88 Tables - Slab Tables

[Khaled Alwassia]

Hello,
I just attended the IFC and was asked during my presentation what the difference between the PADI and the BSAC 88' Tables are. Not beeing to sure I wabbled something about Haldane, what a mistake. I was then told that the 88' tables are Slab (possibly misspelled) Tables. As a reference i was given the Book "Deeper Into Diveing", unfortuneately Amazom does not carry the book.
Could please someone point me to a different source of background information or let me know here else i could get hold of the book.

Many thanks

Khaled

[rogersides]

Have a look at this paper:

Hennessy TR 1988 Modelling human exposure to altered pressure
environments. In: Environmental Ergonomics (eds Mekjavik, IB, Banister, EW, Morrison, JB,). London: Taylor & Francis. This gives some relevant background, but details of the model of the BSAC'88 Tables have not been published.

The BSAC tables are not a slab model. Lippman (page 325) assumed, incorrectly, that Dr Hennessey used a slab model probably because he worked with Hempleman 1976-1981. It is modelled on a triple-compartmental model of a single complex tissue that allows interaction between the three compartments.

Best Regards,
Roger

[Khaled Alwassia]

Have a look at this paper:

Hennessy TR 1988 Modelling human exposure to altered pressure
environments. In: Environmental Ergonomics (eds Mekjavik, IB, Banister, EW, Morrison, JB,). London: Taylor & Francis. This gives some relevant background, but details of the model of the BSAC'88 Tables have not been published.

The BSAC tables are not a slab model. Lippman (page 325) assumed, incorrectly, that Dr Hennessey used a slab model probably because he worked with Hempleman 1976-1981. It is modelled on a triple-compartmental model of a single complex tissue that allows interaction between the three compartments.

Best Regards,
Roger

Roger,
many thanks for the reference i will check it out and am sure that i will ask some more questions.

Khaled

[Chris Cherrington]

As a reference i was given the Book "Deeper Into Diveing", unfortuneately Amazom does not carry the book.

As its wrong you saved yourself a few quid Khaled !!

The volume has been updated, but I have never had the chance to read either. I don't know therefore if the mistake has been corrected.

There are some much better volumes out there for deco theory.

Chris

[Khaled Alwassia]

There are some much better volumes out there for deco theory.


Chris,
thank for your advise could you name such better volumes.
As I want to go for my Theory Instructor Exam i have to read up on those deco theories.

Thanks

Khaled

[Chris Cherrington]

There are some much better volumes out there for deco theory.


Chris,
thank for your advise could you name such better volumes.
As I want to go for my Theory Instructor Exam i have to read up on those deco theories.

Thanks

Khaled

The Deco Matrix by Bob Cole is a good start if (like me) you find it all a bit heavy going. Link supplied.

If you are into maths and heavy theory the books by Bruce Weinke are a good read. However there's lots of RGBM and related stuff that makes these hard going. Its a labour of love to understand this stuff.

Other deco models like VPM require a rethink, just to confuse you more. Happily, there's lots too on the internet for free.

I think the Bob Cole book would cover all you need for the TIE.

Chris

[David Walker]

As I want to go for my Theory Instructor Exam i have to read up on those deco theories.

Anything more in-depth than the absolute basics of deco theory (ie caused by fast ascents, etc) and how to use the BSAC tables is not covered in the TIE, or any BSAC course (unless there's a "Deco Theory" SDC i don't know about). Nice to know for general interest, and to answer the curious questions you might get, but isn't 'required'.

David

[Khaled Alwassia]

David,
Thanks for the feedback, unfortuneately i was asked the following question by the NI running the IFC after my presentation on BSAC 88 Tables for Padi divers.
What is the difference between the Padi and Bsac table.
I was under the inpression that the BSAC Table was based on Haldane and the PADI table on the US NAVY. I was then told that the BSAC table is in fact a slab table, still not sure what that is. On reply on the forun even said it is not a slab table.

In light of the contradicting information and my own experience i want to know the facts.

So if any one can provide internet links or book titles, preferably still in print, i would be very gratefull.


Many Thanks

Khaled

[PeteM]

David,
Thanks for the feedback, unfortuneately i was asked the following question by the NI running the IFC after my presentation on BSAC 88 Tables for Padi divers.
What is the difference between the Padi and Bsac table.
I was under the inpression that the BSAC Table was based on Haldane and the PADI table on the US NAVY. I was then told that the BSAC table is in fact a slab table, still not sure what that is. On reply on the forun even said it is not a slab table.

