in case you were watching the cutie next to you during class

[Dashrynn]

THE GAS LAWS That All Divers Must Know:

BOYLE’S LAW:
The volume of a gas varies inversely with the pressure.
Increase the pressure = decrease the volume (squeeze)
Decrease the pressure = increase the volume (expand)

CHARLE’S LAW:
The volume of a gas varies with temperature.
Cold gas = less volume, Warm gas = more volume

GENERAL GAS LAW:
Pressure 1 x Volume 1 = Pressure 2 x Volume 2
Temperature 1 Temperature 2

DALTON’S LAW:
Law of partial pressures: P = Pp1 + Pp2 + Pp3 ….
Total pressure (P) = sum of all the partial pressures (Pp), nitrogen + oxygen + …

HENRY’S LAW:
As pressure increases the amount of gas dissolved into the body increases.
Bottom time = saturation of gas in tissues.

ATMOSPHERIC ABSOLUTE (ATA):
The atmospheric pressure at sea level is 1 ATA =:
14.7 psi (pounds per square inch)
29.9 inmg (inches of mercury)
760 mmhg (millimeters of mercury) or Torr
1033 g/cm2 (grams per centimeter squared)
1013.3 mbar (millibars)
10.08 msw (meters of sea water)
33 fsw (feet of sea water)
34 ffw (feet of fresh water)
Every 33 feet of sea water adds 1 ATA…so at 100′ you are at 4 ATA.

[Sounder]

Yes, these are important things to know.

Here's a quiz for ya in their application...

How much gas (in cubic feet) do you need to get you, and a buddy on your octopus, with both buddies each breathing a working 1.0 RMV, up from 110fsw, spending 1 minute on the bottom sorting out the OOA, then ascending at 30fpm, with a 1 minute stop at 50% of your depth, a 3 minute safety stop at 15fsw, and surfacing with 300psi in a HP100??

After you calculate it in cubic feet, how many psi is that in your HP100? What about in an Al80?

Show your work.

[spatman]

[dsteding]

Yes, these are important things to know.

Here's a quiz for ya in their application...

How much gas (in cubic feet) do you need to get you, and a buddy on your octopus, with both buddies each breathing a working 1.0 RMV, up from 110fsw, spending 1 minute on the bottom sorting out the OOA, then ascending at 30fpm, with a 1 minute stop at 50% of your depth, a 3 minute safety stop at 15fsw, and surfacing with 300psi in a HP100??

After you calculate it in cubic feet, how many psi is that in your HP100? What about in an Al80?

Show your work.

Answer, 4 cubic feet. 2 cubic feet on the bottom, and 2 on the 80 fpm ascent to the surface.

Honestly, for a recreational profile like that, I DO NOT understand all the preaching about stopping at half the depth and bladdity blah. Get the F to the surface. Screw the safety stop.

[Sounder]

Yes, these are important things to know.

Here's a quiz for ya in their application...

How much gas (in cubic feet) do you need to get you, and a buddy on your octopus, with both buddies each breathing a working 1.0 RMV, up from 110fsw, spending 1 minute on the bottom sorting out the OOA, then ascending at 30fpm, with a 1 minute stop at 50% of your depth, a 3 minute safety stop at 15fsw, and surfacing with 300psi in a HP100??

After you calculate it in cubic feet, how many psi is that in your HP100? What about in an Al80?

Show your work.

Answer, 4 cubic feet. 2 cubic feet on the bottom, and 2 on the 80 fpm ascent to the surface.

Honestly, for a recreational profile like that, I DO NOT understand all the preaching about stopping at half the depth and bladdity blah. Get the F to the surface. Screw the safety stop.

It's an exercise. Though given the gas and a calm-ish buddy, I'd do the stops... and it doesn't mean an appropriate rock bottom at that depth is 4cf. Don't be so grumpy.

[Sockmonkey]

Oh Steding Steding Steding (these words of lament have been uttered countless times all over the world I'm sure)...

Sounder knows you know... it was Dashrynn he was harassing. You ruined his fun... again.

Dashrynn... just for the sake of shoulding all over you... go read Bob's gas management article before Sounder puts his beer down long enough to post another word problem.

-Eric

[Dashrynn]

Yes, these are important things to know.

Here's a quiz for ya in their application...

How much gas (in cubic feet) do you need to get you, and a buddy on your octopus, with both buddies each breathing a working 1.0 RMV, up from 110fsw, spending 1 minute on the bottom sorting out the OOA, then ascending at 30fpm, with a 1 minute stop at 50% of your depth, a 3 minute safety stop at 15fsw, and surfacing with 300psi in a HP100??

