Question on Nitrox Use

[Matt-75]

Ok, well the plan is for me to do a TDI Nitrox course out in Malta with my club (no idea why they dont do a BSAC Nitrox course, but im not really bothered at the end of the day). It will likely just be a basic course, and by then i should be a fully qualified sport diver. I'm seeing it as something i need to do, since most everyone else seems to use nitrox nowadays.

My question is, when do you use nitrox. I have received two answers from several different people, along with some confusing information.

A few i've talked to say they use nitrox when ascending and completing their deco stops, others say they use it for the full dive time. Which is correct? or are they both correct?

I've also read of people carrying on the breathing of nitrox after leaving the water, presumably as a safety precaution, does this help avoid the dreaded bends?

Thanks in advance for any answers i may receive from you all,

Matt

[Nigel Hewitt]

A few i've talked to say they use nitrox when ascending and completing their deco stops, others say they use it for the full dive time. Which is correct? or are they both correct?Both. Why this is will become obvious on the course.

Staying on the gas after surfacing is an added precaution as you still have lots of inert gas in your body. It is quite common for technical divers to surface and keep breathing an elevated oxygen mix for some time before signalling the boat that they wish to be picked up. They want their bodies ready for the sudden effort of climbing the ladder after perhaps several hours of hanging horizontal and weightless.

[Argo]

Both. Why this is will become obvious on the course.

Staying on the gas after surfacing is an added precaution as you still have lots of inert gas in your body. It is quite common for technical divers to surface and keep breathing an elevated oxygen mix for some time before signalling the boat that they wish to be picked up. They want their bodies ready for the sudden effort of climbing the ladder after perhaps several hours of hanging horizontal and weightless.

Not really much to add to that........ short and to the ponit.......:cool:

[Alan Ewart]

Both. Why this is will become obvious on the course.

.


Wot he said.

Everyone in my branch is nitrox qualifed and use nitrox as a back gas or deco gas on every dive

[Steve Pearson]

It's recommended that you use it on most dives less than 36m. It gives you longer No Stop times for dives without going into deco.

A typical example of this from the BSAC tables would be:

Assume a dive to 36m for 35 mins

On air (21%) deco would be 1min@9m, 15mins@6m

the same dive on a 32% Nitrox mix would be

3mins@6m

As you can see there is a significant difference in deco times,

It is also used for accelerated deco, to aid the off-gassing of Nitrogen, which you will learn about on the course. You continue to off-gas on the surface that is why people continue to breathe it once they surface is it continues to speed up the process.

As you will be a sports diver it would be preferable, cost permitting (as it costs a bit more than air) to use it on most of your dives. Even if you stick to normal BSAC 88 tables, with your buddy who may not be using it, as it gives an added conservatism to your diving.

HTH

Steve

[Nick Kay]

Hi Steve

You discussed the deco issues, you could have added the safety issues, including:
1. Divers who have had a "Hit" are often required to dive on Nitrox to reduce the likelihood of a subsequent hit/reduce subclinical DCI, etc

2. I've seen recomendations that divers in any of the following groups should dive on Nitrox
- over the age of 40
- smokers
- unfit
- reduced lung capacity/effectiveness
(all of the above, assuming they are still "fit to dive")

3. Divers who which to increase their "personal safety margin", i.e. dive on Nitrox, but use air tables/computers

I could go on (and probably will do on the Nitrox Theory day this Saturday) :p

[Chris Cherrington]

A few i've talked to say they use nitrox when ascending and completing their deco stops, others say they use it for the full dive time. Which is correct? or are they both correct?

I've also read of people carrying on the breathing of nitrox after leaving the water, presumably as a safety precaution, does this help avoid the dreaded bends?

Thanks in advance for any answers i may receive from you all,

Matt

Nitrox can be used as the primary breathing gas to reduce the decompression needed or to extent the no-stop time as per Steve's example (which contravenes the BSAC SDP as it has a high PPO2 but you get the idea.)

This is its use for you at your current level.

Nitrox can reduce decompression when used as a decompression gas. Typically this gas will have 50% oxygen or more and requires an advanced nitrox certification. In BSAC the ERD course covers this.

