Bottom Timer and Tables vs. Computer

[lamont]

Lamont, that post is a perfect example of what I was trying to say in mine above. You have the tools and the understanding of what's going on, to be able to decide what you need to do, based on where you have been and for how long. Being able to envision the model and how it is going to assess loading in various compartments, gives you a good gestalt for where you need to go and how long you probably ought to stay.

Yeah, and with the unplanned excursion into a little bit of decompression on that sawtooth profile didn't really involve much conscious thought or even communication. I did consciously think something like "we've spent 10 minutes scootering around the honey bear, so that fixes the fast compartment issues with that 90 foot bounce", but the 15 minutes of backgas deco wasn't communicated other than we just wound up hanging around 15-20 feet for 15 minutes. I didn't even think about the fact that the 90 foot excursion had happened 10 minutes after the 100 foot NDL so we were doing about 1.5x deco. After awhile you just get a sense of how much of a mistake you've made deep with your profile and what is more than sufficient to fix that shallow...

For purely recreational shore diving, though, the algorithm that I use on 32% is:

1. send no more than 30 minutes at no more than 100 fsw
2. ascend promptly to 50 fsw or shallower
3. spend no more than 30 minutes between 50-30 fsw
4. spend 5-10 minutes of deco coming up from 30 fsw

I've done a ton of dives following that profile. And usually if you do #1 and #2 correctly then the temperature or bladder issues will get you out of the water before you need to bother thinking about decompression. I usually don't think that much about #3 and #4 but the profiles just work out that way.

It's probably easier to hit decompression issues on 32% if you're diving square profile (wreck) dives to 80 fsw (where you'll probably not want to sit around doing 10 minutes of deco at 10 fsw because there's nothing to look at other than the upline). But we don't have a lot of dives like that around here. 1-1-2-3 deco or something like that will be pretty clean though.

[dsteding]

And, why is it better to stick with the computer rather than figure out which of the above tables works for you.

After reading this again, another thought came to mind. Now it could just be my lack of understanding but in order to figure out Which tables work for me, I'd also have to learn which ones don't work for me, which means experiencing DCS whether it's just feelining like crap, or some other symptoms. If I listen to my computer, that is less likely to happen, right?

I missed this, but figured it is worth a response, here is mine:

Well, not really (you don't need to get bent). If you even have a simple understanding of decompression theory, you can make some choices about risk tolerance, and make some choices on some basic principles (up to 20 and hang ala buhlmann, or stop deeper to minimize bubble growth, for instance).

I'm not sure listening to your computer is less likely to get you bent. Andrew has an interesting slide in his tech 1 class about probability of getting bent. To paraphrase, his belief is that it is poor skills that are the major contributor to getting bent (bad buoyancy, inability to follow a schedule, panicking, that type of stuff). The reality is that many algorithms, as Matt has noted, are pretty well vetted at this point. Picking a strategy for you that works and having sufficient skills to execute the dive will keep you out of the chamber.

There is also, in my opinion, too much fear of DCS. The only thing I truly fear is ox-tox, everything else is manageable.

Of course, at the end of the day, if, say, a straight buhlmann profile gets you out of the water with no acute DCS symptoms but feeling like poo, maybe it is time to revisit the strategy chosen. The deco I've been doing has gotten me out of the water feeling spectacular--like full of energy and refreshed--which is saying something, I think.

[lamont]

http://www.youtube.com/watch?v=eNqPTOb31S8

(saw this awhile ago and i still haven't found zee rare zumatran zee badger, even though i don't use a dive computer)

[CaptnJack]

I guess everybody figured out that I wasn't talking about a sawtooth, but our typical shore dive, where you follow the bottom contour down to 100 feet, back up to 60ish and wander around, up to 40ish and wander around . . . What's your average depth, for figuring out how long you can safely be down there? At what point are you "ascending" and no longer accruing bottom time? The answers to these questions are not obvious, and that's where I think studying some decompression software printouts and noting where offgassing begins, and doing some reading, and attending things like Andrew's Ratio Deco seminar (which is far more than Ratio Deco) all help build the intellectual tools to make choices about what data to gather and how to group them.

Well if you are using a vyper (the last computer I used) with 32% you'll see the NDL time jump up rather dramatically at 40-50ft which dovetails with Lamont's notes. Basically once you hit ~45ft you can dink around all day and your "average depth" is irrelevant (according to computers, according to tables, and Haldane would even agree).

[CaptnJack]

Picking a strategy for you that works and having sufficient skills to execute the dive will keep you out of the chamber.

