What would you do?

*Clare Gledhill* · June 7th, 2006, 01:21 AM

Seems to me that there is a bit of an overlap in deco management in the mid 50s.

Down to 51 metres it seems that an average dive (say between 25 and 40 minutes bottom time) is best done with one deco gas (only take what you need...)

From 57 down it seems best (from a gas management point of view as well as deco) to take 2 gases.

So....where is your personal cut off point for one gas? Is it based purely on depth....or perhaps you view it more as a grey area....based as much on deco obligation time wise.

To put it right in the middle....what would you do for 30 minutes at 54 metres...

vid · June 7th, 2006, 09:40 AM

At least two gases always below 45m - travel and deco - irrespective of dive time.

Travel - normally 32%, sometimes 40% for shallower than 50m
Deco - 100%

remember take this with a pinch of salt cos I haven't done a tech class - so I'm yet to discover optimum deco mixes

vid

*JGrogan* · June 7th, 2006, 10:11 AM

Clare,

it is indeed a grey area! Generally speaking, for me 55m for 30 mins is the cutoff. If I'm going deeper or for longer, then it's a 2 deco gas dive. Anything up to that limit is a single deco gas dive as you don't need to do very much deco and a 7L will hold more than enough gas for 2 divers.

This cutoff is based on personal experience of diving in that range and knowing what works best for me.

Best,
John.

Quote: (Originally Posted by Gledders)

Seems to me that there is a bit of an overlap in deco management in the mid 50s.

Down to 51 metres it seems that an average dive (say between 25 and 40 minutes bottom time) is best done with one deco gas (only take what you need...)

From 57 down it seems best (from a gas management point of view as well as deco) to take 2 gases.

So....where is your personal cut off point for one gas? Is it based purely on depth....or perhaps you view it more as a grey area....based as much on deco obligation time wise.

To put it right in the middle....what would you do for 30 minutes at 54 metres...

aleksi · June 7th, 2006, 10:37 AM

Just a quick side question. Not being GUE trained (at least yet), which decogas you do they tell to take as the only one? I have understood GUE stance is to add gasses from top to deeper so oxygen first. Is this right?

Aleksi

*Clare Gledhill* · June 7th, 2006, 11:19 AM

Quote: (Originally Posted by JGrogan)

Clare,
Generally speaking, for me 55m for 30 mins is the cutoff.

Funny coincidence that

Quote: (Originally Posted by JGrogan)

If I'm going deeper or for longer, then it's a 2 deco gas dive. Anything up to that limit is a single deco gas dive as you don't need to do very much deco and a 7L will hold more than enough gas for 2 divers.

This cutoff is based on personal experience of diving in that range and knowing what works best for me.

Have a feeling your 'experience' would have you do a lot less deco than I would plan John

I'd do in the region of 40 minutes between 21 and 6 plus 5 to the surface so a 7 litre of 50 per cent would not be enough for 2 divers.

What I find intriguing is that using a 1:1 ratio from a 45 metre set point on this dive gives the same amount of deco as using a 2:1 ratio with a SP of 66 - despite the fact that 2:1 gives you the benefit of O2 at 6.

Taking a second bottle therefore does not reduce the deco obligation or exposure time, adds to the complexity of the dive but does make team gas management easier. The risk of exposure time doubling due to lost gas is eliminated as well - which would keep dive time under 90 minutes - always a good plan.

I'm doing quite a few dives in this range over the next few weeks. Given that some of them will be in a buddy pair rather than a 3, I'm leaning towards taking two gases even though I have a feeling that several 55 metre wrecks will, based on actual av. depth and tides, prove to be comfortable one gas dives. Experience is indeed a great teacher but, famously, is gained only just after you need it

*Hassan Adly* · June 7th, 2006, 11:45 AM

Hi,

GUE training practices address this question quite simply by what is taught in each course level. There is a subtle level of protection afforded to Tech 1 graduates by not pushing them into O2 decompression earlier than necessary.

Most Tech 1 courses are done using only 50% as deco mix, and the maximum recommended depth for Tech 1 divers is 51m. Assuming the divers stick to those standards, the risk of oxygen toxicity is minimized. Although Tech 1 training is quite thorough, it should be remembered that it is the entry-level GUE Tech rating, and as such some allowance has to be made for diver mistakes. In the worst case of a diver switching to his deco mix at 51m, the PPO2 would be 3 atmospheres, which is of course extremely high. Nevertheless, the odds of surviving a short exposure at such pressure are actually not so bad (I admit I am saying this at the risk of getting slapped around a bit). In the case of O2 on the other hand, the chance of messing up and switching to O2 at 51m and surviving is next to nothing.

