nitrox or air,

[redacted]

I tend to look at this type of thing from a cost effectiveness standpoint. The dollar cost difference is fairly obvious. You can't do much trade-off without effectiveness measures.

 

[TMHeimer]

Slight cost???

I estmate that using EAN for all dives my wife and I have done would have cost me an additional $10,000.

Right. Maybe $6 vs. $14 fills?

 

[Ghetto Diver]

This one can go on and on...but the OP has not chimed in since their post. What depths during the week, how many dives a day etc.....
@ DD, I wouldn't say singularly, but it is the primary reason to use nitrox in my AO. Double dips @ 80'-ish is simple div-o-nomics...everyone wants MOAR bottom time.

 

[DevonDiver]

I tend to look at this type of thing from a cost effectiveness standpoint. The dollar cost difference is fairly obvious. You can't do much trade-off without effectiveness measures.

Me also. Most of my dives are teaching courses. I'm an independent instructor... I only get my gasses paid for on nitrox and tech courses. I'd have to pay my own gas, out-of-earnings, if I elected for it... where I often work out of in the P.I. it costs ~$5 a tank. I dive sidemount... so that's $10 a dive... twice a day is $20... That's more than I pay for food in a day... more than the sushimi, crab and prawns Valentines dinner I had last night....

However, if I only dove occasionally and for pleasure... I'd use it every time.... even knowing I have a low predisposition to DCI... having never been bent (even when two buddies were...). I'd also carry a 40 of 50% to come up on....

 

[TMHeimer]

Me also. Most of my dives are teaching courses. I'm an independent instructor... I only get my gasses paid for on nitrox and tech courses. I'd have to pay my own gas, out-of-earnings, if I elected for it... where I often work out of in the P.I. it costs ~$5 a tank. I dive sidemount... so that's $10 a dive... twice a day is $20... That's more than I pay for food in a day... more than the sushimi, crab and prawns Valentines dinner I had last night....

However, if I only dove occasionally and for pleasure... I'd use it every time.... even knowing I have a low predisposition to DCI... having never been bent (even when two buddies were...). I'd also carry a 40 of 50% to come up on....

Hats off to you Andy. My Air is free with the shop as a DM. Guess it's a new ballgame as an independent instructor.

 

[Patoux01]

I estmate that using EAN for all dives my wife and I have done would have cost me an additional $10,000.

Yeah, me too, if I had done about 8000 dives that'd be true. Since I've only done a hundred or so, my nitrox costs have been about... 50$

 

[scubadada]

...For further reading, there are a number of threads you can search for where CNS oxygen toxicity, etc., has been discussed in the context of recreational diving. There seems to be some debate as to whether we recreational divers doing a lot of diving over the course of week or so need to be concerned or not.

I think the actual answer is that recreational divers need not be terribly concerned over their cumulative oxygen exposure. Dive computers generally monitor oxygen exposure by two very different algorithms.

Pelagic Pressure Systems (Oceanic, old Aeris, Hollis, Sherwood, Genesis, I assume now Aqualung) use a rolling 24 hour window and the NOAA table 24 hour exposure limits. It is entirely possible to exceed the 24 hour limit using this algorithm (or the table itself) in recreational diving, especially when using rich mixes like 36%. When doing 4 dives per day, there will be 5 dives in the 24 hour window before credit is given, lowering the oxygen exposure. This is the more conservative of the two methods. When one exceeds the 24 hour limit, at least my Oceanic computers, make it more difficult (VT3 and Geo2) to use the computer normally until the oxygen exposure is below 100%. This is really my only major complaint concerning my Oceanic computers. I am able to dive the VT3 by using alternate screens and the nitrogen exposure graphic or by using the graphic on the Geo 2. This really is suboptimal.

Most other computers (including Shearwater) use the Seiko-Epson algorithm to monitor oxygen exposure. This uses the NOAA exposure table but gives you credit for a 90 minute oxygen elimination half life during the SI. It is likely impossible to exceed 100% oxygen exposure using this algorithm in recreational diving. This algorithm is considerably more liberal than the PPS algorithm.

Oxygen exposure guidelines are not based on high science. It is my impression that the 90 minute elimination half life for oxygen was thought to be a relatively conservative estimate of the "true" value, and thus, safe. I would certainly appreciate additional comments or corrections on this topic from those more knowledgeable than me. This is not an easy topic to gather extensive hard facts about.

 

[scubadada]

Is it just me, or do I see many people valuing nitrox singularly for the reason of extending bottom time?

Don't people value insulating themselves from the risk of DCI?

Exclusively for more NDL time. Of course, I don't always use all the time available to me and my nitrogen exposure ends up being less than it would on air as a side benefit

 

[scubadada]

.... and yet there are people in chambers every day..... and a significant proportion of DCI cases are 'undeserved'...meaning that they were inside NDL, no fast ascent and no 'red light' pre-disposing factors....

I prefer "unexplained." We have insufficient understanding of DCS, particularly in a specific individual, for a specific dive, to conclude that it was undeserved. Many of these hits, after careful analysis, reveal one or more risk factors that were not appreciated (colder water, exercise at depth, dehydration...). There are probably individuals at greater risk than others for DCS due to factors that have not yet been identified.

 

[Storker]

Don't people value insulating themselves from the risk of DCI?

I do.

I'm middle-aged, and in typical middle-age shape. While my gas time is pretty close to my nitrogen time on air, I have a comfortable margin if I dive nitrox. Given that most of my diving is in cold water (not good for offgassing) and in a drysuit (larger risk of "corking" from my safety stop), I strongly prefer to not ride my NDLs. IWhile I of course do my best to dive triangular or multilevel profiles, do proper safety stops and ascend as slowly as possible from the safety stop, in reality I don't always succeed. So sometimes I get what I self-diagnose as subclinical decompression stress. IME nitrox helps against that too, in addition to providing a margin towards the NDL.