Using O2 on NDL dives

[gulfdiver]

Running a dive to the NDL limits has a slightly higher risk of DCS than a dive that required only a short amount of decompression time and that time is completed. Supplementing a full no-stop dive with an elevated oxygen content mix is quite helpful.

For example. (using USN tables for discussion)

Let's say you do a 90 foot dive for 45 min using EAN 32. This gives on USN a no stop time of approx 45 minutes. And you cannot fly after this dive for 12 hours. If we add in just 5 minutes of breathing 100% oxygen at 15 feet the divers new "ceiling" is now 4000 foot mean sea level (or can ascend up 4000') extend that 5 minutes to 10 minutes and now the new ceiling is 5000'. Do the same profile and use EAN 50 instead of 100% and your new post dive ceiling is only 3000'. (logical).

If you get out of the water and breath 100% oxygen for 10 minutes on the surface after a 5 min air surface interval (getting out of gear) and you can push the ceiling up to 4000' msl. (similar result)

I've long been a proponent of "padding with gas" adding a little oxygen after the schedule has been completed or after the dive computer has cleared. The benefits are clear when it can be done in a benign environment.


Consider it oxygen as a prophylactic.

Cheers

I agree 100%

[divindoc]

I agree 100%

+1. I swim up the run @ Ginnie breathing off my 02 bottle, after I use it for deco (whether or not I "need" to). Breathing 100% on deco creates a larger driving force to offgas Nitrogen. Take a break on backgas every 20 mins. and you should be fine. I know I feel a hell of a lot better using O2 to deco, and the physiology supports it.

[Burke]

Yes, I sometimes use O2 up the run for a little extra margin and on one occasion breathed 02 post dive in the car, but that's a backup plan rather than something planned. My plan going into the water is to do enough deco so that I feel comfortable coming off 02 at the last stop and coming out on backgas. I certainly don't go into the water planning to come out too early and do the rest of my deco on the picnic table. So when someone feels the need to breathe 02 topside, either there's a problem or the dive wasn't carried out as planned. In either case, it's still a problem, right?

Divindoc, I'm not disputing the benefits of 02. As I have said before, I think 02 and a stage should be SOP for every cave dive. But, when I hear someone talk about not feeling well after the dive, I think classic signs of decompression stress. 02 or not, it is possible to plan enough deco to avoid feeling tired. I think we would both agree that if someone needs to take 02 hits post dive to feel better that would indicate a potential problem.

JS1Scuba, I agree with what you're saying, but I don't do the kind of expedition diving you do and don't normally have a need to do that. I do two cave dives and I'm normally done for the day, one if there was a lot of deco involved.

[Superlyte27]

The dive I did last week was half a mile or more hike from the car. Then a hike upstream for another 1000 yards. Carrying a stage, oxygen and doubles 95's was brutal. I made it in one trip. I'm not sure how much it helped to breathe oxygen for the walk to and from the water to the truck, but it had to help some. It certainly didn't hurt.