After you calculate it in cubic feet, how many psi is that in your HP100? What about in an Al80?

Show your work.

well i haven't had sufficient training for absolute gas figures.


well cu ft breathed at the depth is Respiratory minute volume (rmv) times your Atmosphere absolute (atma) so since it is two people we would do something like....110ft. 2.0 rmv x 4.3 atma = 8.6 cu ft per min(or psi it is a hp100..295.84psi) x 2 = 17.2 cu ft (or 591.68 psi) (or air consumption so you are down there for one min.

Thats 8.6 cu ft or 295.84 psi that you just used for one minute and then doubled for rising to 80 ft

Now next aimed depth...55 ft now we took 2 mins getting there (we are safe divers ) so i suppose every 30 feet we could recalculate this and then a 1 minute stop

so here we go...80ft going to 55ft here is our figure..2.0rmv x 3.4 = 6.8 cu ft sooo 6.8 + 17.2 = 24 cu ft breathed so far (within safe standards)

now 1 more min at 55 ft 2.0 rmv x 2.6 atma = 5.2 cu ft sooo 29.2 cu ft soooo far...

so 55ft to 25 ft 2.0 x 2.6 atma = 5.2 cu ft sooo 34.4 cu ft...

25 to 15 ft sooo 30 fpm = .5 ft per sec....sooooo (my head hurts now) 1/3rd (33.333333%) of 60 is 20 seconds.
sooo im assuming its 1/3rd of 2.0 rmv (soo .66) .66 x 1.75 atma = 1.155 for 20 seconds. so total of 35.555 cu ft used....

now! the big one 15 ft for 3 mins but we will say for 3 mins and 30 since we are adding in the surfacing part.

so thats 7.0 rmv x 1.45 atma = 10.15 cu ft.. so thats a GRAND TOTAL of 45.705 cu ft used (in a safe safe margen). In a hp 100 (hp100 3440 psi total, 34.4 psi for every cu ft. al80 3000 psi total, 37.5 for every cu ft) thats 1572.252 psi used and a al 80 1713.9 psi.

now..i have no training but my ow cert winds tides and current and just reading night limited viz and deep diving (just started) so i wouldn't apply any of these figures until you have been properly schooled in such and hell im not even sure if im right but it was fun trying and educational!

[Dashrynn]

I think i just screwed that alll up dangit >.<

[dsteding]

I think i just screwed that alll up dangit >.<

Dashrynn, step back. Think in terms of round numbers:

110 is four ATA. Four ATA, two people, 1 minute, is 8 cubic feet.

2 minutes up to 50 feet, stop for 1 minute, 1 minute to 15 feet. Average 50 feet (3 ATA), 4 minutes, two divers. 24 cubic feet of gas.

Safety stop, 3 minutes, 1.5 ATA, 2 divers. 5 cubic feet of gas.

Call it 40 cubic feet.

[Dashrynn]

I think i just screwed that alll up dangit >.<

Dashrynn, step back. Think in terms of round numbers:

110 is four ATA. Four ATA, two people, 1 minute, is 8 cubic feet.

2 minutes up to 50 feet, stop for 1 minute, 1 minute to 15 feet. Average 50 feet (3 ATA), 4 minutes, two divers. 24 cubic feet of gas.

Safety stop, 3 minutes, 1.5 ATA, 2 divers. 5 cubic feet of gas.

Call it 40 cubic feet.

sooo i just overanalyzed it with a large marginal room for error?

[dsteding]

sooo i just overanalyzed it with a large marginal room for error?

Yes. No need for three significant figures in scuba math.

[Dashrynn]

sooo i just overanalyzed it with a large marginal room for error?

Yes. No need for three significant figures in scuba math.

i'm used to electronics

[dsteding]

i'm used to electronics

That's okay. I'm used to Sounder asking silly word problems.

Seriously, I was trying to make a point regarding safety stops when people are OOA on recreational dives . . .

[CaptnJack]

Seriously, I was trying to make a point regarding safety stops when people are OOA on recreational dives . . .

Ummm yeah, skip those silly safety stops when you're OOA. Nothin' says oh crap like 2 divers doing a CESA from 15ft cause they ran OOA again trying to share gas for a 3 min safety stop.

[Joshua Smith]

yawn

[Dashrynn]

The initial reason for posting this simple set of lawsis because, during a recent dive someone asked what boyle's law and etc was. I couldn't remember off the top of my head so Today, remembering this i decided to post this list.

To some of you this is nothing, but to some...its a new mountain to climb.....

[Nwbrewer]

The initial reason for posting this simple set of lawsis because, during a recent dive someone asked what boyle's law and etc was. I couldn't remember off the top of my head so Today, remembering this i decided to post this list.

