I was just thinking about using a bag of holding as a breathing apparatus or rather, diving bell, in an underwater setting. The concept is simple; the bag of holding is exposed to air whereby by definition it contains at least 64 cubic feet of air. That's 1812 liters of air; a person breaths 420 to 480 liters per hour. You only get one breath because each exhale is approximately 5% C02 which ~16% to 15% O2 and ~5%CO2 is air considered hazardous to life. You'd be unlikely to get more than one breath per tidal volume.
Now; that's if the air is 1atm. I suppose it is conceivable in your setting that you can pump a bag of holding to more than 1atm possibly getting more air than that. And you may need a tube extended into the bag because as you descend into the water the air will compress into the bag (which forms the seal) and make it deeper within the bag which only has a hole the size of the bag with which to fit your head into.
If in a real diving bell however, the bag of holding can be used as extra air.
Narcosis and oxygen toxicity would apply; which means a maximum depth limit of about 200 feet is all you could expect without exotic gasses.
Since on Earth it's about 1atm per 10 feet you can presume to 2x or 3x etc. your volume of air consumed per 10 feet. A 100 foot excursion would consume 4800 liters of air per hour giving you approximately 22 minutes of usable air at that depth.
I could see coastal villages using bags of holding as breathing apparatus for underwater work.
PS - It might be useful to do such underwater work as early campaign training for any kind of underwater campaign. For instance careening a hull by using a bag of holding to take breaths and hold your breath while you scrape barnacles underneath a ship at berth.
A bag of holding specifically states: “Breathing creatures inside the bag can survive up to a number of minutes equal to 10 divided by the number of creatures (minimum 1 minute), after which time they begin to suffocate.”. Those are the explicitly written rules of the extra dimensional space which governs a bag of holding - so physics really does not come into play (unless your DM decides to deviate from raw).
Further, it should be noted, pressure on the outside might influence the physical bag, but it has no effect on the space inside the bag - that space does not exist in our reality, and therefore our reality cannot really exert external pressure on it. Thus, to anything trying to breathe inside the bag, they will get the same air at a thousand feet as they would at ten.
Additionally, because a bag of holding exists in an extra dimensional space, the DM could rule that the air pressure mechanisms which cause a diving bell to work do not apply (they could reason is no real pressure due to the intersections between different realities) and opening it underwater will just cause water to rush into the extra dimensional space.
A weighted bucket would help pull the bag down. You could even make a diving sled to pull you and the air bag down faster and farther then a normal swim down. At that point pressure would be your problem.
It would be a non spell way to gain a few extra breaths while underwater to go or stay down longer and farther.
Some pro free divers could hold their breath for over 5 or 6 minutes and sled down more than 30 stories deep. When I was younger I could hold my breath for 2 minutes active swimming underwater and over 3 just underwater doing nothing. I could see an untrained normal person doing the same.
A bag of holding specifically states: “Breathing creatures inside the bag can survive up to a number of minutes equal to 10 divided by the number of creatures (minimum 1 minute), after which time they begin to suffocate.”. Those are the explicitly written rules of the extra dimensional space which governs a bag of holding - so physics really does not come into play (unless your DM decides to deviate from raw).
Further, it should be noted, pressure on the outside might influence the physical bag, but it has no effect on the space inside the bag - that space does not exist in our reality, and therefore our reality cannot really exert external pressure on it. Thus, to anything trying to breathe inside the bag, they will get the same air at a thousand feet as they would at ten.
Additionally, because a bag of holding exists in an extra dimensional space, the DM could rule that the air pressure mechanisms which cause a diving bell to work do not apply (they could reason is no real pressure due to the intersections between different realities) and opening it underwater will just cause water to rush into the extra dimensional space.
Pretty much none of what you said applies even if the "rules" state it. The rules would be so nonsensical that you are required to homebrew this.
1) A 64cubic foot area that is a pocket dimension cannot suffocate you in 10 minutes. The game rule is most certainly an error; there's zero reason that physics wouldn't work the same in a pocket dimension.
2) You could not physically insert your hand into said pocket dimension that has different atmospherics to the ambient atmospherics. Delta-P or "change in pressure" alone would cause you to be sucked into or the contents blown out of with the violence of dynamite. If you were underwater and reached into a bag of holding just 20 feet underwater the delta-P would cause you to be sucked into the bag of holding and disembowl you.
3) Issue #2 applies to all conditions. Climbing a mountain from Sea level would cause the contents of your bag of holding to explode in your face at explosive pressures equal to a Nuclear Bomb. And that's not even joking; 8psi over pressure is like having a stick of TNT go off inside your mouth. The overpressure of a nuclear bomb at ground zero is approximately 20psi. Going from sea level to Mount Everest would create a pressure differential of 10psi or half the force of a nuclear bomb.
I simply refuse to even entertain the idea that the nonsense rules you described should ever be used whatsoever at any game table. EVER.
