Air hog etiquette.

[doctormike]

People have mentioned using larger tanks, which is fine if they are available. At dive resorts, I occasionally would find a 100 CUF tank, but usually nothing more than that.

Another option is a stage bottle. This is basically a pony bottle but it's not used for redundancy, it's part of the gas planning (although it does provide some degree of redundancy in case of a failure early in the dive).

While you probably won't find a steel 119, 120 or larger in the Caribbean, an AL40 is often available, especially at places that cater to technical divers. Just sling the 40, breathe it down to 500 psi at the beginning of your dive and then finish the dive with your back gas.

You could even sling an AL80 (I do it all the time), but then you are essentially doing sidemount diving with one of your tanks on your back!

 

[tarponchik]

A question unrelated to etiquette but related to air hogs.

On a busy diving schedule (say, a 7-10-day liveaboard, 3-4 dives per day), will an air hog increase his/her chances of getting DCS if he/she dives with a larger tank or often steals air from other divers, like the Kiwi diver mentioned here earlier? The time spent underwater is the same but the volume of air (and nitrogen) consumed is not. The NDC limits are based on an average diver; will high rate of air consumption multiplied by the same underwater time make a diver an outlier? Is the higher air consumption rate pushing the diver to nitrogen saturation faster, or is it only time that matters?

 

[IncreaseMyT]

A question unrelated to etiquette but related to air hogs.

On a busy diving schedule (say, a 7-10-day liveaboard, 3-4 dives per day), will an air hog increase his/her chances of getting DCS if he/she dives with a larger tank or often steals air from other divers, like the Kiwi diver mentioned here earlier? The time spent underwater is the same but the volume of air (and nitrogen) consumed is not. The NDC limits are based on an average diver; will high rate of air consumption multiplied by the same underwater time make a diver an outlier? Is the higher air consumption rate pushing the diver to nitrogen saturation faster, or is it only time that matters?

Good question and I am interested in hearing the answer. I would assume that people who are breathing more air have more LBM though, and although they are breathing more nitrogen, it takes more nitrogen to get to saturation, because there is more lean tissue.

Shot in the dark but lets see how close I am

 

[doctormike]

A question unrelated to etiquette but related to air hogs.

On a busy diving schedule (say, a 7-10-day liveaboard, 3-4 dives per day), will an air hog increase his/her chances of getting DCS if he/she dives with a larger tank or often steals air from other divers, like the Kiwi diver mentioned here earlier? The time spent underwater is the same but the volume of air (and nitrogen) consumed is not. The NDC limits are based on an average diver; will high rate of air consumption multiplied by the same underwater time make a diver an outlier? Is the higher air consumption rate pushing the diver to nitrogen saturation faster, or is it only time that matters?

Good question!

Nitrogen loading is related to depth, time, and breathing mix. Decompression stress is related to nitrogen loading and ascent profile. Neither is significantly dependant on SAC rate or gas consumption.

The decompression scientists on the board can give you a better answer, but basically ventilation (bulk gas movement) isn't the primary variable that determines nitrogen loading or offgassing. You would think that it might (moving more gas means blowing off N2 faster), but that doesn't seem to be the case. My understanding is that perfusion (blood flow at the tissue level and in the lungs) is the primary determinant of ongassing and offgassing, within the range of normal human physiology.

 

[tarponchik]

Good question and I am interested in hearing the answer. I would assume that people who are breathing more air have more LBM though, and although they are breathing more nitrogen, it takes more nitrogen to get to saturation, because there is more lean tissue.

Shot in the dark but lets see how close I am

Well said but air hogs are not necesary big. It would be interesting to see the profile of a typical air hog, though.

 

[Saniflush]

Well said but air hogs are not necesary big. It would be interesting to see the profile of a typical air hog, though.

Well it is not dead on but it's close....

 

[mmerriman]

If no one in the group gets below 1,000 PSI before an ascent, there will not be an OOA emergency, barring an equipment failure. In that case, the procedure would be the same as ever--the buddy would provide immediate help, the DM would take back the alternate from the other diver (who still has 1,000 PSI), and the DM would render whatever further aid was needed and start the ascent.

What other kind of emergency were you considering?

here's a real situtation from a recent trip. Drift diving in Cancun - group of 6 + the DM. at some point near the end of the dive the DM noticed he was low (maybe 1000 when we all had 1500) on air - and in order to have enough air to have the dive last the planned time, shoot the DSMB, and do a safety stop, he took the octo from another diver until time was up then switched and got everyone out of the water. Not sure if he started with a short fill, or had a leak issue, but that scenario seemed like to could fall apart pretty quickly.

 

[Seaweed Doc]

If no one in the group gets below 1,000 PSI before an ascent, there will not be an OOA emergency, barring an equipment failure. In that case, the procedure would be the same as ever--the buddy would provide immediate help, the DM would take back the alternate from the other diver (who still has 1,000 PSI), and the DM would render whatever further aid was needed and start the ascent.

What other kind of emergency were you considering?

I'll take a shot at this: DM is sharing with air hog when another in group loses buoyancy control and a rapid DM intervention is needed. You have to get the air hog off the sow's teat (so to speak) so she can rescue the other piglet. (Man that metaphor went bad in a hurry......) If air hog isn't a modestly accomplished diver, they've got to recover their own second stage while DM is off attending to emergency. I can imagine all kinds of ways this could go wrong.....

Maybe I've got an over-active imagination?

 

[boulderjohn]

here's a real situtation from a recent trip. Drift diving in Cancun - group of 6 + the DM. at some point near the end of the dive the DM noticed he was low (maybe 1000 when we all had 1500) on air - and in order to have enough air to have the dive last the planned time, shoot the DSMB, and do a safety stop, he took the octo from another diver until time was up then switched and got everyone out of the water. Not sure if he started with a short fill, or had a leak issue, but that scenario seemed like to could fall apart pretty quickly.

Which is absolutely unrelated to the situation being discussed.

 

[boulderjohn]

I'll take a shot at this: DM is sharing with air hog when another in group loses buoyancy control and a rapid DM intervention is needed. You have to get the air hog off the sow's teat (so to speak) so she can rescue the other piglet. (Man that metaphor went bad in a hurry......) If air hog isn't a modestly accomplished diver, they've got to recover their own second stage while DM is off attending to emergency. I can imagine all kinds of ways this could go wrong.....

Maybe I've got an over-active imagination?

Are you under the impression that a DM swimming along with a group following behind him or her will see, react, and reach a diver who loses buoyancy control in time to prevent an uncontrolled ascent? That would be borderline impossible.