Nitrox and Sport Diver Assesment

[MarkA]

This is probably another old chestnut that I missed but can anyone give me an answer please
on one of the sports diver assesment the following questing is asked

Two Sports Divers are diving together, one on
air, the other on Nitrox 36. Which answer
correctly shows the maximum depth and dive
time they can plan for a no-stop dive. They
are at sea level, and have not dived for at
least 24 hours.
depth dive time
in metres in minutes
A: 30 20
B: 30 30
C: 35 12
D: 35 14
E: 35 20

The correct answer is then given as A 30metres for 20 mins
surely this would give the diver a pp of 1.44 which is over the 1.4 recomendation. I can understand there being a facillity for this mix and depth in the tables as there may be a "just deeper or just longer" scenerario but is this question suitable for an assesment
Probably been covered before but an answer would be nice anyway
Cheers
Mark

[Vic]

> a no-stop dive.
^^^^^^^^^^^^^^

This bit's important; it's a no-stop dive.

> The correct answer is then given as A 30metres for 20 mins
> surely this would give the diver a pp of 1.44 which is over
> the 1.4 recomendation.

For reasons currently ill-explained, BSAC's "never ever ever go over 1.4bar ppO2" has an extra clause "except if you're on 32% or 36% and on a no-stop dive, when you can go to 1.44bar ppO2".

Bizarrely, if you plan a 1.44bar ppO2 in this situation, it is considered "safer" to ascend directly to the surface without a safety stop (that's within the "rules", whereas putting a safety stop in isn't). I for one cannot explain or support this practice.

Vic.

[paul beal]

Bizarrely, if you plan a 1.44bar ppO2 in this situation, it is considered "safer" to ascend directly to the surface without a safety stop (that's within the "rules", whereas putting a safety stop in isn't). I for one cannot explain or support this practice.

I do not teach the 1.44 no-stop consession when I run a nitrox course. As far as my students are concerned 1.4 is the limit when diving within BSAC and that is it, no deviation.

It seems silly to drill 1.4 into everyone, and then say, "oh, by the way, if you want to do a no stop dive (without even doing a safety stop [SDPs??]) you can push your ppO2 to 1.44.

Paul

[Andy Nye]

All the maths are wrong.

The correct answer is

A Dive Marshall would NEVER pair off a air and nitrox diver together .

[David Walker]

A Dive Marshall would NEVER pair off a air and nitrox diver together .

What about an instructor and student, where the instructor is planning on doing more dives later in the day, and so works on Nitrox?
Or just those who dive Nitrox but use air tables to give them extra time - doesn't matter what buddy's on, if you are on nitrox you get the extra safety margin that they don't *need*, but which you feel safer with?
Or someone more prone to DCI, and so uses nitrox in very conservatively to get safe runtimes roughly the same as others on air?
Just a few ideas!

David

[Dave]

:=A Dive Marshall would NEVER pair off a air and nitrox diver together .

What about an instructor and student, where the instructor is planning on doing more dives later in the day, and so works on Nitrox?
Or just those who dive Nitrox but use air tables to give them extra time - doesn't matter what buddy's on, if you are on nitrox you get the extra safety margin that they don't *need*, but which you feel safer with?
Or someone more prone to DCI, and so uses nitrox in very conservatively to get safe runtimes roughly the same as others on air?
Just a few ideas!

Plus of course, it said nothing about a Dive Marshal pairing them off in the 1st place

Dave

[Andy Nye]

[QUOTE]Two Sports Divers are diving together, one on
air, the other on Nitrox 36. Which answer
correctly shows the maximum depth and dive
time they can plan for a no-stop dive. They
are at sea level, and have not dived for at
least 24 hours.[UNQUOTE]

It also doesn't say that any training is taking place or it's a instructor student dive either .

If you read it the way i did, it looks like 2 divers just having a dive... ;-)

Rgds

Andy

[David Walker]

[QUOTE]Two Sports Divers are diving together, one on
air, the other on Nitrox 36. Which answer
correctly shows the maximum depth and dive
time they can plan for a no-stop dive. They
are at sea level, and have not dived for at
least 24 hours.[UNQUOTE]

It also doesn't say that any training is taking place or it's a instructor student dive either .

If you read it the way i did, it looks like 2 divers just having a dive... ;-)

But if you had Nitrox, and your buddy didn't, why would you just dive on air? If it gives you an extra safety margin then it doesn't matter if your buddy is on air does it. Most people I know wouldn't buddy up purely on what gas you're diving on for basic nitrox type diving - just don't think you can say that a DM would "never" put Nitrox + air together.

