How much gas in case of accidental deco.

[redacted]

Incidentally the first time I got into deco....

i think i am beginning to understand your problem.

obviously, a few spare tires and a couple cans of gas are probably not enough redundancy for a road trip. how many spare cars do you usually drag behind you?

 

[lowviz]

...//... If you were on a no deco dive and for whatever reason (inattention, dealing with a situation, etc) ran your NDL down and clipped the edge of the deco envelope, how much gas should you have to safely clear your obligation without pushing an out of air situation? ...//...

Just to put this into perspective, I sometimes take enough to get me out of a fairly major screwup of missing 10 minutes of required deco. [Never needed it.] The procedure is 3min_40', 3min_30', 5min_20', and 15min_10'. This requires 30 cuft of gas with my air-hog SAC rate. So a 40 is perfect, as previously posted. Nice size for stage bottles also.

I never take more than a 19cuft pony when I'm doing NDL dives to recreational depths.

 

[decompression]

Take a look into some background information and you will be able to answer your own question. The old techniques of "500 psi back on the boat" and rule of "thirds" have been replaced by the concept of "rock bottom". Do a little research and it will make sense to you and make your diving safer. If you wish to increase this knowledge the next things you can look into are "min deco" and "ratio deco", both are advanced but give you a very solid base for air use and nitrogen loading.

 

[Adobo]

I'm not sure the best place for this topic...move as you see fit.

If you were on a no deco dive and for whatever reason (inattention, dealing with a situation, etc) ran your NDL down and clipped the edge of the deco envelope, how much gas should you have to safely clear your obligation without pushing an out of air situation?
I try to stay in the habbit of using my air in 3rds. So (for simplicity sake) I start with 3300psi, turn at 2200, with the intention of being out of the water with 1100. I want to stress that I have no intention of planning deco dives without formal training, But I have seen a few Rec divers lock out their computers because they clipped that envelope and didnt know it, or didnt know what to do about it. I am also putting togeher a stage kit to carry a sling bottle, but for redundancy, NOT for increased air supply. What I mean by this is if I have 100cf of back gas, and an 80cf sling bottle, I my intention would be to use 33cf, turn, and finish with 33cf of back gas plus 80cf in the sling. NOT breathe my 100 down to 40, and then switch to the sling when the back gas runs out.

What does it mean to "clip the edge of deco"? When do you determine if you have done such a thing? Do you determine that when you get to 15 ft when computer is all of a sudden blinking a number that is greater than 5 minutes? To your mind, what is the consequence if you overstay your no deco limit by 1 or 2 or 3 minutes?

Your approach of bringing an al80's worth of extra gas might work but you are already heaping conservatism on top of conservatism. And by the way, bringing extra resources doesn't always come without expense. In your example, not only are you bringing gear that you wouldn't really need on a properly executed dive, you are also going to make yourself unnecessarily negative at the beginning of the dive. If were to jump into the water and were to find yourself with a BCD failure, that al80 and accompanying stage reg will be a detriment, not a benefit.

A more elegant way to address your concerns is to 1) learn how to calculate your real gas needs for a recreational dive (which would include provisions for the emergencies that are plausible to occur) and 2) learn how to execute a dive wherein "inattention" (which in itself poses more problems than just inadvertently finding yourself in deco) is not a factor.

 

[John_B]

If "inattention" causes you to overstay your NDL, I'd suggest taking less gas, not more.

Plan your dive, dive your plan.

 

[waterpirate]

There is some good info here and a lot of other stuff. Cudos on you for wanting to sling a bottle for redundancy, I would rethink the 80, a 40 will serve you well. As for clipping deco, stop worrying, sling a bottle and get yourself a mentor and some additional training. Listening to putz's on the intranet, myself included will only confuse you more
Eric

 

[lowviz]

...//... Listening to putz's on the intranet, myself included will only confuse you more
Eric

True, but it is a start.

Going back to awap's post, I assume that you are now properly weighted. You experienced the reason for being properly weighted first-hand, so this is job one.

...//... it was a little bit of a reality check that I needed to think about these things.

You ask what to do if you "stray" out of your NDL limits. This implies that you aren't too far into deco. The typical rec diver gets about no real instruction as to what one does in this case.

What you need to know if you lightly violate NDL: Ascend at one foot every two seconds up to 15 feet, do a mandatory stop, then surface slowly.

How long of a stop? Up for discussion, but 10 min is a reasonable wild guess.

How much gas? Learn to estimate underwater. Estimate using a SAC of 0.7 cuft/min. 15 feet is about half and atmosphere since 33 feet is one atm. 1.5 x 0.7 = 1, so you use 1 cuft/min @ 15'.

Now easy to estimate how much gas: Staying 10 min at 15 feet, plan on having 10 cuft to do so. -take a 19 cuft pony...

 

[charlesml3]

I just pay attention to my computer. It's not terribly unusual for me to hit deco after 3 or 4 days of 5-dives-a-day. My computer tells me it's coming and I'll do what I can to avoid it. But sometimes there will be a particularly nice Peterson Shrimp that I want to photograph so I'll linger knowing I'm going to have a mandatory deco stop. From there I plan accordingly. I know I have "6 minutes at 10 feet" or whatever the obligation is. I make sure I have enough gas to cover that. It's easy, really.

-Charles

 

[darushin]

If you are diving an 80 or 100 with a 40 sling while following the rule of thirds you will have enough gas to go 5 minutes or so over and still make your deco (assuming .7 Sac)

But a better answer is for you to download vplanner or some thing similar enter your sac, depth and maz time you want to spend at that depth to see how much gas you really need.

Daru

 

[cbrich]

obviously, a few spare tires and a couple cans of gas are probably not enough redundancy for a road trip. how many spare cars do you usually drag behind you?

On my routine trips down south, I usually have at least 2 to 3 more cars behind.