Chris

[Helen (AKA Hellvet)]

Hi Steve

You discussed the deco issues, you could have added the safety issues, including:
1. Divers who have had a "Hit" are often required to dive on Nitrox to reduce the likelihood of a subsequent hit/reduce subclinical DCI, etc

2. I've seen recomendations that divers in any of the following groups should dive on Nitrox
- over the age of 40
- smokers
- unfit
- reduced lung capacity/effectiveness
(all of the above, assuming they are still "fit to dive")

3. Divers who which to increase their "personal safety margin", i.e. dive on Nitrox, but use air tables/computers

I could go on (and probably will do on the Nitrox Theory day this Saturday) :p

Remember there are some times when medical referees will REQUIRE diving to be done on nitrox and will endorse your medical appropriately (e.g post PFO diagnosis). Caused a drama for one of the 3 PFO's in the last year in our branch who wasn't nitrox qualified - the other 2 of us were. (yes - i know - 3 in 12 months IS excessive - we have no idea why!)

I would also like to add that i also feel better diving on nitrox rather than air - I have more energy for the day after a dive, feel less tiredness in my muscles, and am (almost) always able to get myself into the boat after a dive now (though my club usually haul me in to prevent me exerting myself - its the way to get back into the boat - trust me!).

Helen

[Mike Rowley]

Nitrox can reduce decompression when used as a decompression gas. Typically this gas will have 50% oxygen or more and requires an advanced nitrox certification. In BSAC the ERD course covers this.

Chris[/QUOTE]

Doesn't Adv Nitrox cover the use of 50% for deco?

ERD now allows 100% up to 1.4 bar PO2 and uses Pro-dive Planner for planning.

Cheers

Mike

[Paul Watts]

Oh dear... I must be a real Luddite! :D ... or tight! :D

[PeteM]

Nitrox can reduce decompression when used as a decompression gas.

Doesn't Adv Nitrox cover the use of 50% for deco?
Yes but only to give cleaner deco not to accelerate it (although how you stop someone switching to 50% on thier Vytec I don't know)

ERD now allows 100% up to 1.4 bar PO2 and uses Pro-dive Planner for planning.

I thought the BSAC ERD course only allowed up to 80%?

[Janos]

I thought the BSAC ERD course only allowed up to 80%?

This was changed about a year ago (IIRC). You can use 100% to a depth of 4m.

Janos

[Chris Cherrington]

Yes but only to give cleaner deco not to accelerate it (although how you stop someone switching to 50% on thier Vytec I don't know)


Get the DO to gaffer tape the buttons..... :D

Chris

[Nick Kay]

ERD now allows 100% up to 1.4 bar PO2 and uses Pro-dive Planner for planning.

Cheers, Mike
Not that I want to use 100% (quite happy with 70/80), but does that mean that anyone who "qualified ERD under 80%" is now qualified for 100%?


I would also like to add that i also feel better diving on nitrox rather than air - I have more energy for the day after a dive, feel less tiredness in my muscles.
Helen
Totally agree


Yes but only to give cleaner deco not to accelerate it (although how you stop someone switching to 50% on thier Vytec I don't know)
Pete
From what I've seen within clubs, the region, etc. Vytec's seem to be the "norm" (don't want to start an argument on which computer is best) and also from what I've seen in most diving, Vytec + Advanced Nitrox = Accelerated Deco. I'll go a step further, I've yet to see a "qualified Advanced Nitrox diver" being asked for ERD (or equivalent) certification when asking for 70%. That probably means there is a (large?) number of Vytec/CNx divers out there doing accelerated deco on 70/80%...

[Chris Cherrington]

I'll go a step further, I've yet to see a "qualified Advanced Nitrox diver" being asked for ERD (or equivalent) certification when asking for 70%. That probably means there is a (large?) number of Vytec/CNx divers out there doing accelerated deco on 70/80%...

In my experience a lot of LDS don't know the details of the various grades within different training organisations. (Adv Trox is 50% max IIRC?)

TDI is 100%, IANTD is 50% but IANTD with Deco Specialist SDC is 100%....

What about my FFESSM N3? I can shorten my SI with 100% acording to my training, but its not a trox qual, I can't dive the stuff. Can I buy 100% or not?

I don't think there's any law regarding the sale of nitrox, but most LDS want some form of qual (to satisfy their blender quals agency) plus a signature that you analysed the gas. As an IANTD trained blender I would be outside of my liability agreement to sell to an IANTD trained diver I knew wasn't qualified (for the FO2), but god knows how I would be expected to know all other agencies' standards.....

