Planned deco on a recreational dive?

[KenGordon]

I think you lot are being overly simplistic. Depth is one factor but the rest of the conditions are important too. A 45m dive in good conditions can be safer than a 40m dive in less ideal conditions that the OP might consider himself qualified for.

All the risks need to be considered.

 

[stevensamler]

45m dive, single tank, air, a group of divers, this is nut. I am surprised the so called tec trained diver agree to this.

T1 profile.

 

[Beau640]

Some of the replies on here are absolutely bonkers. People should not be advocating that it is okay for just a "little deco" dive for the average, not decompression trained recreational diver. There is no such thing as "lite deco." 10 minutes of deco is NOT SAFE if you are not trained for decompression. Neither is 5 minutes, etc. Going into decompression essentially creates an imaginary hard overhead for the diver. Would it be okay to recommend the average recreational diver without cave training do just a "lite cave" dive. Only 10 minutes in an overhead. No big deal?

So much can go wrong doing decompression even with a trained diver, not to mention an untrained diver who has no clue what they do not know. It's not about decompressing on air or not. Are you sure you have enough air for your decompression? What if you go deeper or stay longer than planned? Do you have enough air for that? What if you lose gas or free flow? Does your buddy have enough air for you to deco on? Are you going to be able to maintain your buoyancy during deco if something happens like loss of gas or free flow? What about when you lose your mask and can't read your gauge to conduct deco properly? Do you have all the redundant gear you need? You're now in a hard overhead that if you ascend above you are seriously risking your life.

There's no such thing as "lite deco" just like there's no such thing as "lite cave" diving. If you're untrained for it, stay away from it. If you're interested in it, go do the training. Telling people it's "probably okay" to do "just 10 minutes" of deco is irresponsible and is going to get someone hurt.

 

[eelnoraa]

I think you lot are being overly simplistic. Depth is one factor but the rest of the conditions are important too. A 45m dive in good conditions can be safer than a 40m dive in less ideal conditions that the OP might consider himself qualified for.

All the risks need to be considered.

The issue is not just depth of 45m/150', but also single tank and air. It is just too aggressive of a combination IMO.

Sure a 45m in an good condition maybe safer than a 40m in a bad condition. The real issue with this statement is "good" condition, which you can never tell on surface prior to the dive. And do you really want to rely on the "good" dive condtion to bring you back safely?

BTW, I really don't consider a 40m dive with single tank and air to be safe to begin with. Maybe i am just too chicken to die

 

[KenGordon]

Some of the replies on here are absolutely bonkers. People should not be advocating that it is okay for just a "little deco" dive for the average, not decompression trained recreational diver. There is no such thing as "lite deco." 10 minutes of deco is NOT SAFE if you are not trained for decompression. Neither is 5 minutes, etc. Going into decompression essentially creates an imaginary hard overhead for the diver. Would it be okay to recommend the average recreational diver without cave training do just a "lite cave" dive. Only 10 minutes in an overhead. No big deal?

So much can go wrong doing decompression even with a trained diver, not to mention an untrained diver who has no clue what they do not know. It's not about decompressing on air or not. Are you sure you have enough air for your decompression? What if you go deeper or stay longer than planned? Do you have enough air for that? What if you lose gas or free flow? Does your buddy have enough air for you to deco on? Are you going to be able to maintain your buoyancy during deco if something happens like loss of gas or free flow? What about when you lose your mask and can't read your gauge to conduct deco properly? Do you have all the redundant gear you need? You're now in a hard overhead that if you ascend above you are seriously risking your life.

There's no such thing as "lite deco" just like there's no such thing as "lite cave" diving. If you're untrained for it, stay away from it. If you're interested in it, go do the training. Telling people it's "probably okay" to do "just 10 minutes" of deco is irresponsible and is going to get someone hurt.

Clearly this diver ought to get further training if he wants to dives like these. Finding out you can't wait out the deco when it really counts rather on a practice dive contrived to be safe is a poor idea. However I think you underplay the dangers of caves if you equate diving in a cave with deco diving of this sort.

There are points of progression between no stop diving and full up twinset and deco stage which are largely ignored on SB. Comments above include doing AN/DP or it being a T1 dive are typical. Everyone I dive with is taught back gas deco on a single and most that move on to accelerated deco will have been doing back gas deco on a twinset for a good while first. They will do the accelerated deco in order to get much longer bottom times at these depths than decoing on back gas, not because they want to haul round an extra cylinder or risk oxtox.

