setting to nitrox to reduce over conservatism on dive computers

[DaleC]

but the trick is to use a hammer as an adjustable wrench.

 

[Tigerman]

well, that IS for advanced users...

 

[dmoore19]

If you have a big enough hammer..........

 

[John C. Ratliff]

I've come to the thread late, but I'll answer the original question:

Yes, I have done this, with caveat.

Firstly, I won't endorse this as a solution for anyone else. Modern algorithms are calculated for a designed performance and intended to keep you safe. It isn't all about manufacturer liability. If a manufacturer aims to create a 'safe' dive computer, then algorithm conservatism is a very good solution to that.

As an instructor, I dive demanding schedules with students who are unlikely to be using the same computer as me. For the rare recreational-level course I teach (basic wreck or sidemount), I use my old 1st-Gen Suunto Vyper. Over repetitive deepish dives, it often provides significantly less bottom time than my student's computers. I need to maximize training time - so I experimented with setting my computer as per different nitrox mixes to better emulate/match what my student's computer were providing in bottom-time.

So, sometimes I will put my computer onto 22 or 23% EANx, for a air dive. This matches closely what some other manufacturers/ computers are giving.

The caveats:

1) All these dives, I have already planned on decompression software - and I have a bullet-proof understanding of the parameters I am working within. I carry back-up plans, on wetnotes, for all of these dives... and even with the 'adjusted' settings on the computer, I am diving within them.

2) All of my recreational dives end with a minimum ascent procedure (not a traditional safety stop). This is a minimum of 9m/1min, 6m/2min and 3m/3min. If compared against calculated dive plans, this more than covers the off-gassing needed well above and beyond and discrepancies caused by the rather inelegant manipulation of my clunky old computer.

3) My ascents are all performed to a high technical-diving standard, with proper ascent rates, stable buoyancy and no saw-toothed profiles. I am fit, well-hydrated, no other significant DCS pre-disposing factors and I dive very frequently (daily). I have dived for over 22 years and never had a DCS symptom from a recreational/no-stop dive (and only one unconfirmed 'pain-only' possible DCS following a particularly significant multi-week schedule of technical diving).

DevonDiver,

I would highly suggest you get a regular check for dysbaric osteonecrosis; I think you are at high risk:

Aviat Space Environ Med. 2007 Dec;78(12):1150-4.Dysbaric osteonecrosis in experienced dive masters and instructors.

Cimsit M1, Ilgezdi S, Cimsit C, Uzun G.
Author information



Abstract

INTRODUCTION:

Dysbaric osteonecrosis (DON) is a type of aseptic bone necrosis of long bones such as the humerus, femur, and tibia. It is observed in workers who perform in high-pressure environments.
METHODS:

There were 58 volunteer divers included in this study who had performed at least 500 dives, were working as a dive master or instructor, had never performed industrial and commercial dives, and did not have a diagnosis of osteonecrosis. Radiological evaluation was performed according to the guidelines suggested by The British Research Council Decompression Sickness Panel. A total of eight X-rays were taken per patient. When suspicious lesions were detected, MRI of the region was performed.
RESULTS:

Of the 58 divers, 2 were eliminated because of inadequate X-ray studies. A total of 18 DON lesions were detected in 14 of 56 (25%) divers. Age was the only variable independently associated with the development of DON (P < 0.05).
DISCUSSION:

The DON prevalence of 25% in this study is high considering the dive instructors had thorough diving training and strictly practiced the decompression rules. We believe this high prevalence is a result of frequent and sometimes deep dives for many years. Our findings raise the question of whether these divers can be seen as "sports divers" or should be seen as "occupational divers." If the latter description is approved, dive masters and instructors should be kept under periodic screening for DON lesions just like professional commercial divers to help reduce the morbidity associated with this disease.
(emphasis added, jcr)
Dysbaric osteonecrosis in experience... [Aviat Space Environ Med. 2007] - PubMed - NCBI

SeaRat

 

[DevonDiver]

I would highly suggest you get a regular check for dysbaric osteonecrosis; I think you are at high risk:

Yes, it's something I read about and considered before. From what I read, it's a factor any full-time dive pro, or very avid and active diver might consider. (a bit off-topic though)

 

[Storker]

the right tool is always a HAMMER never a screwdriver...

That's just because all you've got is a hammer. We all know that that's when every problem looks like a nail.

 

[DaleC]

This is devolving into a pretty decent philosophical discussion...

 

[Doc Harry]

Why is there a need in increase your risk of getting DCI?

 

[John C. Ratliff]

Devondiver and others,

Instead of fiddling around with your decompression meters, and not doing anything about the basic diving physiology, why not establish oxygen decompression stations at 30, 20 and 10 feet (10, 7 and 3 meters)? We did this on the Warm Mineral Springs Underwater Archeological Project t Warm Mineral Springs aunder Sonny Cockrell and it worked wonderfully in 1975 (I believe). This actually changes the diving physiology to more safely release excess nitrogen and avoid both decompression sickness and micro-bubble formation. We dove tables, but rather than air decompression, we used oxygen and used safety stops even on "no-decompression" dives with oxygen. I think this could easily be established on charter boats using 300 cubic foot cylinders, and hoses down to "T"s with second stages mounted on them.

SeaRat

 

[rhwestfall]

.....