Chris

EDIT I should have pointed out that the FO2% were adv. trox in case Matt was thinking his TDI basic was 100% - all basic trox are 40%.

[Mike Rowley]

[QUOTE=Nick Kay]Not that I want to use 100% (quite happy with 70/80), but does that mean that anyone who "qualified ERD under 80%" is now qualified for 100%?

Yes, it doesn't take any further training to use 100% than 80% however, the PO2 remains the same at 1.4 bar.

Mike

[AndrewA]

Does that mean we should be getting new ERD cards which state that we can use 100% ? My card clearly states Nitrox 80 (while strangely my Advanced nitrox card has no limit on it!)

[Nick Kay]

[QUOTE=Nick Kay]Not that I want to use 100% (quite happy with 70/80), but does that mean that anyone who "qualified ERD under 80%" is now qualified for 100%?

Yes, it doesn't take any further training to use 100% than 80% however, the PO2 remains the same at 1.4 bar.

Mike

Hi Mike
Sorry - wan't inferring that it required additional training - if you can maintain 1.4 ppO2 at 6m, you should be able to maintain it at 4m, i.e. its about buoyancy and, I guess, knowing whether sea conditions will be a detriment to shallower deco
Was more wondering (as per AndrewA) whether BSAC will be re-issuing Qcards, etc

[Mike Rowley]

Was more wondering (as per AndrewA) whether BSAC will be re-issuing Qcards, etc[/QUOTE]

Hadn't considered that Nick. Just looked at mine and it does specify 80%. I will pass that on to the Chief Tech Instructor. Ripples in the pond and all that!

Cheers

MIke

[aquayle]

Can't see where it says ANYTHING about EAN% in the blurb from BSAC

Extended Range Diving
Entry requirement - BSAC Sport Diver + 20 dives with BSAC Advanced Nitrox Diver qualification, or equivalent Nitrox qualification from another agency.

This three day course promotes more efficient, successful and safe deep diving techniques and encourages a responsible and flexible approach to extended range diving.
It identifies the areas of potential problem, discusses the possibilities of management and resolution in practice. Theory and practical sessions cover a wide range of topics to improve your awareness of deep dive organisational skills. The course include a day and a half of diving to further increase experience and understanding of advanced skills employing the appropriate gas mixtures.

So is this the course to do for O2 as deco gas then??

[Paul Morris]

So is this the course to do for O2 as deco gas then??

Short answer, yes. Although the course will teach you that O2 is not necessarily the best deco gas :D And other nice things like accelerated decompression ( that will get you out later, but arguably safer, than BSAC 88s! :eek: ).

See this update from HQ:

http://www.bsac.org/techserv/o2use0304.htm

Regards,
Paul

[Woz]

If you are doing an extended trip then nitrox is great. e.g., a week in the Sound of Mull or Scapa, all 30m ish diving is spot on for nitrox and you'll be doing minimal deco while feeling much better than the air divers in the evening who will all be asleep.

If you are a real tightwad then dive air as a backgas and deco on fiddy cent for a safety factor. This is the way to go for sub-35m diving. Between 20 and 35 pick a suitable mix and it's the ideal way to go. You'll find that alot of people (well me anyway), if they have no idea what they will be diving, stick 32% in as a good "general all round" mix that you won't get caught out on if you suddenly decide to switch sites. It's good to 35m on a 1.44 PO2.

[Matt-75]

Originally i planned to carry say a Nitrox 32 mix in a pony and use it on ascent, since i can probably afford something like this and it gives me some added safety margin. But as of yet i have no idea how much nitrox recharge would set me back, whats everyones avg cost for a fill?

As for doing a full dive on it, well if its affordable then yes, but im more looking to use it on the deco stop. Eventually though, when i get the other cylinder i need for the twin 12's then its definetly going to be a consideration to use it full time.

But thats for the future.

Im starting to reconsider doing the TDI basic/entry level nitrox course, and considering maybe waiting a month or two and do the basic and advanced at the same time. But as it goes i'll probably just do basic since i have no real need for learning about mixes above 40% (or do i?).

[Gordon]

where i work, we charge you for the volume of the gases put into the cylinders, so a fill of the same stuff from 115bar will cost half as much as a fill from empty - dont know how many other places do this tho.
might be worth starting with a rich mix and just topping it off with air?