Actually I think he was probably less after the model behind them than the method of use - after all the IFC is based on the OD and SD sylabus and deco theory is a bit beyond that. What I think he was looking for was the practical differences, I would have given an explination that:-

-we don't rely on maths at all and everything is done on look up tables
-the PADI tables only cover no stop diving but we allow compulsary stops
-On PADI tables you must ascend at 18mpm (shudder) or they become invalid but BSAC tables allow flexibility in ascent rates because they rely on dive time rather than bottom time and our ascent rate is no more than 15/6mpm

[Chris Cherrington]

David,
Thanks for the feedback, unfortuneately i was asked the following question by the NI running the IFC after my presentation on BSAC 88 Tables for Padi divers.
What is the difference between the Padi and Bsac table.
I was under the inpression that the BSAC Table was based on Haldane and the PADI table on the US NAVY. I was then told that the BSAC table is in fact a slab table, still not sure what that is. On reply on the forun even said it is not a slab table.


The 88s are not a slab table and the PADI RDP is not 'based' on the USN tables.

BSAC 88s are three tissue types with interaction - the earlier post was about as good an answer as you can get without talking to Tom personally...
PADI RDP was updated in 1987 by DSAT using doppler testing. AFAIK it was the first rec table to use doppler to establish "Agency" M values. The concept of residual nitrogen time used by PADI (and everyone else) is the format of the USN tables also.

Haldane begat Buhlmann and are the same thing to all intents and purposes. USN are therefore "Haldane". The 88s are more or less unique as virtually all other models use or incorporate Buhlmann. This has lead to some (unfair) slagging of the 88s. Their main fault is a too fast ascent rate, based on things that we have come to know since 1988, something BSAC should address....

The link to the book I suggested will give you all this and more (apart from the 88s which are not mentioned as nothing has ever been published on them). You will be able to correct your NI.

Chris

[martin]

IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

I would comment also that it is interesting that we do know so little about the BSAC tables, and nothing has been published on the theory - what are they keeping hidden???

--
Martin


:=David,
:=Thanks for the feedback, unfortuneately i was asked the following question by the NI running the IFC after my presentation on BSAC 88 Tables for Padi divers.
:=What is the difference between the Padi and Bsac table.
:=I was under the inpression that the BSAC Table was based on Haldane and the PADI table on the US NAVY. I was then told that the BSAC table is in fact a slab table, still not sure what that is. On reply on the forun even said it is not a slab table.
:=

The 88s are not a slab table and the PADI RDP is not 'based' on the USN tables.

BSAC 88s are three tissue types with interaction - the earlier post was about as good an answer as you can get without talking to Tom personally...
PADI RDP was updated in 1987 by DSAT using doppler testing. AFAIK it was the first rec table to use doppler to establish "Agency" M values. The concept of residual nitrogen time used by PADI (and everyone else) is the format of the USN tables also.

Haldane begat Buhlmann and are the same thing to all intents and purposes. USN are therefore "Haldane". The 88s are more or less unique as virtually all other models use or incorporate Buhlmann. This has lead to some (unfair) slagging of the 88s. Their main fault is a too fast ascent rate, based on things that we have come to know since 1988, something BSAC should address....

The link to the book I suggested will give you all this and more (apart from the 88s which are not mentioned as nothing has ever been published on them). You will be able to correct your NI.

Chris

[iainmsmith]

IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

It would be even more unfair on a TIE...! But given that First Class Diver deco theory apparently means "How to use the BSAC '88 Tables", comparison between agencies and (God forbid) the theoretical basis of decompression theories shouldn't come up in the ITS in case, as in this instance, it gives the candidate the idea that such knowledge is required.

Possibly the key learning point from this is, if faced with a question to which one does not know the answer, whether at IFC, TIE or in a real lecture, for goodness sake do not try to guess or make something up. The answer is, "I'm sorry - I don't know. However, I know who to ask about that and/or where to look the detail up and will get back to you in due course."

Iain

[Chris Cherrington]

IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

I would comment also that it is interesting that we do know so little about the BSAC tables, and nothing has been published on the theory - what are they keeping hidden???

