Residual Volume of lungs and OOA

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Ken wrote

>> Good depth to discuss. Most divers find out they are OOA when they have
>> breathed out, not when they have a lung full of gas. Without getting
>> into the question of tidal flow and minimum percentage content of the
>> lungs, assume for a second that your lungs are only 1/4 full when you
>> discover you are out of gas at 30 meters. As you note, you are at a
>> absolute pressure of 4 atmospheres. At the surface, the gas in your
>> lungs will have expanded all the way up to, you got it, one lung full of
>> gas.

> Like so many things, it depends. Sure you tend to find out you're out of
> air when you try to breathe in and can't - so your lungs are at the end of
> a normal exhalation. At which point, for an adult with a total lung
> capacity you'll find your actual lung volume is around 3L. This is made up
> of what you can still forcibly breathe out - your exhalatory reserve
> volume - plus a certain volume which you CANNOT breathe out, your residual
> volume (both these together make up your functional residual capacity).

You'll note that the preceeding discussion quite specifically says "without
getting into the question of tidal flow and minimum percentage content of
the lungs." It also "assumes" the lungs are 1/4 full.

> If you take 3L and multiply it four-fold (4ATA @ 30m to 1ATA at 0m) you
> end up with a 12l vol - twice your total lung volume. If you don't exhale
> AT SOME POINT on your way up, you WILL get a pneumothorax / gas embolus.

>> This is not suggesting it's a good idea to hold your breath while
>> ascending. It is only to point out that the degree of risk is not
>> normally as severe as taught. You should never ascend very far with the
>> airways closed, but breathing out is not the only way to keep them open.
>> They're open when you are inhaling too. As you ascend from our proposed
>> 30 meters, the amount of gas available from the tank benefits from the
>> lowering of pressure. From the 30 meter dive to the surface, you can
>> actually get extra gas equal to 3 times the internal volume of your
>> tanks. One ata stays in the tank. The other two can be used. So figure
>> out what the internal volume of your tanks is, multiply it by 3 and
>> divide it by whatever you figure the tidal volume of your lungs is.

> Not really.

Yes really. My statements are not assumptions and are not guesses. They
are based on actual experience. As it happens, my OOA ascent was from 128
feet, a bit short of 40 meters. I was wearing a single 72 cubic foot tank
at the time.

> Your equipment is already malfunctioning (assuming it's not your lack of
> attention that has put you in this predicament).

Out of air means out of air. It does not mean a total malfunction of all
available regulators. I'm reasonably certain that, if you were to count the
number of OOA situations that resulted from lack of attention, failure to
monitor gas, or some combination of circumstances that caused the diver to
overstay his supply, you'd find that they exceed, by far, the number or
times a complete regulator failure was to blame.

> Note that a well functioning first stage regulates to around 10ATA above
> ambient pressure, so at 30m you will need around
> 14ATA in your cylinder to get a breath.

Nope. A well functioning first stage stops flowing at about 10 ATA. It
starts flowing at a much lower pressure.

> Sure, as you come to the surface your equipment will function with lower
> cylinder pressures, as 10+ambient becomes a smaller
> number.

Right, except for the 10 ATA part. That's exactly what I said. You get to
use more of your gas as you ascend. Trust me, if you ever have to use it,
as I once did, you'll be very glad we had this conversation.

>>> However as you ascend it is the case that there is sufficient oxygen in
>>> the mass of gas in your lungs so that you need never become hypoxic
>>> during such an ascent, so you need not fear for that.

>> That is not something you can depend on. There are too many variables.
>> Shallow water blackout is caused by the combination of O2 used by the
>> body tissues and reduced pressure that combine to bring the PPO2 to less
>> than .16 ATA, the level normally considered necessary to maintain
>> consciousness.

> No, this too depends on your rate of oxygen consumption.

Yes if you mean the rate at which your body consumes oxygen in the tissues,
which is what I meant when I said "O2 used by the body tissues." I'm not
sure what your "no" refers to.

> Of course an option no-one has discussed is using your alternate air
> source - and I don't mean your second 2nd stage connected
> to the same empty cylinder!

Probably because having a redundant gas supply means it's not an OOA
situation. Note that's not a criticism, just an observation. It is clearly
best not to run out of gas included in your dive plan and second best to
have a reduncant supply just in case. If we're going to talk options, they
let's include all that are likely:
1. I sometimes wear twin tanks with an isolation manifold. A single
regulator failure does not mean I'm out of gas or that I can't access all
gas through a regulator working just fine. Even if I were to fail to shut
down a free flowing regulator before all available gas has escaped, I still
have a working regulator to let me take advantage of expansion to get still
more gas from the tank.
2. I don't normally carry a pony, but I do sometimes carry a deco gas
suitable for use from a bit over 20 meters to the surface (50% O2). In a
real emergency, I would use that supply briefly at still greater depths. Ox
tox is a function of both PPO2 and time. I would certainly use it above 20
meters.
3. My gas plan calls for ending the dive while I still have enough gas to
get myself and my buddy safely to the surface. I may have run out once.
I'm not likely to do so again.

