Dive tables take a back seat in SSI training

[mitsuguy]

Why do you need a chart?

I teach decompression theory in the beginning with Boyle's Law. It makes sense there. I teach tables later on, but they have the theory down long before that.

My students have no trouble understanding it.

But Boyle's law doesn't have a lot to do with decompression theory...

in fact, Boyle's law only relates to pressure and volume... the only part related to decompression theory is pressure... Boyle's law would be great to explain to students about why their air doesn't last as long at depth...

Henry's law is the one you are looking for when you talk about decompression theory - it is the law that explains why nitrogen becomes dissolved into the blood due to partial pressures...

 

[utbiomajor]

I am also a pilot, and I see a lot of similarities between dive tables and VOR/pilotage.

VOR is an older method of navigation that uses radio signals and vectors to/from the station to give your location. It is still taught to every single pilot, and I've never flown a plane (even military training jets) that didn't have them. They're the most reliable form of navigation that doesn't require calculation. You plot a line from the station in the direction you are, then plot one from a different station. The intersection is you.

Pilotage is simply using your charts, a compass, and a watch to fly. It's also still taught, usually in conjunction with VOR as your primary navigation for training cross-country flights. You pick checkpoints and calculate the time it should take between them, then look for them when you fly.

Now, almost every pilot I know uses GPS on cross-country flights. It's extremely reliable and accurate, and many pilots rely on them for flight. Some systems are approved for instrument flying, but many of the handhelds that pilots affix to their yokes are not.

Even though newer technology is here that makes flying easier and safer, every pilot must learn pilotage and VOR navigation. They're the basics and they're great backups. Diving should be no different.

 

[mitsuguy]

I am also a pilot, and I see a lot of similarities between dive tables and VOR/pilotage.

VOR is an older method of navigation that uses radio signals and vectors to/from the station to give your location. It is still taught to every single pilot, and I've never flown a plane (even military training jets) that didn't have them. They're the most reliable form of navigation that doesn't require calculation. You plot a line from the station in the direction you are, then plot one from a different station. The intersection is you.

Pilotage is simply using your charts, a compass, and a watch to fly. It's also still taught, usually in conjunction with VOR as your primary navigation for training cross-country flights. You pick checkpoints and calculate the time it should take between them, then look for them when you fly.

Now, almost every pilot I know uses GPS on cross-country flights. It's extremely reliable and accurate, and many pilots rely on them for flight. Some systems are approved for instrument flying, but many of the handhelds that pilots affix to their yokes are not.

Even though newer technology is here that makes flying easier and safer, every pilot must learn pilotage and VOR navigation. They're the basics and they're great backups. Diving should be no different.

exactly... what happens if the tech fails...

I teach tables, because I fully believe students should have a visual of where they are at all times...

I use two computers (I might be required to do 5-6 dives in a day), so redundancy is a must, but, if it came down to it, I would know about where I was on a table - its just something I visualize, and know, from the dives I plan on a daily basis using the table, (used to be wheel), and now erdpml.... Once you have experience, it's great to visualize where you are... until then though, a computer is an amazing piece of equipment, so long as you utilize it correctly...

correct use is the key to ndl diving whether you are using a computer, tables or ML computer...

 

[boulderjohn]

But Boyle's law doesn't have a lot to do with decompression theory...

.

Wow.

I would think that the fact that they are breathing 4 times as many molecules of nitrogen at 99 feet as on the surface thus creating a significant gradient would important. I would think that a rapid ascent creating a significant gradient between the tissues and the inhaled air would be a factor.

 

[mitsuguy]

Wow.

I would think that the fact that they are breathing 4 times as many molecules of nitrogen at 99 feet as on the surface thus creating a significant gradient would important. I would think that a rapid ascent creating a significant gradient between the tissues and the inhaled air would be a factor.

it has nothing to do with breathing 4x more molecules... it has to do with the partial pressures of those molecules against the tissues in the lungs that causes the blood to absorb more nitrogen...

it is this very fact that is why breathing rate has no (published) effect on decompression sickness rates... according to your theory, if you breathed 4x as fast on the surface, it would be the same as breathing 1x at 99 feet - your words, not mine. But in reality, that has nothing to do with blood absorption of nitrogen... it ONLY deals with partial pressures...