--
Martin

Khaled sems to have a general interest and that's a good thing, but I'm sure you are right. Maybe the NI wanting to show off?

I don't think there's much to "hide" about the 88s. The real question is why BSAC uses them to such an extent. As Ian mentions the AD is all about using 88s - altitude and stuff. Given that most divers (and I guess about 99.9% of SD and above) use a computer (ergo Buhlmann) perhaps its about time that the tables thing was looked at again?
I needed to learn 88s for DL as a SD crossover from PADI. I have never, nor ever will I, dive on 88s - I have a computer or V Planner for trimix dives. Waste of time....

Chris

[John Williams]

Khaled,

I'm an ITS Staff Instructor/Examiner who currently holds a "merit" mark in my FCD theory examination. I am a BSAC Nitrox Instructor of long standing.

(there is no longer a theory examination for NI - which means that I have acheived the highest level of theoretical knowledge required for any BSAC examination ...though not in all areas OBVIOUSLY)

I'm not telling you this to show off - I'm highlighting it so that what I say next is in perspective:


I have no idea what the other contributors to this thread are talking about.

I've never even heard of a "slab" table.

I understand tissue compartments, I'm fully familiar with other tables (though again not all) having done my initial Nitrox Training, some years before BSAC entered that area, with IANTD and taken an interest in what other agencies use since then.

Although it is good to read around a subject and to be able to discourse at a level far above that which you need for BSAC purposes - you simply do not NEED to know this much about Deco theory (and certainly not at TIE level)

Good luck in sourcing your references - and better luck in progressing through the Instructor ranks (you sound like the kind of Instructor we need!)

John

PS
I suspect that the contributor who suggested that what the NI was looking for was something about the practical differences in using the tables was correct(i.e. the lack of calculations etc) - but perhaps your waffle answer took the NI off at a tangent when they responded to your answer.

[Nigel Hewitt]

The real question is why BSAC uses them to such an extent.

Probably because they work for no-stop diving and they are very easy to use for students. OK I wouldn't use them for deco diving but the things I use are not simple and not cheap.
If it ain't broke don't mend it.

nigelH

[David Walker]

I suspect that the contributor who suggested that what the NI was looking for was something about the practical differences in using the tables was correct(i.e. the lack of calculations etc) - but perhaps your waffle answer took the NI off at a tangent when they responded to your answer.

Even that sounds a bit beyond the point of the TIE / BSAC instructor in general. Again, it might be useful to know about other types of tables, but if someone has never trained with PADI why should we know about using their tables? Maybe useful to explain to students who are doing crossovers, or maybe it was just a test to see how someone deals with a question they don't know the answer to, but frankly I couldn't tell someone the differences between BSAC and PADI tables, and i'm an OWI. What I could say is that the BSAC tables are very easy to use, allow decompression (for SD+) which I know (think) PADI don't, and they are based on a different model and so will give slightly different dive times. Beyond that, they can find the differences themself!

David

[Chris Cherrington]

:=The real question is why BSAC uses them to such an extent.

Probably because they work for no-stop diving and they are very easy to use for students. OK I wouldn't use them for deco diving but the things I use are not simple and not cheap.
If it ain't broke don't mend it.

nigelH

Easy to use they are that's for sure. Tom Hennessey's design is excellent. They work for no-stop AND deco diving, they must or there would be lots of bent BSAC divers...

Despite this you say you would not use them. This is the nub of it...

However, this is nothing to do with Khaled's request!! This topic has been done to death before. I guess we must continue to live with this for the time being. When I retire I will get on the NDC and shake it up!!!! Meantime don't have the time!

Best

Chris

[iainmsmith]

Easy to use they are that's for sure. Tom Hennessey's design is excellent. They work for no-stop AND deco diving, they must or there would be lots of bent BSAC divers...

Despite this you say you would not use them. This is the nub of it...

It depends what you mean by "bent".

I haven't dived '88s for some time because of how utterly shattered I would feel after diving on them. Switching to Buehlmannesque profiles with gradient-factor-derived deep stops made a huge difference to how I feel in the evening. That tells me that there is something "wrong" with the '88s, in that I'm getting all the "subclinical" signs without a definitive bend.

When I compare the deco requirements between BSAC '88s and the profiles I typically dive, even what I consider to be more "aggressive" profiles are far, far more conservative than the '88s.

