on the boat w/500 psi

[MXGratefulDiver]

I should have included the minutiae. As you pointed out this is the new diver forum.

NWGratefullDiver gave a more verbose answer

Well, everyone who knows me knows that "verbose" is my nature ... one of my former nicknames was "Socrates" ...

But in reality, I was providing an explanation for what you said. Since this is the New Diver's forum, stating that something isn't relevent doesn't do a whole lot without an explanation of why ... I was supplying that explanation.

... Bob (Grateful Diver)

 

[syntaxerrorsix]

Well, everyone who knows me knows that "verbose" is my nature ... one of my former nicknames was "Socrates" ...

But in reality, I was providing an explanation for what you said. Since this is the New Diver's forum, stating that something isn't relevent doesn't do a whole lot without an explanation of why ... I was supplying that explanation.

... Bob (Grateful Diver)

Understood, I should have paid more attention to what room I was in.

 

[MXGratefulDiver]

Hadn't put too much thought before this into how do you arrive back at the boat with 500 psi, and that really shows something that is lacking in diver education. Whether you consider it a topic for recreational diving, technical diving, or somewhere in between, how can recreational divers ever be expected to return with that reserve if they aren't taught how in the first place?

Well, first off, "end the dive with 500 psi" isn't gas management ... it's a goal. And in order to achieve a goal, it helps to understand what it takes to get there.

Think of gas management like a family budget. In order to set up a budget you have to know three things ... how much money you have coming in ... how much you want to save ... and what has to be paid for. You then prioritize your activities around those pieces of information.

Gas management is like that. You know how much gas you have to start with (your "income"). You know how much you want to end up with (500 psi). What you then need to do is plan your dive around how to use up the rest. You must begin that process by establishing your consumption rate (expenses) ... keeping in mind that surface consumption (SAC) is simply a baseline around which to plan your depth and time. As you go deeper, your "expenses" increase accordingly ... and so you have to cut back your "activities" to compensate for the increased spending rate.

My article gives you all the necessary arithmetic. It may seem like a tedious process ... and in reality it's not something even I recommend that people do all the time. The key thing is to (1) determine your SAC rate, (2) create a dive plan, and (3) run the numbers using the dive plan. Just the exercise will help you learn a few things about whether or not the dives you're doing are going to get you back on shore or on the boat with the expected reserves.

When I have my AOW students do that exercise, they quickly realize ... without my even saying so ... why doing deeper dives on an AL80 are not a good idea. They didn't come to that conclusion because some instructor told them so ... they got there by logicking through the process, and understanding how depth affects their air consumption.

As with any budget, people who just "wing it" will inevitably end up with a deficit from time to time, while those who have established a budget will generally spend their money more wisely, and will more easily achieve their objectives. Gas management is no different, except that running a "deficit" on your air while diving can have a serious impact on your health, as well as your ability to enjoy the dive ...

... Bob (Grateful Diver)

 

[Kenny13]

Well, first off, "end the dive with 500 psi" isn't gas management ... it's a goal. And in order to achieve a goal, it helps to understand what it takes to get there.
Think of gas management like a family budget. In order to set up a budget you have to know three things ... how much money you have coming in ... how much you want to save ... and what has to be paid for. You then prioritize your activities around those pieces of information.

Gas management is like that. You know how much gas you have to start with (your "income"). You know how much you want to end up with (500 psi). What you then need to do is plan your dive around how to use up the rest. You must begin that process by establishing your consumption rate (expenses) ... keeping in mind that surface consumption (SAC) is simply a baseline around which to plan your depth and time. As you go deeper, your "expenses" increase accordingly ... and so you have to cut back your "activities" to compensate for the increased spending rate.

My article gives you all the necessary arithmetic. It may seem like a tedious process ... and in reality it's not something even I recommend that people do all the time. The key thing is to (1) determine your SAC rate, (2) create a dive plan, and (3) run the numbers using the dive plan. Just the exercise will help you learn a few things about whether or not the dives you're doing are going to get you back on shore or on the boat with the expected reserves.

When I have my AOW students do that exercise, they quickly realize ... without my even saying so ... why doing deeper dives on an AL80 are not a good idea. They didn't come to that conclusion because some instructor told them so ... they got there by logicking through the process, and understanding how depth affects their air consumption.