[Chris Cherrington]

Originally i planned to carry say a Nitrox 32 mix in a pony and use it on ascent, since i can probably afford something like this and it gives me some added safety margin. But as of yet i have no idea how much nitrox recharge would set me back, whats everyones avg cost for a fill?

As for doing a full dive on it, well if its affordable then yes, but im more looking to use it on the deco stop. Eventually though, when i get the other cylinder i need for the twin 12's then its definetly going to be a consideration to use it full time.

But thats for the future.

Im starting to reconsider doing the TDI basic/entry level nitrox course, and considering maybe waiting a month or two and do the basic and advanced at the same time. But as it goes i'll probably just do basic since i have no real need for learning about mixes above 40% (or do i?).

Depending on the depth you will probably find the trox (as a back gas) will take away the need for a deco stop.

IIRC last time we got a fill in the UK a pony was about 3 quid and a 15 about 7. You may find the combined cost of a pony and an air fill to be more than the back gas alone. Don't forget that you need to plan the dive to have enough gas to deco out on the back gas (air in your example) alone (which as best I can see is your plan) so you will "waste" half a tank of backgas each time.

When you come to do the advanced course all will be revealed about the use of trox for deco as per your plan. In other words you should really be looking at an advanced course. The %age of oxygen is not really the issue, most people use an EAN50 for deco but if you look at most deco software you will find EAN40 does much the same job.

The key issue with this type of diving is preventing the accidental use of trox at depth. A pony is unsuitable as it is switched on all the time. A side slung tank or stage is what is required (this could be the same 3L tank and reg). The correct use of this is covered in most agencies' advanced trox course.

To be honest I think you should think about the TDI advanced course. Most shops do a combined option. Either that or wait for the BSAC course when it is available. Don't get too hung up on O2 %age or fall into the trap of thinking the "advanced" course gives more knowledge about nitrox. The "advanced" courses cover a different use for nitrox - the one that you have outlined.

Have a chat with the TDI people that you are thinking of using.

Chris

[Richard Whitcombe]

Originally i planned to carry say a Nitrox 32 mix in a pony and use it on ascent, since i can probably afford something like this and it gives me some added safety margin. But as of yet i have no idea how much nitrox recharge would set me back, whats everyones avg cost for a fill?


Fill cost tends to vary quite a big. For a single 12l to 15l fill depending on mix i expect to pay between £5 and £7.

The richer the mix the more expensive generally.

[Matt-75]

On a side note of this, what sort of kit would you need to just make it yourself, ie, get a cylinder of o2 and just mix it yourself. Would this sort of route be any cheaper in the long run?

On the advice of everyone, im thinking i should just save up and do the advanced nitrox as a combined course and ignore doing basic as a seperate course.

As far as using certain mixes at the wrong depths i vaguely understand a small bit. Oxygen toxicity is the main one as i remember, but i would assume all of this would be explained on the course (and drummed into you).

Cheers for the advice and views, its enlightened me a fair bit, i now have a clearer view of what i need to do.

Thanks,

Matt

[MattS]

On the advice of everyone, im thinking i should just save up and do the advanced nitrox as a combined course and ignore doing basic as a seperate course.Hmmm. I really hate hearing that advice. I know why people give it, but it somehow goes against the grain of BSACs progressive training.

My somewhat unpopular advice is;
+ If you are making mandatory stops now, do advanced. You will find some agencies willing to let you straight onto their advanced with sufficient deco diving experience.

+ If you are not making stops yet, do a basic course as soon as possible. This gives you the choice to make your diving safer and/or more rewarding as soon as possible

[Matt-75]

Hmm, so your recommendation is to do the basic course as i originally planned then complete the advanced at a later point?

Since my aim is moving towards a tech diving route (although not to the extent of the rebreather fraternity and their mobile gas chambers) and nitrox training being the first step on that route, then i guess i'm now doing the basic nitrox out in malta in june. :)

[Nigel Hewitt]

Since my aim is moving towards a tech diving route (although not to the extent of the rebreather fraternity and their mobile gas chambers) and nitrox training being the first step on that route, then i guess i'm now doing the basic nitrox out in malta in june. :)Once you've done Nitrox you will understand why we use our portable blend-as-you-dive systems.