Not correct. People can get bent on the most benign, innocuous profiles. Computers are not necessarily better or worse with their frequencies of "undeserved" hits.

I think there is A LOT more stigma about DCS than about breaking your arm playing soccer for instance. Both recreational injuries, both potentially quite serious, but both in all likelihood quite fixable with proper treatment and time.

[dsteding]

Picking a strategy for you that works and having sufficient skills to execute the dive will keep you out of the chamber.

Not correct. People can get bent on the most benign, innocuous profiles. Computers are not necessarily better or worse with their frequencies of "undeserved" hits.

I think there is A LOT more stigma about DCS than about breaking your arm playing soccer for instance. Both recreational injuries, both potentially quite serious, but both in all likelihood quite fixable with proper treatment and time.

Yeah, perhaps I was over generalizing, I was really railing against the "fear" of DCS. I certainly don't want to get bent, and I use that desire not to get bent in guiding my dive planning. But, it just seems like there is a huge fear of DCS in the dive industry, and in technical diving, when the real fear should be (in my newbie tech diver opinion) oxygen toxicity.

[CaptnJack]

Yeah, perhaps I was over generalizing, I was really railing against the "fear" of DCS. I certainly don't want to get bent, and I use that desire not to get bent in guiding my dive planning. But, it just seems like there is a huge fear of DCS in the dive industry, and in technical diving, when the real fear should be (in my newbie tech diver opinion) oxygen toxicity.

Yah man I'm on board with that. A little bent is fine, a little ox-tox is the real dealio and places not just me but my buddies at huge risk.

[Maverick]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

[Sounder]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

I think he means you can fix being bent. You can't really fix the likely disposition of dying from ox-tox.

[Maverick]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

I think he means you can fix being bent. You can't really fix the likely disposition of dying from ox-tox.

Oh

[airsix]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

I'm interested too. I'm concerned about 'cumulative effects'. As in, a little bent or 'almost' bent x multiple occurences = ??? Does it add up to something bad at some point? I would think yes. Our bodies are analog, not digital. I think we get bent on every single dive we do. It's just a matter of degree. On a conservative recreational dive maybe it's inconsequential. Like 5 parts per billion of arsenic in your drinking water. But at some point there's got to be damage going on at a measurable level even before you declare yourself formally bent. I don't know. Maybe I'm way off here.

-Ben

[Joshua Smith]

If by "a little bent," you mean a skin rash, I guess I could see it that way. But I would see a skin rash as a sign that I did something wrong, or pushed my deco too hard.
Anything requiring a chamber is not "fine," in my book.

And I don't understand why you're so concerned about ox tox, Doug- it's pretty simple to avoid, no? Even looking at the main cause of death for CCR divers, who are probably at the greatest risk of ox tox, it seems to rank much lower than hypoxia or hypercapnia, for example. On OC, it's even easier to avoid- analyze your gasses, know your MOD, don't push the o2 clock, etc. Why the big deal?

[dsteding]

Why the big deal?

Because you tox, you are most likely going to die. Very few divers possess the skills to rescue a toxing diver, we practice it, but if it happens, I'm honestly going to do my best to rescue my buddy, but am not horribly optimistic on that front.

How many times have you practiced toxing diver rescue?

All the items you list-not pushing PPO2, understanding MODs, having good procedures in place, knowing your O2 exposure, all those are designed to avoid it. But, unlike DCS, we really don't understand the mechanisms of ox-tox, and all the above are fudge factors to minimize the risk. While the same may be said for DCS, we do know what causes DCS and we do have a much better statistical grasp on how to avoid it, and, by and large, the consequences are less severe.

I know of two ox-tox rescues, one by Andrew, one down in California last year. I also know of at least two toxing incidents that happened at 1.4 PPO2. There are also many mysterious deaths that are simply unexplained-and could be toxing incidents.

Mind you, I'm not adopting a cavalier attitude to DCS when I make the comparison between the two, just noting that among the two, I'd much rather be bent than toxing.

[dsteding]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

I'm interested too. I'm concerned about 'cumulative effects'. As in, a little bent or 'almost' bent x multiple occurences = ??? Does it add up to something bad at some point? I would think yes. Our bodies are analog, not digital. I think we get bent on every single dive we do. It's just a matter of degree. On a conservative recreational dive maybe it's inconsequential. Like 5 parts per billion of arsenic in your drinking water. But at some point there's got to be damage going on at a measurable level even before you declare yourself formally bent. I don't know. Maybe I'm way off here.

