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Originally Posted by Paul Oliver

Why do you need to buy a personal filter and analyser? Thats all done at the shop and no need for your own.

Hi Paul, It’s what I was thought on my nitrox course.

Always analyse your own gas on the dive site.
I have the suspicion that the tales some sort of gas stratification in cylinders that disappears over time leading to different readings in the shop than a day later on the dive site are just fairytales, but I don’t know enough about Reynolds numbers, the flow of air into a cylinder and Fick’s law, to dismiss them out right and take the risk.

Breathing air allows higher hydrocarbon contamination than nitrox, and since most of my fills are from the club air compressor. The residues left in the cylinder may not be significant but I don’t know so wont risk it. But what would be interesting is how effective the personal filters are.

From the info so far I may well end up curtailing my ambitions, or end up buying an UW MP3 player if I can find some suitably engaging but not to distracting MP3 files, or take up some sort of mediation.


Ardhill

Thanks for the Information; I should have put it in the question section that I was looking for 30 min bottom time as a sort of minimum.

Matt thanks for your extensive post.
I was not aware of how much fudge factor there is in deco models.
I wrongly assumed the to be some sort of quantifiable risk along the lines of : this profile will result in 1/1000 average diver doing it who do it in a skin bend/ 1/10000 with X 1/100000 with a severe neurological bend…. Even it was clear to me that there would be few data points and values in between extrapolated.

Originally Posted by MattS

It is perhaps only condescending/patronising if you take the attitude that you know better. The answers you were given were good ones - whether or not they are what you want to hear.

Why would I bother asking the question if I think I know better already?
Even if you don’t know me I think I deserve to be given the credit of having enough common sense to realize that a couple of lines on an internet discussion board (and I would go as far as extending it to having read extensively in reputable books about the subject) can be no substitute for a 3 day intensive course.
The default assumption that having read your post I will now go, by some sneaky way acquire a bottle of 80%, then go to somewhere next weekend, pick a dive that would give me 30min air deco, do the dive and cut deco to 15 min because I took a bottle of 80% is in IMVHO absurd!

Originally Posted by MattS

A basic rule of accelerating decompression is being prepared to do the air stops in case you lose access to the deco gas. Personally I do not think it is enough to assume you can do the longer stop times, you should try them and be comfortable with them.

Quite, just as we train for any other eventuality, but just because I’m prepared to do it occasionally for training and in an emergency, dose not mean I’d want to do on the majority of my dives.

Originally Posted by RogerViking

best option find a good instructor and do the course find out about deep stops and best gas to use for that dive...i did mine with TDI david carson he was great runs a course in Tenerife so rather than waiting for the water to warm up just go over to his center he has two sets of twin 10s and stages.
dive Tenerife 24:7

I’m afraid on my budget it is a either the course or Tenerife in any one year.
I live on less than what some people on here spend on diving.
Hence I want to know before I sign up whether the course will be more than a rather expensive (if very interesting) but largely academic exercise for me.

Originally Posted by PBrown

Personally I think accelerated deco is great and well worthwhile for the type of diving I do, but its not suited for everybody. Given the info in your first post, I'd question if you need it.

Thank you very much for that (and the tip of putting it into a spread sheet).
I shall compare to highest possible mix back gas (BSAC nitrox = less conservative than the majority on here seems to like) and back gas deco times.
Highest mix back gas and High mix for deco for 40 min 35m and 45m anyone?
Pretty Please.

The whole point of this thread is that I’m asking myself whether or not it is worth while for the diving I can (at the moment) envisage myself doing.

Originally Posted by PBrown

Btw, (and this isn't aimed at just the OP, but anybody else reading this), I haven't given you the rest of the parameters used to generate this info, so if you are dumb enough to use this info to try and do a dive & get bent, you deserve it.

Exactly why do people feel this kind of posturing is necessary?
Esp. since it is apparently so easy to download the software and have it generate the numbers for oneself?
If you must add something as your worried about litigation or something.
Would a polite note at the end pointing out that the numbers by them selves are no substitute for proper training/experience do the trick

Regardless
A big THANK YOU to anyone who took the time to reply!!!