In short, O2 is a much less forgiving gas than 50% and should be treated with respect. A team needs to be totally sure that their switching protocols are second-nature, buoyancy needs to be perfect, etc.

I find that an efficient curve on 50% from dives up to 51m makes for a very nice deco. if gas management is an issue one can always take a second stage with 50%.

When we enter the range past 51m where 18/45 or 15/55 becomes necessary as bottom gas, then we are at a level where we should have done the Tech 2 course or equivalent, and with at least 25 staged deco dives under our belt, our stage management skills, switching protocols, knowledge of decompression, and of course buoyancy should be at a much higher level. The decision to add O2 to the deco should be a rational one, with all benefits and risks taken into consideration.

A well-trained, experienced team might find it useful to add O2 to their deco planning even on shallower dives in the 45m range - for example to shorten the shallow deco times in cold water. So to answer your question, in my view there is no "cutoff depth" where I add O2 to the deco, rather I consider the decision to be based on training and necessity.

*Clare Gledhill* · June 7th, 2006, 12:15 PM

It's an interesting response Hassan - although more on the reasons behind certification limits within GUE than what makes efficent deco.

The PPO2 of deco gas at depth is not an argument that I have heard used as a restriction on Tech 1 dives - indeed given that we are certified to use O2 for deco on 30/30 dives one could take your argument that depth is limited by gases carried to suggest that GUE would be content to see a 'mistaken switch' to O2 at 36 metres....but I know you are not suggesting that

Taking two deco gases however is, without doubt, more complex and whilst we should have great discipline switching on a Tech 1 single deco gas dive, taking two gases requires even more stringent adherence to proceedures. Switching to O2 at 21 metres is not forgiving, as some divers on this board have sadly experienced and thus, as I said, the complexity of taking two bottles should be considered when weighing up whether or not to do so.

*Hassan Adly* · June 7th, 2006, 04:06 PM

Hello,

Keep in mind I am not saying that GUE tells Tech 1 divers never to use O2 - in fact in my Tech 1 course we were told in theory how we could shorten ratio deco profiles if we used O2 instead of 50% on the 6m stop. In practice dives, however, we only used 50%. The standards only require the use of 50% for deco during the Tech 1 course.

davy · June 7th, 2006, 04:22 PM

For what it's worth,

I only use AL40 and AL80 bottles for deco.
And the 80's generally only in cave unless for some logistic issue in OW.

Since I plan my single AL40 as a 30min deco bottle I add another (with 100%) if decotime gets bigger than 30mins.
2 AL40 are just as much hassle as a single AL80, so IMHO it's better to get some more redundancy.
Maybe that's because I usually dive cold water and don't want to plan on decoing out on back gas if decotime gets bigger than 30mins.
It's my rule of thumb and not cast in stone... for example in warm water I might be happy doing longer times on a single decotank.

So to answer the original question, no I do not have a specific depth where I take 1 or 2 decobottles, however... by their nature, beyond 54m is generally a 2 bottle dive if you want a 'decent' bottom time.

limeyx · June 7th, 2006, 05:35 PM

Quote: (Originally Posted by Hassan Adly)

Hello,

Keep in mind I am not saying that GUE tells Tech 1 divers never to use O2 - in fact in my Tech 1 course we were told in theory how we could shorten ratio deco profiles if we used O2 instead of 50% on the 6m stop. In practice dives, however, we only used 50%. The standards only require the use of 50% for deco during the Tech 1 course.

The way it was explained to us was essentially "1 slung bottle" so in that case you'd take either 50% or 100%, not both. That way the chances of you going for the 50% and getting the 100% are at least minimized.

Of course, some people who only have T1 start taking bottom stages and saving the gas in their doubles for bailout etc. to avoid bringing lots of sets of doubles with them, but that's only after a level of comfort has been acheived, and again doesn't seem as dangerous as having the 50% and 100%

There was nothing in our T1 class that said we *couldn't* take 100% althogh we didn't really go into the details of it, and used 50% for all dives.
I guess the 100% makes more sense on shallower longer dives (say 60 mins at 100 feet) where you are more dominated by the slower tissues?

June 7th, 2006, 01:21 AM	#1 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	What would you do? Seems to me that there is a bit of an overlap in deco management in the mid 50s. Down to 51 metres it seems that an average dive (say between 25 and 40 minutes bottom time) is best done with one deco gas (only take what you need...) From 57 down it seems best (from a gas management point of view as well as deco) to take 2 gases. So....where is your personal cut off point for one gas? Is it based purely on depth....or perhaps you view it more as a grey area....based as much on deco obligation time wise. To put it right in the middle....what would you do for 30 minutes at 54 metres... __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk Last edited by Clare Gledhill; June 7th, 2006 at 01:47 AM.

