughly if you squint your eyes, seems to work for EAN32 operating ranges. So if you did stay within MOD as (wrongly) indicated by your computer, it could work as a reference point.
c) Ascent slowly with 1 minute stops at 21-18-15-12-9 meters (I think that's about 63-54-45-36-27 feet but I am not too familiar with imperial units)
d) do all the time (1.5x your bottom time) at 6 meter (18 feet).
e) ascent with 1 meter / minute (3 feet / minute) all the way to the surface

- Ascent slowly with 1 minute stops at 21-18-15-12-9 meters (I think that's about 63-54-45-36-27 feet but I am not too familiar with imperial units) and stay at 6 meter as long as possible

- go up and stay at 6 meter as long as possible

In any case, try to get support from the boat / other divers so they can bring gas if possible.

I can't think of any universal "get out of jail free" procedure, it really is a situation that is best prevented. All my suggestions only work if you prepared them upfront by studying and creating tables, but as you are doing deco dives I suspect you know how to do that.

 

[rjack321]

If you really want the conservatism of 35/70, no recreational table is going to give you that. If you want that level of conservatism after you have forgotten to program the correct mix then you really should be aborting the dive while doing a long safety stop. If you do choose to continue the dive you need to approach this from the perspective that you've already had one strike. You could always get a second computer and leave one set to nitrox and the other set to air so you could decide in the water which one if applicable. I know that sounds silly but that's kind of what you are asking to do just minus the second computer.

 

[PBcatfish]

...
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'm not going to say that this is the correct thing to do & I'm not going to recommend that other people do this, but what I would have done in that situation is slowly ascend to 30' & hang out there until I had 500psi left in the tank, then ascend to 15' & hang out there until I had 200psi, then surface slowly & immediately let me buddies know that I goofed up & ask them to keep an eye on me while I look to see if the oxygen bottle on the boat is full or not.