> If you do this (Breath from your BCD), you can breathe in and out
> continuously as you ascend - but not enough gas there to do a safety stop,
> just come up. The composition of the gas there is the same as whatever
> your cylinder held. You breathe in and out from the hose and yes, you do
> accumulate some CO2 BUT you'll have probably made the surface BEFORE this
> becomes a real issue.

This method presumes you have significant gas in your BCD. The closer to
the end of the dive you are, the less gas you're likely to have there. If
you're out of gas, you're as buoyant as you're ever going to be and will
have less gas in your BCD than at any other point in your dive. It's better
than nothing, but not by much.

Lee

Hi guys,
I have a query that I thought someone here may be able to help me
with. I was in a conversation about lung capacities etc, and my friend
was of the opinion that during a free ascent in an out of air
situation, the expansion of the residual air in the lungs would cause
more O2 to diffuse into the blood and 'buy more time' as it were. I
would have thought that this wouldn't happen, as the PO2 in the lungs
would decrease on the ascent and perhaps the reverse would happen
(i.e. some of the bloods O2 would diffuse into the lungs, further
lowering the PO2 in the blood). What would be more likely?
Thanks,
Eddie

"Eddie" <eddiej@gmail.com> wrote in message
news:1174855982.380356.298620@l77g2000hsb.googlegr oups.com...
> Hi guys,
> I have a query that I thought someone here may be able to help me
> with. I was in a conversation about lung capacities etc, and my friend
> was of the opinion that during a free ascent in an out of air
> situation, the expansion of the residual air in the lungs would cause
> more O2 to diffuse into the blood and 'buy more time' as it were. I
> would have thought that this wouldn't happen, as the PO2 in the lungs
> would decrease on the ascent and perhaps the reverse would happen
> (i.e. some of the bloods O2 would diffuse into the lungs, further
> lowering the PO2 in the blood). What would be more likely?

First, in such an ascent you must NEVER hold your breath and in fact breathe
out continuously. As you ascend the volume of gas in your lungs would
increase so as to pressure-equilibrate with the water surrounding you, which
pressure is decreasing all the time. Hold your breath and the pressure in
your lungs may well cause an alveolar rupture which would give to a
pneumothorax or a gas embolus. Neither is pretty, both are capable of
killing you.

As you ascend (and take the example of breathing air at 30m) your PiO2
(press. of inspired oxygen) in your lungs would fall from 84kPa (4ATA at
30m) to 21kPa (1ATA at surface, 0m). (Actually they'd be a bit less than
this becuase of dilution with nitrogen in your residual lung volume, but
this will do for this argument.) There is then no question then of more
oxygen diffusing into the circulation as you ascend. However, when breathing
21kPa O2 (as we are when sitting at our PCs) we are able to saturate the
haemoglobin in the blood to its maximum capacity, and having higher inhaled
oxygen concentrations does not add any more to this. What will happen of
course is that the amount of oxygen in solution in your blood will fall, but
that part of the oxygen in our blood is a very small part of the total and
does not contribute significantly to the amount of oxygen our blood carries.

However as you ascend it is the case that there is sufficient oxygen in the
mass of gas in your lungs so that you need never become hypoxic during such
an ascent, so you need not fear for that.

Carbon dioxide is another matter. Your desire to breathe is far far more
significantly regulated by the partial pressure of CO2 in the blood than
that of oxygen in the blood. Normally you remove CO2 from the circulation by
venting it to the atmosphere with each breath. As you ascend, and as you
breathe out continuously, CO2 is also being vented continuously as you go so
the PaCO2 (pressure of CO2 in the arteries) is NOT NECESSARILY raised
either. I say not necessarily because frankly it all depends how well you
vent. Under-vent and it builds up a bit.

So, you should arrive at the surface in a (gas pressure terms) fit state. Of
course you will probably experience a certain amount of shortness of breath,
as likely to be brought about by anxiety / fear / panic rather than any
alteration of your blood gas profile. There is also the question of the
strech receptors within the lungs that frankly like to be kept moving. As
you vent and maintain a farily constant lung volume so your lungs do not
expand and contract during such an ascent. These receptors fire off,
reminding you to breathe. You can see their effect by your PC. Take a breath
(NOT a full lung capacity!) and hold it. Just as you get the desire to
breathe, while neither breathing in nor out, move your chest wall AS IF
breathing - you'll find you can buy yourself a few more seconds of breath
hold.

Hope this helps.

Ken