Planning is the key skill. Experience is important. Having done a few dozen 15 to 25m second dives that require stops before attempting aggressive profiles is reassuring.

 

[NAM001]

Some one or more keeps referencing 12 ltr tanks. Earlier it was 15 ltr tanks. sounds like lp95's and with that,,,, probably over filling to maybe 3500 to get more gas they may as well be diving lp121's with an overfill if they want a lot of gas. Either way it would be too aggressive for me. I prefer O2 for deco rather than air, it make more sense and it is one more thing that says they are pushing the envelope too much. the odds of a problem really increases given the numbers in the group and all the common sense limits being pushed.

 

[Edward3c]

Some one or more keeps referencing 12 ltr tanks. Earlier it was 15 ltr tanks. sounds like lp95's and with that,,,, probably over filling to maybe 3500 to get more gas they may as well be diving lp121's with an overfill if they want a lot of gas. Either way it would be too aggressive for me. I prefer O2 for deco rather than air, it make more sense and it is one more thing that says they are pushing the envelope too much. the odds of a problem really increases given the numbers in the group and all the common sense limits being pushed.

It isn't the physical size of the cylinder that matters, it's the working pressure it's rated to. I have 12Lt tanks rated to:
* 207bar = 2484Lt
* 232bar = 2784Lt
* 300bar = 3600Lt

It's not worth the risk of one of these going off, so no I do not overfill them. Just use the right size cylinder for the dive.

 

[KenGordon]

Some one or more keeps referencing 12 ltr tanks. Earlier it was 15 ltr tanks. sounds like lp95's and with that,,,, probably over filling to maybe 3500 to get more gas they may as well be diving lp121's with an overfill if they want a lot of gas. Either way it would be too aggressive for me. I prefer O2 for deco rather than air, it make more sense and it is one more thing that says they are pushing the envelope too much. the odds of a problem really increases given the numbers in the group and all the common sense limits being pushed.

A steel 15l found in Europe is usually 232bar, rarely 300bar. So he probably has 3500l full and about 2250l available for the dive. With realistic deco and breathing rates that is enough for a 15 minute bottom time so long as you choose an appropriate mix (a bit less bottom time for air). A risk is that all the gas is in one cylinder. How much do you trust your buddy?

I think o2 deco is counter productive on a dive like this. The is not much deco to do so doing it faster is not very advantageous but having o2 is a risk. Carrying more gas and doing a longer bottom time is when the rich deco gas helps. Then you are into proper AN/DP land and need all the skills as getting it wrong will happen with three times the deco owing.

 

[NAM001]

A steel 15l found in Europe is usually 232bar, rarely 300bar. So he probably has 3500l full and about 2250l available for the dive. With realistic deco and breathing rates that is enough for a 15 minute bottom time so long as you choose an appropriate mix (a bit less bottom time for air). A risk is that all the gas is in one cylinder. How much do you trust your buddy?

I think o2 deco is counter productive on a dive like this. The is not much deco to do so doing it faster is not very advantageous but having o2 is a risk. Carrying more gas and doing a longer bottom time is when the rich deco gas helps. Then you are into proper AN/DP land and need all the skills as getting it wrong will happen with three times the deco owing.

I am looking at american fills the lp tanks like the lp95 is what 185 bar 2640 psi if ou have the + otherwise its 2400. a 15 minute dive at 150 ft is about 45 cuft min used at depth. I would never ttempt it on an al80

 

[NAM001]

It isn't the physical size of the cylinder that matters, it's the working pressure it's rated to. I have 12Lt tanks rated to:
* 207bar = 2484Lt
* 232bar = 2784Lt
* 300bar = 3600Lt

It's not worth the risk of one of these going off, so no I do not overfill them. Just use the right size cylinder for the dive.

Ed I agree. with an lp95 you get shy of 110 cuft at 200 bar and what 125 cuft at about 3500. you are going to use min 45 cuft at 150' for the 15 minutes. at 3500 psi its 1/3 of your tank. closer to half as the over fill goes away. .will probably use 25 cuft going down adn another 25 coming up. or 20 down and 30 up with deco. Thats all your air if filled to 2640 with a sac of .5. You either have to over fill a 15 ltr or goto a 20 ltr tank and start with a legit 125 cuft. There is not a lot of forgiveness going down with 90 cuft.

I agree that overseas fills makes this a much safer dive . as least as gas supply goes. I visualize a dive like that as a doubles dive. probably twinset of lp85's. or my lp121 at 3k.