Dive tables take a back seat in SSI training

[Doppler]

This thread is totally derailed but since you guys are well off-topic, may I point out that if one mentions Avogadro and gas laws, it is more correct to say that if we consider the gas laws en mass and include Avogadro’s hypothesis, then we can derive the Universal Gas Constant: PV=nRT, where R is derived as a constant from: PV/T=Constant, n is the number of moles.

If we consider teaching decompression theory and we want to discuss the real physics of it, we have to consider Fick's and Graham's; floppy tables or not.

 

[tomfcrist]

This thread is totally derailed but since you guys are well off-topic, may I point out that if one mentions Avogadro and gas laws, it is more correct to say that if we consider the gas laws en mass and include Avogadro’s hypothesis, then we can derive the Universal Gas Constant: PV=nRT, where R is derived as a constant from: PV/T=Constant, n is the number of moles.

If we consider teaching decompression theory and we want to discuss the real physics of it, we have to consider Fick's and Graham's; floppy tables or not.

off topic indeed......

 

[mitsuguy]

If your lungs got smaller the deeper you dive (therefore holding the same volume and density of a given gas) partial pressures would be irrelivant. when you calculate your PPO2 etc. do you use ata as part of the formula? Of course you do because the more of any given gas you have in your lungs, the more you will absorb.......

no, it has nothing to do with volume of gas in your lungs - our lung volume does not change when diving... the density increases, but the volume stays the same... again, its not about volume, it is about pressure... why is that so hard to comprehend???

when you calculate P02, you use ata - ata is pressure... still no reference to VOLUME!

 

[tomfcrist]

no, it has nothing to do with volume of gas in your lungs - our lung volume does not change when diving... the density increases, but the volume stays the same... again, its not about volume, it is about pressure... why is that so hard to comprehend???

when you calculate P02, you use ata - ata is pressure... still no reference to VOLUME!

One last time, As you decend pressure increases which in a closed system decreases volume. In an open system(your lungs) volume does not decrease but density increases, you will have X amount more molecules of air in your lungs.

The fact that there are more molecules of air in your lungs means that more will transfer into solution from your lungs to your bloodstream:to tissues.

Henrys law would make no sense in diving if you dont go through Boyles law, and Daltons law first.

I am not trying to tell you that boyles law is all you need to know when it comes to diving or Partial Pressures. What I am saying is that if you really think that Boyles law has no bearing or effect on Daltons law or Henrys law then you are horribly mistaken.
The gurus who came up with decompression theory knew this and that is why they constructed the General Gas Law(or Principle) and it is included in every dive text that i can recall, no matter the agency.

Recap: Boyles Law implies that as we go deeper the density of gas in our lungs increases(due to compression), Daltons law says that as density increases, the partial pressure is higher, and Henrys law says that the higher the partial pressure, the more you will in-gas.

Understand yet?

 

[mitsuguy]

Recap: Boyles Law implies that as we go deeper the density of gas in our lungs increases(due to compression), Daltons law says that as density increases, the partial pressure is higher, and Henrys law says that the higher the partial pressure, the more you will in-gas.

Understand yet?

yes I understand... in fact, you may have just solidified my argument... my argument was that the original text said that he taught his students boyles law, and I said that that was not an accurate way to describe to students, or anyone, for that fact, why we on gas nitrogen...

because it simply doesn't matter... all we need to know about on-gassing and off gassing is that the pressure changes - it doesn't matter why the pressure changes, and it doesn't matter what the volume of the gas is either, it just matters that there is a pressure change...

when we talk decompression theory, henrys law is still the only thing we need to worry about teaching, because all students need to know is that pressure increases which causes the liquid (blood and tissues) to absorb nitrogen and any other gasses we breathe... trying to teach boyles law to describe this is completely inaccurate, because it is not the volume of air we breathe, but the pressure of the air we breathe...

take your recap, and delete boyles law from it - instead, we know that as we dive deeper, there is increased pressure on our bodies... as you said, daltons law says that the sum of the partial pressures in a gas is equal to the total pressure of the gas... we don't need to know from boyles why volume is affected other than when we calculate sac rates... we just need to know the pressure... so, 99 feet is 4 ata... simple... po2 = .21 x 4 = .84 pn2 = .79 x 4 = 3.16 nowhere in there does volume or density that we might have tried to find from boyles law apply... then we'd use henry's law to see what that 3.16 ata of N2 does as far as absorption into the bloodstream...

so, if you can tell me what we gain by figuring out boyles law when we do these calculations, then please, show me...

 

[tomfcrist]

Once mor because they are all related. The poster didn't say that he doesn't cover the other laws, he just said that he starts with Boyle. Also, boyles law has alot to do with nitrogen coming out of solution, therefore it has to do with decompression.

 

[mitsuguy]

Once mor because they are all related. The poster didn't say that he doesn't cover the other laws, he just said that he starts with Boyle. Also, boyles law has alot to do with nitrogen coming out of solution, therefore it has to do with decompression.

thats still more henry's law than boyles... boyles law doesn't do anything with offgassing though like you say... it has to do with bubble growth while still absorbed in the tissue... offgassing is still directly henry's law...

lets just agree to disagree...

 

[dashthrash]

I heard that about computer and the dive tables. Here is what it comes down to.... Instructors don't have to teach tables if all the equipment that is being taught on has a computer... if not then they have to still teach tables. Now the $25000 dollar question is what shop is going to invest all the money and time in computers so they don't have to teach tables.

 

[tomfcrist]

thats still more henry's law than boyles... boyles law doesn't do anything with offgassing though like you say... it has to do with bubble growth while still absorbed in the tissue... offgassing is still directly henry's law...

lets just agree to disagree...

We disagree without an agreement to disagree

 

[boulderjohn]

I heard that about computer and the dive tables. Here is what it comes down to.... Instructors don't have to teach tables if all the equipment that is being taught on has a computer... if not then they have to still teach tables. Now the $25000 dollar question is what shop is going to invest all the money and time in computers so they don't have to teach tables.

What you heard is not accurate. It will not cost a shop a dime more to teach one way or the other.