That's why I say, "I would not use them".

Iain

[Will Swift]

:=
:=:=The real question is why BSAC uses them to such an extent.
:=
:=Probably because they work for no-stop diving and they are very easy to use for students. OK I wouldn't use them for deco diving but the things I use are not simple and not cheap.
:=If it ain't broke don't mend it.
:=
:=nigelH

Easy to use they are that's for sure. Tom Hennessey's design is excellent. They work for no-stop AND deco diving, they must or there would be lots of bent BSAC divers...

My car's speedo says it goes to 160MPH - lots of people drive the same car as me and have done for quite a few years, so it must be safe to drive at 160MPH - maybe I'll even get away with it the first few times i do it?

[nick kay]

I haven't dived '88s for some time because of how utterly shattered I would feel after diving on them. Switching to Buehlmannesque profiles with gradient-factor-derived deep stops made a huge difference to how I feel in the evening. That tells me that there is something "wrong" with the '88s, in that I'm getting all the "subclinical" signs without a definitive bend.

When I compare the deco requirements between BSAC '88s and the profiles I typically dive, even what I consider to be more "aggressive" profiles are far, far more conservative than the '88s.

That's why I say, "I would not use them".

Iain

>> Its not just BSAC '88s - its basically any form of deco plan for a dive where the diver plans an ascent which is "straight up to min stop depth & stay there for xx minutes", i.e. the way most divers use their computers "to do the minimum"
>> Take a look at the research carried out by DAN and NAUI towards the end of last year that (strongly) recommends that deep stops be carried out in preference to longer stops at shallower depths
>> And, this was for "sports/recreational" NOT techie diving...

[rogersides]

I saw that for the agenda of the DOC this year, one of the lectures is "New Thoughts on Decompression" by Jean-Pierre Imbert. This is then quickly followed by the Open Forum. It could be an interesting afternoon.

I believe that instructors and committee members are invited to this. I'm not sure but I think that may include assistant instructors.

[Philip Smith]

Given that most divers (and I guess about 99.9% of SD and above) use a computer (ergo Buhlmann)

Suuntos do not, and I think never did, use a Buhlmann algorithm.

Philip Smith

[Philip Smith]

I'm an ITS Staff Instructor/Examiner who currently holds a "merit" mark in my FCD theory examination. I am a BSAC Nitrox Instructor of long standing.

I have no idea what the other contributors to this thread are talking about.

I've never even heard of a "slab" table.

For historical interest, the RNPL/BSAC 1975 table was based on a so-called "slab" model.

Philip Smith

[john williams]

Exactly!

[David Walker]

I believe that instructors and committee members are invited to this. I'm not sure but I think that may include assistant instructors.

DOs, instructors, assistant instructors, and a "branch representative" (ie anyone else who is interested and wants a day out in London!) :O)

David

[Mike Rowley]

(there is no longer a theory examination for NI - which means that I have acheived the highest level of theoretical knowledge required for any BSAC examination ...though not in all areas OBVIOUSLY)


That is not strictly true John. There is no formal written paper for the NIE but certainly up to this year there have always been spot oral examinations of theory knowledge.

Were you unlucky enough to have encountered some examiners on a spot oral you may well have been asked about Haldanian models and bubble theory, the problem of ballancing the need to prevent bubble growth with the Haldanian model of bringing a diver as close to the surface as possible within a given ratio of pressure gradient and how these interact in modern decompression thinking. You certainly would be expected to have some knowledge of gradient factors and how they are used and why deep stops are being incorporated into even recreational diving computers.

On the NIE the usual practice is to give each examiner a spot oral subject that he or she is very familiar with so the examiner asking these questions would probably be one who is into technical diving and has a good working knowledge. He or she would typically begin asking about the basics and continue to probe progressively deeper.

However, I do agree that it is a most unfair question to ask a candidate any of this on a TIE and like others I suspect the NI concerned was not looking for anything other than practical implications. Equally it is most unreasonable to ask questions about PADI material on a BSAC exam.

As amatter of interest we have been forced to abandon the 88 tables for the BSAC Inspiration Course because we cannot get a difitive answer regarding their suitability to use EAD and the fact that multi-level calculations are impossible with then so bailout would have to be calculated on the basis of a given weakest mix for the whole dive.

