Bottled gas is a term used for substances which are gaseous at standard temperature and pressure (STP) and have been compressed and stored in carbon steel, stainless steel, aluminum, or composite bottles known as gas cylinders.

Gas state in cylinders

There are four cases: either the substance remains a gas at standard temperature but increased pressure, the substance liquefies at standard temperature but increased pressure, the substance is dissolved in a solvent, or the substance is liquefied at reduced temperature and increased pressure. In the last case the bottle is constructed with an inner and outer shell separated by a vacuum (dewar flask) so that the low temperature can be maintained by evaporative cooling.

Case I

The substance remains a gas at standard temperature and increased pressure, its critical temperature being below standard temperature. Examples include:

Case II

Butane gas cylinder
modest Tea Kettle boiling water over small Bottled gas at a tea house.

The substance liquefies at standard temperature but increased pressure. Examples include:

Case III

The substance is dissolved at standard temperature in a solvent. Examples include:

  • acetylene
    • Note: Acetylene cylinders contain an inert packing material, which may be agamassan, and are filled with a solvent such as acetone or dimethylformamide. The acetylene is pumped into the cylinder and it dissolves in the solvent. When the cylinder is opened the acetylene comes back out of solution, much like a carbonated beverage bubbles when opened. This is a workaround to acetylene's property to explode when pressurized above 200 kPa or liquified.
  • carbon dioxide in the form of a soft drink

Case IV

The substance is liquefied at reduced temperature and increased pressure. These are also referred to as cryogenic gases. Examples include:

Note: cryogenic gases are typically equipped with some type of 'bleed' device to prevent overpressure from rupturing the bottle and to allow evaporative cooling to continue.

Expansion and volume

The general rule is that one unit volume of liquid will expand to approximately 800 unit volumes of gas at Standard temperature and pressure with some variation due to intermolecular force and molecule size compared to an ideal gas. Normal high pressure gas cylinders or bottles will hold from 200 to 400 atmosphere (unit)s. The atmosphere units pressure held by the bottle is equivalent to the number of volumes of standard temperature and pressure of the gas held by the bottle for an ideal gas.

Special handling considerations

Because the contents are under high pressure and are sometimes hazardous, there are special safety regulations for handling bottled gases. These include chaining bottles to prevent falling and breaking, proper ventilation to prevent injury or death in case of leaks and signage to indicate the potential hazards.

In the United States, the Compressed Gas Association (CGA) sells a number of booklets and pamphlets on safe handling and use of bottled gases. (Members of the CGA can get the pamphlets for free.) The European Industrial Gases Association and the British Compressed Gases Association provide similar facilities in Europe and the United Kingdom.

Nomenclature differences

In the United States, 'bottled gas' typically refers to liquefied petroleum gas. 'Bottled gas' is sometimes used in medical supply, especially for portable oxygen tanks. Packaged industrial gases are frequently called 'cylinder gas', though 'bottled gas' is sometimes used.

The United Kingdom and other parts of Europe more commonly refer to 'bottled gas' when discussing any usage whether industrial, medical or liquefied petroleum. However, in contrast, what the United States calls liquefied petroleum gas is known generically in the United Kingdom as 'LPG'; and it may be ordered using by one of several Trade names, or specifically as butane or propane depending on the required heat output.

Colour coding

Different countries have different gas colour codes but attempts are being made to standardise the colours of cylinder shoulders:

  • Colours of cylinders for Medical gases are covered by an International Organization for Standardization (ISO) standard, ISO 32; but not all countries use this standard.
  • Within Europe gas cylinders colours are being standardised according to EN 1089-3, the standard colours applying to the cylinder shoulder only; i.e., the top of the cylinder close to the pillar valve.
  • In the United States, colour-coding is not regulated by law.

The user should not rely on the colour of a cylinder to indicate what it contains. The label or decal should always be checked for product identification.

European cylinder colours

The colours below are specific shades, defined in the European Standard[1][2][3] in terms of RAL coordinates. The requirements are based on a combination of a few named gases, otherwise on the primary hazard associated with the gas contents:

Specific gases

Gas Colour Notes
Acetylene maroon
Argon dark green shoulder
Carbon dioxide grey shoulder
Chlorine yellow shoulder
Helium brown shoulder
Hydrogen red shoulder
Nitrous oxide blue shoulder
Nitrogen black shoulder previously grey in the UK
Oxygen white shoulder previously black in the UK

Based on gas properties

Gas property Colour Examples
Toxic or corrosive yellow shoulder ammonia, chlorine, fluorine, arsine, carbon monoxide, sulfur dioxide
Flammable red shoulder hydrogen, methane, ethylene, forming gas
Oxidising light blue shoulder nitrous oxide, oxygen-containing blends
(nontoxic, nonflammable, nonoxidising)
bright green neon, krypton, xenon
Toxic and flammable or
Toxic and corrosive
yellow and red shoulders (either two bands or quartered)
Toxic and oxidising or
Corrosive and oxidising
yellow and light blue shoulders (either two bands or quartered)

Gas mixtures, mostly for diving

Diving cylinders are left unpainted (for aluminium), or painted to prevent corrosion (for steel), often in bright colors, most often fluorescent yellow, to increase visibility. This should not be confused with industrial gases, where a yellow shoulder means chlorine.

Gas Colour Alternative
Air white and black quartered shoulder or a white top and black band
mixture of nitrogen and oxygen
white and black quartered shoulder or white top and black band green stripe on yellow bottom
mixture of helium and oxygen
white and brown quartered shoulder
mixture of helium, nitrogen and oxygen
white, black and brown segmented shoulder

See also




  • ISO 32: Gas cylinders for medical use—Marking for identification of content.
  • CEN EN 1089-3: Transportable gas cylinders, Part 3 - Colour Coding.

External links