Ascending without a dive computer

[KenGordon]

But we are always taught that ascending too quickly is dangerous. You can't make the claim that faster is safer. At least not as a blanket statement.

Too quick is dangerous, too slow more risky as well. You can’t just assume slower is safer, it increases on gassing. You certainly cannot assume that faster is more dangerous than slower when talking about rates like 3m/minute as the exposure at depth during the ascent will be three times as long as it ought to be.

You should read some of the discussion around the NEDU deep stops study and the reasoning about increased oversaturation of slow tissues leading to more bent divers.

Rules of thumb are not appropriate for this. Maths is appropriate.

 

[Bob DBF]

But we are always taught that ascending too quickly is dangerous. You can't make the claim that faster is safer.

The rate of ascent is a given for a table. Going faster than that can be dangerous, and going slower can also give problems, because the human research to determine the safety of those tables only used the rate specified.

One problem I know of is that one can wind up in deco by not ascending fast enough, btdt. Considering OW divers are trained for NDL diving, this is hazardous for a number of reasons.

I don't know. Nine just seems high, still does. If 3 ft/min is at least in a ballpark, we're probably good.

As for 3'/min, that's 40 min to the surface from 120', aside from the gas planning, it's hard for me to believe that could be done without a deco obligation, since 4 min is normal. If someone could put that on a deco planner I'd appreciate it, since I'm just guessing.


Bob

 

[doctormike]

But we are always taught that ascending too quickly is dangerous. You can't make the claim that faster is safer. At least not as a blanket statement.

Well, ascending too quickly is certainly dangerous, but that phrase is sort of an oversimplification for an introductory OW class, where the students are unlikely to get into trouble by a slow ascent given gas limitations. I don't think that as a general rule, anyone said that "faster is safer". Ken was just pointing out that for many recreational dives, most of the tissue compartments don't reach saturation at all, so they continue to ongas during part of the ascent. If you go too slowly and spend too much time on that part, you will increase N2 loading in those compartments and possibly reduce your NDL to zero.

A good analogy would be driving. You might tell a new driver that speeding is dangerous, but that doesn't mean that it's not more dangerous to be driving 15 MPH in the left lane on the highway than it would be to be doing 55 MPH.

As with most things, the devil is in the details!

 

[txgoose]

Rules of thumb are not appropriate for this. Maths is appropriate.

Yep. I was actually using maths, and theSSI tables with NDL times listed. I haven't seen you use maths yet.

The rate of ascent is a given for a table. Going faster than that can be dangerous, and going slower can also give problems, because the human research to determine the safety of those tables only used the rate specified.

I don't guess I have seen a minimum ascent rate posted anywhere. I've seen max ascent rate, but not min. Or are you saying that all divers should only ascend at 30 ft per minute? Seems very restrictive for shore divers.

One problem I know of is that one can wind up in deco by not ascending fast enough, btdt. Considering OW divers are trained for NDL diving, this is hazardous for a number of reasons.

Agreed. Which we had talked about. Two feet per min would be bad. But what is the safe number?

As for 3'/min, that's 40 min to the surface from 120', aside from the gas planning, it's hard for me to believe that could be done without a deco obligation, since 4 min is normal. If someone could put that on a deco planner I'd appreciate it, since I'm just guessing.

Can you show me how 3 feet per minute would incur a deco obligation? Hell, I'm willing to talk about 4 or 5, but no one else seems willing. Now, I do agree that 3 ft/min could bump up against a diver's turn pressure, I've stated as much, but that is vastly different than saying something is dangerous. I would LOVE someone to put this into a deco planner for sure. Sweet mary, please, please, please.

Well, ascending too quickly is certainly dangerous, but that phrase is sort of an oversimplification for an introductory OW class, where the students are unlikely to get into trouble by a slow ascent given gas limitations. I don't think that as a general rule, anyone said that "faster is safer". Ken was just pointing out that for many recreational dives, most of the tissue compartments don't reach saturation at all, so they continue to ongas during part of the ascent. If you go too slowly and spend too much time on that part, you will increase N2 loading in those compartments and possibly reduce your NDL to zero.

A good analogy would be driving. You might tell a new driver that speeding is dangerous, but that doesn't mean that it's not more dangerous to be driving 15 MPH in the left lane on the highway than it would be to be doing 55 MPH.

As with most things, the devil is in the details!

I keep trying to talk about the details and people keep making up random analogies that I don't see how they apply. I expect to have a diver drop on my head at some point. I am not expecting a diver to blow up through me on a fast ascent. But, never say never. Can we get past the "you're gonna die if you ascend too slow" comments and actually look at defining what too slow might be? I've already acknowledged two feet per min is probably too slow. Seems like God and everybody is afraid of actually discussing any number at all.

The statement made was that nine feet per min was the safe minimum ascent speed. No one has defended that statement as close to reality, but everyone seems hell bent on me being wrong for exploring what that safest minimum might be. I'm going to go back to the threads about diver training being watered down. Seems easier than exploring for answers here. I'm actually sad to say it but this now seems like a royal waste. If anyone has a deco program that might come up with a real number for rec diving, I'd love to hear from you.

I guess we don't even all have to agree to disagree, we can all just agree to argue about split fins because we don't have enough of those threads.

tx "a bit disappointed in SB today" goose

 

[doctormike]

I keep trying to talk about the details and people keep making up random analogies that I don't see how they apply. I expect to have a diver drop on my head at some point. I am not expecting a diver to blow up through me on a fast ascent. But, never say never. Can we get past the "you're gonna die if you ascend too slow" comments and actually look at defining what too slow might be? I've already acknowledged two feet per min is probably too slow. Seems like God and everybody is afraid of actually discussing any number at all.

tx "a bit disappointed in SB today" goose

It's not a random analogy, but sorry if you don't understand how it applies.