-Ben

Maverick has sorta chopped up Richard's post to provide a diversion, I believe. Look at the post in its context, compared to ox tox, being a little bent is WAY more than fine in my book.

I disagree that we are a "little bent" on every dive. While there is evidence of bubbles forming on every dive, I'm not so sure you have a chronic exposure that leads to health problems-many divers have done many recreational profiles that are probably sub-optimal. At this point, I'd conclude there would be a formally recognized disease associated with those profiles if the cumulative argument you make above was indeed the case.

[Joshua Smith]

OK, looking at it that way, I can see your point

- ox tox, while rare, has severe, often fatal, consequences 99% of the time
-dcs, while not rare, has mild, or survivable consequences 80% of the time

Or something like that? (I made up my own percentages, there, obviously.)

Why the big deal?

Because you tox, you are most likely going to die. Very few divers possess the skills to rescue a toxing diver, we practice it, but if it happens, I'm honestly going to do my best to rescue my buddy, but am not horribly optimistic on that front.

How many times have you practiced toxing diver rescue?

All the items you list-not pushing PPO2, understanding MODs, having good procedures in place, knowing your O2 exposure, all those are designed to avoid it. But, unlike DCS, we really don't understand the mechanisms of ox-tox, and all the above are fudge factors to minimize the risk. While the same may be said for DCS, we do know what causes DCS and we do have a much better statistical grasp on how to avoid it, and, by and large, the consequences are less severe.

I know of two ox-tox rescues, one by Andrew, one down in California last year. I also know of at least two toxing incidents that happened at 1.4 PPO2. There are also many mysterious deaths that are simply unexplained-and could be toxing incidents.

Mind you, I'm not adopting a cavalier attitude to DCS when I make the comparison between the two, just noting that among the two, I'd much rather be bent than toxing.

[dsteding]

OK, looking at it that way, I can see your point

- ox tox, while rare, has severe, often fatal, consequences 99% of the time
-dcs, while not rare, has mild, or survivable consequences 80% of the time

Or something like that? (I made up my own percentages, there, obviously.)

Yeah, I'd say that "ox tox, while rare, is unpredictable, and is highly likely to result in dead . . ."

Whereas:

"DCS can be rare if dives are planned/executed accordingly, and even if it occurs, is highly likely to be survivable."

Steering this back to the whole UTD thing, we try and perform a risk/benefit analysis for all parts of a dive, and apply to that risk/benefit analysis a strong predisposition AGAINST the risk side of things. Put in that light, the RISK of ox-tox is HIGH, while the benefits, from, say pushing your MOD, PPO2 or overall oxygen exposure is LOW (i.e., slightly reduced decompression times).

Added to this is the fact that the ox-tox risk is uncontrollable because the mechanisms are relatively unknown and we get to the place where I make statements that "I'd much rather be a little bent than toxing."

People looking at UTD from the outside just see a rigid adherence to protocols, people diving this way understand the whys behind those protocols, and try and educate themselves so they can make an appropriate risk/benefit decision on how to plan and execute dives. This is an example of that.

[Maverick]

A little bent is fine,

What do you mean by a little bent if Fine? that seems like a strange statement?

I'm interested too. I'm concerned about 'cumulative effects'. As in, a little bent or 'almost' bent x multiple occurences = ??? Does it add up to something bad at some point? I would think yes. Our bodies are analog, not digital. I think we get bent on every single dive we do. It's just a matter of degree. On a conservative recreational dive maybe it's inconsequential. Like 5 parts per billion of arsenic in your drinking water. But at some point there's got to be damage going on at a measurable level even before you declare yourself formally bent. I don't know. Maybe I'm way off here.

-Ben

Maverick has sorta chopped up Richard's post to provide a diversion, I believe. Look at the post in its context, compared to ox tox, being a little bent is WAY more than fine in my book.

I disagree that we are a "little bent" on every dive. While there is evidence of bubbles forming on every dive, I'm not so sure you have a chronic exposure that leads to health problems-many divers have done many recreational profiles that are probably sub-optimal. At this point, I'd conclude there would be a formally recognized disease associated with those profiles if the cumulative argument you make above was indeed the case.

I only chopped it because that was what i didn't understand, o understood the seriousness of the OX tx, but didn't get why a little bent is ok. now i see the point made and understand the statement. But i do agree with josh that a bit of a skin rash means something was not done right or pushing the envelope, why not stay in the water a few more minutes to avoid the rash. I mean after all we enter the water because we like to be in it, what's the hurry to want to get out so fast that risking a rash is necessary ?

