50 feet for 3.5 hours

[jbd]

What is the decompression schedule for this dive? The dive is a working dive on the bottom and the gas is surface supplied air. No other deco gases are available. There is a second question to go with this scenario but I would like to see the decompression schedule before asking it.

Disclaimer---I am NOT the person that did this dive. I just know that it was done and curious about it.

 

[Charlie99]

This is the sort of thing where a deco program is good to play around with. I played around a bit, to see how good my guesses were.

With no conservatism, GAP say deco on air is 32 min at 10' or 39 minutes at 15'.

Using gradient factors of 20%/85% ends up with 1@30', 5@20' and 68@15'. 74 minutes total. For last stop 10', and still 20/85 its 1@30', 17@20, 45@10'. 63 minutes total.

For a shallow dive of this length, you probably would want to make the stops at 5' increments. That changes the 20/85 profile to 3@25', 8@20, 11@15, 40@10'. 62 minutes total.

Even using a single tank of commonly available EAN36 will decrease these schedules dramatically.

24 minutes at 10' with no conservatism added.

WIth 20/85 gradient factor, 2@25', 6@20', 7@15', 29@10'. 44 minutes total.

Of course, if you did the whole dive on EAN36, the only stops, even with GF 20/85 is 1 minute at 15', 1 minute at 10'. You would still be withing NOAA CNS limits, but over 50% of the clock.

Personally, I'd do the dive on something around EAN32. CNS clock around 50%, a bit beyond PADI NDLs, but within ZHL16 NDL. With 20/85 GF, just 9 minutes of stops on EAN32.

If it weren't possible to do surface supplied EAN, then I'd just grab a bottle of EAN50 for the deco.

 

[Charlie99]

http://diver.net/navy_tables/Navy_air_tables.pdf

For 50' depth, 220 minutes, the Navy air table is 40 minutes stop at 10'. To my surprise, this is more conservative than GAP running ZHL16B.

 

[100days-a-year]

VPM,nominal conservatism,air had a 24min hang @10'

 

[blacknet]

Hello,

Using 100% the stops become 1/5/13 mins at 30/20/10. with no conservatism it becomes 12 mins at 10'

Same dive done on 36% bottom mix and 100% o2 becomes 1/1 at 15/10 feet.

This is clearly a good example of a nitrox dive.

Ed

 

[vodolaz]

blacknet once bubbled...
Hello,

Using 100% the stops become 1/5/13 mins at 30/20/10.

O2 at 30'? Which agency advocates that?

 

[blacknet]

vodolaz once bubbled...
O2 at 30'? Which agency advocates that?

I never said 100% o2 at 30 feet. I said if you use 100% o2 the stops are as listed, using air and o2.

Ed

 

[vodolaz]

Sort of a "deep stop"?

 

[jbd]

responses. I noticed that most of you used little or no conservatism. I think V-planner had set on 2 for conservatism had longer stops.

Second question for this scenario--The diver made an ascent directly to the surface in probably a little less than a minute. The diver made no mention of any symptoms of DCS at all. Any explanation for this?

 

[blacknet]

jbd once bubbled...
responses. I noticed that most of you used little or no conservatism. I think V-planner had set on 2 for conservatism had longer stops.

Second question for this scenario--The diver made an ascent directly to the surface in probably a little less than a minute. The diver made no mention of any symptoms of DCS at all. Any explanation for this?

Hello,

A few things comes to mind.

A) the dive was not on air but nitrox.
B) the diver falsely reported symptoms.
C) surface decompression was used?

Is there any more details of this dive you care to share with us?

Ed