Henry's law states that when a gas comes in contact with a liquid, that said gas will dissolve into said liquid until partial pressures become saturated... so, when you dive to any depth, the partial pressure of O2 and N2 rises. This increase in partial pressures is what causes the N2 to be absorbed into the bloodstream. N2 in the bloodstream is what can cause DCS... Excessive, that is. The problem, and what causes DCS is that when the partial pressure of N2 in the inhaled air is lower than that in the bloodstream, the N2 tries to escape. On a normal ascent, it escapes through the lungs in the air we exhale, however, on a rapid ascent, there is not enough time for blood to flow through, or surface area, in the lungs, for the N2 to escape, thus it expands in small bubbles, thought to start out as microbubbles, then gathering together in what we call the bends, or DCS...

You actually sound like you know the theory when you state the simple word "gradient" meaning change in pressure, I assume. However, that is still not Boyles law, it is Henrys law...

Boyles law might deal with those molecules in the blood that expand when pressure is reduced, but, unfortunately, it still falls under Henry's law due to on-gassing and off gassing of the blood...

perhaps you should re-read henry's law...

 

[boulderjohn]

who said anything about breathing rate/

Well, I was gong to explain to you that at 99 feet there is a pressure gradient that will cause nitrogen to be absorbed faster by the tissues. This will result nitrogen loading in the tissues. As they ascend, the effect of Boyle's law will be that the air they are breathing will have less nitrogen than they have in their tissues, so...

but we are really getting nowhere in this. I'm signing off.

it has nothing to do with breathing 4x more molecules... it has to do with the partial pressures of those molecules against the tissues in the lungs that causes the blood to absorb more nitrogen...

it is this very fact that is why breathing rate has no (published) effect on decompression sickness rates... according to your theory, if you breathed 4x as fast on the surface, it would be the same as breathing 1x at 99 feet - your words, not mine. But in reality, that has nothing to do with blood absorption of nitrogen... it ONLY deals with partial pressures...

Henry's law states that when a gas comes in contact with a liquid, that said gas will dissolve into said liquid until partial pressures become saturated... so, when you dive to any depth, the partial pressure of O2 and N2 rises. This increase in partial pressures is what causes the N2 to be absorbed into the bloodstream. N2 in the bloodstream is what can cause DCS... Excessive, that is. The problem, and what causes DCS is that when the partial pressure of N2 in the inhaled air is lower than that in the bloodstream, the N2 tries to escape. On a normal ascent, it escapes through the lungs in the air we exhale, however, on a rapid ascent, there is not enough time for blood to flow through, or surface area, in the lungs, for the N2 to escape, thus it expands in small bubbles, thought to start out as microbubbles, then gathering together in what we call the bends, or DCS...

You actually sound like you know the theory when you state the simple word "gradient" meaning change in pressure, I assume. However, that is still not Boyles law, it is Henrys law...

Boyles law might deal with those molecules in the blood that expand when pressure is reduced, but, unfortunately, it still falls under Henry's law due to on-gassing and off gassing of the blood...

perhaps you should re-read henry's law...

 

[mitsuguy]

who said anything about breathing rate/

Well, I was gong to explain to you that at 99 feet there is a pressure gradient that will cause nitrogen to be absorbed faster by the tissues. This will result nitrogen loading in the tissues. As they ascend, the effect of Boyle's law will be that the air they are breathing will have less nitrogen than they have in their tissues, so...

but we are really getting nowhere in this. I'm signing off.

but that still isn't boyles law...

how in the world do you get p1v1=p2v2 into pressure gradients...

that is all partial pressure stuff and has nothing to do with boyles law...

it isn't that the air will have less nitrogen than is in their tissues, it is the same percentage - it is the partial pressure

here is the one:
Henry's Law

Henry's Law

Henry's law and divers

So, you can keep telling your students you are teaching them Boyles law, but if you are talking decompression theory, it is most definitely Henrys law that you are talking to them about...