The only thing that makes sense is exactly what I described. The bag of holding is a pocket dimension with free-flowing exchange of media between the bag and the external. The bag of holding is not hermetically sealed as to cause pressure differentials.
The bag of holding contains 64 cubic feet which at 1atm provides one human approximately 3hrs and 45min of air.
PERIOD.
EDIT - I did some rough calculations of a cavitation bubble caused by opening a bag of holding underwater IF we assume a pressure differential. At 10 feet the explosion would be the equivalent of 1/3rd stick of dynamite. A Mark48 torpedo has approximately a 40kg TNT warhead which causes a 5meter radius bubble in explosion at typical depth of ~10 feet. So a bag of holding representing about 64 cubic feet is a cavitation bubble approximately 1/295ths the size of a torpedo's detonation at that depth. 1/295ths of 48kg of TNT is about 1/3rd stick of TNT.
However; a bag of holding's bubble size does not change at depth. Thus the deeper you go the more explosive potential. The explosion is exponential per foot of sea water.
SECOND EDIT - the 10psi differential between sea level and mount Everest means you can fill your bag of holding with nails and walk up to the Storm Giant King's castle and open the bag of holding in the Storm Giant's face and blow his head off instantly.
With a bag of holding BY "rules" of the game. I simply refuse to believe that, it must therefore be homebrewed to make any sense.
Your argument is that physics doesn’t work right in a magical demiplane? So you’re ok with a backpack being able to hold the same volume of stuff as an SUV, but breathable air is where you draw the line?
Don't try to apply real world physics to D&D. Obviously physics doesn’t work exactly the same, people can shoot lightning out of their fingertips, and run across water, and fly. It’s a game, not a simulation. It doesn’t even try to be a simulation.
Speaking as someone who regularly does physics in D&D to calculate silliness like the coefficient of gravity and other random D&D things (and who plays D&D with folks who have extremely advanced science degrees), let me be very clear on this - someone pointing out what RAW says, and justifiably pointing out that our real world physics might not apply to the barriers between different planes of existence is hardly being "lazy." They are just going with what the rules say.
The rules may be dumb at times when you apply real world physics; but this is a fantasy game. Certain things simply might work differently--after all, here in the real world, we do not really have any analog to pocket dimensions that exist in their own completely separate bubble of reality, as a Bag of Holding does.
If you brought up your suggestion at my table, I would find it fascinating, nerd out over the science, but ultimately rule that the Rules as Written control. If you then followed up in the way you did, you would be out of my game--it is one thing to be sad that your suggestion did not work, but rudely lashing out at folks for deciding the rules of the magical game trump real world physics? I think most people would see that as a one-way ticket to finding another group to play with.
I was just thinking about using a bag of holding as a breathing apparatus or rather, diving bell, in an underwater setting. The concept is simple; the bag of holding is exposed to air whereby by definition it contains at least 64 cubic feet of air. That's 1812 liters of air; a person breaths 420 to 480 liters per hour. You only get one breath because each exhale is approximately 5% C02 which ~16% to 15% O2 and ~5%CO2 is air considered hazardous to life. You'd be unlikely to get more than one breath per tidal volume.
Now; that's if the air is 1atm. I suppose it is conceivable in your setting that you can pump a bag of holding to more than 1atm possibly getting more air than that. And you may need a tube extended into the bag because as you descend into the water the air will compress into the bag (which forms the seal) and make it deeper within the bag which only has a hole the size of the bag with which to fit your head into.
If in a real diving bell however, the bag of holding can be used as extra air.
Narcosis and oxygen toxicity would apply; which means a maximum depth limit of about 200 feet is all you could expect without exotic gasses.
Since on Earth it's about 1atm per 10 feet you can presume to 2x or 3x etc. your volume of air consumed per 10 feet. A 100 foot excursion would consume 4800 liters of air per hour giving you approximately 22 minutes of usable air at that depth.
I could see coastal villages using bags of holding as breathing apparatus for underwater work.
PS - It might be useful to do such underwater work as early campaign training for any kind of underwater campaign. For instance careening a hull by using a bag of holding to take breaths and hold your breath while you scrape barnacles underneath a ship at berth.
A bag of holding specifically states: “Breathing creatures inside the bag can survive up to a number of minutes equal to 10 divided by the number of creatures (minimum 1 minute), after which time they begin to suffocate.”. Those are the explicitly written rules of the extra dimensional space which governs a bag of holding - so physics really does not come into play (unless your DM decides to deviate from raw).
Further, it should be noted, pressure on the outside might influence the physical bag, but it has no effect on the space inside the bag - that space does not exist in our reality, and therefore our reality cannot really exert external pressure on it. Thus, to anything trying to breathe inside the bag, they will get the same air at a thousand feet as they would at ten.