As with any budget, people who just "wing it" will inevitably end up with a deficit from time to time, while those who have established a budget will generally spend their money more wisely, and will more easily achieve their objectives. Gas management is no different, except that running a "deficit" on your air while diving can have a serious impact on your health, as well as your ability to enjoy the dive ...

... Bob (Grateful Diver)

Thanks for the reply Bob. And I completely understand that "end the dive with 500 psi" isn't gas management, but that gas management is somewhat of a tool that allows you to plan your dive and arrive more times than not with that reserve in your tank. The budget analogy is a good one.

I do have a copy of your article printed up to read when I get a chance.

 

[eponym]

I find the poll results so far very encouraging. More than three-quarters of respondents are saying they learned how in their basic open water courses. If true, this would suggest instructors are doing a good job of providing the necessary knowledge and rules of thumb.

Regarding the semi-hijack on gauges: When teaching gear assembly, I now include checking that your pressure gauge reads zero before you turn on the air. Then you can be reasonably sure it won't stick at 200 or more when you're actually draining the last of your gas.

-Bryan

 

[captndale]

When I took my entry-level course spg's were not common. My instructor told me to go up when it starts to get hard to breathe.

 

[syntaxerrorsix]

I find the poll results so far very encouraging. More than three-quarters of respondents are saying they learned how in their basic open water courses. If true, this would suggest instructors are doing a good job of providing the necessary knowledge and rules of thumb.

Regarding the semi-hijack on gauges: When teaching gear assembly, I now include checking that your pressure gauge reads zero before you turn on the air. Then you can be reasonably sure it won't stick at 200 or more when you're actually draining the last of your gas.

-Bryan

The problem is they don't know WHY it's 500PSI or how much gas they actually need. I have also not read a standard from any training agency that states 500PSI or it's related volume is the "magic" number.

It's unfounded and in my opinion not relevant otherwise.

 

[Bubbletrubble]

Regarding the semi-hijack on gauges: When teaching gear assembly, I now include checking that your pressure gauge reads zero before you turn on the air. Then you can be reasonably sure it won't stick at 200 or more when you're actually draining the last of your gas.

@Bryan St.Germain: Part of my pre-dive reg check is to verify that the SPG reads zero prior to pressurization and that the SPG goes to zero after I turn off the tank valve following depressurization. I watch the SPG needle for smooth travel all the way down to zero as I'm purging or breathing down one of the second stages. By breathing it down to zero, I'm doing a quick vacuum test on the second stage.

I could be completely wrong about this, but...I wouldn't assume just because the needle reads zero prior to pressurization that the needle won't stick as tank pressure falls.

 

[Teamcasa]

We did not have SPG's when I first started diving. After a layoff, I went on a charter where the Captain announced that anyone coming up with <500 psi would be charged a fee for tank inspection for water intrusion.

No wanting to bother asking him how water can enter a tank with even a 100 psi left in it, (it can't BTW) I just shook my head and followed the axiom, his boat, his rules. Now I bring my own tank where possible.

 

[Blue Sparkle]

I don't completely understand the question. It's making me think two different things, neither of which seem exactly right when I re-read the question:

1) Where/when/how did you learn gas management?

2) Where/when/how did you learn that you were supposed to be back on the boat with 500psi

My answer to #1 would be here on Scubaboard first (which was after I was certified), then from SB linked articles written by NWGD, and Lamont, and then confirmed/added to by a one-day individualized class I took from an instructor (whom I chose partially because I knew he would approach gas management similarly to the articles I had read). I don't remember learning anything substantive about gas management from my OW or AOW classes.

In the Wreck and Deep specialty classes, there may have been something in the book (?), but I had already taken the one-day class so I really don't remember for sure other than that I was thinking "I wish they would cover it more; and I'm glad I already learned about it." The instructor of the latter classes didn't talk about it other than the basic "be able to see the upline at 1500, be on the way up at 1000." Those dives did not really match up with what I had learned here.

My answer to #2 is from the DM's on dive boats (not the "how" but the simple fact that that is what one was supposed to do - be back on the boat with 500 psi). As I remember it, it was not only a diver safety concern but also that the op would have to do time/$ things to the tanks if they were run very low.