[MattS]

Hmm, so your recommendation is to do the basic course as i originally planned then complete the advanced at a later point?Yep. Do Basic, dive Nitrox for a while and then decide what you want to do next.

If you are thinking of going down the technical path the TDI course will teach you everything the BSAC course does and a little more beside. Use of any mix up to 40% and knowing how to apply EAD to a Buhlmann table makes for a very flexible qualification.

[Paul Morris]

Hmm, so your recommendation is to do the basic course as i originally planned then complete the advanced at a later point?

Since my aim is moving towards a tech diving route (although not to the extent of the rebreather fraternity and their mobile gas chambers) and nitrox training being the first step on that route, then i guess i'm now doing the basic nitrox out in malta in june. :)

Matt, from reading your first post I guess you are at Ocean diver grade at the moment, so a Basic nitrox course is probably the best way forward. The advanced course isn't much different, however your diving skills are examined much more closely for good buoyancy control, and "advanced" skills such as launching DSMBs mid-water whilst holding a stop. If you were an experienced Sports Diver doing deco diving, then moving straight to the advanced course would probably be the best bet.

Nothing against the basic TDI course, but if you're a BSAC member why not look at the BSAC Nitrox Diver course. BSAC Nitrox diver can be run in Branch from as little as £27, including all your course materials, qualification card, and a copy of the BSAC Nitrox tables. Its one day of lectures, a dry practical on gas analysis and a short knowledge review. Will qualify you to use "standard" nitrox mixes (32% & 36%).

If you don't have Nitrox instructors in your branch, ask your regional coach to help out. They should be able to provide a local instructor if there are enough of you to run a small course in your branch, or point you towards a regional course if there is one running near you.

http://www.bsac.org/coaching/index.html

[PeteM]

Hmmm. I really hate hearing that advice. I know why people give it, but it somehow goes against the grain of BSACs progressive training.

My somewhat unpopular advice is;
+ If you are making mandatory stops now, do advanced. You will find some agencies willing to let you straight onto their advanced with sufficient deco diving experience.

+ If you are not making stops yet, do a basic course as soon as possible. This gives you the choice to make your diving safer and/or more rewarding as soon as possible

I tend to agree - I'm a firm believer in nitrox and want to get people on it asap, the basic course is trivial (hence it's incorporation into Ocean Diver soon) and gets people using it.

The Advanced Course is non trivial, I would say I fail/insist on a repeat about 25% of students for depth control either during DSMB deployment or on the stop. If these people are not up to doing the advanced then keeping them away from deco with straight forward basic nitrox (which is for most people pretty much analyse it then go and dive) has got to be a good thing.

[Chris Cherrington]

On a side note of this, what sort of kit would you need to just make it yourself, ie, get a cylinder of o2 and just mix it yourself. Would this sort of route be any cheaper in the long run?


Hi Matt,

If you have access to a club compressor then blending your own trox is a possibility. Our old club compressor gave air low enough in hydrocarbons (oil) that we could blend nitrox easily, but check to see if this is the case.

At least one supplier (British Oxygen) will only sell O2 to clubs or shops so it would be the club's decision not yours alone.

You (and a few others) would need a blending qualification.

You can save a few quid by this route but the main advantage is convenience. If you are part of a club that does their own great, if not its almost certainly easier and cheaper to buy from a dive shop.

Hope that helps.

As to the training I would second MattS - if you are making deco stops then the advanced is the way forward. I re-read the first post a couple of times and figured that was the case. Either way the TDI will give you more options than the BSAC trox course and I would take that route myself. (You can always do the BSAC Advanced at a later date instead of the TDI Advanced).

Where are you going in Malta? Maltaqua are a BSAC school and would be able to put the training into a BSAC context for your on-going diving.

Chris

[Paul Morris]

As to the training I would second MattS - if you are making deco stops then the advanced is the way forward. I re-read the first post a couple of times and figured that was the case.
I hope not. I read the first post and figured he was an Ocean diver, expecting to reach Sport Diver qualification by June. So I hope he's not into deco diving just yet :)

[Matt-75]

Sport Diver Exam is in two weeks, im doing Dive Leader lectures at the minute and hopefully with some practice and a few dives over summer, i can get that signed off and move towards the dreaded instructor levels.

