RMV math…

[60plus]

Doesn’t the PADI Deep Diver speciality course cover SAC and redundant backup gas?

You can get PADI advanced which is 30m without redundant air supply or knowing what one is. I have just glanced through the PADI deep diver 40m instructor manual and although redundant supply is mentioned there does not seem to be any requirement to be tested on it or use it. There is no mention of SAC or gas planning, it just points out that you should really have 12L or bigger cylinder at that 30 m is a better depth for optimum diving because you only have a limited time at 40m.

 

[tursiops]

Doesn’t the PADI Deep Diver speciality course cover SAC and redundant backup gas?

Yes

 

[60plus]

I Have attached the PADI deep diver (40m) instructor manual. Can anyone find where SAC is in it?

I did my deep diver 40m with SSI and there was nothing in either the practical lessons or the theory and written exams.

I point out once again that my original post (which questioned the need for SAC knowledge) was in the Basic scuba section. By moving this topic out of the basic scuba section out of basic scuba it seems the moderator(s) are also of that opinion.

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A ScubaBoard Staff Message...

ScubaBoard moderators have removed the attached instructor manual. Please don't post entire copyrighted materials here -- snippets are often OK, entire books are not.

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[inquis]

Can anyone find where SAC is in it?

It's covered in the prerequisite material (AOW or Adventure). Further, see p34 of the Deep Instructor Guide you posted, including:

Ask student divers to read both “Air Consumption Calculation” and “How Much Reserve?” side bars in their student manual to formulate a good all-round air management plan. [emphasis mine]

 

[Wibble]

I Have attached the PADI deep diver (40m) instructor manual. Can anyone find where SAC is in it?

I did my deep diver 40m with SSI and there was nothing in either the practical lessons or the theory and written exams.

I point out once again that my original post (which questioned the need for SAC knowledge) was in the Basic scuba section. By moving this topic out of the basic scuba section out of basic scuba it seems the moderator(s) are also of that opinion.

That's a good point. Where is it in the manuals?

(All my deep learning was post PADI. I believed SAC etc would be there, but it's certainly not particularly explicit in that manual.)

 

[Angelo Farina]

That's a good point. Where is it in the manuals?

(All my deep learning was post PADI. I believed SAC etc would be there, but it's certainly not particularly explicit in that manual.)

In CMAS manuals the concept of personal air consumption rate is introduced already in the first one-star course.
It is explained that an average prudential value is 20 liters/minute and that you must multiply this value for the ambient pressure in bars. So at 10m it will be 40 liters/minute, at 20m it will be 60 liters/minute and so on.
The standard tank here is 3000 liters (15 liters x 200 bars), and one should reserve 1/3 of it for emergency, so you plan your dive with a total volume available of 2000 liters. You divide this by the air consumption rate at the max depth (say 20 meters), and you get the duration of your tank.
Example: 2000 liters divided 60 liters/minute = 33.33 minutes max.
As the SPG is in bars, the amount of air available, in any instant, is simply the pressure with an added 0 at the end. When the SPG shows, say, 120 bars it means that you can count of 1200 liters of air still available.
As these calculations are fairly simple in SI units, they are taught even to novice divers.
Of course at higher level more complex calculations are done, accounting for using multiple tanks with different capacity and possibly different gas mixtures, or multi-level diving profiles.
But at the first level the 10 rows reported above are that all is taught, which is plenty enough for an OW diver.

 

[Wibble]

In CMAS manuals the concept of personal air consumption rate is introduced already in the first one-star course.
It is explained that an average prudential value is 20 liters/minute and that you must multiply this value for the ambient pressure in bars. So at 10m it will be 40 liters/minute, at 20m it will be 60 liters/minute and so on.
The standard tank here is 3000 liters (15 liters x 200 bars), and one should reserve 1/3 of it for emergency, so you plan your dive with a total volume available of 2000 liters. You divide this by the air consumption rate at the max depth (say 20 meters), and you get the duration of your tank.
Example: 2000 liters divided 60 liters/minute = 33.33 minutes max.
As the SPG is in bars, the amount of air available, in any instant, is simply the pressure with an added 0 at the end. When the SPG shows, say, 120 bars it means that you can count of 1200 liters of air still available.
As these calculations are fairly simple in SI units, they are taught even to novice divers.
Of course at higher level more complex calculations are done, accounting for using multiple tanks with different capacity and possibly different gas mixtures, or multi-level diving profiles.
But at the first level then 10 rows reported above are that all is taught, which is plenty enough for an OW diver.

Experienced divers know that a SAC of 20 litres/min is high, but not outrageous. From apocryphal evidence from novice divers on ScubaBoard, it seems that many people have gas consumptions way over that; the proverbial gas hog.

More importantly when you're stressed, your gas consumption gets considerably higher. Which is why technical divers will use a multiple of your normal SAC for min gas calculations, e.g. x2 -- or x3 for special cases (CO2 hit).

What's odd about the Deep Diver manual posted above (N.B. it's an old 2010 manual, so well out of date) is the lack of any real maths to calculate or even properly understand how much you consume at depth AND how to calculate your minimum gas for the ascent.

I've spoken an instructor at my LDS about this who says they will always get the students to note their gas pressures on getting to the bottom and on leaving the bottom of a deep dive, as well as the narcosis tests. I would expect that is a standard sort of thing for people teaching the Deep speciality.

Anyways, as a technical diver, I find it quite disconcerting that people don't realise how important knowing their own SAC is and the reasons why this is so important.

 

[tursiops]

I Have attached the PADI deep diver (40m) instructor manual. Can anyone find where SAC is in it?

I did my deep diver 40m with SSI and there was nothing in either the practical lessons or the theory and written exams.

I point out once again that my original post (which questioned the need for SAC knowledge) was in the Basic scuba section. By moving this topic out of the basic scuba section out of basic scuba it seems the moderator(s) are also of that opinion.

That's the instructor guide, not the student manual. And you have violated copyright by posting it. Nice job.

 

[Belzelbub]

Anyways, as a technical diver, I find it quite disconcerting that people don't realise how important knowing their own SAC is and the reasons why this is so important.

Same, and I'm a recreational diver. I will say, however, that I don't pre-calculate on every dive. It really depends on the nature of the dive. For a relatively benign hunting dive in the 50-60' range, I know my HP120 will be more than enough, and as the exit is pretty much right over my head, my planning is relatively simple. Still, I know enough to have my rough dive time, which is important because if my GTR time is showing less than it should be, I know there's something to look into and adjust accordingly. Could be higher exertion, or I could have a leaky o-ring.

If I were diving and needed to get back to a particular exit point, knowing my consumption rate would be more important as I need to make sure to turn toward the exit at the right time.