Bottom Time, beginner question

[rick00001967]

Good one.

It's still Workman's fault, though: Haldane had 2:1 across the board and things were easy. Workman came up with different M-values for different tissue compartments so now you have to pick the least "tolerant" compartment in your model to work out the no-limit depth.

thats why god invented the dive computer lol

 

[rick00001967]

I'm still a little confused, having heard numbers of 24' and 33'. Also that NAVY tables say 371 no deco minutes for 30 feet (according to that 33' doesn't fit the bill as "unlimited"). Seems some disagreement. Maybe where I read 18 or 22 feet was someone being very conservative?

just google haldane and workman and you will find the theory

 

[dmaziuk]

I'm still a little confused, having heard numbers of 24' and 33'. Also that NAVY tables say 371 no deco minutes for 30 feet (according to that 33' doesn't fit the bill as "unlimited"). Seems some disagreement. Maybe where I read 18 or 22 feet was someone being very conservative?

E.g. take DSAT M-values for RDP from Powell (p.224 in mine). The smallest M0 is for 480-minute compartment at 13.33 msw. Divide by 10 for bar/atm: 1.333: a bit more conservative than 1.58 in #18.

Divide 1.333 by 0.79 to get back to ambient pressure: 1.687. 1 is for atmospheric pressure at sea level, 0.687 is your no-limit depth of 6.78 msw or about 22 fsw. Give a take or foot or three for round-offs and more accurate conversions etc.

That's where you can stay literally forever and never on-gas to the point of having "unsafe" overpressure upon surfacing, according to RDP.

Repeat the exercise with Buhlmann's ZH-L16 (p.222) where the 635-minute compartment has M0 of 12.7 msw. That'll give you a slightly shallower no-stop depth than DSAT's 13.33: 1.60 bar or 6 msw or about 19 fsw.

You could instead go by a more practical (than "forever") runtime of 6 hours and calculate this for the 60-minute compartment (recall that it takes 6 half-times to 98% saturation, so 6 * 60 minutes). DSAT 60-minute TC has M0 of 15.79 msw, or 1.579 bar, practically no different from 1.58, and it will give you 10 msw or 33'. But at that depth you will have an NDL determined by those slower compartments.

 

[TMHeimer]

So there is disagreement according to the last 2 posts as to which theory/info. is correct.. 33 fsw or a depth like 22' or 19', am I correct?

What I take from this is 33' is "forever" for practical situations, but there is a NDL limit regarding the slow compartments. 22' or less there is no NDL on any compartments, so that's truly "forever". Agreement on that?

 

[dmaziuk]

So there is disagreement according to the last 2 posts as to which theory/info. is correct.. 33 fsw or a depth like 22' or 19', am I correct?

Different models have different no-limit depths, determined by their surfacing M-values (M0). You choose your model, you choose your no-limit depth. It may be that they come with slightly different probabilities of clinical DCS, i.e. they're all "correct".

 

[rick00001967]

remember guys......the 2:1 ratio (or more precisely the 1.58ppN) is based on the theories that haldane and workman proved.
any modern day computers or dive tables may, and have, used algorithms based on those theories, but have been tweaked in various ways.
so depending on the algorithm used, you may get a variety of different ndl's when comparing similar dive profiles.

 

[BRT]

So there is disagreement according to the last 2 posts as to which theory/info. is correct.. 33 fsw or a depth like 22' or 19', am I correct?

What I take from this is 33' is "forever" for practical situations, but there is a NDL limit regarding the slow compartments. 22' or less there is no NDL on any compartments, so that's truly "forever". Agreement on that?

Probably depends on the person. We learned 33' for forever, 60 feet for 60 minutes. I don't want to try either one right now.

 

[dmaziuk]

remember guys......the 2:1 ratio (or more precisely the 1.58ppN) is based on the theories that haldane and workman proved.

OTOH Haldane didn't have Doppler ultrasound, he asked 19th century caisson workers if they felt "the bends". Back when men were men and ate beer for lunch (probably) and all that.

Edit: OTGH they were working down there and on-gassing way more than we recreating lazy bums...

 

[broncobowsher]

I think he will be just fine in that 8' deep swimming pool. Nobody has shown anything that it could be a problem.