PADI Gas Matching

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boulderjohn

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Shouldn't the gas guzzler be forced to bring his/hers/it's own redundant gas -- perish the thought, a pony?
The question of this thread relates to technical diving, in which redundant gas is a requirement.

This issue illustrates one big difference between recreational and technical diving. Except for unusual cases, gas matching is not involved much in recreational diving, and gas guzzlers frequently carry more gas so that they can stay at depth as long as their companions.That does not work in technical diving. In technical diving, the gas planning depends upon the diver with the least gas. One day when I was in cave training, we were accompanied by an instructor intern. My instructor and I were diving cave-filled LP 104s. The intern brought LP 85s, and my instructor was clearly annoyed that our dives would be limited by the intern's gas supply.
 

Wibble

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The question of this thread relates to technical diving, in which redundant gas is a requirement.

This issue illustrates one big difference between recreational and technical diving. Except for unusual cases, gas matching is not involved much in recreational diving, and gas guzzlers frequently carry more gas so that they can stay at depth as long as their companions.That does not work in technical diving. In technical diving, the gas planning depends upon the diver with the least gas. One day when I was in cave training, we were accompanied by an instructor intern. My instructor and I were diving cave-filled LP 104s. The intern brought LP 85s, and my instructor was clearly annoyed that our dives would be limited by the intern's gas supply.
Just to be clear, I mean that people of high SAC should be more responsible for their high SAC rates and they should maybe bring additional redundant gas and not "rely" on others curtailing their bottom time just in case the high SAC person cleans everyone out of gas in extremis.

I appreciate that this is the backup to the backup, but as it's such an impact on the other "team" members, then there should be additional gas just for that person and carried by that person.

By additional I mean another pony even if it's a simple backgas only dive. A "reserve bottom stage"?
 

Imbodie

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Just to be clear, I mean that people of high SAC should be more responsible for their high SAC rates and they should maybe bring additional redundant gas and not "rely" on others curtailing their bottom time just in case the high SAC person cleans everyone out of gas in extremis.

By additional I mean another pony even if it's a simple backgas only dive. A "reserve bottom stage"?
That is why it is technical diving and not recreational... Gas matching is VERY important when you are diving in a 3rds rule environment... however in an open water deep technical dive the diver should have learned to calculate their RMV/SAC and should plan accordingly... they should be bringing enough gas to complete their dive WITH deco included.... I don't really know why the rule of 3rds is even taught for deep open water dives they are a whole different beast than doing a cave dive.
 

grantctobin

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A short video on the concept of gas matching. The video includes an animation illustrating why gas matching can be important.

You do you know that you use the wrong volume for an AL80 cylinder right?
 

divezonescuba

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77 versus 80 yes. 100 cf tanks don’t have 100 cf either at the rated pressure. And I also know your reg won’t work at very low pressure.
 

Imbodie

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A short video on the concept of gas matching. The video includes an animation illustrating why gas matching can be important.
I love the animation, what program did you use to create it?
 

divezonescuba

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The animation was made within videopad. This is the publishing software. It is fairly inexpensive around $50.

It would not have been too difficult to make the bubbles go up and the fins to kick, but I was limited on the time i had available.
 
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A short video on the concept of gas matching
Several interesting things:
1. You based the size of the reserve on SAC, which isn't either of the gas matching approaches discussed so far. Which agency teaches this?

2. If you're going to always assume the larger SAC diver always has the larger volume, why not just say the reserve is based on the larger volume? The explanation is simpler, and is exactly what PADI teaches. (Though that approach is not without issues, as shown in the initial post.)

3. Diver 2 COMPLETELY ignored Thirds! The selected reserve was 66.7 cf (1150 psi). They should have turned around when Diver 2 reached about 2300 psi. In fact, they penetrated with over 70% of their tank. Remind me to never dive with Diver 2!
 
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