What if you need to use some of that 500 psi contigency reserve?

[DandyDon]

It's been a few years since I took OW, and they may have called it something else - but I think we are generally taught these days to have at least 500 psi left in our tank at the end of a dive. Over the years of reading SB, I have wondered in some accidents if things went badly at times because a new diver may have not realized that should a need arise to use some of it - use it! I have on a very few* occasions, one last month when some things came up approaching the ladder and I dipped just a little below 500 psi, but I was much more concerned about swimming out of the problem safely that I was at boarding with 500. (*Please do note that I said very few; I know how sometimes we read over a post and think the poster said something differently than written.)

In a few different threads here and there lately I have read of other divers who routinely breath down to 300 psi in the shallow, even less. I do not, I don't consider that a good practice at all, but I didn't want to hijack any of those threads to discuss that further.

In another thread today, I posted....

I generally don't push NDL - too much of an air hog, but even on my "liberal" Oceanic PDCs, I don't worry if I get into the yellow zone approaching it. .....I will adjust my remaining dive plan to allow for deep and longer safety stops with a goal of surfacing in the green. Extending a safety stop and using half my contingent reserve down to 250 psi would be a prudent action in my mind with that goal in mind if there were no other challenging factors in play - but then I have tested my reg and spg below 250 psi, I do carry a pony, and I have not panicked when I had to orally inflate my BC on the surface, etc. Riding to 250 psi does have its risks even at 15 ft. :11:

I was surprised that I was asked "what risks?" I don't know the training and experience of the person asking, but thot it would be better to discuss this on a separate thread. He really wanted an answer, so here I am opening the thread here.

I can think of a number of risks involved with breathing a tank down to 250 psi, aside from the charter operator may demand I pay for a viz or ground me for the rest of the dives of the day. Here are a few for starters...
1-Even tho I have tested my reg down to less than 250 with no breathing problems, that may have changed.
2-Even tho I have tested my spg down to 100 psi and even to empty, there is a chance it may have changed.
3-Even if I don't run out of air, I might not have enough back gas to inflate my BC? I have orally inflated my BC in a surprise incident once when the hose came lose (check that part closer now) with no problem and not the least bit of panic, but we all have a bad day now and then. To avoid an accident should this need ever arise again, my home bud and I routinely practice orally inflating, but that practice hole doesn't have waves so we also practicing grabbing our weights as if we were about to jerk them out and away.

Now, I'd like to ask for other reasons why we try to return with 500 psi - some skippers require 700 I've heard, if y'all would like to help me out here...??

Additionally, it would be beneficial to hear from divers who do intentionally breath their tanks below 500, along with why, and what if?? If you would prefer to post that anonymously, you will need to ask a Mod to do it for you, or - PM me and I will, like I did with a denture thread.

thank you...!

 

[NorthWoodsDiver]

For dives below say 20-30 ft I like to come home with 1000psi as I follow the rule of 3rds. stuff shallower than 30ft I dont much worry about as long as I have air in the tank and I am in a comfortable familiar area.

Now in new places or rough water or current or in overly cold water I like to come home with at least 500 on those shallow dives. I think the lowest I ever drained a tank was down to 200 +/- and my max dept was 21ft lookin at fish in a fresh water lake with a buddy in familiar territory. Carelessness is all in ones own opinion but I see no reason when diving in semi controlled, shallow, warm water conditions why a person needs to have over 250 in a tank.

Like I aid before dives in an overhead or artificial overhead I keep a nice 1000.

 

[hudson]

IMHO, the reason you are asked to return with 500psi or more is really that the average diver is not trusted to plan his gas properly. Otherwise the risks you cite are about in the same ballpark ask "what if I bust the tank o-ring".

*If the charter operator is going to play air-, I don't use that charter.
*My air integrated computer is +-60psi, the chances of that changing is again very remote.
*I don't have a problem with a hard breathing regulator at safety stop depths.
*Inflating the BC takes a very small amount of air, I don't see it ever being a factor.

I'll plan to surface with 500 only if I think I may need air after surfacing. If not, I have no problem draining it down to 200 and that's how I plan my dives. Given a common sense conservative approach I almost always end up with more anyway, but I don't see any big risk in getting down to 200psi in the shallows.

 

[Papa_Bear]

When I learned to dive we used J valves that kept 500psi in your tank to come up with! No gage! When you started to breath hard you pulled your reserve! No big deal, and we didn't do safety stops either, and no one died! The only reason to bring back 500psi is that's the operators policy and two you should have positive pressure to keep water out of the tank. it's still 15% of your tank! On the surface it's probably 10 to 15 minutes air! I have sucked a few tanks dry! But remember the volume in crease the most in the last 10ft to the surface! If you are on the surface and have a problem manually inflate your BCD if you have to! Drop your wight belt! Take off your tank and sit on it! If its aluminum it will float along with your BCD and if the BCD won't hold air the tank will float! So I don't know what emergency you would have that would require SCUBA gear that you couldn't do in snorkel gear? Many times I have taken my gear of in the water many times and handed it to the boat! So the idea is to have positive pressure in the tank and be safe! Remember a SCUBA diver without a tank is a swimmer! Can you swim?