No one said "you're gonna die"

You aren't going to get precise numbers for "too slow" since no one has spent decades developing tables for a sufficiently wide range of ascent speeds.

The point at which you may reach NDL on ascent with an excessively slow ascent rate would depend on your profile (mix, gas and depth), so no one is going to be able to give you that specific number.

Sorry you are disappointed. I'll stop bothering to reply, since my efforts seem to have upset you. Dive safe!

 

[boulderjohn]

Can you show me how 3 feet per minute would incur a deco obligation?

A study done in 2002 compared ascent rates by measuring bubble formation in the divers. It compared 60 FPM, 30 FPM, and 10 FPM. The one that got the best results was 30 FPM, which is what nearly every expert recommends. The second best was 60 FPM. The worst was 10 FPM.

If you are talking 2,3, or 4 FPM, you are going to an extreme that no one has ever mentioned in any place I have seen before this thread. No, it has not been studied, because I am sure anyone considering a study would dismiss such an ascent as being absurdly slow. While you are ascending at that rate, your slower tissues are loading up with nitrogen. Perhaps you can explain the benefits of loading the slower tissues with nitrogen during an ascent, because I can't imagine one.

 

[txgoose]

You aren't going to get precise numbers for "too slow" since no one has spent decades developing tables for a sufficiently wide range of ascent speeds.

The point at which you may reach NDL on ascent with an excessively slow ascent rate would depend on your profile (mix, gas and depth), so no one is going to be able to give you that specific number.

Sorry you are disappointed. I'll stop bothering to reply, since my efforts seem to have upset you. Dive safe!

I guess I assume that if we have deco programs that people trust, there must be some amount of knowledge that would be able to produce a number that is at least halfway thought out. It would appear some folks have studied this area. Maybe not.

I agree that this thread has probably run its course. I appreciate you and have stated that several times in multiple threads. Just not sure why ANY number seems taboo. Well, except nine ft. per min. It seems well regarded.

 

[txgoose]

A study done in 2002 compared ascent rates by measuring bubble formation in the divers. It compared 60 FPM, 30 FPM, and 10 FPM. The one that got the best results was 30 FPM, which is what nearly every expert recommends. The second best was 60 FPM. The worst was 10 FPM.

If you are talking 2,3, or 4 FPM, you are going to an extreme that no one has ever mentioned in any place I have seen before this thread. No, it has not been studied, because I am sure anyone considering a study would dismiss such an ascent as being absurdly slow. While you are ascending at that rate, your slower tissues are loading up with nitrogen. Perhaps you can explain the benefits of loading the slower tissues with nitrogen during an ascent, because I can't imagine one.

I have never, ever proposed benefits. This was an academic discussion. Someone said nine feet per minute is the lowest safe ascent rate. I simply questioned that and wanted to converse about what that minimum might actually be. that is all. nothing more. nothing less. no agenda. We talk about limits all the time so that we can speak intelligently about what our bodies are experiencing. I simply wanted to talk about what that lowest limit might really be. I will now accept 9 feet per minute like everyone else does. Sounds good. I capitulate.

 

[doctormike]

Can you show me how 3 feet per minute would incur a deco obligation? Hell, I'm willing to talk about 4 or 5, but no one else seems willing. Now, I do agree that 3 ft/min could bump up against a diver's turn pressure, I've stated as much, but that is vastly different than saying something is dangerous. I would LOVE someone to put this into a deco planner for sure. Sweet mary, please, please, please.

OK, since we disappointed you before, and since you asked so nicely, I'll take a shot at this. I could be wrong, I always questioned these "average depth" models, but they are pretty commonly used in teaching.

You are diving air to a bottom depth of 100 feet. You stay for 15 minutes. NDL of air at 100 feet is 20 minutes, so you are still within your recreational, no-stop limits when you decide to ascend.

You ascend at 3 FPM, so it takes 33 minutes to surface (ignoring the safety stop). Your average depth for this leg of the dive is approximately 50 feet (a bit deeper if you include a safety stop).

So for decompression calculation purposes, you can model this as a multi level dive: 15 minutes at 100 feet, and 33 minutes at 50 feet.

Here is that ascent on MultiDeco, assuming gradient factors of 30/70. Note that it uses a standard ascent rate between the levels:

Dec to 100ft (1) Air 60ft/min descent.
Level 100ft 13:20 (15) Air 0.85 ppO2, 100ft ead
Asc to 50ft (16) Air -30ft/min ascent.
Level 50ft 33:00 (49) Air 0.53 ppO2, 50ft ead
Asc to 20ft (50) Air -30ft/min ascent.
Stop at 20ft 21:20 (72) Air 0.34 ppO2, 20ft ead
Surface (72) Air -30ft/min ascent.


So you have gone from being 5 minutes away from your NDL at depth, to a 21 minute deco obligation at 20 feet, because of the ascent rate of 3 FPM.

 

[Rred]

Dunno, guys. I was told it (45d ascents) was something that French instructors in the Carib were teaching as standard. Not being French and not being in the Carib, I never looked into the details. I figured conservative use of the USN tables would be good enough. And mind you, this was at a time when recreational divers--and instructors--were using the standard USN tables, which are "warm water tables" when diving in cold water with wetsuits, which the USN said was unsafe, and should require cold water compensation of 1-2 groups, or the cold water tables.

Very few cold water divers in the Carib, no?

Coincidentally, I saw Mike Nelson on a SeaHunt rerun the other day. He just followed his bubbles, and somehow, he also survived.

I believe the key is to drink red wine before diving. The bubbles get inebriated from the alcohol, and they are too confused to make a rapid ascent. So, following them results in a slower ascent rate.(G)