[mattwave]

I have a question, what's the UTD max ppO2 for Bottom Mix and/or Deco Mix?

[dsteding]

I only chopped it because that was what i didn't understand, o understood the seriousness of the OX tx, but didn't get why a little bent is ok. now i see the point made and understand the statement. But i do agree with josh that a bit of a skin rash means something was not done right or pushing the envelope, why not stay in the water a few more minutes to avoid the rash. I mean after all we enter the water because we like to be in it, what's the hurry to want to get out so fast that risking a rash is necessary ?

Agreed. We aren't implying that getting out with a rash is okay. Clearly it isn't. But, between getting out with a rash versus getting out drowned, I'll take the rash.

[dsteding]

I have a question, what's the UTD max ppO2 for Bottom Mix and/or Deco Mix?

Average 1.2 on the bottom, 1.6 max on deco (which if you average over a range of deco stops ends up at 1.2).

[mattwave]

I have a question, what's the UTD max ppO2 for Bottom Mix and/or Deco Mix?

Average 1.2 on the bottom, 1.6 max on deco (which if you average over a range of deco stops ends up at 1.2).

Ok, how long at 1.6 on the average?

[dsteding]

I have a question, what's the UTD max ppO2 for Bottom Mix and/or Deco Mix?

Average 1.2 on the bottom, 1.6 max on deco (which if you average over a range of deco stops ends up at 1.2).

Ok, how long at 1.6 on the average?

12 on, 6 off, for 50% you never really get there at 70 feet, my usual 1.6 exposures are ~2-3 minutes at 70.

[lamont]

i've heard this before as something like:

"we can fix bent, we can't fix drowned"

that doesn't imply that bent is "okay", but its just a sports injury that can usually be repaired. drowned is dead, which you don't usually come back from. oxtox generally leads to drowned.

[CaptnJack]

I have a question, what's the UTD max ppO2 for Bottom Mix and/or Deco Mix?

This deserved a more thorough answer...

Max max for bottom mix contingency planning is 1.4
Typical average bottom is 1.2ish
Shallow deco max is 1.6 (planned for) (120,70,20ft gases)
Deco average over the range where a gas is used is ~1.2
That deco average is achieved with 50% by ascending. For O2 the 1.2 average is achieved by backgas breaks onto the leanest breathable mix.
The deep deco gases like 21/35 are not used at a ppO2 of 1.6 Their max is 1.4 since there's is little benefit in maxing out your CNS loading before you even get to 70 and 20ft.

So deco ends up being (e.g.):
switch with O2 spike
decline with ascent
spike at next switch
decline with acsent
spike at O2, decline with backgas break, spike again after break etc

The ppO2 ends up looking like a sawtooth. The average ppO2 of 1.2 across that entire profile means that UTD OC deco is not much different in total runtime to a CCR dive with a setpoint of 1.3


ps
"regarding a little bent" that was spoken strictly relative to O2 tox which is basically dead, not a little niggly fixable dead, all dead.

[Grateful Diver]

Bottom timers and cut tables are good. But they do not give you the freedom and flexibility a computer can give you. A good technical dive computer will figure out the little things that have been mentioned as well as many other parameters including workload at depth and sac rates to figure total deco. One should alway have backups ie spg's, timers, and cut tables or be ready to do ratio deco also as backups. All they are are tools in the toolbox. I always dive with two computers and cut tables as backup. I have only had 1 technical computer ever fail on in thousands of hours of bottom time, i took it too deep and folded it. Hell I folded a UWATEC BT a few weeks ago in Monterey.

http://www.divecochran.com/cgi-local/ge ... parison.pl

Well, I bent the crap out of the X1 on Lobster Shop Wall yesterday. Of course, it was operator error ... I inadvertently programmed in the wrong deco gas and didn't realize until after the fact that the computer would actually let me reprogram the correct gas in real time.

Fortunately I wasn't actually using the computer to call deco anyway ... we had our schedule and followed it. The computer was just along for "sanity checking" ... and because I just LOVE having all the information glaring at me when it's deep and dark.

The X1 display gets really interesting when it's unhappy ... thing lit up like a slot machine in triple-cherry mode, with flashing lights, blinking displays, and cascading down arrows ... I kept looking for the little tray where the quarters come out. Half-expected it to call 911 and have the EMTs waiting for us when we got back to the parking lot.

Technology's a wonderful thing ... but I'd really prefer keeping it for a backup. There's just no substitute for a bit of knowledge and the ability to apply your own brain power to the circumstances at hand ...

... Bob (Grateful DIver)