Why do computers rot the brain?

[AquaTec]

Bob3 once bubbled...
OK, going to jump in now.
I've been grumbeling for a long time now that dive computers can become a potential safety hazard when used as intended.
The following sorta covers the Pugster's comment of:
The most common time dive computers are at risk of making mischief are when a person goes on vacation and packs multiple dives in a series of consecutive days, pushing the crap out of the NDL's. They're setting themselves up as prime candidates for those so-called "undeserved hits" that happen all too often.
A person using tables tends to "round off" towards the conservative side.

The most common statement heard by the DMTs as they're dogging the chamber hatch is: "I don't understand it, my computer was still in the green!".
It's nice to get a lot of bottom time in, but a measure of conservatisim may keep you from needing to use a cane sometime in the future.

This is a good point and very acurate, i believe it is more of a problem with the lack of understanding about the principles of decompression, the understanding of residual nitrogen, and the result of multi day repetative dives.

weather you are using tables or a computer you need to apply extreme conservatism to this type of diving, and this may be the one area that dive computers are missleading, or the education is missleading.

 

[AquaTec]

people where getting "undeserved hits" long before computers where around. tables can give you just as many "undiserved hits" as computers.

Its all about how close to the edge you want to live, or unknowingly reside

 

[Uncle Pug]

Now so you don't get your knickers in a knot... I am actually very busy and doing this on the side... so when I leave to teach a class it is not abandonment.... I still love you... it is just that some things take precedence.

SCUBA: no it is not semantics... your computer & computes your watch measures. But hey... I understand your need... so quibble away.

Aquatec: 1. computers fail... and if you haven't been paying attention then you had better have two... or three... or four. But there is more to it than this. I have limited my discussion to recreational diving here in this forum and thread. But the idea of paying close attention to details and teaching your brain to collect, process and use information goes further than I have explained... or probably will be able to explain.

2. As Bob3 points out the advantage in safety goes to tables.

3. There are techniques that you will learn in DIRf and GUE tech classes that will allow you to handle these situations... by adjusting your profile.

4. Same answer as 3.

And now dear friends I must step away from the computer.

 

[MikeS]

Uncle Pug once bubbled...

That would be hyperbole.... this is a metaphor

Indeed, and a hyperbolic metaphor at that; and yet one cannot but think that these specific words were chosen to express other than their literal meaning, in a humorous if not sardonic sort of way.

 

[Jarhead]

Bob3 once bubbled...
A person using tables tends to "round off" towards the conservative side.

Bob,

You make it sound like computers don't round to the conservative side. Granted, Not all computers are create equal. Some are very close to the US Navy tables but other are much more consevative.
An example of this occured last Friday. After our first dive of the day, we were comparing tables and two different computers. After an 1 hour SI, my computer (Orca Pilot EAN) and the US Navy tables were right together for the NDL of the second dive. The other computer (Suunto Cobra) was seven minutes shorter to NDL. Some computer are much more conservative than tables.
Note: Not all tables are the same either. My understanding is that PADI tables (or wheel) are more conservative than the US Navy tables. And NAUI has just release new tables (I think they are based on RGBM, but I'm not sure of that).

Respectfully Submitted,
Philip (Jarhead)

 

[AquaTec]

the PADI tables used to be the same as the Navy tables

60 for 60 etc. but then they changed them to 60 for 55 etc.
to make them more conservative

 

[nradov]

Bob3 once bubbled...
The most common time dive computers are at risk of making mischief are when a person goes on vacation and packs multiple dives in a series of consecutive days, pushing the crap out of the NDL's. They're setting themselves up as prime candidates for those so-called "undeserved hits" that happen all too often.
A person using tables tends to "round off" towards the conservative side.

The problem there is not with the computer or tables as such, although most will give you completely inaccurate information when it comes to doing repetive dives. DCS is not random and an "undeserved hit" in the circumstance you describe will have one of three underlying causes. 1. PFO or similar circulatory system shunt. 2. Bounce diving ( http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm ). 3. Poor physical fitness . You guys who are doing a bunch of dives over a few days need to understand how all the pieces fit together or else someday you're likely to get hurt and not know why.

Also, there is really no such thing as an "NDL" (unless we are talking about diving into the swimming pool). That's why we do the correct deco from every dive regardless of what any tables say.

 

[boomx5]

It's good to have some more inteligent people around here.

 

[nradov]

AquaTec once bubbled...
I would love to hear more about this one. I beleive I have a good understanding of decompression and how it works, tell me more about the simple rules of thumb that will allow me to throw away my tables and computer

If we are talking about a simple open water dive to 100ft with about 30% O2 in the breathing mix then anything up to about 32 minutes bottom time falls into the category of minimum deco. Your first deco stop would be at about 80% of maximum pressure rounded off, or 70ft in this case. Ascend at 30fpm to that point, then stop every 10ft to give a total ascent time of 10 minutes or so. If you want to be a deco weenie you can pad the last couple stops a bit, no harm in that as long as you have the gas. For a multi-level dive with the deeper portion first we would just treat the shallower part as a long deco stop, then deco from that.

Then after a reasonable surface interval we can go back and do the same dive again and again, just be a little more careful to ascend slowly in case there were still some bubbles in the bloodstream. Don't bother with trying to figure out "RNT" or anything like that, it isn't relevant.

The problem many divers run into with the common tables or computers is that they are based around the false concept of an "NDL" and so end up doing less than the optimal deco. For a 100ft, 30 minute dive they might tell you to go straight up to 15ft, do a "safety stop" for a few minutes, and get out. That profile is likely to leave you bubbling quite a bit. Bad tables are no better than a computer in this regard.

Managing open water dives this way is really quite easy in practice. The only hard part is unlearning the nonsense that most divers are taught in typical classes (it took me a long time to break through that mental block).

Deeper dives can also be handled in a similar matter, but the rules are slightly more complex and I'm probably not qualified to explain all the details.

 

[AquaTec]

interesting you are right i would need to unlearn all of what i know about deco procedures.

so on the dive you discribed, lets say you do not want to do any deco at all. constantly being able to surface at any time.

and lets say you are moving up and down through the water collum along a reef between 100 feet and 50 feet, how do you know how long you can do this dive for and still remain within the NDL