But thats not really my reason for the nitrox. Im interested in adding in a safety margin to my diving. Diving air is ok i suppose, but enriched air is better, ie, less nitrogen in the old bloodstream, but carries more risks such as toxicity from the O2.

I've incidentally found a cheap enough company in the uk that offers the TDI basic nitrox, and will be talking to them sometime after easter about getting on that course. One theory session over half a day, which is what some of the ppl i know who've done it had to do. Better to get it done before malta, then at least i can make a choice to spend a little more cash and dive safer over there.

[Chris Cherrington]

Sport Diver Exam is in two weeks, im doing Dive Leader lectures at the minute and hopefully with some practice and a few dives over summer, i can get that signed off and move towards the dreaded instructor levels.

But thats not really my reason for the nitrox. Im interested in adding in a safety margin to my diving. Diving air is ok i suppose, but enriched air is better, ie, less nitrogen in the old bloodstream, but carries more risks such as toxicity from the O2.

I've incidentally found a cheap enough company in the uk that offers the TDI basic nitrox, and will be talking to them sometime after easter about getting on that course. One theory session over half a day, which is what some of the ppl i know who've done it had to do. Better to get it done before malta, then at least i can make a choice to spend a little more cash and dive safer over there.

Well take things easy mate. No need to rush.

Trox makes things safer if you use reduced N2 mixes on an air profile, otherwise its much the same. The amount of N2 you absorb is a product of pressure (depth) and time.

Sounds like you have found a good solution. All the best with the course and have a great time in Malta.

Chris

[Tony Dwyer]

Sport Diver Exam is in two weeks, im doing Dive Leader lectures at the minute and hopefully with some practice and a few dives over summer, i can get that signed off and move towards the dreaded instructor levels.

But thats not really my reason for the nitrox. Im interested in adding in a safety margin to my diving. Diving air is ok i suppose, but enriched air is better, ie, less nitrogen in the old bloodstream, but carries more risks such as toxicity from the O2.

I've incidentally found a cheap enough company in the uk that offers the TDI basic nitrox, and will be talking to them sometime after easter about getting on that course. One theory session over half a day, which is what some of the ppl i know who've done it had to do. Better to get it done before malta, then at least i can make a choice to spend a little more cash and dive safer over there.

What I'm about to suggest could be seen as heresy!

Consider doing the PADI 'Enriched Air Diver' course, if you can find it cheap enough.
Unlike the BSAC Basic Nitrox course, it covers diving with Nitrox mixes from 22% to 40% and includes Equivalent Air Depth calculations.
For many people it's all they need.
Apart from the course materials, I do it free of charge for club members.

regards

Tony
BSAC OWI
PADI MSDT

[Matt-75]

No nothing is heresy to me, my background was with PADI. I see the differences, but my PADI school was just as good as my BSAC school, in fact better in some ways (more high class instructors for one, most ex navy).

They were probably what most divers would consider a good diving school, cared for students etc. So ideas using any route, im open to.

As far as diving air tables on nitrox, well that was my original thought. I'm not really looking to go down the nitrox route with the aim of doing stupid depths for the minute. Most of my dives have been around the 20-25m mark, and i see little point to go deeper unless its a requirement of whatever training course im doing. Even then its unlikely i'd go any deeper regularly, unless i found something interesting that i wanted to explore.

But i do have aspirations towards wreck penetration eventually, but my club doesnt seem to offer that sort of training, so i may go back to my old club in wales and do a PADI Rescue Diver since we were going to get compulsory wreck penetration training with that, then maybe expand it with the wreck speciality course. Alternative routes within BSAC probably exist, but not from an official standpoint that i've seen so far. It seems to be more a skill you pick up with fellow divers.

[PeteM]

I'm not really looking to go down the nitrox route with the aim of doing stupid depths for the minute. Most of my dives have been around the 20-25m mark, and i see little point to go deeper unless its a requirement of whatever training course im doing. Even then its unlikely i'd go any deeper regularly, unless i found something interesting that i wanted to explore.

I think you might be getting confused here: Nitrox definitely does not equal stupid depths


Nitrox is a shallow gas and at its best between about 20m and 35m

[Tony Dwyer]

No nothing is heresy to me, my background was with PADI. I see the differences, but my PADI school was just as good as my BSAC school, in fact better in some ways (more high class instructors for one, most ex navy).