Cheers

Mike

[Dave]

IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

There is nothing wrong with the question and there would be nothing wrong with a reply saying that you don't know since you have never done anything through PADI but will get back to them later. As long as you don't start guessing and giving the wrong answer u'd be fine.


I would comment also that it is interesting that we do know so little about the BSAC tables, and nothing has been published on the theory - what are they keeping hidden???


istr it is due to the copyright owner keeping hold of it

Dave

[iainmsmith]

:=IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

There is nothing wrong with the question and there would be nothing wrong with a reply saying that you don't know since you have never done anything through PADI but will get back to them later. As long as you don't start guessing and giving the wrong answer u'd be fine.

Agreed...but only if that specific feedback were given at the time. I may be wrong, but from the tone of the original post, it sounded very much as if a brand new ADI had been left with the impression that details of a variety of decompression theory were required for becoming a BSAC instructor. THAT, IMO, is grossly unfair.

Iain

[Khaled Alwassia]

IMHO, it is a grossly unfair question to ask, especially on an IFC. A BSAC diver should not be expected to know anything about the PADI tables. They are not a part of the syllabus.

Chris,
thanks for your comments unfortuneately i am a PADI DIVE MASTER as well so should know about their tables. The problem was i did not know about the BAC tables engough. As the training subject was the introduction of Padi divers (maybe still a sensitive subject) the question was IMVHO more then justified as a normal student could have asked the same question.

Khaled

[Khaled Alwassia]

Hello All,
Thank you very much for all your replies.

As many have questioned the circumstances during which the NI asked his question please let me explain:

The correctness, appropriatness or suitability of the question was not challenged at any time. I am a PADI DIVE MASTER and should know about the PADI tables.
Working in automotive training I beleave that a trainer / instructor should be prepared for most, if not all, questions a student may ask.

Having said that I also beleave that there is nothing wrong with telling a student that you do not know at the moment and that you will get back to him.

Reflecting on things I should have done that during the IFC, but even if I would have, now I am trying to find out an answer to the queston asked.

So, does anyone know a website or book (still in print, titel & author) which would give background on the decompression theory and dive tables beyond normal necessary BSAC or Padi levels.

Please consider that i am not a Physics Graduate, so simple language without to much formular will be perfect.

Again thanks for all your feedback.

[Chris Cherrington]

:=Given that most divers (and I guess about 99.9% of SD and above) use a computer (ergo Buhlmann)

Suuntos do not, and I think never did, use a Buhlmann algorithm.

Philip Smith

According to the manual it is Haldane based. There is not enough therefore for me to cofirm or repudiate this. AFAIK it is a modified Bulmann, but if you know better I would be happy to be educated as the missus uses one....

Chris

[Chris Cherrington]

So, does anyone know a website or book (still in print, titel & author) which would give background on the decompression theory and dive tables beyond normal necessary BSAC or Padi levels.

Please consider that i am not a Physics Graduate, so simple language without to much formular will be perfect.

Again thanks for all your feedback.

Look back at my earlier post - the Bob Cole book is very accessable. Its what got me started on the PFO trail for my missus. The link is to the diver bookstore, but you can get it in most good dive shops.
The missus read it and understood it so that must be some recommendation. I haven't got it to hand but it does cover deco theory and the history of deco tables background on AAB and how M values got started (Workman) etc.

If you need to know more about things like RGBM you need to read Wienke's stuff and that is hard going.

Its only 15 quid give it a shot....

Chris

[Nigel Hewitt]

According to the manual it is Haldane based. There is not enough therefore for me to cofirm or repudiate this.

I think most systems use Buhlmann's extension of the Haldane model for compartments and dissolved gases or something reasonably similar. All the debate comes on how you then generate stops from those tissue dissolved gas tensions.

[Mike Rowley]

Eric Baker wrote an excellent paper on bubble theory and VPM with some background on general deco theory. It is available on the web somewhere but I can't remember the site. Just type in Variable Periability Model into Google and it should come up.

Bruce Weinke's stuff is very good but he blinds you with science. You need to ignore the formulae and read the text unless you are a maths grad.

Cheers

Mike



So, does anyone know a website or book (still in print, titel & author) which would give background on the decompression theory and dive tables beyond normal necessary BSAC or Padi levels.

