DIR- GUE Min gas (MGR) table?

[rsingler]

Also, 1 minute to deal with the emergency isn't a lot.

This was my biggest eye-opener. If you contemplate a wreck emergency, where you are not only at max depth, but several minutes from an opening with two stressed divers, min gas gets quite large. With both CCR, and unless you are planning two simultaneous breather failures, it gets a little more manageable, but stressed SAC x 6 min plus ascent and deco to first gas switch is an interesting exercise.

 

[barth]

I'm gonna go all instructor here and answer a question with a question: why do you think GUE does NOT want to publish a fixed MG table?

In other words, what crucial bit of information should divers be tracking in order to calculate the MG for their team for a dive?

(I'm not saying that MG tables are bad --- but this knowledge above is pretty important!)

What is different between tech 1 and fundamentals? In tech 1 the lecture did have a mg table and we did use that table for planning our dives.

But I agree with you. I don’t like the mg table in ccr1. If you are using oxygen instead of ean50 as decogas you should have more backgas then the numbers of the table.

 

[Wibble]

This was my biggest eye-opener. If you contemplate a wreck emergency, where you are not only at max depth, but several minutes from an opening with two stressed divers, min gas gets quite large. With both CCR, and unless you are planning two simultaneous breather failures, it gets a little more manageable, but stressed SAC x 6 min plus ascent and deco to first gas switch is an interesting exercise.

Unless you factor in a CO2 hit when all bets are off as breathing rates go though the roof.

 

[ginti]

This was my biggest eye-opener. If you contemplate a wreck emergency, where you are not only at max depth, but several minutes from an opening with two stressed divers, min gas gets quite large. With both CCR, and unless you are planning two simultaneous breather failures, it gets a little more manageable, but stressed SAC x 6 min plus ascent and deco to first gas switch is an interesting exercise.

The OP is discussing dives at fundamental level, only OW

 

[Jack Hammer]

Calculating MG seems difficult at first. Once you get the concept it actually becomes quite simple to do.

 

[San Diego Climber]

I made something similar to what salty posted but with multiple different sac rates. It’s very common for fundies students to make such a chart

For gas tracking I have a range of SCR in my wet notes; used the standard 20l/min for MG. Current fundies student and yes part of our homework was to do this for a few different tanks (below, D12, HP100 and Al80). The math is easier in metric!

 

[PfcAJ]

This was my biggest eye-opener. If you contemplate a wreck emergency, where you are not only at max depth, but several minutes from an opening with two stressed divers, min gas gets quite large. With both CCR, and unless you are planning two simultaneous breather failures, it gets a little more manageable, but stressed SAC x 6 min plus ascent and deco to first gas switch is an interesting exercise.

Yea, you can quickly plan yourself out of a dive if you go through every worst case scenario.

 

[mer]

0.75 cuft/min is a reasonable estimate though.

/lurkmode

This is the assumption we want each and every diver to challenge and track. You need to be using an SCR from your crappiest, hardest working, hooved like a son-of-a-gun, recent training dive in the same type of environment (e.g. cold water, thick undergarments, drag of a large camera, whatever you schtick is) as your SCR in MG calcs. Not your "optimistic" SCR.

I've seen Fundies students range from 0.3 to 1.3 cf/min SCR while just practicing kicks.

Point is we never use less than 0.75 cf/min (or 20 L/min for those not on freedom units) AND we need to plug in our brains and make sure that SCR is reasonably high enough for when the brown matter hits the rotary oscillator. And sometimes 0.75 ain't high enough!

If we gave Fundies students a table, there would be too much temptation to just follow the table and not challenge its assumptions, as this is the course where we are setting them down the path of becoming thinking divers... but Fundies students are drinking from the firehose and may not be there yet... it is a recreational course after all. At the CCR level (so you've done at least Fundies-Tech, Tech 1, then CCR1), I hope the thinking diver mentality has already been fully engrained in that CCR student that they are not just tempted to follow the table.

Re-engaging lurk mode... what am I doing on scubaboard...

 

[mer]

What is different between tech 1 and fundamentals? In tech 1 the lecture did have a mg table and we did use that table for planning our dives.

See my rant here on the difference between Fundies and past-Fundies: DIR- GUE - Min gas (MGR) table?

Also, did you do the math to verify the table in the materials? I know there are still errors in version 4.0 of Tech 1.

Bottom line: I agree that the tables are useful. I have them in my own wetnotes, as I don't do math on a rocking dive boat. I do it when I plan my (especially more complex) dives before heading to the site. But the process of HOW that table is arrived at is also important if we want thinking divers.

 

[huwporter]

If you contemplate a wreck emergency, where you are not only at max depth, but several minutes from an opening

We're talking open water here. Nobody is questioning that overhead environments require different rules.