Safety stops

[Charlie99]

They are not considered the DIR approach to minimum deco, regardless of his affiliations, and that fact has been stated here by more than just me, I believe.



Contact Bob Sherwood, MHK, or BCS here on the board or on TDS. Good, bad, or indifferent, it's what I was taught. You don't have to like it. I am just explaining what I do. I've also stated that I usually add time at the shallower stops, especially on repetative dives.

I know some are still teaching to do a 30 ft/min ascent with pauses at ever atmosphere up to 30 ft, where you do 1@30, 1@20, and 1@10. I'm not sure of why some are teaching one and others teaching the other, but either way, you end up with a similar profile.

What were you taught in your Fundies class?

As this has strayed from the original thread into a DIR question, I've posted it over in the DIR forum. http://www.scubaboard.com/showthread.php?p=844330#post844330

 

[jonnythan]

Here's what Vplanner has to say for 100' for 30 mins on 32%....

Off gassing starts at 57.1ft

See, this is what I was talking about in post #9. I said that one should not just guess about where to do a deep stop. You suggested starting stops at 70 feet for a 100 foot dive of basically any duration.. 30 minutes at 100 feet is not a short dive, and offgassing doesn't start til you past 60 feet.

This is the reason I think it's not a good idea to incorporate "made up" stops on NDL dives. "Minimum deco" is a great idea, but "deep stops" where you have no idea if you're even offgassing or not for NDL dives does nothing.. and might be counterproductive.

IMO, again, keeping the ascent controlled and slow until your first stop at 30 feet, then keeping the last 10 feet especially slow (and perhaps adding a couple of minutes to the 10' stop for repetetive dives) seems to make the most sense.

 

[Soggy]

This is the reason I think it's not a good idea to incorporate "made up" stops on NDL dives. "Minimum deco" is a great idea, but "deep stops" where you have no idea if you're even offgassing or not for NDL dives does nothing.. and might be counterproductive.

Hmm, I was venturing to say that the profile I suggested matched up with the offgassing depth given in Vplanner pretty well. 70ft vs 57ft isn't substantial, especially when Vplanner is just a model also.
Most of the profile is above the offgassing depth and those stops aren't exactly 'made up'. They fit in with the model fairly well.

Do what you want, I'll do what I do.

 

[jonnythan]

Hmm, I was venturing to say that the profile I suggested matched up with the offgassing depth given in Vplanner pretty well. 70ft vs 57ft isn't substantial, especially when Vplanner is just a model also. Do what you want

I beg to differ, but 13 feet is a pretty substantial difference. 2.7 atm vs 3.1 atm isn't exactly trivial.

When does Vplanner say offgassing starts for a 15 minute dive to 100 feet? My guess is the difference will now be 20 feet or more.

Remember your dive to 100 feet, starts offgassing 13 feet above your proposed first stop.. and this dive is right up on the NDL limits. What happens when you do one that's not that close to the NDL limits? If you don't do the deep stop, where do you draw the line?

Are you comfortable saying that a 70 foot stop when you don't start offgassing for another 13 feet (at the start of the stop) is the best possible ascent for the dive?

 

[Soggy]

I beg to differ, but 13 feet is a pretty substantial difference. 2.7 atm vs 3.1 atm isn't exactly trivial.

If deco were an exact science, I'd agree with you. But it isn't

When does Vplanner say offgassing starts for a 15 minute dive to 100 feet? My guess is the difference will now be 20 feet or more.

Didnt' check. I would not do all that on a 15 minute dive...that would be pretty silly.

Remember your dive to 100 feet, starts offgassing 13 feet above your proposed first stop.. and this dive is right up on the NDL limits. What happens when you do one that's not that close to the NDL limits? If you don't do the deep stop, where do you draw the line?

Man, you want hard and fast rules where there aren't any. Sheesh.

Are you comfortable saying that a 70 foot stop when you don't start offgassing for another 13 feet (at the start of the stop) is the best possible ascent for the dive?

I'm comfortable saying that offgassing doesn't start at 57.3 ft every dive, every day and that 1 extra minute around 70 ft isn't going to have any noticeable effect....

 

[Soggy]

Let's be real here...we're talking about a short dive to 100', not an expedition to the Britannic. A couple minutes here or there and exact shaping of the curve is not really that big an issue. I know I feel better after doing a dive with profile I stated vs the industry standard. I've also posted this question to the FifthDX yahoo group to get some clarification on the issue.

 

[jonnythan]

I'm not sure you answered my question.

Sure, in reality, an extra minute at 70 probably won't make a difference. However, DIR is not about what you can get by with.. it's about what's right.

Do you really feel that the level of imprecision you're displaying (13 feet here or there, an extra minute here or there, I'll do deep stops for x dive but not y dive at the same depth though I can't articulate why) is right? Do you think that's DIR?

Do you think you could get by with that sort of thing for, say, Tech 1?

 

[jonnythan]

Didnt' check. I would not do all that on a 15 minute dive...that would be pretty silly.

Precisely how many minutes do you need to spend at 100 feet before you feel a deep stop is necessary?

Where would you start your deep stop and why would you start it at that depth? I don't think "because they said so in DIRF" is an appropriate answer.

I don't mean to hammer you, but IMO something is wrong here.

 

[Soggy]

Sure, in reality, an extra minute at 70 probably won't make a difference. However, DIR is not about what you can get by with.. it's about what's right.

Talk to anyone trained in decompression (which you and I are not, BTW), and they will tell you there is no "right" decompression. It changes from person to person and day to day...there is only 'this works most of the time for most people'

Do you really feel that the level of imprecision you're displaying (13 feet here or there, an extra minute here or there, I'll do deep stops for x dive but not y dive at the same depth though I can't articulate why) is right? Do you think that's DIR?

I think I understand enough about recreational level profiles that I am comfortable making choices and extrapolating about what would work

I never said I was Mr. DIR. I just gave a profile that I was taught in a GUE class and explained what *I* do.

Ask yourself this...is what I am doing more or less safe than ascending straight to 30 ft (a difference of 2 ATM, in this case) and just doing 3 minutes of total deco time?

Do you think you could get by with that sort of thing for, say, Tech 1?

I think as you read more and progress more, you'll realize that decompression is a lot less black and white than you think. *Nobody* really understands how it works, just that certain types of profiles seem to work.

 

[Soggy]

Eh, I'd probably chop off around 10 ft of the deep stops for every 5-10 minutes I have of remaining 'ndl' time. We'd plan it ahead of time using all the tools available.

Hello...recreational profile. Reread what I said about the Britannic.

Try using a little common sense here. IT IS NOT CUT AND DRY. I do what seems best based on my limited knowledge. If you don't like it, don't do it. You can continue to do 1@30, 1@20, 1@10 on every dive you do regardless of duration.

Precisely how many minutes do you need to spend at 100 feet before you feel a deep stop is necessary?

Where would you start your deep stop and why would you start it at that depth? I don't think "because they said so in DIRF" is an appropriate answer.

I don't mean to hammer you, but IMO something is wrong here.