[Philip Smith]

According to the manual it is Haldane based. There is not enough therefore for me to cofirm or repudiate this. AFAIK it is a modified Bulmann, but if you know better I would be happy to be educated as the missus uses one....

The older Suuntos used a Haldanean model, but not Buhlmann. The model was developed from that used to generate the US Navy tables and modified by Spencer's doppler studies. The newer models use Suunto's reduced gradient bubble model.

Philip Smith

[Chris Cherrington]

Eric Baker wrote an excellent paper on bubble theory and VPM with some background on general deco theory. It is available on the web somewhere but I can't remember the site. Just type in Variable Periability Model into Google and it should come up.

Start here for VPM:

Chris

[john williams]

That is not strictly true John. There is no formal written paper for the NIE but certainly up to this year there have always been spot oral examinations of theory knowledge.


Of course!...I forgot about the theoretical pressure put onto candidates for the practical exam - to check that NI candidates are capable of firing on ALL cylinders simultaneously and when under pressure.

Were you unlucky enough to have encountered some examiners on a spot oral you may well have been asked about Haldanian models and bubble theory, the problem of ballancing the need to prevent bubble growth with the Haldanian model of bringing a diver as close to the surface as possible within a given ratio of pressure gradient and how these interact in modern decompression thinking.

I would consider that unlucky!..but even if I could not give a definitive answer I'd like to think I could hold my own in a conversation on the subject and ask some insightful questions to show my currwent level of knowledge was acceptable - and the desire to learn more was evident. Perhaps this attitude and willingness would have been enough?

You certainly would be expected to have some knowledge of gradient factors and how they are used and why deep stops are being incorporated into even recreational diving computers.

Give up! Now I'm getting Pyles!


On the NIE the usual practice is to give each examiner a spot oral subject that he or she is very familiar with so the examiner asking these questions would probably be one who is into technical diving and has a good working knowledge. He or she would typically begin asking about the basics and continue to probe progressively deeper.

Hopefully I'd get far enough through the discussion to suffice (and then distract the Examiner into some other topic that I'm better at!) Tactics and strategy!


However, I do agree that it is a most unfair question to ask a candidate any of this on a TIE and like others I suspect the NI concerned was not looking for anything other than practical implications. Equally it is most unreasonable to ask questions about PADI material on a BSAC exam.

On that we certainly agree- though I tend to feel that there has been a misunderstanding/distraction leading to confusion over the aim of the original question.


As amatter of interest we have been forced to abandon the 88 tables for the BSAC Inspiration Course because we cannot get a difitive answer regarding their suitability to use EAD and the fact that multi-level calculations are impossible with then so bailout would have to be calculated on the basis of a given weakest mix for the whole dive.

Now that is interesting! Given the three hour dive to 20m that features prominently in all the ads for a well-known CCR and the fact that the bailout is often based simply on the diluent being used as OC - do all CCR dives that go beyond tables require a comprehensive back-up trapeze system as part of the bailout provision? (otherwise divers would need to return straight to the surface and face DCI and immediate evacuation to a chamber or the highly suspect option of grabbing a cylinder and doinfg in-water recompression (not something I'd ever advocate!)

John

[Mark Powell]

Hello All,
Thank you very much for all your replies.

As many have questioned the circumstances during which the NI asked his question please let me explain:

The correctness, appropriatness or suitability of the question was not challenged at any time. I am a PADI DIVE MASTER and should know about the PADI tables.
Working in automotive training I beleave that a trainer / instructor should be prepared for most, if not all, questions a student may ask.

Having said that I also beleave that there is nothing wrong with telling a student that you do not know at the moment and that you will get back to him.

Reflecting on things I should have done that during the IFC, but even if I would have, now I am trying to find out an answer to the queston asked.

So, does anyone know a website or book (still in print, titel & author) which would give background on the decompression theory and dive tables beyond normal necessary BSAC or Padi levels.

Please consider that i am not a Physics Graduate, so simple language without to much formular will be perfect.

Again thanks for all your feedback.


I have gathered together a number of good references on deco theory including Pyle's article on deep stops, Eric Baker's description of M-Values and gradient factors and descriptions of VPM and RGBM.

[Khaled Alwassia]

Thank you all for the information of reference material.
I will order the books mentioned and read the articles on the different webpage.