June 7th, 2006, 11:19 AM	#5 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	Quote: (Originally Posted by JGrogan) Clare, Generally speaking, for me 55m for 30 mins is the cutoff. Funny coincidence that Quote: (Originally Posted by JGrogan) If I'm going deeper or for longer, then it's a 2 deco gas dive. Anything up to that limit is a single deco gas dive as you don't need to do very much deco and a 7L will hold more than enough gas for 2 divers. This cutoff is based on personal experience of diving in that range and knowing what works best for me. Have a feeling your 'experience' would have you do a lot less deco than I would plan John I'd do in the region of 40 minutes between 21 and 6 plus 5 to the surface so a 7 litre of 50 per cent would not be enough for 2 divers. What I find intriguing is that using a 1:1 ratio from a 45 metre set point on this dive gives the same amount of deco as using a 2:1 ratio with a SP of 66 - despite the fact that 2:1 gives you the benefit of O2 at 6. Taking a second bottle therefore does not reduce the deco obligation or exposure time, adds to the complexity of the dive but does make team gas management easier. The risk of exposure time doubling due to lost gas is eliminated as well - which would keep dive time under 90 minutes - always a good plan. I'm doing quite a few dives in this range over the next few weeks. Given that some of them will be in a buddy pair rather than a 3, I'm leaning towards taking two gases even though I have a feeling that several 55 metre wrecks will, based on actual av. depth and tides, prove to be comfortable one gas dives. Experience is indeed a great teacher but, famously, is gained only just after you need it __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk

June 7th, 2006, 11:45 AM	#6 (permalink)
Hassan Adly(Offline) GUE Instructor Join Date: Feb 2006 Location: Red Sea Posts: 286	Hi, GUE training practices address this question quite simply by what is taught in each course level. There is a subtle level of protection afforded to Tech 1 graduates by not pushing them into O2 decompression earlier than necessary. Most Tech 1 courses are done using only 50% as deco mix, and the maximum recommended depth for Tech 1 divers is 51m. Assuming the divers stick to those standards, the risk of oxygen toxicity is minimized. Although Tech 1 training is quite thorough, it should be remembered that it is the entry-level GUE Tech rating, and as such some allowance has to be made for diver mistakes. In the worst case of a diver switching to his deco mix at 51m, the PPO2 would be 3 atmospheres, which is of course extremely high. Nevertheless, the odds of surviving a short exposure at such pressure are actually not so bad (I admit I am saying this at the risk of getting slapped around a bit). In the case of O2 on the other hand, the chance of messing up and switching to O2 at 51m and surviving is next to nothing. In short, O2 is a much less forgiving gas than 50% and should be treated with respect. A team needs to be totally sure that their switching protocols are second-nature, buoyancy needs to be perfect, etc. I find that an efficient curve on 50% from dives up to 51m makes for a very nice deco. if gas management is an issue one can always take a second stage with 50%. When we enter the range past 51m where 18/45 or 15/55 becomes necessary as bottom gas, then we are at a level where we should have done the Tech 2 course or equivalent, and with at least 25 staged deco dives under our belt, our stage management skills, switching protocols, knowledge of decompression, and of course buoyancy should be at a much higher level. The decision to add O2 to the deco should be a rational one, with all benefits and risks taken into consideration. A well-trained, experienced team might find it useful to add O2 to their deco planning even on shallower dives in the 45m range - for example to shorten the shallow deco times in cold water. So to answer your question, in my view there is no "cutoff depth" where I add O2 to the deco, rather I consider the decision to be based on training and necessity. __________________ Hassan Adly Red Sea Discovery "Today I will finally see the sea again, which will smell of salt, wind, sand - and the cold of winter. Finally I will not only travel on it but dive in it, again I will become water, a bird - and I will remember the feeling of gliding above the abyss" Elena Sundukova, tragically lost at sea, January 2007

June 7th, 2006, 12:15 PM	#7 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	It's an interesting response Hassan - although more on the reasons behind certification limits within GUE than what makes efficent deco. The PPO2 of deco gas at depth is not an argument that I have heard used as a restriction on Tech 1 dives - indeed given that we are certified to use O2 for deco on 30/30 dives one could take your argument that depth is limited by gases carried to suggest that GUE would be content to see a 'mistaken switch' to O2 at 36 metres....but I know you are not suggesting that Taking two deco gases however is, without doubt, more complex and whilst we should have great discipline switching on a Tech 1 single deco gas dive, taking two gases requires even more stringent adherence to proceedures. Switching to O2 at 21 metres is not forgiving, as some divers on this board have sadly experienced and thus, as I said, the complexity of taking two bottles should be considered when weighing up whether or not to do so. __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk

