# What is the temperature (and pressure) of the oxygen inside an oxygen bottle?

In the hospital or in a lab, one can see the huge oxygen bottles. A question is, what is the temperature of the oxygen inside the bottle? And what is the pressure inside?

We know the critical temperature of oxygen is far below the room temperature. Therefore, if the temperature is room temperature, the oxygen is in a gaseous phase. Since the density is high, the pressure must be very high.

If the temperature is below the critical temperature, then why does not it equilibrate with the environment?

• For a non-kryogenic bottle it is just the temperature of the environment (why should it have another temperature?). May 24, 2015 at 19:17
• It is stored both as high pressure gas and liquid. It does not equilibrate because it's being cooled. en.wikipedia.org/wiki/Oxygen_therapy#Storage_and_sources
May 24, 2015 at 19:34
• If it is just the environment temperature, then the pressure is very high. But i saw in the lab, that when they opened the bottle, it was not so violent. May 24, 2015 at 20:12
• Many years ago I worked with liquid nitrogen (which, coincidentally, was a byproduct from a plant the Air Force operated to generate liquid oxygen for aircraft). The liquid nitrogen (just like liquid oxygen in general properties) was kept in a "Dewar flask" (giant Thermos bottle). The pressure inside the bottle was essentially atmospheric pressure (a slight pressure was used to force the liquid out via a siphon tube). The temperature was of course the boiling point of nitrogen at atmospheric pressure (plus or minus a small delta due to not quite being at equilibrium). Oxygen would be similar. May 24, 2015 at 21:13
• This is approximately what the Dewer flasks looked like (only not nearly as pretty). They also apparently come in a few other form factors, based on what Google found looking for this image. May 26, 2015 at 2:09

The answer depends on the nature of the "huge oxygen bottles"...

You often see large ( around two stories high) tanks outside a hospital. They are distinguished by the name of the chemical firm, Union Carbide or Linde among others, painted on the side, and by the thick layer of frost found on the attached plumbing.

These tanks hold liquid oxygen at low pressure (a few atmospheres at most) and very low temperature with very effective(but cheap) insulation. The low amount of inward heat flow causes some liquid oxygen to vaporize, raising the internal pressure. The tank isn't very structurally strong, so the generated pressure is relieved by usage in the facility, or by a pressure relief valve, which of course wastes oxygen. In extreme cases, a heater may be used to raise the internal pressure to meet the needs of the facility. Failure of this pressure relief valve (closed) is a major danger for this type of tank.

The other type of oxygen tank is the much smaller (maybe 6 feet by 12 inch diameter) steel tank.

This is a very strong steel tank containing compressed oxygen gas at ambient temperature and very high pressure. The tank is heavy, expensive, and must be treated with great care. (I wouldn't use the set up in this photo; too tippy!) A complex pressure reducing valve is needed to give a controlled low pressure flow, If you examine such a tank (in a lab, for example), you may find a series of date stamps, possibly covering decades, on which the tank has been tested at some huge overpressure.

Note: image edited to eliminate problematic stamp on tank...

• You might want to edit to add some images of Dewer flasks. May 26, 2015 at 2:10

In some high-demand medical facilities, liquid oxygen at cryogenic temperatures (in tanks) is used (http://208.76.246.34/~ava/Oxygen-source.pdf). More often, gaseous oxygen in metal cylinders is used. The pressure may vary, but the above source gives 13700kPa (for UK).

Liquid oxygen has an expansion ratio of 860:1. This means that as it boils off from -297°F to ambient, it expands 860 times its volume. This is why aircraft have “build-up” coils” that allow the liquid to expand into gaseous form prior to the oxygen breathing regulators. In the LOX servicing cart there is a build-up tube, vent valve, and rupture disk to prevent the warming expansion from creating so much pressure that it blows the cart’s lines.

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Feb 10, 2020 at 16:03