By the way I think they website are a great value and a credit to the person runing them.

Khaled

[vic]

> -On PADI tables you must ascend at 18mpm (shudder) or they
> become invalid but BSAC tables allow flexibility in ascent rates
> because they rely on dive time rather than bottom time and our
> ascent rate is no more than 15/6mpm

Linked to this, it's probably worth emphasising that the '88s define "bottom time" rather differently to the PADI RDP...

Vic.

[PeteM]

> -On PADI tables you must ascend at 18mpm (shudder) or they
> become invalid but BSAC tables allow flexibility in ascent rates
> because they rely on dive time rather than bottom time and our
> ascent rate is no more than 15/6mpm

Linked to this, it's probably worth emphasising that the '88s define "bottom time" rather differently to the PADI RDP...

Hactually I don't recall a definition of "bottom time" in the 88's

[Chris Cherrington]

-On PADI tables you must ascend at 18mpm (shudder) or they become invalid but BSAC tables allow flexibility in ascent rates because they rely on dive time rather than bottom time and our ascent rate is no more than 15/6mpm

I think the PADI table are no MORE than 18mps or invalid....

ALL the outdated, old-fashioned tables had a too high ascent rate to build a high gradient. The 88s are no different.

9mpm is nearer today's thinking with the last 4-5m slower still..

PADI's motto is be a SAFE diver - 'Slowly Ascend From Every dive'. That remains good advice.

Does anyone actually USE recreational tables? I know of no-one.

Chris

[Mike Rowley]

:=Were you unlucky enough to have encountered some examiners on a spot oral you may well have been asked about Haldanian models and bubble theory, the problem of ballancing the need to prevent bubble growth with the Haldanian model of bringing a diver as close to the surface as possible within a given ratio of pressure gradient and how these interact in modern decompression thinking.

I would consider that unlucky!..but even if I could not give a definitive answer I'd like to think I could hold my own in a conversation on the subject and ask some insightful questions to show my currwent level of knowledge was acceptable - and the desire to learn more was evident. Perhaps this attitude and willingness would have been enough?

You may take that view John, I couldn't possibly comment !



:=On the NIE the usual practice is to give each examiner a spot oral subject that he or she is very familiar with so the examiner asking these questions would probably be one who is into technical diving and has a good working knowledge. He or she would typically begin asking about the basics and continue to probe progressively deeper.

Hopefully I'd get far enough through the discussion to suffice (and then distract the Examiner into some other topic that I'm better at!) Tactics and strategy!

Hm ! Those who the Gods wish to destroy they invariably imbue with delusion ! Good luck with the strategy, you may need it !


:=As amatter of interest we have been forced to abandon the 88 tables for the BSAC Inspiration Course because we cannot get a difitive answer regarding their suitability to use EAD and the fact that multi-level calculations are impossible with then so bailout would have to be calculated on the basis of a given weakest mix for the whole dive.

Now that is interesting! Given the three hour dive to 20m that features prominently in all the ads for a well-known CCR and the fact that the bailout is often based simply on the diluent being used as OC - do all CCR dives that go beyond tables require a comprehensive back-up trapeze system as part of the bailout provision? (otherwise divers would need to return straight to the surface and face DCI and immediate evacuation to a chamber or the highly suspect option of grabbing a cylinder and doinfg in-water recompression (not something I'd ever advocate!)

I am really quite baffled by your last paragraph John. I don't think anyone other than yourself mentioned anything about a comprehensive trapeze system being a requirement for CCR diving. The reality is that for a given bottom time the staged decompression liability is likely to be less on any CCR dive due to the maintenance of an optimum PO2. Consequently, the requirement for elaborate decompression systems is vastly reduced compared to open circuit.

