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

[Doc]

After years of watching resort and dive operations, I can tell you that you are only viewing it from your perspective, not that of those who are making the rules.

The reason dive ops don't want you to breathe the air down past 500 psi and get real rabid about enforcing the same? (one of the symptoms of Caymania)

It all came about resulting from the corrosion damage that was being done to tanks, valves and rental regs when salt water seeped in after positive pressure was lost.

If you are looking at a rule, look for the real rea$on that caused it to be made.

IE: Smoking on airliners being banned. You think you know why?

Aeroflot (the Russian Airline and others, too) seems to be able to run great smelling planes with great air quality, yet still allowed smoking. Why? How? They continue to build aircraft that still are built with three "air packs" (air conditioners) that are heavy to carry, take up space, cost money to maintain- and use fuel to operate. Our US designs now specify 2 air pack planes and the no-smoking has little or nothing to do with health and safety- sure they may save on cleaning or cigarette burns- but airlines let the anti-smokers take the hit for what the corporations wanted. Cheaper operations~ the pilots resist even running more than one.

The dive op industry made no such cohesive plan to manipulate our behaviors or modify the process. They just didn't want corroded tanks. The urban legend of theoretical safety is a more understandable reason, although no more accurate for its widespread acceptance.

Follow the money... and the corrosion.

 

[1_T_Submariner]

I have used some of the air below 500 PSI in my tank. I had done a Saftey stop and the seas were kind of rough. There was an OW class of 6 getting back on the boat and having some trouble so I spent some extra time at 15 feet watching them I got down to 400, I would have got on with 600 which equals a healthy 500 IMHO.
I agree you shouldn't plan to use it but, I didn't see a point floating on the surface in rough seas waiting either.

 

[DandyDon]

Interesting feedback, thanks! Not often that I find myself on the overly conservative side of an issue.

BTW, the requirements are often set by the skipper, and his orders are law in some cases - especially liveaboard. Going to be with that guy all week, rather dive some of it.

 

[Scotttyd]

When I was on a dive in Belize told us that we were low at 500 not out. We ended our dive at 30 feet (max of 60). We were instructed that if we were heavy breathers, we were ok to start our ascent at 500 psi when we were at 30 feet. In their worlds, we had plenty of air to do our safety stop and make it back to the boat. This is exactly what happened to me. Reminder that I only had logged 8 dives at this point so I was trusting our DM. Although I did feel nervous when I ended with about 250 psi in my tank while doing my safety stop. I think this is bad advice for a new diver, maybe if you are more comfortable and in a familiar place, but not when you are new and in unfamiliar territory.

 

[Nylorac]

.....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...![/quote]

I dove with the same DM for a week in Cozumel who was very "serious" about showing us how to be good divers - move slow! breathe slow! (drift dives-just miror me!). I learned great hovering techniques - but every time anyone let him know it was time to go up (around 750 for good safety stops after 90-100' dives -based on his dive plan) he routinely ignored them with an annoying wave and took his time getting ready to asend. After my third dive when I came up with 250 after listening to him, I (and my buddy who had even less air than me ending that dive) just ignored him and trusted our own judgement the rest of the trip.

I'm not an advanced diver and I want the insurance of a little extra psi....I'm not into the "trust me" thing - learn to trust yourself.

 

[Blox]

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...??

The 500 PSI (or 700, as the case may be), aren't yours, they are your buddy's (if you do dive with a buddy). I agree with other posts, that suspect that the dive ops impose these exit pressures because many people are unable to to plan their gas properly, and since such people are unable to deal with calculating the value of the variable "how much gas do I need to do the planned dive?" instead replace the "gas volume" variable with a "time" variable ("come back with 500 psi in the tank"), because not knowing the answer to "how long will it take?" doesn't draw punishment.

Additionally, it would be beneficial to hear from divers who do intentionally breath their tanks below 500, along with why, and what if??

Sorry, gotta pass on that question. I've never done it. Not that much because I am strictly opposed to doing it (I am, when diving with a buddy though), but because I never got a chance to do it.

 

[gcbryan]

... But remember the volume in crease (increases) the most in the last 10ft to the surface! ...

I've seen you make this point several times in several posts but what is your point?
It's true the volume of air increases as you ascend in your BC or drysuit but that doesn't seem to be your point. It doesn't increase in your tank so help me to understand exactly what is the point you are trying to make with this statement.

 

[spt29970]

My feeling is that the 500psi is a reserve. Of COURSE you use if you need it. You just don't plan on using it. Last weekend, I surfaced with 500psi and had a bit of a surface swim and I don't carry a snorkel. I usually surface swim on my back, but in this case there was a strong current running and I wanted to keep my eye on the boat. What I did was keep my reg in, turn on my stomach, and swam to the boat. I ended up with 200 when I hit the current line. I won't breathe the tank any lower unless I am in distress because I don't want to chance getting water in the tank.

Similarly, I have occasionally used a few hundred psi to swim under kelp (instead of crawling through it). IMHO 500psi is a planning number, not an absolute rule. Similarly, I wouldn't hesitate to breathe down below 500psi to extend a safety stop if needed.

 

[Papa_Bear]

It is the inverse of going deeper! It stays the same but it expands as you breath it so you have a much greater volume on the surface, The lack of knowledge of todays divers is amazing! I have made the point to let people know its at pool depth they have a lot of time to surface. I have seen people blow their safety stop because they were below 500psi when all they had to do is relax make the stop and surface! It isn't rocket science it a matter of comfort! What's your point?

 

[Papa_Bear]

The 500 PSI (or 700, as the case may be), aren't yours, they are your buddy's (if you do dive with a buddy). I agree with other posts, that suspect that the dive ops impose these exit pressures because many people are unable to to plan their gas properly, and since such people are unable to deal with calculating the value of the variable "how much gas do I need to do the planned dive?" instead replace the "gas volume" variable with a "time" variable ("come back with 500 psi in the tank"), because not knowing the answer to "how long will it take?" doesn't draw punishment.

All the air in my tank is mine! Period and if I let someone have it I will choose and control it! If you have been taught that get better training! You are not a baby sitter it is your life support not your buddies! If you are diving as a buddy team you turned on the less air tank and you are at 15ft with 500psi of your air! He can suck his tank dry in go up! If you think he needs a little more time give him your backup and when you both run out go up! Why do you and a few here try to make this such a complicated endeavor? A safety stop is just that! I made 1500 dives without one and until the 80s you never heard of such a thing unless you were doing deco dives! It is not a required stop! If my buddy miss judges he needs to learn not to!