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Old 05-08-2004, 22:07   #1
Sdiver
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It's time for some SCUBA questions

Okay, I know that alot of the SF guys here aren't scuba qual'ed, but I do know that there are some here that are certified and seeing that Scuba is an SF fieldcraft, I thought I'd post this here.

Okay, here goes....

----How is it possible to do two seperate recreational dives, where your 2nd dive is your deeper dive and not run the risk of DCS (Decomperssion Sickness)?

***For those of you that aren't certified, It's ALWAYS taught that you do your DEEPER dive first, then move in progressivly shallower.***

Here's what you have to work with.....

1st Dive is at 80 feet
2nd dive is at 70 feet

***Remember, your 2nd dive is the deeper one.***

Both dives are for 30 minutes.
You have a 1 hour and 30 minute (1:30) serface interval.
You are diving on AIR only. No NITROX or mixed gases.
No computers can be used.
No protable chambers.

You must SHOW YOUR WORK !!!! I want to see dive profiles.
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Old 05-08-2004, 23:32   #2
Roguish Lawyer
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Re: It's time for some SCUBA questions

Quote:
Originally posted by Sdiver
Here's what you have to work with.....

1st Dive is at 80 feet
2nd dive is at 70 feet

***Remember, your 2nd dive is the deeper one.***

Both dives are for 30 minutes.
You have a 1 hour and 30 minute (1:30) serface interval.
You are diving on AIR only. No NITROX or mixed gases.
No computers can be used.
No protable chambers.

You must SHOW YOUR WORK !!!! I want to see dive profiles.
It's been a while, but I'll try.

I assume you mean that the 1st dive is at 70 and the second is at 80; otherwise the second would not be deeper!

Pressure interval after first dive (70 feet, 30 minutes) is O.

1:30 surface interval takes you down to pressure group C.

Residual nitrogen time after surface interval at 80 feet is 10 minutes, and total permitted time for next dive is 20 minutes. So, we're proposing to dive for 20 minutes longer than we should (i.e. 30 Dive 2 + 10 RNT).

I take it that we can't increase the surface interval, right?

I don't recall how to address this problem. Decompression stops? Seems to me this is not a recreational dive!

I am the acorn that becomes the oak. Teach me, oh divemaster.

Last edited by Roguish Lawyer; 05-08-2004 at 23:51.
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Old 05-09-2004, 00:25   #3
Sdiver
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Re: Re: It's time for some SCUBA questions

Quote:
Originally posted by Roguish Lawyer
It's been a while, but I'll try.

I assume you mean that the 1st dive is at 70 and the second is at 80; otherwise the second would not be deeper!

I take it that we can't increase the surface interval, right?

Seems to me this is not a recreational dive!

First...NEVER ASSUME !!!!Assumtion is the mother of all F**k ups.


Again Dive Profile is as follows.....


1st dive .... 80 feet

1:30 surface interval

2nd dive .... 70 feet


2nd dive is the deeper dive.



This is/can be a recreational dive.
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Old 05-09-2004, 00:35   #4
Roguish Lawyer
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Re: Re: Re: It's time for some SCUBA questions

Quote:
Originally posted by Sdiver
First...NEVER ASSUME !!!!Assumtion is the mother of all F**k ups.


Again Dive Profile is as follows.....


1st dive .... 80 feet

1:30 surface interval

2nd dive .... 70 feet


2nd dive is the deeper dive.
70 feet is deeper than 80 feet? What am I missing here?
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Old 05-09-2004, 00:41   #5
Sdiver
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Re: Re: Re: Re: It's time for some SCUBA questions

Quote:
Originally posted by Roguish Lawyer
70 feet is deeper than 80 feet? What am I missing here?
I don't know....You Tell Me !!

Work the problem.
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Old 05-09-2004, 00:58   #6
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Re: Re: Re: Re: Re: It's time for some SCUBA questions

Quote:
Originally posted by Sdiver
I don't know....You Tell Me !!

Work the problem.
I think this is above my pay grade. Matchanu!
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Old 05-09-2004, 03:02   #7
Solid
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What are the ATMs for each dive?

Thank you,

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Old 05-09-2004, 08:19   #8
Desert Fox
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Simple: dive tables

30 min for the first dive.Secure round-up in dive table is 35min with a decompression schedule of 10 min at 10 feet.

RDG for 80 feet 35 min is: G.

Surface interval:
RDG = G and surface interval is 1:30. The result is class V.

Nitrogen penalty times:

second dive at 70 feet and class V:
nitro penalty time = 18
no decompression limit = 17

return to table 1:
30 min + 18 min = 48 => 50
70 feet at 50 min => 10 min decompression stop at 10 feets.

The second dive is not necesarely deeper, it's just 'longer', in the point of view of nitrogen penalty.


RMK: I'm running a canadian table from ACUC.
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Last edited by Desert Fox; 05-09-2004 at 09:19.
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Old 05-09-2004, 08:50   #9
froglegz
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what is the altitude at each dive site???
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Old 05-09-2004, 10:59   #10
Sdiver
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Quote:
Originally posted by Desert Fox
Simple: dive tables

30 min for the first dive.Secure round-up in dive table is 35min with a decompression schedule of 10 min at 10 feet.

RDG for 80 feet 35 min is: G.

Surface interval:
RDG = G and surface interval is 1:30. The result is class V.

Nitrogen penalty times:

second dive at 70 feet and class V:
nitro penalty time = 18
no decompression limit = 17

return to table 1:
30 min + 18 min = 48 => 50
70 feet at 50 min => 10 min decompression stop at 10 feets.

The second dive is not necesarely deeper, it's just 'longer', in the point of view of nitrogen penalty.


RMK: I'm running a canadian table from ACUC.
Sorry bud, Waaaay off.
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Old 05-09-2004, 11:01   #11
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Quote:
Originally posted by froglegz
what is the altitude at each dive site???
You're getting warm.

If I told ya, you'd get it easy.


This is a no BS, dive profile. I've done this dive several times and is a sample question I give my students.
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Old 05-09-2004, 11:24   #12
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Quote:
Originally posted by Sdiver
You're getting warm.

If I told ya, you'd get it easy.


This is a no BS, dive profile. I've done this dive several times and is a sample question I give my students.
You are diving in caves!
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Old 05-09-2004, 11:47   #13
Sdiver
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Quote:
Originally posted by Desert Fox
You are diving in caves!
NO !!!!

As I stated above, this is/can be a Recreational dive.
Diving in Caves/Caverns is not classified as Recreational.
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Old 05-09-2004, 16:05   #14
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By changing the position of the two dives relative to sea level, you can create the atomspheric effect of having the second dive be 'deeper'. If the first takes place at over 10ft above sea level, the second dive will be 'deeper'.

I think.

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Old 05-10-2004, 11:18   #15
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waiting for answer from those who know

my wild-ass guess:

you are up a 5000 ft mountain, wait 12 hours so you have no starting pressure group, do a 60 ft dive that counts as an 80 ft dive, new pressure group of 'R', your 1:30 SI time is spent driving down to sea level which somehow lowers your pressure group to 'A' rather than 'C' (maybe excess off-gassing), leaving you with 5 minutes RNT and a maximum TBT of 35 for a 70 ft dive.
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