How does a scuba diver’s oxygen tank last for ~1 hour but an astronaut’s lasts ~6-8 hours when both tanks are around the same size?

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How does a scuba diver’s oxygen tank last for ~1 hour but an astronaut’s lasts ~6-8 hours when both tanks are around the same size?

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14 Answers

Anonymous 0 Comments

1/ it’s air not oxygen
2/ one is a closed system – astronauts and wastes very little the other is an open system and wastes a lot
3/ one is under pressure (diver ) one is not astronaut

So a closed system used by a diver at 1m would last the same as an astronauts

If we put both the diver and the astronaut at 100m they both would consume their air quicker as the air is under pressure so squashed by 10x so they need 10x more of it to fill their lungs and breath

Anonymous 0 Comments

The pressure under water compresses the air. The deeper you go, the less your air lasts. If you have access to a pool, take a tall empty glass and turn it upside down. Hold your breath and dive to the deep end holding the glass upside down. See the glass is no longer full of air. It is compressed. Go back towards the surface. It appears there is more air.

Anonymous 0 Comments

Normal air is 78% Nitrogen (inert), 21% oxygen and 1% the rest (important part is carbon dioxide).

With a normal scuba setup, each time a diver takes a breath and exhales, all of the gas is expelled. That’s why you see all of the bubbles leaving the diver’s mouth. This wastes a lot of air. Also, the deeper the diver goes, the more air is needed for each breath – the ocean is pushing on them and more air pressure is needed for the diver to breathe easily. Every 10m / 33ft of depth needs another “atmosphere” amount of air for each breath.

With a space suit, the air is fully recirculated in the backpack. With each breath, only a portion of the oxygen is consumed and replaced by carbon dioxide. The space suit scrubs out carbon dioxide, removes moisture (humans breathe moistly) and a tiny bit of oxygen is put back in to replace what the body absorbed. Also, a space suit provides less air in each breath due to lower air pressure because outside is the vacuum of space, not a lot of water pushing on them. In this way, a space suit can last many hours.

Back in the scuba area, there are more advanced “rebreather” systems that do not dump all of the gas out with every breath, but they are more expensive, more complicated and not common in recreational diving. When diving with a group, everyone would need a rebreather or the dive is limited in length, and no-one wants to sit and wait on the surface for 3 hours after the dive. Navy seals use rebreathers.

Anonymous 0 Comments

You need about 2-3 liters of air to fill your lungs with every breath. The problem is that these are 2-3 liters at ambient pressure. If you breathe at a depth of 50 meters, the pressure is about 6 times higher than at sea level. So now you are using the equivalent of 12-18 liters of air per breath.

Anonymous 0 Comments

Scuba divers operate on a “total loss” system. The tanks contain plain air, and they breathe in a breath, and when they exhale it gets released as bubbles. Also, Scuba divers are supplied air at the same pressure as their surroundings, pressure underwater increases by 1 atmosphere every 33 feet, so you go through your air faster the deeper you go. I have made tanks last almost 2 hours on shallow dives by breathing slowly.

Astronauts tanks contain pure oxygen, their suits and life support systems contain complex computers and instruments which monitor oxygen levels and co2 levels in the air in their suit. As oxygen gets low, they add more from the tank, and as co2 gets high, it gets scrubbed out.

Some very advanced scuba divers use a re-breather which is similar in concept to what astronauts use.

Anonymous 0 Comments

I haven’t seen a comment addressing the fact that astronaut suits usually supply an air pressure of 4.3PSIA. That a vacuum. Atmospheric pressure is 14.7PSIA or 0PSIG. The astronaut doesn’t need much pressure because the little osmosis that occurs in the lungs is enough from the oxygen concentration.

Anonymous 0 Comments

You made a false assumption. “Both tanks are around the same size”. A scuba tank is typically made up of air.

I don’t know what an astronauts stuff is made of but a rebreather requires several different components to work.

1. A small bottle of pure O2. These bottles can be very small, like the size of a spair air canister.

2. A bag to maintain positive pressure. This bag would hold the scrubbed exhalation that has already passed through a filter (scrubber) + additional O2 to make up for the loss of O2 your body utilizes on the previous breath of air.

3. A filtration system to scrub out the CO2 from exhalation. This is typically about the size of a lunch box and as far as I’m aware, must be this size because of the chemical processes occurring with the amount of breath exhaled from the average astronaut.

All these components can pack pretty tightly together in something the size of a small backpack.

Anonymous 0 Comments

A rebreather absorbs the exhaled carbon dioxide from the breath and then recycles the air which still contains significant amounts of oxygen so that it can be breathed a second time enabling the air supply to last longer than would normally be the case. https://youtu.be/2_OL4sOyeEw

Anonymous 0 Comments

First of all, except for very specific circumstances, you never use pure oxygen in scuba diving. It’s usually a regular air (21% oxygen) or slightly enriched air (up to 40% oxygen). The reason is that deeper than 6m/20ft breathing pure oxygen is toxic to central nervous system. The common symptoms are convulsions, seizures and death from drowning.

The deeper under water you go the faster the gas in the tank is used up. At 30m each breath consumes twice as much air from the tank as at 15m, and 4 times more than at the surface. That’s because to make a breath you need to inhale a certain more or less fixed volume of air which is the same at any depth, but since the pressure doubles with each 10m of depth the same volume of air holds different amount of air.

In space they would breathe air at the same or slightly lower pressure that we breathe at the surface of the earth because the space suits are pressurized to about normal atmospheric pressure. In contrast, without using specialized equipment you can dive to 40m where the pressure of water on you is 5 times more than at the surface.

Everything above is about a typical common scuba set up that you would see on vacation. It’s called an open loop.
Rebreathers are closed loop. They are popular among more advanced technical divers. It’s possible to dive for 6-8 hours with rebreather too.

Anonymous 0 Comments

People are answering on the astronaut side, but I wanted to give an answer from the scuba side:

When a SCUBA diver breaths in on their tank, the air is pressurized to their depth pressure. Pressure under water increases by approximately one atmosphere every 10 meters you go down. So if you take a 4 liter breath of air at 20m depth, that uses 12 liters of air at standard atmospheric pressure. This is why it is very important to breath out while ~~assessing~~ ascending when diving, if you try and hold your breath the air will expand in your lungs and can cause serious issues.