To some of you this is nothing, but to some...its a new mountain to climb.....

Exactly the reason Sounder posted his word problem. The academics are great, the application most important.

[Sounder]

NWBrewer is exactly right. Gas Management is an important tool and skill to know, and it comes from the physics laws posted... but there is little good in knowing the laws without knowing how they apply to the dive, and most importantly, how you need to use them to keep yourself safe. Knowing the term "Boyle's Law" doesn't help you one bit, and knowing the law itself doesn't do any good either if it's not applied. Explaining that because of this law, it is important that you never hold your breath because you can get injured if you do and ascend... that's useful information.

As Grumpy pointed out, there is no need for precise critical math in scuba math, but I generally round up just to be sure I don't accidentally round the wrong direction... and as CaptJack sort-of pointed out, safety stops are optional. If you're not 100% sure you have the gas, or things are going sideways in the water, get out. However, knowing that you have enough gas, and having your buddy know you have enough gas for him/her, can help decrease stress and this may afford you the chance to slow your ascent and make a safety stop if you wish.

Here are two resources many of us believe all divers (especially newer ones) should read, understand, and apply... and they're free. There are also free seminars here and there which are VERY good to attend where this is broken down into pieces and made easy. It's not hard to do, and it doesn't require ANY "formal training," but it is pretty important.

Lamont's kick-ass Rock Bottom article.

Bob's kick-ass Gas Management article.

(This is near and dear to my heart as I've been involved in two rescues involving senseless and needless OOA emergencies)

[BDub]

I love Friday threads!

Dashrynn-

There's a lot of good information in this thread, and I think it's great you're taking an interest in this.

A few things to keep in mind (a couple of which has been mentioned)....

First, none of this is precise. In fact, it's all based on assumptions (time to assess and fix the problem and initiate the ascent, breathing rate, ascent rate, etc). Don't worry about being precise because you can't be....it's all based on assumptions anyway. However, these assumptions provide us with much more usable info than simply "Be back on the boat with 500psi" or "Thirds". Also, since many people are intimidated by math, let alone "scuba math", we typically round up and use easy to use numbers (typically whole numbers or halves).

This information could be lifesaving. However, it can also lead to more problems as well. If you have the knowledge, but lack the skills to apply the knowledge, more problems can present themselves. In other words, if you've planned for 1 minute on the bottom, a combined breathing rate of 2 and a solid 30' per minute ascent rate, you need to possess the skills for 1 minute on the bottom (not a very long time) with a controlled ascent while air sharing (very tough if you haven't practiced that), etc.

In other words, if the reg exchange is fumbled on the bottom, it takes you a while to calm your buddy, figure out what the H just happened, start the exit, and you both are huffing over your planned combined 2.0 RMV on the ascent, you've shortchanged your calculation. The result is the possibility that you both will now run out of air at your safety stop. Hence the need to keep in mind that a safety stop is optional.

I don't want to downplay this information, because this is critical to safe diving. However, remember, this is on paper, and it looks good on paper, but as most of us know, the dive plan always looks good until it touches the water.

[CaptnJack]

yawn

Its all fun and games until you run out of O2 on your CCR at 200ft Then who you gonna call???


OC!!!

[Joshua Smith]

yawn

Its all fun and games until you run out of O2 on your CCR at 200ft Then who you gonna call???


OC!!!

Hey, gas laws and calcs are all good. I'm a big fan. It's all the stuff in between the lines I was commenting on.

[BDub]

Hey, gas laws and calcs are all good. I'm a big fan. It's all the stuff in between the lines I was commenting on.

The coalition for reason is extremely weak.

[Joshua Smith]

Hey, gas laws and calcs are all good. I'm a big fan. It's all the stuff in between the lines I was commenting on.

The coalition for reason is extremely weak.

Hi. Sorry. Crazy day. You've seen how the sausage gets made, come in the conference room and I will show you a finished sausage.

[BDub]

Hey, gas laws and calcs are all good. I'm a big fan. It's all the stuff in between the lines I was commenting on.

The coalition for reason is extremely weak.

Hi. Sorry. Crazy day. You've seen how the sausage gets made, come in the conference room and I will show you a finished sausage.

If I'm gonna back you up, I need a weapon without drawing suspicion. And I had to justify it somehow, so... I'm a mechanic with a tire thing.

[CaptnJack]

Hey, gas laws and calcs are all good. I'm a big fan. It's all the stuff in between the lines I was commenting on.

The coalition for reason is extremely weak.

Hi. Sorry. Crazy day. You've seen how the sausage gets made, come in the conference room and I will show you a finished sausage.

Sorry to tell you this but nobody wants to see your sausage