Sharing air to maximize bottom time.

[ianr33]

I'd not make a practice of this. Use it up and then an emergency comes up and where are you? If you burn air that badly, run doubles or something.

Hey why dont you fill out your profile so we can all judge if you know what you are talking about?

Again,who said anything about "using it up" ??

 

[wtxblaze]

I did share air like that on my first few dive's in the ocean, but by the end of the week I learned to calm down and enjoy the dive and my SAC improved greatly. Now after a few dives under my belt I can keep up with most of the other divers. And with the computer I down load my dives and I can see how my SAC rate is going though out the dive and go back and see what I was thinking at the time to make it go up or down.
Just get in some more dive and relax.

 

[Alex777]

It's not exactly sharing air, but my wife and I will sometimes swap gear to extend a dive because her SAC rate is better than mine. (Our weighting requirements are the same.) I see nothing wrong with it. (I am referring to warm water recreational diving).

 

[micklock]

Do you think women have better sac rates because they can't talk under water with a reg in there mouth. (Just kidding, I'm glad my girlfriend doesn't dive or even know about Scuba Board.)

 

[DA Aquamaster]

Boy...you need hip waders to wade through all the sactimonious BS in this thread. Sharing gas to extend bottom time is not going to get anyone killed.

It's a no deco recreational dive, so if either diver hits their reserve, you ascend and aend the dive. If you adjust that to either diver hitting their rock bttom pressure needed to get both divers to the surface safey on either person's tank, then it even works for overhead environments as well.

You are gas sharing in an established buddy team where the drill is well practiced so there should be no surprises - and it is great practice.

Having one buddy ascend with 1500 psi just because you are at 500 on a shalow water tropical dive that you are paying through the nose for is pretty stupid when you could enjoy more fo the dive by sharing gas.

Getting a larger tank for the hoover in the buddy team is a good idea, but not one that is real practical in destination diving where every one gets an AL 80. Same thing with using a slung pony as the recreatonal version of a stage with bottom gas - it would work great at home, but not so great when you have to fly somewhere.

One of the few intelligent and well thought out arguments opposing this practice is the potential problem with sharing gas in extremely cold water. Having two divers breathe off one first stage in water colder than about 45 degrees will increase the potential for a freeze flow. The degree to which that may be a problem depends on the particular regulator being used. In the event it happens, you just end the dive and ascend immediately with diver borrowing gas going back on their own reg and the other diver sharing in the event that they run out of gas.

I would suggest two things if you share gas to extend bottom time.

1. Get a 6' or 7' hose primary and donate the primary to the "borrowing" diver as it allows a lot more freedom of movement and you and the buddy can swim side by side effortlessly.

2. Share gas early in the dive when it is convenient rather than toward the end. It may be less convenient to share at the end and if you know the differential you usually have, you will be able to figure out how many PSI you should share to leave things even at the end. Also, doing that way will ensure that you have ample gas in both tanks in the event of gas loss.

 

[Oddsnends]

There was a good thread on this topic: An interesting dive

In post #37 TSandM made a very reasonable argument:

When I reach safety reserve (rock bottom) the dive is over, period. If, for some reason, I have an equipment malfunction or gas loss and have to go on someone's long hose, I am by definition below safety reserve, and the dive is over, period.

HOWEVER . . . Peter's SAC rate is about .6; mine is .4. If we are diving in the tropics on the same sized tank, Peter's gas consumption will cut our dive short while I still have a lot of excess in my tank. For that reason, and only EARLY IN THE DIVE, Peter will go on my long hose for a while. I not only don't think that's dangerous, I think it's a good thing. We get the practice of air-sharing and swimming while sharing gas; both of us have oodles of our own gas, so even if somehow we got separated, there's no problem. And we end up with equalized gas consumption.

We have had problems with DMs seeing us do this (even, sometimes, after we have explained that we are going to) and literally freaking out, and I've had a PADI instructor tell me that he felt it was unconscionable, because once you are sharing gas, the only thing you can do is an immediate ascent. But we're CAVE DIVERS . . . If we share gas, we swim out. I think it's good to practice that.