They were probably what most divers would consider a good diving school, cared for students etc. So ideas using any route, im open to.

Matt

Thanks for that.

The BSAC Basic Nitrox course covers only 32% & 36% mixes and as I said does not cover Equivalent Air Depths (EAD). Despite the best will in the world, there will be occasions when the 36% mix you requested turns our to be 37.5% and perhaps you won't have time to get the cylinder refilled.
This can present problems with the max depth planning but at least if you are qualified to dive on ANY mix between 22% & 40%, you will be able to plan a dive that's OK with the mix you have available and track your O2 exposure appropriately.

I'd go for a certification that gives you that flexibility.

[PeteM]

The BSAC Basic Nitrox course covers only 32% & 36% mixes and as I said does not cover Equivalent Air Depths (EAD). Despite the best will in the world, there will be occasions when the 36% mix you requested turns our to be 37.5% and perhaps you won't have time to get the cylinder refilled.
This can present problems with the max depth planning but at least if you are qualified to dive on ANY mix between 22% & 40%, you will be able to plan a dive that's OK with the mix you have available and track your O2 exposure appropriately.

I'd go for a certification that gives you that flexibility.

You do get that flexibity - the course covers you for how to dive on tables in exactly the circumstances you quote, in fact I am pretty sure that is exactly one of my worked examples on my slides but with 38%

[Paul Morris]

You do get that flexibity - the course covers you for how to dive on tables in exactly the circumstances you quote, in fact I am pretty sure that is exactly one of my worked examples on my slides but with 38%

Absolutely, BSAC teach dive to the MOD of the mix as analysed, and to the most conservative table. So for a mix analysed at 38% a BSAC Nitrox diver would dive using the EANx36 table with a MOD of 27m (26.8m).

If the mix analysed as 34.8% you would dive using the EANx32 table wth a MOD of 30m.

No big deal, just increases the safety factors.

[Tony Dwyer]

Absolutely, BSAC teach dive to the MOD of the mix as analysed, and to the most conservative table. So for a mix analysed at 38% a BSAC Nitrox diver would dive using the EANx36 table with a MOD of 27m (26.8m).

If the mix analysed as 34.8% you would dive using the EANx32 table wth a MOD of 30m.

No big deal, just increases the safety factors.

Interesting, I've never used the BSAC Nitrox tables (though I do own a set, which are not to hand), I've always calculated EAD & MOD and compared it to what my computer says.

I've just done a MOD calc for 38% & came up with 26.84 mtrs

[PeteM]

Interesting, I've never used the BSAC Nitrox tables (though I do own a set, which are not to hand), I've always calculated EAD & MOD and compared it to what my computer says.

I've just done a MOD calc for 38% & came up with the same number that the BSAC Eanx 36 table gives. Looks like the table has been set to be more conservative. What does it say for 40%?

Bet you've got a Suunto

They calculate things in a funny way for some reason

[Tony Dwyer]

Bet you've got a Suunto

They calculate things in a funny way for some reason

I do and it's at home, that calculation was done on my PDA using a spreadsheet which runs pretty standard formulae.:)

[PeteM]

I do and it's at home, that calculation was done on my PDA using a spreadsheet which runs pretty standard formulae.:)

Interesting, calculation I would use for MOD is ppGas / FractionGas (= Absolute pressure)

So for 36% we get 1.4/.36 = 3.888 = 28.88 meters or 29 meters which is what the BSAC tables say.

What do you get and what formula is the spreadsheet using to get to it?

[Paul Morris]

So for 36% we get 1.4/.36 = 3.888 = 28.88 meters or 29 meters which is what the BSAC tables say.

Well, pretty much, but then for simplicity we break the sacred 1.4bar rule and say that for no-stop diving the MOD of EANx32 is 35m, and for EANx36 its 30m (1.44bar) :D

Suuntos do something weird with their MOD value. A buddy of mine spent 25minutes hovering above a wreck because he believed the MOD of the Suunto (set to 1.4 bar), over the simple mathematics! I don't think it was a rounding error, it was around 2m-3m out on this occasion :p

[PeteM]

Well, pretty much, but then for simplicity we break the sacred 1.4bar rule and say that for no-stop diving the MOD of EANx32 is 35m, and for EANx36 its 30m (1.44bar) :D

Suuntos do something weird with their MOD value. A buddy of mine spent 25minutes hovering above a wreck because he believed the MOD of the Suunto (set to 1.4 bar), over the simple mathematics! I don't think it was a rounding error, it was around 2m-3m out on this occasion :p

All Suuntos except the Vytec do this, I set my Vyper to 1.5bar to compenstate

[Tony Dwyer]

Interesting, calculation I would use for MOD is ppGas / FractionGas (= Absolute pressure)

So for 36% we get 1.4/.36 = 3.888 = 28.88 meters or 29 meters which is what the BSAC tables say.