Additionally, because a bag of holding exists in an extra dimensional space, the DM could rule that the air pressure mechanisms which cause a diving bell to work do not apply (they could reason is no real pressure due to the intersections between different realities) and opening it underwater will just cause water to rush into the extra dimensional space.
Buoyancy would be a problem.
A weighted bucket would help pull the bag down. You could even make a diving sled to pull you and the air bag down faster and farther then a normal swim down.
At that point pressure would be your problem.
It would be a non spell way to gain a few extra breaths while underwater to go or stay down longer and farther.
Some pro free divers could hold their breath for over 5 or 6 minutes and sled down more than 30 stories deep.
When I was younger I could hold my breath for 2 minutes active swimming underwater and over 3 just underwater doing nothing. I could see an untrained normal person doing the same.
Pretty much none of what you said applies even if the "rules" state it. The rules would be so nonsensical that you are required to homebrew this.
1) A 64cubic foot area that is a pocket dimension cannot suffocate you in 10 minutes. The game rule is most certainly an error; there's zero reason that physics wouldn't work the same in a pocket dimension.
2) You could not physically insert your hand into said pocket dimension that has different atmospherics to the ambient atmospherics. Delta-P or "change in pressure" alone would cause you to be sucked into or the contents blown out of with the violence of dynamite. If you were underwater and reached into a bag of holding just 20 feet underwater the delta-P would cause you to be sucked into the bag of holding and disembowl you.
3) Issue #2 applies to all conditions. Climbing a mountain from Sea level would cause the contents of your bag of holding to explode in your face at explosive pressures equal to a Nuclear Bomb. And that's not even joking; 8psi over pressure is like having a stick of TNT go off inside your mouth. The overpressure of a nuclear bomb at ground zero is approximately 20psi. Going from sea level to Mount Everest would create a pressure differential of 10psi or half the force of a nuclear bomb.
I simply refuse to even entertain the idea that the nonsense rules you described should ever be used whatsoever at any game table. EVER.
The only thing that makes sense is exactly what I described. The bag of holding is a pocket dimension with free-flowing exchange of media between the bag and the external. The bag of holding is not hermetically sealed as to cause pressure differentials.
The bag of holding contains 64 cubic feet which at 1atm provides one human approximately 3hrs and 45min of air.
PERIOD.
EDIT - I did some rough calculations of a cavitation bubble caused by opening a bag of holding underwater IF we assume a pressure differential. At 10 feet the explosion would be the equivalent of 1/3rd stick of dynamite. A Mark48 torpedo has approximately a 40kg TNT warhead which causes a 5meter radius bubble in explosion at typical depth of ~10 feet. So a bag of holding representing about 64 cubic feet is a cavitation bubble approximately 1/295ths the size of a torpedo's detonation at that depth. 1/295ths of 48kg of TNT is about 1/3rd stick of TNT.
However; a bag of holding's bubble size does not change at depth. Thus the deeper you go the more explosive potential. The explosion is exponential per foot of sea water.
SECOND EDIT - the 10psi differential between sea level and mount Everest means you can fill your bag of holding with nails and walk up to the Storm Giant King's castle and open the bag of holding in the Storm Giant's face and blow his head off instantly.
With a bag of holding BY "rules" of the game. I simply refuse to believe that, it must therefore be homebrewed to make any sense.
Your argument is that physics doesn’t work right in a magical demiplane? So you’re ok with a backpack being able to hold the same volume of stuff as an SUV, but breathable air is where you draw the line?
Don't try to apply real world physics to D&D. Obviously physics doesn’t work exactly the same, people can shoot lightning out of their fingertips, and run across water, and fly. It’s a game, not a simulation. It doesn’t even try to be a simulation.
Speaking as someone who regularly does physics in D&D to calculate silliness like the coefficient of gravity and other random D&D things (and who plays D&D with folks who have extremely advanced science degrees), let me be very clear on this - someone pointing out what RAW says, and justifiably pointing out that our real world physics might not apply to the barriers between different planes of existence is hardly being "lazy." They are just going with what the rules say.
The rules may be dumb at times when you apply real world physics; but this is a fantasy game. Certain things simply might work differently--after all, here in the real world, we do not really have any analog to pocket dimensions that exist in their own completely separate bubble of reality, as a Bag of Holding does.
If you brought up your suggestion at my table, I would find it fascinating, nerd out over the science, but ultimately rule that the Rules as Written control. If you then followed up in the way you did, you would be out of my game--it is one thing to be sad that your suggestion did not work, but rudely lashing out at folks for deciding the rules of the magical game trump real world physics? I think most people would see that as a one-way ticket to finding another group to play with.
I would just rule the open upside down bag of holding would work just like a real diving bell.
You could stick your head in and catch a breath or two.
Because its a magic bell/bag there is no chance of compression or implosion. A portable hole would be even better. Its just bigger.