If you are going to practice this behavior,
1) Do it early in the dive.
2) Have a pre-defined pressure you are shooting for.
3) Make sure the other divers/instructors know what you are doing and sign off on it.

 

[ianr33]

One of the few intelligent and well thought out arguments opposing this practice is the potential problem with sharing gas in extremely cold water. Having two divers breathe off one first stage in water colder than about 45 degrees will increase the potential for a freeze flow. The degree to which that may be a problem depends on the particular regulator being used. In the event it happens, you just end the dive and ascend immediately with diver borrowing gas going back on their own reg and the other diver sharing in the event that they run out of gas.

Agreed. But if freeflows due to icing while sharing air are likely to be a problem then the dive should not be done on singles in the first place.

 

[DA Aquamaster]

Are you a smoker or out of shape or have some other health problems because you should get at least 100 minutes on a al80 at 30'. If you have health concers maybe you should get checked out by a doctor to see if you are fit for diving or...

maybe its just an excitement issue and all you need to do is calm down and concentrate more on breathing technique until it comes more natural or...

maybe your wetsuit and bc and reg are not adjusted to your needs. If a wetsuit is to tight it will squeeze your chest and make breathing harder and same goes with jacketed bcds or if a regulator is not adjusted right or...

you might have to much lead and be constantly fighting the feeling of sinking or if you not weighted and trimmed properly you could be causing undue resistance under water.

after saying all that I dont share air, I dont ask for others and I dont offer mine but I carry a redundant air source and all my fellow divers do too. in the diving we do there is total redundancy so that may not apply to you but if you find yourself needing someone elses air than there is something wrong with what you are doing.

Some of your advice is well spoken but it unfortunately gets lost in the otherstuff.

100 minutes at 30 ft from an AL 80 (assuming a 500 psi reserve) is a SAC of 13 psi/min or .33 cu ft per minute.

That is an impressive SAC at rest. But then again a SAC twice that amount while swimming constantly at a good pace in cold water in a stressful situation is also an impressive SAC, so without stating the conditions it's not meaningful to create an expectation of 100 minutes at 30 feet on an AL 80.

Besides, I'd rather see a diver use more air than to try to stretch it with a resulting build up of CO2 levels, particularly as they begin to dive deeper or start techical diving as CO2 buildup increases the effects of narcosis and increases the risk of oxygen toxicity.

 

[diver 85]

We just returned from a trip to San Andres, Colombia. On the first dive out the DM shared his air with me when he saw what an air pig I was. I piggybacked with him for about 15 mins, extending my bottom time. On subsequent dives a different DM had me share with my wife, he was not much better for air consumption than me. My wife enjoyed telling people how I was literally sucking the life from her.

I did get better near the end of the week, had one dive @80mins. with 700 psi to spare, without piggybacking. Of course this was a shallow dive @ 30ft max.

Is this a normal practice between mismatched air consumers? Does your dive buddy/SO share their air with you?

Not the norm but can remember bumbing off our daughter from years ago when she was a teenager(she's now 36)......If I remember correctly, she made air UW in those early diving years.....The worse it can do is make a better buddy breathing team out of the 2 of you.....

 

[seaducer]

Still a relative newb and not very good at air consumption skills. I have a hard time exhaling slowly, it rushes out and I breath deep immediately. Starting to relax and improve, I'm sure it will come with time.

Try to breathe normally while diving. There is no need to fill your lungs or breathe deeper than normal unless you are working hard. Lots of people have an urge to fill up your lungs when U/W, as if you were about to do a breath hold dive.

Not only will breathing at your normal pace conserve the air in your tank, but your bouyancy will improve dramatically as the amount of air changing in your lungs decreases, and that will help your air consumption as well.

Relax, think about your breathing, get a bigger tank if you can, and most of all have fun!