What do you get and what formula is the spreadsheet using to get to it?

Pete

Have a look at:

http://www.diveinstruct.org.uk/downloads4/Nitrox%20EAD%20calculator.xls

regards

Tony

[Fiona]

It's recommended that you use it on most dives less than 36m. It gives you longer No Stop times for dives without going into deco.



Steve why only on most dives ? when would you not use it.

[Ben Thompson]

Steve why only on most dives ? when would you not use it.

According to the BSAC Nitrox Course, there's the bit for not bothering for the really shallow dives due to the limited benefits... however... if you're diving repeatedly, then it's good, as it keeps you awake at the end of the day :)

[Fiona]

According to the BSAC Nitrox Course, there's the bit for not bothering for the really shallow dives due to the limited benefits... however... if you're diving repeatedly, then it's good, as it keeps you awake at the end of the day :)

Interesting must have changed since I assisted on a nitrox course.

Limited benefits - any benefit will do for me.

What do BSAC call a shallow dive ?

[PeteM]

Pete

Have a look at:

http://www.diveinstruct.org.uk/downloads4/Nitrox%20EAD%20calculator.xls

regards

Tony

OK so that agrees with me and the BSAC tables as it gives 28.89 for 36%

Also gives 26.84 for 38% compared to the BSAC tables 27m

What MOD did you get? Are you getting mixed up somewhere?

Cheers

Pete

[PeteM]

Interesting must have changed since I assisted on a nitrox course.

Limited benefits - any benefit will do for me.

What do BSAC call a shallow dive ?

The books say air is the "right gas" up to 18 meters. Personally I think you are well into nitrox benefits by then

[Ben Thompson]

The books say air is the "right gas" up to 18 meters. Personally I think you are well into nitrox benefits by then

Yep, I agree with you on that one! esp. if you're on something like a liveaboard and doing multi-diving-multi-day-type-diving!

[Nigel Hewitt]

The books say air is the "right gas" up to 18 meters. Personally I think you are well into nitrox benefits by thenI'm not sure air is ever the right gas but in the pool I might not care...

[Matt-75]

I'd agree on air for pool use, and possibly any shallow dives like 10-15m. But after that from what i gather the benefits of nitrox show themselves.

I know for sure my club has some 20-30m dives planned for us qualified divers out in malta and since those sort of profiles seem to warrant nitrox, then i think thats where i need to be going.

[Tony Dwyer]

OK so that agrees with me and the BSAC tables as it gives 28.89 for 36%

Also gives 26.84 for 38% compared to the BSAC tables 27m

What MOD did you get? Are you getting mixed up somewhere?

Cheers

Pete

Lost something in translation somewhere. :) I was busy and may have misread the PDA, which is using the same spreadsheet (wot I wrote).

I have edited my previous quote to make my statement clearer.

[PeteM]

Lost something in translation somewhere. :) I was busy and may have misread the PDA, which is using the same spreadsheet (wot I wrote).

I have edited my previous quote to make my statement clearer.

Fair enough - the confusion is caused by the fudge factor that BSAC apply to no stop dives. The rules are

The max ppO2 you are allowed to dive to is 1.4bar...

Unless you are doing a no stop dive planned using the 32% or 36% tables in which case you are allowed to use 1.44bar

As I said a fudge

[garethwebber]

On a 6-10m pier dive, the benefits would be negligible and you would be paying more for the nitrox mix.

G

[Fiona]

On a 6-10m pier dive, the benefits would be negligible and you would be paying more for the nitrox mix.

G

If I was doing this, it would be a second or third dive so I would still be using nitrox, for me cost doesn't come in to it.

Last pier dive I did was pre 2000 under kepple pier, little Cumbrea :D