How those idiots (us) run out of air

[flots am]

Something doesn't quite add up here. You made it to the ascent line at 50 fsw with 500 psi. At 30 ft per min ascent rate you are at 20' in one minute. Sure seems like you should have had enough to do a full 3 minute safety stop and still be at the surface with 200 -300 psi or more.

I don't even understand the sharing of air at 500.

A moderately stressed diver with an RMV of 0.9 would use a little less than 9 cubic feet, or about 340PSI on an AL 80, to surface from 50', including a safety stop.

Not all regulators are breathable at very low tank pressures, and not all SPGs are accurate at the low end of the range, so 500PSI might actually be 300 or 600.

While a safe ascent would be possible with the given amount of gas, it could easily be very close or insufficient, depending on a few different variables.

If air sharing, the numbers would easily be doubled, and in "Holy Sh**! I'm Gonna Die!" mode, it might not be enough to even get to the safety stop.

flots.

 

[Superlyte27]

Well here's the situation in a nutshell.

What do you figure a DM makes in a day? $50 - $100? So, in the course of a 14 hour job (they get up to fuel the boat, fill tanks, load the boat, dive dive dive, then get back, clean the boat, fill the ice trays, put away the tanks, blah blah blah) they get if they are lucky $100 bucks. Bear in mind, I'm basing this off my own observations as a DM and Boat Captain in Key Largo for a large operation in the summertime. So $100/14 hours = $7.14/hour.

So here's the real question: Do you trust your life to someone who is making $7.14 per hour? Lets up it. Do you trust someone who makes $14, $28 or $50/hour? The answer should be: Hell No.

Only YOU are trustworthy with YOU. You can't count on ANYONE else. I don't DM dives anymore thankfully. But even when I'm teaching a technical class, the very first day of class, my students are made aware the fact that they CANNOT count on me to get them out of the cave. I could have a heart attack. I could get knocked unconscious by another diver kicking me in the face. I could have a stroke. They are taught from the very beginning how to survive step by step. Day 1 teaches them how to get out on the dives we do day 2. Day 2 teaches them how to survive dives we do day 3. Day 3 teaches them how to survive the dives on day 4. At no point do they progress until I am confident they can survive on their own.

So, we move back to the OP. You knew you were running low on air. What are YOU tasked with doing? You are tasked with surviving. That's it. Well, how do you survive?

My question about depth was simple. If you were at 50' on the ascent line, and you had 500lbs (I'm assuming your wife had 500lbs also, or something near this) why did you run out of air prior to reaching the surface? 50' / 33 + 1 = 2.51ata. An AL80 (77.4cu') at 500psi holds roughly 13cu'. At 50' it would take you less than 2 minutes to get to the surface. Even if your SAC rate was 2cu' per minute (which would be extremely high), you'd still have more than double the gas you needed to make it to the surface. So with that said, we're missing something in the story here. I just did the math, even with a 4.0 SAC rate (which I don't believe is possible) 4 x 2.51ata = 10cu' and you have 13 cu' of gas. What aren't we being told?

At any rate, you are responsible for you. No one else is, regardless of what you paid them to do. Survive. It's your job.

 

[uncfnp]

First dive in a new location (St Eustatius). Heavy (for us) current at surface. Descended and regs sucked water. Returned to surface, changed regs and went down again with 2200 lbs. A bit anxious due to new environment and surface conditions. Had 1800 at bottom( 50 ft). Swam around a bit and signalled to DM at half a tank. Went a little bit more (1st mistake) and signalled to DM 1800 (but I meant to signal 1300). As with every dive guide I have ever had, she turned and went further from ascent line. Now the anxiety increased and air consumption with it. Back to ascent line at 500 and we began sharing air. My wife ran our of air shortly after me, she probably was overanxious about me.

We all returned safely and ascended slowly. So a happy ending. But we did both run out, and good thing there were TWO dive guides!

Second dives of the day were much easier and uneventful.

Bill

Apparently used 400 psi just to descend...

 

[Steve_C]

1. We would NEVER consider pulling down an anchor line to reach the bottom....if there is so little current that the boat can anchor, then you gear up, get totally ready, negatively buoyant( suck all air out of BC), and then together you hit the water, and should be swimming head down and more than 20 feet deep within the first 6 seconds....you should make the bottom on this dive described, long before the current should have been sufficient to push you far enough down current for it to matter...and since at the bottom, with skin friction drag and very slow or no bottom current, you can go where ever you need to easily, again there would have been no reason to go down an anchor line. I see this as a sloppy dive operation that expects this course of action, and one I would do MY way, and it would work out much better my way.

