What did you just say?

[Tigerman]

I'd question whether 300psi was insufficient to end a dive with.
Considering that we end the dive after a safety stop it means 300psi to get from 15' to the surface. That's a lot of gas for me.

I know the generalized rebuttal might be that some divers need overly simplistic rules because they don't know better but I prefer not to dumb down my behavior to equal the lowest common denominator. We should be pulling those people up, not forcing ourselves down.

300 psi is about 20 bar (according to supergaijin, havent checked it) according to supergaijin his fairly new rental gauges can show anything from 205 to 190 - thats a 15 bar difference. Which of the gauges would be the one reading most accurate?
Also, how much air would one need if the pickup/exit is rough and you need to use the regulator not to swallow the ocean?

 

[Dirty-Dog]

Basically, what I meant was that to insist on coming onboard with 500 PSI is a bit overly conservative because if we're talking about recreational open water diving, to end the dive and start ascending at the 500 PSI mark should be sufficient for a slow relaxed ascend plus the mandatory safety stop.

Would that 500PSI be sufficient for you AND your buddy to safely ascend while stressed by whatever problem resulted in your sharing air?

 

[boulderjohn]

Basically, what I meant was that to insist on coming onboard with 500 PSI is a bit overly conservative because if we're talking about recreational open water diving, to end the dive and start ascending at the 500 PSI mark should be sufficient for a slow relaxed ascend plus the mandatory safety stop.

Would that 500PSI be sufficient for you AND your buddy to safely ascend while stressed by whatever problem resulted in your sharing air?

The Tech divers I know assume that in an emergency, they will have a SAC rate of 1.0 cubic feet/min. They assume that completing the air sharing maneuver will take a minute.

Let's say you and your buddy are at 99 FSW and have an OOA emergency.

1. It will take one minute to compete the exchange. At 4 ATA, you will each need 4 cubic feet of air, for a total of 8 cubic feet.

2. If you ascend at about 60 FPM to the safety stop, it will take 1.5 minutes at an average depth of roughly 3 ATA. You will each use 1.5 X 3 = 4.5 cubic feet, for a total of 9 cubic feet.

3. For your safety stop, you will take 3 minutes at 1.5 ATA, so you will each need 3 X 1.5 = 4.5 cubic feet, for another 9 cubic feet total.

4. You will need a little gas for that last 15 feet, let's say 2 cubic feet total.

That means the two of you will need 8 + 9 +9 + 2 = 28 cubic feet to ascend from 99 feet on an air share and do a safety stop.

If you are diving an AL 80, 28 cubic feet is more than 1,000 PSI.

That means, BTW, that 500 cubic feet will not get one person to the surface with a safety stop from 99 feet, let alone two.

 

[Tigerman]

I actually HAVE, but this is only because both of us was completely unphased - due to the fact that my tank was pretty much FULL and the recipient being a very petite woman, done an air share ascent from 20 meters including a "safety stop" on less than 500 psi .
It was actually more a swim back towards the reef to get away with boat traffic than a safety stop per say, but it was pretty much the same time spent.
I would NOT plan on it being that smooth though as I have seen situations where people blow through their air faster than a hoover even without 2 people on the tank.

The event in question is in my sig..

 

[Dirty-Dog]

I actually HAVE, but this is only because both of us was completely unphased - due to the fact that my tank was pretty much FULL and the recipient being a very petite woman, done an air share ascent from 20 meters including a "safety stop" on less than 500 psi .
It was actually more a swim back towards the reef to get away with boat traffic than a safety stop per say, but it was pretty much the same time spent.
I would NOT plan on it being that smooth though as I have seen situations where people blow through their air faster than a hoover even without 2 people on the tank.

The event in question is in my sig..

Exactly. Plan for the worst, hope for the best.

 

[Tigerman]

We saw the mantas for a while before we had to surface, so it was the best

 

[BradMM]

Im not sure how its to suck water in

Yogis do this... so I'm told.

 

[Sphyrnidae Amicus]

Craziest thing I've ever heard from a diver?

Me (teaching another student) "blah blah blah, witty teaching story, blah, no decompression limit, blah"
Certified diver overhearing (with over 300 dives under her belt): "What's a no decompression limit?"
Me: 'insert clear concise explanation here while doing best to keep bafflement from facial expression'
Certified diver: "why would I want to know how long I've been underwater?'
!!!!
She'd been diving her computer in guage mode since she bought it and had no idea, her dive guide had been assuming the thing on her wrist that she kept checking was doing more than just letting her know, out of curiosity, how deep she was...eek!

Dumbest thing I've ever said to a student? (and I hasten to add this is way back when I was a newbie and my mental teaching toolkit was sadly empty)
Me: Now we really need to get in the habit of problem solving underwater, you know, like I already explained. How about this time when you flood your mask, I'll hold you down there while you clear it to prove to you that we can fix this underwater?"
We go down
We partially flood mask
He problem solves.....
We surface
Student: Oh my god I'm so sorry, I have never in my life hit a woman before!"

Giggle. Glad I got better at this whole teaching thing!

 

[DaleC]

300 psi is about 20 bar (according to supergaijin, havent checked it) according to supergaijin his fairly new rental gauges can show anything from 205 to 190 - thats a 15 bar difference. Which of the gauges would be the one reading most accurate?
Also, how much air would one need if the pickup/exit is rough and you need to use the regulator not to swallow the ocean?

Beware the boogey man - I know my gauges but that shouldn't matter anyways.

What happens if you breath through 500 instead of 300 because of rough conditions.. do you drown on the surface? If you are diving in recreational conditions where 200psi makes the difference between success and failure you need to rethink your plans. If I think I'm going to spend time on the surface I bring a snorkel or pad my reserve volume but I don't default to a general "rule of thumb" for every dive because of it.

500psi in a 72 or 80 is a lot of gas to get from 15 ft to surface, so is 300psi. Have you ever known a competent diver to come close to being OOA in that situation?

But let's look at some of the practices now espoused for rec diving on this board:

Don't dive with a snorkel
Don't practice CESA's
Don't use ditchable weight

No wonder some then believe they need to rely on canned gas to survive on the surface.

 

[boulderjohn]

But let's look at some of the practices now espoused for rec diving on this board:

Don't dive with a snorkel
Don't practice CESA's
Don't use ditchable weight

No wonder some then believe they need to rely on canned gas to survive on the surface.

I have to admit I am a bit puzzled by this.

A lot of people do denigrate the use of the snorkel, but I am not clear on how having or not having a snorkel on your mask has an impact on whether or not you run out of air at depth. Please explain.

I read a lot of ScubaBoard, and I don't see a lot of people saying you should not practice CESAs. In fact, I'm drawing a complete blank on that one. Please direct me to these prevalent threads, and then explain the influence on CESA practice on the amount of air needed at depth.

I am also drawing a blank on the prevalence of threads in which people are advised not to have ditchable weight. Perhaps you could supply me with some links to that, and while you are at it, tell me what this has to do with the amount of gas needed to ascend at the end of a dive.