Skirting the Tables

[PerroneFord]

With the uncertainty of the tables, trying this again could result in Type I DCS.

In fact, you may have taken a hit but are in denial about it.

Don, I am not trying to condone running the limit of the tables for ANY diver, nor am I saying it was "ok this time". I think that has been well established. As has been said a dozen times, the guy is aware he screwed up.

I guess I just don't agree with scare tactics to get people to "act better". I am a newbie diver. Doesn't mean I'm dumb, and it doesn't mean I can't think. The same for this gentleman. I've taken the time to learn all I can about deco theory, he hasn't and that is a difference I hope he corrects ASAP.

In the end, the guy is ok, and thank goodness for that. He made a mistake, apparently has learned from it, and is moving on. As for me, well I don't intend on pushing the limits this early in my diving, but I am certainly not going to fret on overstaying a minute at 40 feet. Maybe I'll get punished for it.. but I really doubt it based on how I plan deco.

 

[PerroneFord]

Oh, BTW, my tables all clearly state that bottom time ends when I begin my DIRECT ASCENT to the surface, and if I make any stops (say, 5 minutes at 30') that is to be considered bottom time.

Out of curiousity, I pulled out my PADI OW table. It gives no succint definition of bottom time. However it does tell me not to exceed 60ft per minute on ascent. Do other people's tables indicate the 60ft/m ascent or do they now say 30?

 

[MB]

Out of curiousity, I pulled out my PADI OW table. It gives no succint definition of bottom time. However it does tell me not to exceed 60ft per minute on ascent. Do other people's tables indicate the 60ft/m ascent or do they now say 30?

You text describes the conventions for using the padi tables, including when to start and stop the clock.

 

[-mitch-]

Out of curiousity, I pulled out my PADI OW table. It gives no succint definition of bottom time. However it does tell me not to exceed 60ft per minute on ascent. Do other people's tables indicate the 60ft/m ascent or do they now say 30?

My NAUI tables say 30

 

[PerroneFord]

I thought there was a shift away from the 60ft/m ascent in the mid to late 90s but I was certified before that, so I was wondering.

 

[Somethin-Fishey]

Whoa man., aren't you being a bit harsh here?

He had 42 minutes of BOTTOM TIME to play with. Or have you forgotten tables are bottom time and not run time? He spent considerable time at 30ft (he was already offgassing whether he knew it or not) and was on the 15ft deco at 40 minutes. He actually used LESS bottom time than indicated by the table and stayed under the water for an additional minute over his plan. Any additional on-gassing at 52 feet was more than paid back at 30, because the recreational planners don't credit any deep stop or deco below 15ft.

How the heck is he gonna take a hit swimming around in 30-40ft of water with an AL80 on his back? Heck, I just ran a profile of 90 minutes at 40 feet and Vplanner asked for a 2:36 stop at 10 feet.

The BIGGEST problem here is that he was ignorant to the fact of what he was actually doing, but don't blame the guy for making a logical and well reasoned decision and then coming here and asking about it.

He DIDN"T have 42 minutes to play with once he went below 50FT.

If you are going to use tables, USE them, DON'T violate them. At which point does which corner cutting get you in trouble? If you know the answer to this question...disregard the rest of my post.

Realistically, the tables are CRAP. I use US Navy dive tables and a Cochran, both are VERY liberal, but only have half the assumptions. Padi/NAUI/SSI tables have to account for a 60YO overweight diver that has been smoking for 40+ years. Navy tables start with younger men, in better than average physical shape.

If you want more time GET A COMPUTER. I violate tables on EVERY dive, they are just not able to compensate for everything a computer can, but I do NOT violate my computer. By my third dive in 100FT with 32% nitrox, I can cut my surface interval by a third and still have twice the bottom time available with the best scenario afforded by the tables.

 

[lamont]

He DIDN"T have 42 minutes to play with once he went below 50FT.

However, at one point I dropped to 52 feet for a few seconds (literally).

Assuming NSDiver is reporting correctly here, there will be very little diffusion into either tissue or free phase gas as a result of hitting 52 feet for a few seconds. The free phase gas will have gotten slightly compressed via boyle's law and then expanded back again. Using the 50 foot table value here is not going to get anyone bent, novice or otherwise.

 

[in_cavediver]

If you want more time GET A COMPUTER. I violate tables on EVERY dive, they are just not able to compensate for everything a computer can, but I do NOT violate my computer. By my third dive in 100FT with 32% nitrox, I can cut my surface interval by a third and still have twice the bottom time available with the best scenario afforded by the tables.

I have just a few points to add:

1) If you dive table's, take a few minutes to learn about decompression theory. It can really help you make informed and intellegent decisions about dive profiles underwater. Be sure to understand all of the assumptions made and why.

2) If you dive a computer, take a few minutes to learn about decompression theory. Then take a few more to learn about what specifically your computer is doing. Both of these can help you make informed decisions about your dive profile underwater. Be sure to understand all of the assumptions being made and why.

3) It doesn't matter if you dive a computer or tables, there may come a time when you find yourself off the edge of the computer passed the mystical NDL line. Even through no fault of your own. If you understand what that means in terms of the model/tables you are using, you can then act appropriately.