Given that the minimum entry level for "BSAC Inspiration Diver" course is Sports Diver plus Adv nitrox cert I don't think we have ever been saying that CCR diving is only for technical divers. The level one air diluent course allows for a maximum 15 min of planned decompression. You can achieve one hell of a bottom time within this parameter.
For instance, your example of 180 min @ 20 m. Using Pro-Planner on 10% safety factor with 80% micro bubble stops gives 13 min @ 4.5 m with a total TTS of 195 min (based on 1.25 bar PO2). However, this would be outside of the scope of the BSAC course since on a PO2 of 1.35 bar this gives a CNS loading of 109.8 % and a UPTD total of 279. In addition the Inspiration scrubber is rated at a maximum of 180 min.
If you recuce the bottom time to 131 min the decompression liability reduces to 5 min @ 4.5 m (Based on a PO2 of 1.25 bar), the CNS reduces to 79.91 % and the UPTD to 202.65 (based on a PO2 of 1.35 bar. You may, of course have a problem with the cold or the bladder or even boredom by this time if you are diving under Swanage Pier !
In mitigation the exothermic reaction of the sodium hydroxide absorbent removing the CO2 recuces the heat loss considerably and the moist gas mitigates against dehydration which, in itself has positive implicactions on DCI and other potential diving ailments.

Open circuit bailout from this dive, given a worst case scenario and using the air diluent supply would necessitate a 14 min stop at 4.5 m with a TTS of 147 min. Still within the 15 min of decompression liability. The BSAC advocates that the bailout plan should cater for this scenario using a RMV of 50 l/min for the ascent from 20 m to the 4.5 m stop then a more normal RMV for the duration of the 4.5 m stop. Well within the scope of normal recreational diving where many divers cary a bailout gas supply consisting of a 3l pony cylinder.

Of course, if you dive deeper than 20 m the BSAC Inspiration certification requires you to have an adequate off-board bailout plan and provision. Consequently the CCR diver may carry an off-board bailout nitrox gas and the bailout plan would reflect this so the requirement for elaborate decompression stations does not arise.

The fact is that CCR diving does not go beyond tables, it is just that most tables, not being designed as constant PO2 tables do not cater for CCR diving and were never designed to do so.

I hear that examiners on NIE have been known to explore candidates knowledge on rebreather related subjects !

Cheers

Mike

[vic]

>> On PADI tables you must ascend at 18mpm (shudder)

> I think the PADI table are no MORE than 18mps or invalid....

Nope. *At* 18 m/s.

The dive time on the RDP ends when you leave bottom. The ascent is planned with a fixed 18 m/s ascent rate. If you ascend more slowly than that, you've spent more time at depth than your plan allows for - so your plan is now invalidated ;-(

> ALL the outdated, old-fashioned tables had a too high ascent
> rate to build a high gradient. The 88s are no different.

The '88s are *very* different in that the dive time is measured up until the point where you reach your first check dpeth (i.e. start of shallow stops). IOW, if you ascend slowly, you are penalised as if you'd spent the extra time at maximum depth, not somewhere up the ascent. This means that '88s cater for slower ascent rates - albeit using a fairly draconian algorithm...

Vic.

[Chris Cherrington]

The '88s are *very* different in that the dive time is measured up until the point where you reach your first check dpeth (i.e. start of shallow stops). IOW, if you ascend slowly, you are penalised as if you'd spent the extra time at maximum depth, not somewhere up the ascent. This means that '88s cater for slower ascent rates - albeit using a fairly draconian algorithm...

Vic.

This makes it hard to follow a dive plan surely? If you have a slow ascent you add deco penalties that were unplanned - with all the gas management issues that this raises.

I wish I'd paid more attention when I was shown the 88s in the pub....

Chris.

[PeteM]

:=The '88s are *very* different in that the dive time is measured up until the point where you reach your first check dpeth (i.e. start of shallow stops). IOW, if you ascend slowly, you are penalised as if you'd spent the extra time at maximum depth, not somewhere up the ascent. This means that '88s cater for slower ascent rates - albeit using a fairly draconian algorithm...
:=
:=Vic.

This makes it hard to follow a dive plan surely? If you have a slow ascent you add deco penalties that were unplanned - with all the gas management issues that this raises.

That's why we prefer the 88's...

I wish I'd paid more attention when I was shown the 88s in the pub....

Actually I think your knowledge of the 88's is OK its RDP that is the problem

[CAS]

>> On PADI tables you must ascend at 18mpm (shudder)

> I think the PADI table are no MORE than 18mps or invalid....

Nope. *At* 18 m/s.


Sorry to delve into old topics but...

It *is* "No More Than".

Quote from PADI's RDP Instructions For Use, Page 6, Point 5 (Complete with big triangular "!" sign)...

"Slowly ascend from all dives at a rate that does not exceed 18 metres per minute. Slower is acceptable and encouraged."

CAS