Pony bottle ascent schedule?

[RJP]

So, do I have a lovely case of DCS, or shall I crack open a beer and have a cigar?

In your assumptions you said you were within NDL. You can ascend directly - albeit slowly - directly to the surface.

Do you have enough gas in your "no specific size mentioned" pony bottle to do the schedule you proposed?

 

[GrumpyOldGuy]

In your assumptions you said you were within NDL. You can ascend directly - albeit slowly - directly to the surface.

Do you have enough gas in your "no specific size mentioned" pony bottle to do the schedule you proposed?

The OP specifically stated he has a 30 cu ft full of air.

 

[RJP]

The OP specifically stated he has a 30 cu ft full of air.

Oops - thanks

 

[scubadada]

I'd be interested to hear peoples thoughts on a hypothetical situation I was considering on the way to work this morning.

Imagine I'm cruising along at the end of my 130' dive on 32%. I'm within my NDL and dive plan as I reach the ascent line. Just then, Neptune appears, decides he hates me, and puts his trident through my back gas. Luckily, I have my handy 30 cu ft pony full of air, so I start my ascent using that.

The question is, what is my ascent schedule? I was planning on using nitrox to ascend, but now I'm on air at 130 ft.. My computer doesn't know what I'm breathing (nor even if I'm breathing). So I'm breathing more nitrogen and less oxygen than I had planned on as I ascend.

My instinct, based on no information or knowledge, would be something like this:

130 -> 70 @ 30 ft/min
70 - 1 min stop
70 -> 50 @ 30 ft / min
50 - 1 min stop
40 - 1 min stop
30 - 1 min stop
20 - 5 min stop or breathe it down to about 300 psi, whichever comes first.
Done diving for the day

So, do I have a lovely case of DCS, or shall I crack open a beer and have a cigar?

thanks,
dave.

Hey Dave,

This is not complicated. Dive was within no decompression limits using 32% nitrox below usual MOD without toxicity and then run out of back gas. Make normal ascent to surface using the more than ample 30 cu ft pony. For me that would be a normal rate ascent to 15 feet and then a 3+ minute safety stop prior to surfacing. Anything more conservative would be to personal taste and would not likely hurt. I would not limit my diving for the rest of the day.

I would crack the beer at the end of the day but would bag the cigar, personal taste again.

Good diving, Craig

 

[RJP]

This is not complicated...

...anything more conservative would be to personal taste and would not likely hurt.

I would not limit my diving for the rest of the day.

Really?

Inexplicably going OOG at 130' wouldn't cause you to want to take some time to stop and rethink... SOMETHING... before diving again?

:cool2:

 

[Dr Wu]

You went OOA with a mix most would consider a bit rich for the planned depth of your dive. Now you want a pony to save your ass and have no idea if you will survive.

Sounds about right.

 

[gcbryan]

Really?

Inexplicably going OOG at 130' wouldn't cause you to want to take some time to stop and rethink... SOMETHING... before diving again?

:cool2:

Yes, Really. Why stop diving just because "Neptune disrupted the first dive"?

Sure, if you ran out of gas because of poor planning that's one thing but if a burst disc blew or a hose erupted if you have other gear why end the dive for the day?

 

[DaleC]

Putting aside the 32% faux pas, if I went totally OOA on back gas at 130' within the NDL and had to bail to a pony I would ascend directly to my SS and due an extended stop there rather than at depth.

My reasoning is that by using a pony you/I have demonstrated that our primary reliance for a second air source is the pony, not a buddy. Lingering at depth with that as my (now) only air source poses more risk (to me) than skipping the deep stops (which may or may not provide a reduced DCS risk).

At those depths there is a difference between 21 and 28% though. Recently we did a wreck dive to 100' with my buddy on 32% and myself on 25% (long story). This resulted in him having an approx. 7 minute deco obligation and I a 19 minute deco obligation for the same depth/dive/duration.

 

[RJP]

Yes, Really. Why stop diving just because "Neptune disrupted the first dive"?

Sure, if you ran out of gas because of poor planning that's one thing but if a burst disc blew or a hose erupted if you have other gear why end the dive for the day?

Well then, that's not "inexplicable" is it?

 

[Dr Wu]

Well then, that's not "inexplicable" is it?

At least it is within the "not my fault" range.


That has to count for something.