 

[MikeFerrara]

I plan to end the dive with enough gas to get me and a buddy back to the surface...I don't need any gas at all on the boat.

Don, your reg will deliver gas until the tank pressure is equal to ambient pressure.

 

[Rick Inman]

After I surface, I like to have 14.7 PSI to breath (actually, a little less in my neck of the woods).

 

[Ana]

I'm not sure I get the question.
I see several issues on the subject. Is the answer that you are looking for to
a- keep operators happy
b- follow rules that are set to take care of the casual divers that rather follow as good little lambs instead of engaging their brain
or
c- keeping thinking divers within a reasonable safety margin.

For 'a' and 'b' there is no discussion needed. You do as you're told period. Punishments of payments for VIP's and being in time out I can't even consider, I left grade school quite a bit a go so I can't comment on that

For the 'c' group I would say that you should plan your dive to be at your safety stop with about 500psi. Once I'm at the safety stop I can either do my minutes and get out or decide to hang a little longer.

I don't see why anyone get all worked up about the 500psi line, I always thought of it as a prudent reference amount. Besides that... if inflating a BC/wing orally is a challenge I'm not sure we are talking the same language.

 

[Zieg]

Wow Don, you managed to turn a simple question ("What risks?") into quite a production.

It's been a few years since I took OW, and they may have called it something else - but I think we are generally taught these days to have at least 500 psi left in our tank at the end of a dive. Over the years of reading SB, I have wondered in some accidents if things went badly at times because a new diver may have not realized that should a need arise to use some of it - use it! I have on a very few* occasions, one last month when some things came up approaching the ladder and I dipped just a little below 500 psi, but I was much more concerned about swimming out of the problem safely that I was at boarding with 500. (*Please do note that I said very few; I know how sometimes we read over a post and think the poster said something differently than written.)

In a few different threads here and there lately I have read of other divers who routinely breath down to 300 psi in the shallow, even less. I do not, I don't consider that a good practice at all, but I didn't want to hijack any of those threads to discuss that further.

In another thread today, I posted....

I was surprised that I was asked "what risks?" I don't know the training and experience of the person asking, but thot it would be better to discuss this on a separate thread. He really wanted an answer, so here I am opening the thread here.

I can think of a number of risks involved with breathing a tank down to 250 psi, aside from the charter operator may demand I pay for a viz or ground me for the rest of the dives of the day. Here are a few for starters...
1-Even tho I have tested my reg down to less than 250 with no breathing problems, that may have changed.
2-Even tho I have tested my spg down to 100 psi and even to empty, there is a chance it may have changed.
3-Even if I don't run out of air, I might not have enough back gas to inflate my BC? I have orally inflated my BC in a surprise incident once when the hose came lose (check that part closer now) with no problem and not the least bit of panic, but we all have a bad day now and then. To avoid an accident should this need ever arise again, my home bud and I routinely practice orally inflating, but that practice hole doesn't have waves so we also practicing grabbing our weights as if we were about to jerk them out and away.

Now, I'd like to ask for other reasons why we try to return with 500 psi - some skippers require 700 I've heard, if y'all would like to help me out here...??

Additionally, it would be beneficial to hear from divers who do intentionally breath their tanks below 500, along with why, and what if?? If you would prefer to post that anonymously, you will need to ask a Mod to do it for you, or - PM me and I will, like I did with a denture thread.

thank you...!

In your original post you stated "Riding to 250 psi does have its risks even at 15 ft" and were simply asked what were the risks that you found. You seemed to desire that this question would require a discussion, and I guess you have it. I didn't realize that this was such a difficult question to answer. But you did finally respond to the original question, so let your discussion commence.

Considering your first two points, about the risk to the regulator and spg, you actually test these each time you shut the value on your tank and purge the excess pressure. Your third point, about not having enough air to inflate your BCD, please note that it doesn't require 250 psi to inflate this device. If it does, perhaps you should consider going to a smaller device. You also stated "and I have not panicked when I had to orally inflate my BC on the surface", well, I don't think I better comment on your bravery.

 

[dumpsterDiver]

the 500 psi rule is silly and is mandated because so many divers have poor skills. Running the tank down to 200 psi at 15 feet might be much safer for an experienced diver rather than blowing off the safety stop simply so some $9.00 per hour tank monkey is satisfied.

Also, as was mentioned, the BC inflator will continue to work (slowly) at very low pressures.

 

[TSandM]

Gauges aren't as accurate at the far ends of their ranges. Fill station operators may require a viz if the tank is brought in empty. Inexperienced divers have no idea what their reaction will be if they go to take a breath and there is nothing there. Those are the big reasons I can come up with for surfacing with 500 psi.

I have gone below that, when there was some very interesting stuff to look at in the 10 - 15 foot range. I did it with the knowledge that a) the surface was close by, and I had done my deco and could surface if I needed to; b) I was surrounded by people who had more gas than I did (bigger tanks -- I got the short straw) and were prepared, on an instant's notice, to donate to me if I needed it, and felt that was a better option than simply surfacing.

I would never recommend that a new or occasional diver take those risks. I dive constantly, and I know my buddies very well.