Gas planning and the associated math - controversies over need and how to teach

[Jim Lapenta]

Very well said. The only thing that makes gas planning difficult for ow students is not giving them the time to learn and grasp the concept. With a 6-8 week course it's easy. With a weekend or two it's damn hard. To teach it and for them to understand it. It's also difficult to teach it when you have already made the assumption that they are not able to learn it because it's too much info. I've taught students from age 12 to mature adults. They all did not grasp it in the same amount of time or in the same manner, but they did all get it. The key was putting it in terms they can relate to and understand. Gas in a car is a good analogy. Nearly everyone understands that.

 

[MXGratefulDiver]

I've been giving free gas management seminars now for about three years ... next week-end I'm gonna be travelling down to the Portland area for one, in fact. When I first started, I had to overcome the perception that it wasn't something a typical recreational diver wanted to know. The first couple weren't well attended. Over time, as people who came started talking to their dive buddies and shops, invitations came more frequently and more people attended. The last few have been so well attended that we've started finding bigger venues for them.

So what's the point? Well, I think the point is that if dive students are told they don't need to know this stuff, they'll tend to believe it ... until experience tells them otherwise. And I've been giving this seminar to very mixed audiences ... from the not-yet-certified to instructors who've been teaching for a lot longer than I have. Sometimes it surprises me when a grizzled instructor who I've known and respected for a long time tells me he learned something ... sometimes I'm even more surprised when he asks if I mind him using some of my material in his class (of course I don't mind ... that's why I'm doing it for free).

Personally, I believe that a lot of instructors underestimate what their students are capable of learning ... or what they SHOULD be learning. I think one of the reasons why tech instruction is becoming so popular (even with a lot of people who perhaps shouldn't be taking it) is because that's the only venue a lot of people have for getting this information.

Personally, I'd prefer to teach it at an early stage ... and let my students decide after they've completed the class whether or not they think it's valuable ...

... Bob (Grateful Diver)

 

[NudeDiver]

I was taught in an open water course to assume a sac rate of about 1.0.

Someone should have taught the instructor that unitless numbers mean very little in the real world. A SAC rate of 15 sounds pretty bad, until I write it as 15 L/min.

They learn to do VERY simple math...

The simple math gets complicated, and probably incorrect, if you don't have an understanding of the units being used, in addition to whatever theory applies.

 

[Peter Guy]

Pearldiver, a PADI Course Director, wrote:

Oddly enough, this post seems to have started with thinking that teaching gas consumption may be beyond PADI standards.
Making a student pass a test using SAC rates and other related formulae may be, but introducing gas consumption is a logical step following the OW lesson about how air compresses at depth, etc. is a perfect place.

In a prior thread, I raised this specific issue because I had received the following from an instructor as part of a discussion of "What could be taught within PADI Standards":

You would also have to accept that adding in tech diving topics in the PADI courses would be a standards violation....
What I meant by "tech topics" are things like SAC rates and decompression models in an OW class. That would be considered task loading and confusing at that point.

I believe it is comments like the above that drive some people nuts! Is adding in "tech diving topics" "elaborating" on Standards or "exceeding" them? OK -- couldn't help myself -- had to bring that in!

Off to my PADI AI class in a couple of minutes.

 

[vshearer]

You know, we realy should all go to the metric system. Makes much more sense. Makes all calc's simpler.

I am.

 

[dumpsterDiver]

You know, we realy should all go to the metric system. Makes much more sense. Makes all calc's simpler.

I am.

yeah, yeah, First we teach everyone the metric system and THEN calculations....Sorta like the time I bought this used air integrated computer at the dive shop sale for only $50! . I didn't really look at it much and decided to test it out for the first time in 180 feet of water. When I turned it on (on the boat), it was giving me a crazy pressure reading and then I realized it must be giving me pressure in BAR.

What a pain! So I go diving and the first time I read the depth it gives me something crazy like 546. I'm really baffled now, 546 feet deep!? ... Then I look really close and see a little dot. The depth is actually 54.6 METERS.

What a total pain in the ass! Who needs decimals when reading a display underwater? feet is definitely superior to meters when reading depth. I eventually learned to multiply my depth by "about 3" and my pressure by around 15, but it was not that easy when narced.

 

[mikemill]

If you don't like using meters for depth because of the decimal just use centimeters

 

[b1gcountry]

I was taught in an open water course to assume a sac rate of about 1.0. The instructor said that is a pretty good guess and unless you swim really hard, you probably won't get in too much trouble. Teaching students to do the math with a sac of 1 cu-ft/min and then give them a simple table of rock bottom for different tanks seems like a decent compromise to me.

They learn to do VERY simple math and have a single table to refer to in the future that tabulates tanks versus depth and where they intersect is the pressure to start the ascent.

If they ever advance they can make corrections for their own consumption rate.

This is a great place to start.

Also, someone said once you calculate your RB for 100' you don't have to do it again. Also, once you calculate it for 100', you can use it at any shallower depth you want. It will be conservative, but that's a good thing. For a new student, calculate the RB for 60', then for 30' (or use 66' and 33' to make the math easier). Once they know these two values, they can do any dive they want safely. Anyone should be able to understand these values, and what they represent. Get them to remember and use these values, as their diving continues, hopefully they will want to learn how they calculate them so they can tailor for their exact SAC.

Tom

 

[Kern]

yeah, yeah, First we teach everyone the metric system and THEN calculations....Sorta like the time I bought this used air integrated computer at the dive shop sale for only $50! . I didn't really look at it much and decided to test it out for the first time in 180 feet of water. When I turned it on (on the boat), it was giving me a crazy pressure reading and then I realized it must be giving me pressure in BAR.

What a pain! So I go diving and the first time I read the depth it gives me something crazy like 546. I'm really baffled now, 546 feet deep!? ... Then I look really close and see a little dot. The depth is actually 54.6 METERS.

What a total pain in the ass! Who needs decimals when reading a display underwater? feet is definitely superior to meters when reading depth. I eventually learned to multiply my depth by "about 3" and my pressure by around 15, but it was not that easy when narced.

Well, when you get yourself together enough to check your equipment prior to doing a 179.13ft/54.6mt dive, you might be together enough to realise that using the metric system when narced is probably simpler than using the imperial system.

For eg. whats the ambiant presure at 179.13 ft. hint if you use 54.6mts an instant calculation tells you it's 6.46ata narced or not.

 

[bleeb]

yeah, yeah, First we teach everyone the metric system and THEN calculations....Sorta like the time I bought this used air integrated computer at the dive shop sale for only $50! . I didn't really look at it much and decided to test it out for the first time in 180 feet of water. When I turned it on (on the boat), it was giving me a crazy pressure reading and then I realized it must be giving me pressure in BAR.

What a pain! So I go diving and the first time I read the depth it gives me something crazy like 546. I'm really baffled now, 546 feet deep!? ... Then I look really close and see a little dot. The depth is actually 54.6 METERS.

If you don't like using meters for depth because of the decimal just use centimeters

You mean decimeters, don't you?