David

[Matts]

I can understand there being a facillity for this mix and depth in the tables as there may be a "just deeper or just longer" scenerario but is this question suitable for an assesment

Personally I think the question could be presented better. The object is for the student to demonstrate they understand the Nitrox diver is depth limited and the Air diver is time limited.

If I had compiled the question I would have included
27m 24mins as an option. If the student picks that answer you would know that he comprehends the problem but needs reminding about BSACs Nitrox caveats. A brief chat and it could be marked correct, after all sticking to a PPO of 1.4 is effective and not unsafe.

Regards
Matt

[Andy Nye]

FOUND on Bsac Tech pages.

Marshalling Notes for Dives involving Nitrox and Air Divers - Download Word 6 file - Download PDF file

When working with mixed groups of divers, the Dive Marshal must consider the following:
1. Air divers should be paired according to qualifications and experience.
2. EANX divers should be paired according to qualifications and experience - and similar mixes.
3. If pairing nitrox divers with air divers, the Dive Marshal must consider the safest dive profile and decompression for both divers. The pair should therefore observe the maximum operating depth of the Nitrox diver and limit their dive time to the maximum dive time of the air diver. These considerations allow the greatest safety margin for both divers.

BSAC - May 1996


Now surely ,


2. EANX divers should be paired according to qualifications and experience - and similar mixes.

** Surely similar mixes for a pair of sport divers is not Eanx 21 & Eanx 36 **

Yeah , i know it's 8 years old , but some clubs still work in Dinosaur age.

[PeteM]

2. EANX divers should be paired according to qualifications and experience - and similar mixes.

** Surely similar mixes for a pair of sport divers is not Eanx 21 & Eanx 36 **

They may be the most similar mixes available or may be the best compromise. Real example, I've got 30% in my cylinders at the moment they're full because I got blown out when I planned to use it. This weekend I'm taking some Ocean divers for thier first sea dive, so they are going to be on air and I'm going to be on 30% because I see no point in blowing the cylinders off and repumping them with air. The limiting factor on dive time will be goverened by the air divers no stop limit, if it was not over the ocean divers limit the depth would be limited by my MOD.

It's all perfectly logical

[David Walker]

2. EANX divers should be paired according to qualifications and experience - and similar mixes.

** Surely similar mixes for a pair of sport divers is not Eanx 21 & Eanx 36 **

And as point 3 says, if they not the same you limit to MOD of Nitrox and time of air - whats the problem? In a lot of clubs you won't get everyone on Nitrox, and for the extra safety margin theres absolutely no reason that someone Nitrox qualified shouldn't always dive with a suitable Nitrox mix, even if they are only diving with an air buddy. If they have the mix, use it!

David

[iainmsmith]

All the maths are wrong.

The correct answer is

A Dive Marshall would NEVER pair off a air and nitrox diver together .

Rubbish.

I've spent the past week diving nitrox, while my students were on air.

Why? Because when I'm doing three or four dives a day, often involving rescue skills (ie bouncy stuff) I want to push my nitrogen loading down as far as I can.

That's an entirely sensible thing to do which is in keeping with (in no particular order):
a) common sense
b) the BSAC Nitrox materials
c) SDPs

There are many other situations where an air/nitrox pairing is appropriate.

Iain

[iainmsmith]

FOUND on Bsac Tech pages.

Marshalling Notes for Dives involving Nitrox and Air Divers - Download Word 6 file - Download PDF file

When working with mixed groups of divers, the Dive Marshal must consider the following:
1. Air divers should be paired according to qualifications and experience.
2. EANX divers should be paired according to qualifications and experience - and similar mixes.
3. If pairing nitrox divers with air divers, the Dive Marshal must consider the safest dive profile and decompression for both divers. The pair should therefore observe the maximum operating depth of the Nitrox diver and limit their dive time to the maximum dive time of the air diver. These considerations allow the greatest safety margin for both divers.

BSAC - May 1996


Now surely ,


2. EANX divers should be paired according to qualifications and experience - and similar mixes.

** Surely similar mixes for a pair of sport divers is not Eanx 21 & Eanx 36 **

What part of:

"3. If pairing nitrox divers with air divers, the Dive Marshal must consider the safest dive profile and decompression for both divers. The pair should therefore observe the maximum operating depth of the Nitrox diver and limit their dive time to the maximum dive time of the air diver. These considerations allow the greatest safety margin for both divers."

did you fail to understand?

Iain