Gas management skills...

not having them makes for some exciting diving! :tease:

So, what were you taught and when? What are your currently using? Does a buddy play a predominant role in your strategy?

When I stated I was doing all my diving in the Red Sea. The usual Gas plan was to follow a reef until the first person hit 100 bar (1450 psi), Then turn, ascend to a shallower depth and head back. Adjust your depth on the way back so you arrive back with 50 bar (700 psi). The water was always calm and the surface viz good so you could surface anywhere if you had a problem. Not a great plan but it is pretty common over there.

Now, diving in the UK, I calculate rock bottom (enough for me and my buddy to surface, etc.) and manage the rest of the gas depending on how important it is to get back to where we started.

I make sure I have enough for my buddy but I don't rely on my buddy's gas.

I'll elaborate if required but I'll let a few more people get in first.

Nick

Much 99% of OW courses, I was taught the surface w/ 500psi rule of thumb....but I was also taught...."in order to do that, you have to compensste, so you should start your ascent around 700 depending on your depth and safety stop"

This was fine with me and my buddy, but when we were somewhere we weren't familiar with, we decided that 1000 was a good number to use, and followed that rule.

Within the last year-ish I had begun to think...how much gas do I really need for that OOA ow-diver who somehow screwed it up thanks to my DM training. So during my DM class, I started working with SAC rates, and converting pressures/volumes to what I called "Fail-safe psi"...I never really shared it with anyone for fear of looking like a baffon. Recently I took the DIR-F class and I found out "fail-safe" was damn near the exact same thing as rock bottom. The big difference was adding in a deep stop and doing some conservative conversions to make the math easier....whimps....

At Any rate, nearly all the diving I do is in a quarry at less than 100', so rock bottom or fail-safe is what I determine. I figure how much gas/air I'm going to need for myself and my buddy to do a safe controlled ascent....ususally it ends up being around 700psi depending on depth.

I have seen the 500-700 psi given by charters and some instructors misinterpreted to the extreme. Incredibly, divers have blown off safety stops and shortened deco stops to MAKE SURE they got on the boat with the prescribed minimum. Sorta makes my jaw drop.

The bottom time is dictated by several variables. Tables (or computer), SAC rate and the amount and type of gas I am diving with (Nitrox).

The PSI number I use to start my asecent depends on the depth and conditions (water currents and top side weather). on a 100 foot ascent, 1100 PSI is typical with an ascent rate slower than 30 feet/minute and a one minute stop at 50 feet and 3-5 minutes at 15-20 feet. This always places me in the boat with at LEAST 500 PSI under any condition. I typically dive with a 120 Cu. FT. tank. There is still a lot of good diving during this interval!

Bottom time gas is managed by making the dive a multiple level dive if possible. I know I can do 40 minutes on the wreck of the Duane (dive to surface). Other sites I can do 50 to 55 minutes (example, the Busch in Cudjoe Key).

By staying with the multiple level principle my very first dive on the Spiegel Grove was 42 minutes.

If I am planning a single level bottom time dive then the dive time is simplied and the max time is always to the 1.4 PO limit for my gas.

This is my level of training and experience. I will not exceed those limits until I am certified in planned decompression diving techniques.

As to starting your ascent from depths of 100 feet or more with 500 PSI, as NetDoc has alluded too will not allow for any safety stops due the amount of immediate pressure required to just make the regulator work normally. I have seen boats and DM's take the extra time and include the statement that you should start your ASCENT with 1000 psi, etc. What you come on board with is basically unimportant, especially if you did your stops and ascent rate correctly.

NetDoc once bubbled...
not having them makes for some exciting diving! :tease:

So, what were you taught and when? What are your currently using? Does a buddy play a predominant role in your strategy?

Click to expand...

I was never tought gas mangement beyond "watch your gauge". I had to invent it like everything else concerning diving. Of course later I found out that somebody else invented it first and it was just kept secret.

Later, in tech and cave training, gas management was part of the program but even recreational divers need to breath.

MikeFerrara once bubbled...
I had to invent it like everything else concerning diving.

Click to expand...

Certainly you do not want to take credit for Split Fins do you?

covers SAC and gas/dive management in detail. Although, I only present the concept of SAC in BOW and how Boyle's law creates a different DAC as well.

Lets face it, there is a lot to learn about diving. Not sure I could convince many to take a two year course to get it all in :tease:

But Mike, there are lots of people who invent these tools to help them cope, only to find that there are lots better tools out there.

Started out in basic OW to turn the dive with half your gas left (or whoever uses it the fastest) and then ascend with approximately 700-800 psi to allow for safety stops. As I went through AOW and then Nitrox the gas management skills were taught in order to plan the length of your dive at a given depth (square profile and allowing for safety stops). I have since spent more time trying to learn and expand on my knowledge by spending time on this board. I have begun using the method of subtracting the rock-bottom (gas amount to ascend from a given depth) for me as well as my buddy and then diving on whats left (1/2 out 1/2 back). I also use the deep stops as well, but the rock-bottom amount is calculated with just the standard safety stops.

Cheers

Learned that back in the days before SPGs, the '72 had a different sound when it was nearing empty, definately had a different ring if you smacked it with your knife or a rock. Dull thud when full, like a bell when empty.