Accelerated Deco (ERD) is it worth it?

[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 tyhan 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

[PBrown]

Here you go, this should give you some sort of idea what accelerated deco can do for you. I'd suggest that you cut & paste into a spreadsheet to align the data.

The numbers are the total deco time required (not dive time). So on a 30M dive for 20 min bottom time on 21% would require a total deco of 4 mins, 21% + 100% a total deco time of 4 mins, 21% + 50% + 100% a total deco time of 2 mins.

On a 48M dive for 50 mins bottom time, 21% would require a total deco time of 149 mins, 21% + 100% a total deco time of 74 mins, 21% + 50% + 100% a total deco time of 53 mins.

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.

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.

cheers,
Paul


Bottom Time 20 25 30 35 40 45 50
30M
21% 4 6 10 14 23 <30> <37>
21%/100% 4 5 6 8 11 <14> <17>
21%/50%/100% 2 3 4 6 7 11 <14>

33M
21% 5 11 15 24 <32> <42> <53>
21%/100% 4 7 9 12 17 <21> <26>
21%/50%/100% 2 4 6 8 12 <15> <18>

36M
21% 9 14 23 <33> <44> <56> <67>
21%/100% 6 9 13 18 <22> <27> <34>
21%/50%/100% 3 6 9 13 <17> <20> <25>

39M
21% 12 19 31 <43> <57> <69> <87>
21%/100% 8 11 17 <23> <28> <35> <42>
21%/50%/100% 5 8 12 17 <22> <27> <32>

42M
21% 15 27 <39> <55> <69> <89> <107>
21%/100% 10 15 22 <28> <37> <45> <56>
21%/50%/100% 7 10 17 <22> <27> <32> <38>

45M
21% 21 35 <50> <66> <85> <105> <126>
21%/100% 13 19 <27> <35> <43> <54> <65>
21%/50%/100% 11 15 <20> <26> <32> <38> <46>

48M
21% 26 <42> <61> <80> <103> <121> <149>
21%/100% 15 24 <32> <42> <53> <63> <74>
21%/50%/100% 12 19 <25> <31> <38> <44> <53>

[Garf]

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.

Perhaps some of those people that are responsible are fed up seeing idiots attempting to learn technical diving off the Internet and subsequently filling up recompression chambers? Some of those idiots came to technical diving because they were not comfortable doing long deco hangs...it is sort of the antithesis of the technical attitude where you use the techniques to get what you want out of a risky dive with the minimum of risk. I decide on my bottom time and then do the deco it requires.

I was doing the air times for a few years before venturing outside BSAC for Nitrox and technical training 12 years ago. I have been a bit of a Nitrox evangelist ever since.

Well let's see what I can do then. Very roughly speaking 30mins at 30m to 50m on air + 80% or higher - deco times will approximate bottom times. Obviously it depends on the exact depth and time the longer and/or deeper the more deco and at 50m for an hour I might spend 90mins (150% of bottom time) decompressing . You can usually make it out the water faster on BSAC 88s if the profile is not off the end of the table.

Nitrox tables (other than 88s) and accelerated deco tables are based on EAD extrapolation. It is more theory than experiment so most people use a conservative (compared to 88s) table based, to one extent or other, on Buhlmann's. Even so very few people stick exactly to the table they have chosen and will alter their profiles according to their gut feelings. It is very difficult to say what is or is not correct because the statistical verification models just do not exist. If this worries you, you probably should not be technical diving.

Anything over 75% will keep your PPO above 1 for the bulk of decompression. As shallow stop times increase the greater the difference this makes. For short stops there will be virtualy no significant difference over backgas or 50%. It takes time for accelerated deco to do it's stuff. Personally I don't bother accelerating any less than 30 minutes of air stops, about 15 mins on 80%, but I do the air stops up to 15 mins on 80%.

There are a number of cons when it comes to using 100%, CNS exposure rises significantly and heavy sea states can make a 6m MOD very uncomfortable. With 80% the gas switch is out the way before ascending into the surf zone in any remotely divable conditions. 100% offers little theoretical time advantage over 80%. It has the advantages of being devoid of Nitrogen and the treatment gas for DCI.

A basic rule of accelerating decompression is being prepared to do the air stops in case you lose access to the deco gas. Personlly 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.

Ideally you would be using a Nitrox backgas to extend the bottom time at 30m to 35m but yes it can get expensive. Using 50% to decompress from your 30min 30m air dives, according to the air tables, will cost similar to accelerating deeper/longer dives. What is likely to change is how you feel after the dive. Only you can say if it is worth it, but it stands a chance that if you do not think so you are not going to find much use for accelerated deco.

Once you start extending times well beyond no stop times a lot of additional risks come into play. DCI is quite a small one. DCI is however almost inevitable if you run into the consequence of those other risks. The worse possible scenario is having to surface with the equivalent of a massive backgas decompression obligation because you fell prey to one of the other risks. Hence technical diving tends to favour those who are adventurous in their objectives and conservative in their plans.

An excellent response, good effort Matt !

[Step]

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!!!

[Bottle Maker]

I have had a look back through my Suunto dive manager and found a 35 metre dive for 40mins breathing 32% when I gas switched to 65% the time to surface went from 25mins to 14mins hope this gives you some idea.

I would reccomend that you do the ERD course, it is not just about reducing your decco time but more about teaching you more advanced diving tecneques.

[ardhill]

Originally Posted by Step

Highest mix back gas and High mix for deco for 40 min 35m and 45m anyone?
Pretty Please.

35m - Highest Mix @ 1.4 PPO2 = 31%
45m - Highest Mix @ 1.4 PPO2 = 25%

40min @ 35m on 31% Back Gas
Deco gas - Time on Deco (plus you need to add ascent time)
50% - 22 mins
80% - 15 mins
100% - 15 mins

40min @45m on 25% Back Gas
Deco gas - Time on Deco (plus you need to add ascent time)
50% - 53mins
80% - 48mins
100% - 51mins

[GLOC]

Originally Posted by Step

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

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.