Depends on the area. Off NC it is SOP to tie in to the wreck/ledge. You follow a line forward and down the anchor line to the wreck/ledge. If you just drop off the the boat as the boat briefing will remind you every time, there ain't nothing but sand and you are probably out of sight of ledge/wreck. It is far more effort to swim against an even mild surface current then to slowly pull yourself along the lines. Something I have had to remind more than one instabuddy who wondered why he was already a few hundered PSI behind me when we hit bottom.

While I have dove in situations where your recommendation would be appropriate it is absolutely the wrong thing to do off our coast unless doing a drift dive.

 

[scubadada]

First dive in a new location (St Eustatius). Heavy (for us) current at surface. Descended and regs sucked water. Returned to surface, changed regs and went down again with 2200 lbs. A bit anxious due to new environment and surface conditions. Had 1800 at bottom( 50 ft). Swam around a bit and signalled to DM at half a tank. Went a little bit more (1st mistake) and signalled to DM 1800 (but I meant to signal 1300). As with every dive guide I have ever had, she turned and went further from ascent line. Now the anxiety increased and air consumption with it. Back to ascent line at 500 and we began sharing air. My wife ran our of air shortly after me, she probably was overanxious about me.

We all returned safely and ascended slowly. So a happy ending. But we did both run out, and good thing there were TWO dive guides!

Second dives of the day were much easier and uneventful.

Bill

500 psi in an AL80 is just under 13 cu ft of gas. If one ascended from 50 ft at 30 ft per minute, performed a 3 minute safety stop at 15 ft, and then finished the ascent, even at a very high SAC of 1.5 cu ft per minute, one would surface just short of empty. Of course one could truncate or skip the safety stop as needed.

Maybe bilt4sf and his wife did not have 500 psi each at the beginning of the ascent? Why share air before you are out or nearly so? Did they share air with the DMs? If I were one of the DMs, I think I would have been reasonably concerned about the pair's ability to safely execute a dive and certainly would have been very vigilant on the 2nd dive. Gas management is a wonderful thing

PS. Apologize for the redundant post, several others had the same idea while I was writing

 

[bbarnett51]

It sounds rough but I will never understand the logic behind trusting a person you have never met to make decisions that could end your life.

I personally don't give a damn what my DM does unless he is pointing out something cool underwater. Again this sounds like macho talk but EVERY dive is controlled by you and EVERY dive should be treated like a solo dive... possibly with the exception of sole redundant gear.

That is just the way I treat diving.

 

[Lorenzoid]

The thing that interests me about this post is that billt4sf has been reading SB for some time and he has probably seen people repeat the mantras that you are only responsible for yourself, don't fall prey to "trust me" dives, etc., thinking he would never get into a situation like that, and yet that's what happened. I think about the vast majority of divers--who do not read SB and have never bothered to get any advice beyond what they were taught in OW/AOW class. In my OW class, nobody ever said these things to me. On the contrary, in my OW class I felt an implicit message that I should obey the person leading the dive, and if he asks me to signal when I reach half a tank, then he is taking responsibility for managing the group and getting everyone up safely. Dive agencies like PADI should really be more explicit about this aspect of diving--that you have every right to ignore the divemaster if you believe he is compromising your safety. Independence was never emphasized in my OW training; indeed, a cynic would say that they have an incentive to make you feel dependent for as long as possible, so they can sell you more courses. If billt4sf, who knows better, got into such a situation, I shudder to think about how many divers out there are running out of air in situations just like this.

 

[TSandM]

The VAST majority of the tropical operations we've dived with, when they drop divers on a buoy or off an anchored boat, request that the divers descend in contact with the downline. I think it's because so many people can't end up anywhere near the bottom of the line if they don't. Bill may well have been instructed to his descent that way.

 

[drbill]

Imagine what it would be like if you were diving a J-valve with no SPG like we did in the 60s and 70s.

On a recent dive in the Philippines, I was very low on air and started to ascend but the DM pulled me back down to show me a new nudibranch. Filmed it and ascended (from only 15 ft) with an empty tank. It was great to be able to return with 0 psi (although all ascents with an empty bottle were at shallow depths < 15 fsw.

As others have said, your safety is your primary concern... you can't always expect the DM to be looking out for you. Based on your initial post I think you already understand that though. Also keep in mind that SPGs are not always spot on accurate.

 

[Keith.M]

The VAST majority of the tropical operations we've dived with, when they drop divers on a buoy or off an anchored boat, request that the divers descend in contact with the downline. I think it's because so many people can't end up anywhere near the bottom of the line if they don't. Bill may well have been instructed to his descent that way.

More than one person has mentioned this in this thread. I went back and read the original post, I don't see any mention of descending on the line or pulling himself down the line as was mentioned earlier... Confused...