4) If you are NOT diving a square profile (IE multilevel), it is more 'dangerous' to push a computer to its limits than tables (wheel is closer to the 'puter). If you don't understand why this is, see #1 and #2. (NOTE: Not recommended to ever push the limits of the model you are using)

5) If you haven't already, take some time to read up on deco theory and deco models. Maybe play with some programs like GAP, Vplanner etc. Try to understand what is going on and why. Then try to understand what that magical NDL number really means in terms of what is going on in your body.

I do not condone what NSdiver did and I credit him for coming here and asking for assistance. In his case, he pushed his tables without understanding how he was pushing them. That said, If I personally was in his shoes on dive, I would have done the same thing. I might have stayed longer at 15-20' but not necessarly.

Mike

 

[JustinW]

This might not apply to everyone, since I'm sure a lot of you use computers instead of strictly adhering to tables, but here goes. For some background, I was certified a few weeks ago and was on dive 10 today in Haymarket, VA. I use an OMS bottom timer and NAUI air tables for NDLs.

It was my second dive of the day, I started in group E. Planned depth was 50 feet, which would give an AMDT of 42 minutes. For 60 feet, AMDT would be 25 minutes (not including any safety stop).

For most of the dive, our depth was in the 40-45 foot range. However, at one point I dropped to 52 feet for a few seconds (literally). Towards the end of the dive, having already seen what we wanted to see, we spent several minutes watching some OW students at a 30' platform. At 40 minutes we were at 15 feet doing a safety stop, and surfaced 43 minutes after submerging.

Strictly adhering to practices taught by (I think) all the agencies, I should have calculated this as a 60 foot dive and come up 15 minutes earlier. However, I rationalized that the stay at 52 feet was brief enough (and most of the dive shallow enough) that the dive could be calculated as a 50 foot dive.

Though I'm safe (not bent) - was this bad practice? Perhaps I should have stayed at safety stop depth for a couple more minutes (the schedule on the NAUI tables calls for a 7 minute stop)? Thoughts/experiences if you have any...

The people here who seem to be patting this guy on the back and saying "its ok" must not see what is in bold. Not only was he dancing at the limits of the tables, he blew them. Remember who the tables were designed from. Navy Seals that are young, in shape and not overweight. Most of us do not have the bodies of a NAVY SEAL, we have more fat, are older and don't run 50 miles a week.
So after the dive, the guy here says that he thinks it could be calculated as a 50 foot dive, NO IT CAN'T. The table rules don't say "round up unless you don't think you need to"

So in the end, this diver made a conscious decision while on a dive to blow the tables to watch a group of students. And we wonder why so many new students get hurt and why we agency bash. Agency Bashing occurs because they turn out students like this, that think they can blow the tables for some reason, and then we have a bunch of other divers on Scubaboard that ALSO think its OK. This is a serious problem.

I don't see how it is acceptable for anyone here to condone blowing the tables, with whatever rationalization. He isn't asking if he is bent, he is asking directly if this "is bad practice" and if it can be done again. YES, it is bad practice and it cannot be done again. Do not PRACTICE this!! When he noticed that he hit 52' (for however instantaneously) he should have recalculated the dive instantly and made an ajustment as necessary. If you are using the tables, you need to either dive your plan, or take your tables with you so when you blow your plan, you can make a new plan. Proper planning and execution is vital. This diver is way too new to start blowing tables. IF he wants more time, then learn how to plan a multilevel dive, you will find that your NDL time is increased, but if you are using tables, follow them. The built in safety is built in there for safety (imagine that), but it doesn't mean you can desregard it without understanding the issues involved. With 10 dives under this diver's belt, they do not understand the proper theories and associated planning tools that can allow longer NDL times for a dive.

 

[lamont]

The people here who seem to be patting this guy on the back and saying "its ok" must not see what is in bold.

No, I read it. I'm more concerned with a novice diver running up against the NDLs and starting to wonder about extending safety stops. That's a fine idea for someone more experienced, but a bad idea for a novice diver who doesn't know enough to ensure that they actually will hit a longer safety stop.

I'm also not patting him on the back. He needs more experience before getting agressive with the NDLs, period. However, everyone who is slamming him on a couple second violation of his floor and claiming that he's risking a "Darwin Award" for this needs to get hit by a clue-by-four. You are focusing on some rule you got told to never break in your OW class and missing the real dangers. I'd be concerned about him running up against the NDLs even if he didn't break 50 fsw for a few seconds.

Not only was he dancing at the limits of the tables, he blew them.

See my previous post and get a grip.

Remember who the tables were designed from. Navy Seals that are young, in shape and not overweight. Most of us do not have the bodies of a NAVY SEAL, we have more fat, are older and don't run 50 miles a week.

The PADI and NAUI tables were designed for recreational divers.

So after the dive, the guy here says that he thinks it could be calculated as a 50 foot dive, NO IT CAN'T. The table rules don't say "round up unless you don't think you need to"

Get a grip. The nitrogen ongassing into your body doesn't know that you went below 50 feet for a few seconds.