Deco gas planning and risk mitigation.

[elan]

Sorry Elan, but this isn't completely accurate. If you have a "total loss" of back gas at say 150 fsw, and your immediate solution to the problem was to go tour EAN 50 bottle, I give you maybe 2 minutes to live... tops.
The key here is to think through the potential problems and evaluate your resources. Employ available resources as necessary. I completely agree that you need to be self sufficient. But that doesn't mean you ignore your buddy as a resource.
At this level of diving you really cannot expect to be 100% self reliant in every emergency situation.

K

I think you got me wrong. stage is a stage with the same mix as the back gas. Deco is deco. So 2 tanks in total on the side. So if the doubles are completely f..cked up and I have a stage I can ascend on the stage and do my deco on the deco.

 

[elan]

BTW, stuff you're likely to need most often in the right pocket (wetnotes, smb, spool), mask in the left pocket. Outside of training, hopefully it's the item you need the least.

K

You see the problem with the mask in the left is I cannot deploy it quickly as I have the light in my hand and the bottles are on my way. After doing some re-evaluation I now have the smb + spool in the left. mask , safety spool + notes in the right. I can deploy it much quicker now, do signaling at the same time. SMB, I do not care if it takes me 10 seconds to take it out or 30

 

[Captain12Pk]

You see the problem with the mask in the left is I cannot deploy it quickly as I have the light in my hand and the bottles are on my way. After doing some re-evaluation I now have the smb + spool in the left. mask , safety spool + notes in the right. I can deploy it much quicker now, do signaling at the same time. SMB, I do not care if it takes me 10 seconds to take it out or 30

You're right, it's not as quick to get to on the left. That's why it's on the left. A lost mask is not in itself an emergency. I can complete the dive if necessary without a mask. So as long as there are no other impending emergencies, it doesn't matter to me if it takes me 1 minute or even two minutes to deploy my spare mask and close the pocket.

 

[Captain12Pk]

I think you got me wrong. stage is a stage with the same mix as the back gas. Deco is deco. So 2 tanks in total on the side. So if the doubles are completely f..cked up and I have a stage I can ascend on the stage and do my deco on the deco.

So you're diving doubles with one stage and one deco bottle? So assumably a minimum of 240cf of bottom gas and probably 40cf of deco gas?

Is the stage being used in place of the doubles (maybe an additional dive where you couldn't get a fill)or in addition to the doubles?

 

[Captain12Pk]

I think you got me wrong. stage is a stage with the same mix as the back gas. Deco is deco. So 2 tanks in total on the side. So if the doubles are completely f..cked up and I have a stage I can ascend on the stage and do my deco on the deco.

In re-reading this I think I see what you're getting at. Please correct me if I'm wrong. You're carrying the stage as redundancy for your doubles. Thus eliminating the need to share your buddy's back gas. The self reliance issue you mentioned earlier. Yeah?

 

[elan]

In re-reading this I think I see what you're getting at. Please correct me if I'm wrong. You're carrying the stage as redundancy for your doubles. Thus eliminating the need to share your buddy's back gas. The self reliance issue you mentioned earlier. Yeah?

It's just one of the options I have in mind. I"m still going through different possible scenarios. If say I have enough back gas to carry out a dive and do the deco on the back gas (in case I lose the deco bottle) + I have enough extra for emergency then it will not be necessary (but may be nice to have) to carry the stage. Or to carry it as an additional source of back gas to be less relied on the buddy.

I'm going to talk to the instructor about the in details, I just want to have many options in mind, think them though before I talk to him.


Answering your previous post.
We do dive stages while doing rec dives and use it as the main source and the back gas as a backup and when the stage is done. 1 Al 80 is usually good enough for good 1 rec dive 60-70 mins long at 30-40 ft and shorter deep dive. I still have to think how this applies to the deco. Modulating the valve in case of free-flow is easier to do on the stage so while doing this on a deco dive it would probably be better to leave some gas (say 50% or 2/3) for the end of the dive.

While I learned this from my buddy I later found this approach was mentioned in Quest magazine when the guys were treating the stages as the main transport supply while the back gas was used as the backup.

 

[elan]

You're right, it's not as quick to get to on the left. That's why it's on the left. A lost mask is not in itself an emergency. I can complete the dive if necessary without a mask. So as long as there are no other impending emergencies, it doesn't matter to me if it takes me 1 minute or even two minutes to deploy my spare mask and close the pocket.

I tried to do it. While in warm water I can stay long w/o mask and can even surface if I can see the reference in cold water it's painful. I cannot surface bu feel yet. Just on the scale of priorities for me the mask stands higher than SMB

 

[Blackwood]

Some of the tec instructors will weigh in soon enough, but I was always taught you carry a 50% reserve on your bottom gas, and a 50% reserve on your deco gases.

I have never heard of gas planning that requires you to carry enough back gas to accomplish your deco with back gas. And to do so would be almost impossible to do if you were using a hypoxic bottom mix.

If you are on a profile which requires hypoxic bottom mix, you probably have multiple deco gases. If you are soloing, your back gas should cover the loss of your first deco gas, your first deco gas should cover the loss of your second, and so on.

 

[Garth]

I would just like to comment that the word "mitigation" might not be used in basic scuba discussions.

Just a thought.

Carry on...

 

[adm3745]

I'm just playing here with deco profiles and it would be interesting how would you plan this case.

Say you have a deco profile for which you have enough back gas + some safety margin amount. + you have one deco bottle with you which covers the deco. While the amount of back gas is enough for the bottom it is not sufficient to complete the deco in case you lose your deco bottle for any kind of reasons.

What would you prefer to do.
- reduce the profile so you can complete the deco on the back gas in case of deco lose
- sling a stage with the back gas
- count on the team to cover you

other


Thanks

You have to plan for deco gas loss and do a back gas deco. I'd prefer to reduce the profile. If you are only carrying one deco tank and saving 50% of the deco amount, then your really not doing alot of deco and the backgas hit shouldn't effect the profile badly.