Or is it that you still don't understand - you keep talking about volume, but as far as on-gassing concerns, volume has no published effects. Volume is directly related to lung displacement and pressure. This is Boyles law. However, the amount of nitrogen that we uptake has nothing to do with the volume of air we breathe. If the volume mattered, then it would mean we could get DCS if we sat around and breathed really really fast on the surface. But we don't. Again, it has nothing to do with breathing 4x the density, it has to do with breathing 4x the partial pressure...

its partial pressure, partial pressure, partial pressure that determines nitrogen on-gassing and off-gassing, NOT volume....

please please re-read your laws and re-learn why our bodies absorb nitrogen...

 

[tomfcrist]

its partial pressure, partial pressure, partial pressure that determines nitrogen on-gassing and off-gassing, NOT volume....

please please re-read your laws and re-learn why our bodies absorb nitrogen...

Hate to be the bearer of bad news, but Boyles Law, Henrys Law and Daltons law are all directly related.

 

[mitsuguy]

Hate to be the bearer of bad news, but Boyles Law, Henrys Law and Daltons law are all directly related.

noooo... volume has nothing to do with henry's law, ZERO!

here is yet another site explaining henry's law... note that volume is not talked about once, because volume is irrelevant... henry's law works because there is an increase in pressure, but has ZERO to do with volume...

Solubility of gases in liquids, Henry's law


Now, wanna talk about related laws, then we can talk about Boyles, Charles, Gay-Lussac's laws, which together make up the combined gas laws. Add Avogadros and we have the ideal gas law.

Charles Law = volume and temperature
Boyles law = volume and pressure
Gay-Lussac = pressure and temperature
Avogadros = deals with the above three and makes some statements about the ideal gas law

then we have henry's law... henry's law = the absorption of molecules from a gas into a liquid because of partial pressures

here's why it doesn't deal with the above three...

I'll use the picture from the link above...

in this image, we have a fixed amount of liquid at the bottom. on the left, we'll assume that the gas and the liquid are in equilibrium. On the right, we could use Boyles law to increase the pressure by reducing the volume - this would then cause more molecules to start being absorbed into the liquid at the bottom, because the new pressure of the molecules in the gas is higher, the partial pressure is higher. To figure this out, we would use Henry's law to determine how much would be absorbed into the liquid. Funny thing about Henry's law though, is that it doesn't matter the volume - there is no place to input volume on the calculation... So, lets theorize one other option... lets add pressure, but not reduce the volume... This is simple to do, and in effect, every breath we take on scuba, we are doing this - the volume of our lungs does not change a whole lot as we dive - we increase the pressure to prevent this... so, lets add air to the container above with an air compressor... volume has not changed, but the pressure is higher, so, does Boyles law matter? Absolutely not... because we have increased the pressure without changing the volume by adding more molecules to the container, we have increased the pressure without worrying about the volume... this causes henry's law to take action, and again, because the partial pressure of the gas is higher than the partial pressure of the gas in the liquid, the liquid will start absorbing the gas...

forgot you mentioned daltons law... it is related to henry's law, and essentially just says that the sum of all partial pressures in a gas equal the total pressure of the gas... that is the basis for calculating the differences between standard air diving and mixed gas diving... boyles law still doesn't come in to play, because volume, again, is irrelevant...

 

[tomfcrist]

Boyles law IS about volume......However because your body stays in tune with the environment(depth doesnt decrease your lung capacity) it also implies that the air within tyour lungs at depth is more dense.........that is where Boyle's and Henrys, and Daltons laws all come together.....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.......All the gas laws relate directly to each other in one way or another.....OBTW Physics is kinda a specialty of mine, and with physics if you dont understand why a law is what it is and all the laws relating to it you are only getting half the story.

A quote from your link"This means the concentration to pressure ratio is the same when pressures change.".......Very true unless you are talking about human anatomy while diving where the concentration does change.