Very good, and as soon as you use any source of air which is not deemed clean your cylinder O2 service is next to useless. If using non-clean air (and some club compressors supply clean air), then a personal filter is a must, or another source of air.

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.

Nope, Deco is educated guess work. Someone was quoted as saying something like, "deco is theorised using a fine pencil, tabulated using a thick pen and enacted upon using a crayon" There are people on here who have done a 70m dive one day and then 6 months later, completed the same dive using the same gases and profiles and got bent to shit. Deco is not an exact science and the computer manufacturers try to make their solutions as safe as possible by putting conservative levels in them, even 0 is 'fairly safe'.

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.

You say that, but YD has its fair share of bods who come on here professing to know something (which subsequently they have been proven that they don't).

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!

Why do you say that is absurd? I know someone who dives well beyond their current Normoxic trimix (to 100m) and has completed cave dives inside a mine despite not having any cave training. I personally think he will be a statistic. This is all we are trying to say. Deco diving can potentially be fatal and if you do not understand the risks, then you should not be conducting the dives.

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.

Therein lies the problem, you are admitting that you are willing to go to this level despite not having the training and fully understanding the implications. However, if you want to know what happens in the event of an emergency and what you need to do, then fine. Follow your computer, it will give you a good idea of how to get out the water unbent but it won't tell you if you have enough gas for the task.

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.

This depends on the attitude that you go into the course with and your choice of instructor. Most people on here would choose an instructor over an agency (or if they are tied into an agency, then an instructor which they have heard good things about)

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.

The other thing to bear in mind is that depending on how long you go into deco, depends on whether you need independence for your air supply? Be that twins manifolded or isolated, or a large pony (). If you are willing to blow off 5mins worth of deco in the event of an emergency that is your call, but if you are going to blow 20mins off then you seriously need to think about redundancy. I don't know off the top of my head, but I am pretty sure that all the agencies require independent air sources once you get into a deco overhead.

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

They would do, but the comments are slight tongue-in-cheek, but they are also correct. maybe there should have been a smilie at the end of Paul's comment. YD is a community and we don't like to see people get hurt through stupidity. Every dive is a decompression dive, just how much it is going to hurt if you surface straight away!!

There is a lot information to be had about deco and the vagueries of it. Have a look at the Team Foxturd website under theory, Mark Powell's website and a whole host of other sites.

The bottom line I have to say though is it appears that you should continue to dive to the limits you currently have until you have some more time and money to invest in training and equipment for decompression diving. No-one is going to stop you but please dive safe.

Finally, you haven't mentioned any other buddys. What do they do? Because whatever you do, they will need to do the same, or they the same as you. Deco diving and solo diving, increases the risks much much more, especially if you haven't had an deco training.

Dive safe Step.

[scuba steve irl]

go do the course . you will learn alot more than just accelerated deco . if your thinking of going twins do it on a course that will be strutered ariund twins .

when the course is finished this is the start of your learning curve . the course gives you the tools and the insight to move on and learn safely ,

start by putting nos and depths and mixs into vplanner . it can be dl free .

[Gareth J]

Excellent posts by Gloc & Matt

Step

As has been stated here, I would strongly recommend you get the proper training.

Diving is not a cheap sport, if additional cost is an issue, then settle where you are, reinforce your current skill base until you can afford to progress.

You will find that we worry more about those that throw money at the sport & go from nothing to hero in a year or two.

As has been stated by others, YD is a community (as is 'diving' as a whole), we don't want to see anyone hurt or killed. On a purely selfish note the publicity doesn't help any of us & just results in insurance premiums going up & mortgage companys & life insurance companys putting us down as high risk.

If you look at the profiles of a lot of those giving advice, they have been diving for a considerable time, they have built up knowledge & experience over this period, this is what keeps them safe.
They will all have done something stupid at some point, & survived due to the training & experience they have invested in.
You can bet they have all seen 'the accident waiting to happen', sometimes having to intervene to ensure that they got out of the water in one piece.

Diving is very easy - when all is going well, any idiot can do it. The majority of what we teach & learn especially on the more advanced courses, is seldom related to purely a diving skill (descent, swim on the bottom, & ascent), but to the emergency & rescue skills. The majority of the planning that we do relates to the what if's, & how to survive a major equipment / buddy failure.
Which is why we tend to look for instructors doing the type of diving we are aiming at rather than the agency the instructor teaches for. We want real world experience, rather than accademic informations from books. A good instructor will tell us of their past mistakes (and the solutions), in the hope that we won't repeat them!

The information given here is in good faith, as are the recommendations. We can but hope you get the right training & apply it!

Dive safe

Gareth

[scuba steve irl]

good post gar .

correct and right that alot of people go from zero to hero in as little time as it takes to read all the books / as quick as the shop can spend your money for you .

steps you are asking all the right questions . there are alot of experienced guys here and they can give great advice . where did they get there knowledge . they done the course and then built on that knowledge . do the course as it is a different type of divin .

for instance the surface is not an option in case of emergancy , and you only do your best for your buddy then he is his own . if theres a problem and your buddy must surface he surfaces alone and you finish your deco . loads of different thing like this .

the extended range course is inexpensive in comparision to other courses . shop around as it may be cheaper futher a field . this course delves deeper into decompression and its benifits as well as kit configuer , emergancy procedures and a nitrox overview .

it is meant as an entry level course whereas to be built upon by experience as are most course's in the divin comunity . link up with some1 in your area after the courses and dive with them and let their knowledge rub off . never know there may be a new dive buddy in here.