Low air limit?

[scubasteve27]

On my first dive trip to Bonaire[2nd day]we dove on the Witchs hut dive site.I dove with two divers that had quite a bit more experience than I[my first dive in the carribean].Anyway we're diving on this really beautiful wall [10-15 minutes]when I look at my gauges and they read 110 ft depth and 850 psi,this is not good!!They are behind me about 50-60 ft taking videos of some fish,I try and signal them,but they're to engrossed to notice.I think ok I still have to acsend at a reasonable rate,AND make my safety stop.So I started my accent without them,went over the coral head,found a nice little sandy spot and hung there for 4 minutes.I surfaced to find them about 20 ft away saying they should get back to the boat,and what were they going to tell my wife!!!I'am writing this to say I am now MUCH more careful about adhering to my dive plan,,,staying close to your buddy-and watching my gauges CLOSELY at depth.I to go by thirds,with an extra safety margin[200-300 psi] at least,at the end of the dive.Have fun and dive safe!!

ASTA__SCUBA STEVE:mean:

 

[jray]

I usually try to end my dives with at least 500 psi left in my tanks. I only say that because tha's what PADI taught me to say. I usually have a lot more because I don't use it all before the dive is over. I plan for X minutes at X depth and end the dive when the plan is complete. This usually leaves me with more than 500.

 

[mattengstrom]

I always payed attention to the dive briefings that were given, and timed everything to be back on the boat at or before the set time limits. I usually had anywhere from 900-1200 psi left in the AL80 tanks that we were using when I would start to head up. After ascent and safety stops, I usually had 700 or more by the time I got back on the boat.

Except for the time my OW instructor made me practice a "tired diver tow" on him. Really sucked air doing that...

 

[scuberd]

I usually end my dive when my buddy has 500 left. School rules, except in an emergency, you come up with at least 500.

 

[Genesis]

is that I leave the bottom with roughly 100 psi for each 10 feet that I'm down, with a minimum of 600 psi. My "low air alarm" is set to go off at 725. If I get that beep on a dive over 70' before I have started my ascent, I screwed up. Even so, I've gotten the beep on a 110'er before, and was back on the boat, with a 5 minute safety stop, with roughly 400 psi. Then again my resting gas consumption during an ascent and safety stop is very low. If yours is not, or if you're freaked at that particular point in time, then you don't have the same amount of safety margin.

Now with that said, I also carry a pony on deep dives where its possible I might get separated from my buddy. That's an extra 19cf, but I do not "count" it, as its not there for amusement or extending time, and its AIR (while the gas on my back is typically Nitrox of some description.) Why AIR? Because I can top it quickly from my compressor without having to re-transfill or dump the tank, which encourages me to keep it COMPLETELY full, and if I need it I don't care about nitrogen loading, as I'm heading up and will burn almost all of what I have in the pony at 15' before making my final ascent to the surface. I can also gas-switch my computer to AIR in such a circumstance (Vytec), for profile computation and nitrogen loading accuracy sake.

I have never run out. I HAVE, however, surfaced with fumes in the tank - it had positive pressure in it, but not by much (I was definitely near the IP of the reg!) Those are C.F. dives, and hopefully you learn from them - I know I did. In one case it wasn't the dive or ascent, but that we got blown off the wreck and surfaced in free water away from the boat, and had a nice surface swim back in rough water - where I wanted to use the reg rather than breathe free air. Good thing I had some

Remember that you need enough gas not only for you, but also for your buddy if something breaks on his kit as you begin your ascent (the worst possible time.) In my case I can hand my buddy the pony in such a situation, so I only "absolutely need" to get mself back to the surface, but I still plan for both of us on backgas if necessary.

 

[PhotoTJ]

On a beach dive, I surface with 100lbs., (I seldom go below 30' on my beach dives here in So Cal.), any other time, well, depends on the situation.