How do divers not realize their air isn't on?

[broncobowsher]

The couple breaths after the air is off is a big one. Couple of breaths and watch the pressure is all it takes.
IF you check tank pressure and shut off the tank, depressurize the lines ALWAYS. Don't care if you purge a reg, fill a wing, just depressurize the lines. Same on open circuit as closed circuit.

As for a rebreather, you can get several minutes of breathing with the oxygen turned off. With the scrubber working you will have no CO2 rise, just a loss of O2. If starting with a rich mix in the rebreather you can get about a minute of oxygen per liter of counterlung volume. Now there will be protocol violations, and ignoring warning signs as well. Pool training involved turning the O2 off and watching what happens (in a pool, with instructor watching very carefully, one on one only). It is amazing how long it takes to burn off the O2 in a rebreather with the tank turned off.

 

[Landlocked123]

So after hundreds of dives my checklist proved useful today. I check my air two times before I dive. Once when I put the rig together (I make sure its on and I check the PSI) on the staging tables, once before descent while standing on the submerged platform entry point. This is when I breathe from both regs. I first test breathe my primary back gas and thenmy bail out pony. Well today when I went to test breathe my pony....zippo... I have no idea how I missed it on the first check other than I was switching tanks and I moved it over to the 2nd tank I was diving and somewhere along the way stupid showed up and took control and turned the valve off ! That is why I always check again before I descend. **** happens.

 

[johndiver999]

Is reaching to your cylinder harder with a rebreather or something? Both guys seem to have been really experienced.

So in both cases, they must have been entering the water with zero air in the BCD. He must have realized it quickly and just wasn't fast enough to dump weight? Even a steel tank is only around 8 pounds, right?

You may not realize this, but many good, experienced divers do not enter the water with half filled BC, return to the surface upon entry, give the OK sign and then begin to vent air from their BC and then slowly sink feet first...(let alone take more time to coordinate with a buddy).

What they MAY do, is enter the water with zero air in their BC, no ditchable lead, a heavy steel tank(s) and flip over immediately and kick straight down hard and deliberately not inhale much. This allows them to descend very quickly and any residual air in the BC is quickly compressed and with only partial inhalations their lungs are not providing much buoyancy , they stay negative and can power down to 30 feet while only taking in one or two half breaths.

Now, under this scenario, the diver is very streamlined, sinking rapidly, is at a depth of 30 feet or more and his legs are already slightly fatigued from hard kicking and NOW after a big exhalation, they find the regulator delivers nothing!

They instinctively press the inflator and that gives no so much as a fart and they are sinking fast and heavy. Nothing to breath, no air in the lungs, no way to put air in the BC, no ditchable lead and they now have a decision:

Do they assume the tank was off and they want to relax and continue sinking and try to reach back and work the valve (and if they fail they die) OR

Do they turn around and kick like a maniac for the surface and hope they make it - even though they are quite heavy. Again, failure is death and their is no time to weigh options, you must do one or the other immediately.

Few people would recommend that any one dive as described above, especially with their tank turned off, but it should explain how a very experienced, skilled, confident (and complacent) diver can EASILY get killed by simply forgetting to turn the tank valve on,

What they MAY do is turn the tank on when setting up, check the pressure and then turn the valve off so the tank can not leak air which would be hard to hear over the sound of a boat engine. They leave the tank with the regulator charged and at 3000 psi, but the valve is OFF.

What I like to do is to - after setting up the tank and checking for leaks, I turn the tank off AND completely purge the regulator. That way, if I screw up and fail to test the reg when I jump in, a least I should figure it out right away before getting too deep, I don't leave the reg charged and the tank valve off- if I can help it.

 

[northernone]

It is possible.

Nine days ago I did my predive two heavy breathes after long shore entry, making sure nothing was stuck. (If I can't overbreath that reg on the surface, I'm ok down to ~120ft.)

Tank closed.

Turns out my buddy had 'helped me' by opening my tank while I was getting my fins on and using him for stability. This was after we did our normal reg checks. (Watch needle etc)

If that was a negative drop off a boat, and I skipped my last minute breath check, it could have been worse.

Just because you do predive checks minutes before diving, doesn't mean the situation hasn't changed.

Cameron

 

[gypsyjim]

I do a pre-dive breath test, but I have still had a couple of entries where my valve was closed. Maybe I forgot, or maybe someone "helped" me? I do not know for sure.
BUT
I damnsure know how to turn that valve on and off under water...and quickly.

 

[ScubaJCBS]

I do the same as a lot above 3 breathes and inflate my bcd while watching gauge because like a lot have said you set up your gear turn off air then it's easy to forget to turn it back on. I also try to remember before I set down to my bc to turn air back on. It would probably just be a better habit to just not turn the air back off after charging the system.

 

[ChuckP]

Before you step off the boat, inflate your aircell and take a couple of breaths from the reg (pref. both) watching your SPG. If the needle goes down, you air is off. Then hold on to your junk and step off. I'm sure "inflate" and "hold on to your junk" was in OW but I forget if our instructor mentioned the SPG needle or I picked it here on SB or from a DM somelace.

No, we didn't have "air off". That would be a bad idea in an OW course.

I certainly wouldn't turn off air underwater in OW, but sitting on the edge of the pool - a valuable lesson with zero danger. It appears that isn't in PADI standards and not sure of SSI but that is how I was taught in SSI.

We just did this today with my 11 year old on the boat before rolling in......

I can say in PADI Divemaster training we turned our air off underwater - reading thru the standards, I'm not clear if it really should be taught that way.

 

[ChuckP]

I'd highly recommend a PADI re activate class with a quality instructor.

Bring your questions to an instructor and have them personally show you along with a few common skills - sounds like it'd be well worth it.

All the answers above mean something but bottom line is complacency and it'll kill you quicker than a wrong turn in South Chicago.

 

[teonchagi]

Yeah, my instructor never mentioned doing a breath test while looking at the gauge. Probably would be a good idea for them to teach that. I know I'll do it from now on in.

My instructor wanted me to know what it feels like to be OOA, so he went behind me and turned off my tank. We were about 10-15ft deep if I recall correctly. He told me to watch my SPG and breathe. As soon as I didn't get a breath, I signaled OOA and he turned my tank on immediately. It was a very valuable lesson for me, because I learned how it feels to get low on air.

 

[hammet]

My instabuddy jumped into the water couple of weeks ago with his air off. I was already at 30' when I saw he wasn't coming down. Hovered for a few more seconds and decided to make my way back to the surface where he informed me of the problem.