June 7th, 2006, 04:06 PM	#8 (permalink)
Hassan Adly(Offline) GUE Instructor Join Date: Feb 2006 Location: Red Sea Posts: 286	Hello, Keep in mind I am not saying that GUE tells Tech 1 divers never to use O2 - in fact in my Tech 1 course we were told in theory how we could shorten ratio deco profiles if we used O2 instead of 50% on the 6m stop. In practice dives, however, we only used 50%. The standards only require the use of 50% for deco during the Tech 1 course. __________________ Hassan Adly Red Sea Discovery "Today I will finally see the sea again, which will smell of salt, wind, sand - and the cold of winter. Finally I will not only travel on it but dive in it, again I will become water, a bird - and I will remember the feeling of gliding above the abyss" Elena Sundukova, tragically lost at sea, January 2007

June 7th, 2006, 09:40 AM	#2 (permalink)
vid(Offline) New Member Join Date: Nov 2005 Location: london/surrey border, UK Posts: 353	At least two gases always below 45m - travel and deco - irrespective of dive time. Travel - normally 32%, sometimes 40% for shallower than 50m Deco - 100% remember take this with a pinch of salt cos I haven't done a tech class - so I'm yet to discover optimum deco mixes vid

June 7th, 2006, 10:11 AM	#3 (permalink)
JGrogan(Offline) GUE Join Date: May 2006 Location: London Posts: 439	Clare, it is indeed a grey area! Generally speaking, for me 55m for 30 mins is the cutoff. If I'm going deeper or for longer, then it's a 2 deco gas dive. Anything up to that limit is a single deco gas dive as you don't need to do very much deco and a 7L will hold more than enough gas for 2 divers. This cutoff is based on personal experience of diving in that range and knowing what works best for me. Best, John. Quote: (Originally Posted by Gledders) Seems to me that there is a bit of an overlap in deco management in the mid 50s. Down to 51 metres it seems that an average dive (say between 25 and 40 minutes bottom time) is best done with one deco gas (only take what you need...) From 57 down it seems best (from a gas management point of view as well as deco) to take 2 gases. So....where is your personal cut off point for one gas? Is it based purely on depth....or perhaps you view it more as a grey area....based as much on deco obligation time wise. To put it right in the middle....what would you do for 30 minutes at 54 metres...

June 7th, 2006, 10:37 AM	#4 (permalink)
aleksi (Online) New Member Join Date: Dec 2005 Location: Finland Posts: 88	Just a quick side question. Not being GUE trained (at least yet), which decogas you do they tell to take as the only one? I have understood GUE stance is to add gasses from top to deeper so oxygen first. Is this right? Aleksi

June 7th, 2006, 04:22 PM	#9 (permalink)
davy(Offline) DIveR Join Date: Nov 2005 Location: Belgium Posts: 274	For what it's worth, I only use AL40 and AL80 bottles for deco. And the 80's generally only in cave unless for some logistic issue in OW. Since I plan my single AL40 as a 30min deco bottle I add another (with 100%) if decotime gets bigger than 30mins. 2 AL40 are just as much hassle as a single AL80, so IMHO it's better to get some more redundancy. Maybe that's because I usually dive cold water and don't want to plan on decoing out on back gas if decotime gets bigger than 30mins. It's my rule of thumb and not cast in stone... for example in warm water I might be happy doing longer times on a single decotank. So to answer the original question, no I do not have a specific depth where I take 1 or 2 decobottles, however... by their nature, beyond 54m is generally a 2 bottle dive if you want a 'decent' bottom time.

June 7th, 2006, 05:35 PM	#10 (permalink)
limeyx(Offline) New Member Join Date: Nov 2005 Location: Los Angeles, CA Posts: 707	Quote: (Originally Posted by Hassan Adly) Hello, Keep in mind I am not saying that GUE tells Tech 1 divers never to use O2 - in fact in my Tech 1 course we were told in theory how we could shorten ratio deco profiles if we used O2 instead of 50% on the 6m stop. In practice dives, however, we only used 50%. The standards only require the use of 50% for deco during the Tech 1 course. The way it was explained to us was essentially "1 slung bottle" so in that case you'd take either 50% or 100%, not both. That way the chances of you going for the 50% and getting the 100% are at least minimized. Of course, some people who only have T1 start taking bottom stages and saving the gas in their doubles for bailout etc. to avoid bringing lots of sets of doubles with them, but that's only after a level of comfort has been acheived, and again doesn't seem as dangerous as having the 50% and 100% There was nothing in our T1 class that said we couldn't take 100% althogh we didn't really go into the details of it, and used 50% for all dives. I guess the 100% makes more sense on shallower longer dives (say 60 mins at 100 feet) where you are more dominated by the slower tissues?