Surface pressure

[rick00001967]

Is it safe to arrive at your safety stop with only 500 psi/35 bar left in your tank? Frankly, I don't think so. And I think you should start thinking about min gas calcs.

keeping in mind this is the "basic" forum......the answer is "NO", it is not. and to those that think it is ok to plan a dive to hot the surface with 300psi, i would ask how your buddy feels about that.

 

[scubadada]

keeping in mind this is the "basic" forum......the answer is "NO", it is not. and to those that think it is ok to plan a dive to hot the surface with 300psi, i would ask how your buddy feels about that.

I'm by myself, I can surface with what I want. With drift diving, you have 100% access to the surface at any time.

 

[CuzzA]

keeping in mind this is the "basic" forum......the answer is "NO", it is not. and to those that think it is ok to plan a dive to hot the surface with 300psi, i would ask how your buddy feels about that.

Let's look at this a different way. If you surfaced from a dive with 300 psi in an Aluminum 80 that means you and your buddy could still hang at 20 feet for 3 minutes huffing at a combined RMV of 1.68 (that's a lot of huffing)) on that one tank before running out of gas.

There's too many variables to have some arbitrary rule of surfacing with 500 psi left in your tank.

For new divers, which the basic scuba forum is not a new diver forum, rather general basic scuba discussion, should certainly be more conservative before gaining experience and understanding gas consumption and diving.

 

[yle]

<Rant mode=“on”>
“50 bar/500 psi on the surface” is the dumbest rule.

Have to disagree. It's a simple rule designed for the masses, trying to keep them relatively safe because we know most of them quickly forget most of what they learned in OW class (especially if they only dive once or twice a year).

The rule wasn't designed for those of us that have situational awareness, plenty of experience, and understanding of things like gas management. I think as a simple rule for beginners to remember, it's not so bad.

 

[yle]

Is it safe to arrive at your safety stop with only 500 psi/35 bar left in your tank? Frankly, I don't think so. And I think you should start thinking about min gas calcs.

Every dive op that I've heard talk about this issue during the dive briefing has specified back on the boat, not starting a safety stop, with no less than 500 psi. Most of them also talk about arriving at the safety stop with 1000 psi.

 

[M-Cameron]

When I got my OWD cert, I was taught to surface with at least 50 bar left in my tank. No matter whether I dived a 10L, a 12L or a 15L. I gotta admit, I stretched that "rule" a little bit. As long as I arrived at my safety stop with 50 bar left, I was good. Or at least, I thought so.

Now, 50 bar in a 10L tank is 500 surface liters, while 50 bar in a 15L tank is 750 surface liters. So that rule didn't make sense. Over in Imperial country, you're supposed to surface with 500 psi left in your tank. That's about 35 bar, and for an Al80 (11 liters water volume), it's about 350 surface liters.

A standard SPG has an accuracy of some 10-20 bar. So, if your SPG tells you that you have 50 bar left, worst case you might have only some 30 bar left. For a 10L tank, that's some 300 surface liters or about 10 minutes of gas. On the surface, so perhaps 50% less at safety stop depth. If your Imperial unit SPG has the same error, you might be down to almost zero minutes.

Is it safe to arrive at your safety stop with only 500 psi/35 bar left in your tank? Frankly, I don't think so. And I think you should start thinking about min gas calcs.

the industry is focusing too hard on turning out higher and higher volume of divers.....trying to get people certified in a weekend, trying to sell OWD certs for $99......and A LOT of corners are being cut.

the "surface with 500 psi" is evident of that....and by and large, they arent even being taught HOW to arrive at the boat with 500...

as you mentioned, 500psi is a a different volume depending on tank size.

gas planning, SAC rate, and honestly, planning a dive are not components of OWD...its essentially "follow the computer and come back with some amount of air in the tank"...

and the thing is....its really not that hard to do....

when i do a dive, i calculate the amount of gas it takes for 2 people to ascent at my max depth at 30ft/min, and do a Safety stop., then add in a small buffer....and frankly i dont know why that isnt the standard thats being taught in OWD

 

[M-Cameron]

Safety stops are optional. So if we're talking about no stop diving, as long as I can get to the surface at less than 30 ft. per minute, all is well. Most dives where I finish off the tank I surface with about 300 psi. AI should not have inaccuracies like an analog SPG.

wearing a seatbelt is optional too.....doesnt make it a good idea to skip it.

SS can technically be skipped in the event of an emergency...its not something one should get in the habit of doing because they were to lazy to plan a dive.

 

[rick00001967]

I'm by myself, I can surface with what I want. With drift diving, you have 100% access to the surface at any time.

agreed. but i don't recall this being a post about solo diving. perhaps i missed that part.

 

[CuzzA]

wearing a seatbelt is optional too.....doesnt make it a good idea to skip it.

SS can technically be skipped in the event of an emergency...its not something one should get in the habit of doing because they were to lazy to plan a dive.

No. Wearing a seat belt is the law. There is no law that you must do a safety stop, and as already pointed out, this didn't become a thing until just a couple decades ago. Which I'd say was based solely on protecting the absolute most prone diver based on age, skill and fitness from getting bent.

Anecdotally, once you've seen thousands of dives completed at sub 60ft depths with no stops, and know tens of thousands more are being done the same way, and you consider your own age, skill and fitness, you begin to look at safety stops a bit differently. Personally, for sub 60ft. dives at 30 ft. I just slow my ascent to around 10 to 15 ft. per minute and make sure I'm taking nice deep breaths expelling nitrogen.

Regardless, the argument was made that it's dangerous to arrive at safety stop depth with 500 psi and I argue that is ultra conservative. This would mean both you and your buddy have already ended the dive, there was no emergency, and now you're sitting for 3 minutes at 10-20 feet. Two kicks from the surface. And as I pointed out, even with one diver running out of gas, one diver with 300 psi in an AL80, you both would have to be huffing a lot of gas and could still do the 3 minute optional stop.

 

[M-Cameron]

No. Wearing a seat belt is the law. There is no law that you must do a safety stop, and as already pointed out,

no seatbelt law in my state.....i still wear one.....

this didn't become a thing until just a couple decades ago.

neither did seatbelts.