Dangerous goods: Class 2 - Gases
Jun 19, 2018

Dangerous goods: Class 2 - Gases

Rachel Chesterfield Rachel Chesterfield

Gas and Gases: No doubt you have gone from knowing that gas was one of the four known elements of life (air, water, fire and earth) to something much more complex.  If you have ever studied gases in chemistry or physics, or even in a more practical sense, such as within your workplace, you will be aware of just how technical they can get.  But back on topic; what are class 2 dangerous goods besides just gases?

What Are Gasses?

Gases are considered as a state of matter.  The three commonly known remaining states of matter include solids, liquid and plasma.

The term ‘gas’ extends to an extremely wide range of articles.  Some of the more commonly known forms of gasses can include compressed gases, dissolved gases, liquefied gases, refrigerated liquified gases, mixtures of gases and aerosol dispensers or similar vessels containing gas.

A gas can be defined by the kinetic monocular theory or rather, comparing its properties to those of liquid and solid forms.  That is, a gas is a substance that does not have a fixed form or volume itself, is relatively compressible and has a relatively low density.

As defined by the Australian Dangerous Goods Code, a gas is:

A substance which at 50 degrees Celsius has a vapour pressure greater than 300kPa; or a substance which is completely gaseous at 20 degrees Celsius at a standard pressure of 101.3 kPa.

Basic Classification of Gases

Calling a substance a gas is just as bad as describing water as a liquid….

There would have to be thousands, if not more ways to break down the classification and definition of a gas, or in this case more pointedly, a compressed gas.  But even the term compressed gas covers a whole range of products, specifically seeing that it is in general, a generic term used to describe not only compressed gasses (non-liquefied gases), but liquified compressed gases, cryogenic gases, and dissolved gases.

  • Liquified Compressed Gases

Liquified gases are further classified into refrigerated and non-refrigerated liquified compressed gases, or otherwise, liquified and cryogenic gases.  Liquified compressed gases are pressurised at normal temperatures to become a liquid. When in a cylinder, the vessel is initially filled with the condensed gaseous substance in liquid form.  The liquid will naturally evaporate within the cylinder, creating a vessel filled to a liquid-vapour state of equilibrium. As gas is released from the cylinder, liquid will evaporate to fill the space that has been vacated, keeping the pressure within the cylinder constant.  As more gas is released from the cylinder, the ratio of liquid to gas within the bottle will decrease. Examples can include anhydrous ammonia, methane, carbon dioxide, chlorine, and propane.

  • Cryogenic Compressed Gases

Cryogenic gases, or comparatively put; refrigerated liquified gases, are liquefied compressed gases that have been cooled, rather than compressed, to form a liquid state within a vessel.  Cryogenic gases can be further classified into three categories: flammable, inert and oxygen. All cryogenic gases have very low boiling points (-150’ C), and hence need to be kept very cold.  Possibly the most significant feature of cryogenic gases is the ability for small amounts of the gas to expand rapidly into extreme volumes of gas. Examples can include liquid nitrogen, liquid helium, and argon.

  • Non-Liquified Compressed Gases

Non-liquefied gases can be known as real ‘compressed gases’ or sometimes permanent or pressurised gases.  Non-liquified gases do not form liquids at normal temperatures when compressed, even when under high pressure. Examples can include argon, oxygen, nitrogen and helium.

  • Dissolved Compressed Gases

The only commonly used dissolved gas is acetylene.  Chemically, acetylene is extremely unstable. To counter for this, acetylene is stored in a cylinder that is filled with a solvent (generally acetone) saturated porous.  The gas dissolves in the acetone, stabilising the substance. This allows the gas to be relatively safe for storage and handling.


It is unknown how early the form of gas as a substance was really understood.  However, we may attribute the beginnings of the study of gases to 17th century alchemists attempting to make gold.  A few of the significant names can include Richard Boyle, who studied the inverse relationship between the volume and pressure of a gas; Joseph Preistly, who proved that air could be divided into a number of different gases; Jacques Charles, who continued Boyles’ work and Lavoisier’s work and in turn, heavily contributed to the law of conservation of mass.

A name that may be more familiar is Amedeo Avogadro; who was a lawyer, mathematician and scientist.  Avogadro defined the difference between atoms and molecules, created a law stating that ‘equal volumes of all gases, at the same temperature and pressure, have the same number of molecules, and is possibly most renowned for the constant named after him, Avogadro’s number:  6.023 x 1023.  (6.023 x 1023 Molecules = 1 mole.)

John Dalton experimented with water vapour, determined a number of relative masses for several known elements and created the first atomic theory of matter.  Naturally, with each new discovery relating to the atomic model, and the various other breakthroughs in physics and chemistry, the general knowledge of gases gradually increased. But because the topic of gases is so varied and blurred, points of specific breakthrough within the industry can be difficult to pinpoint.  As far as the elements on the periodic table go, Hydrogen was the first gas to be discovered in 1766, with Nitrogen and Oxygen being discovered in 1772 and 1774 bringing the discovery of chlorine. Helium and Fluorine were discovered in the mid-late 1800’s, and all five noble gases being discovered in the 1890’s by Sir William Ramsay.

As with all scientific breakthroughs, research today is still ongoing, and ever increasing.  Who knows how much further we have to go, how much more we have to learn?

The Basic Chemistry Behind Gasses

Gases.  The first basic knowledge of a gas generally begins with the comparison between gases, liquids and solids.  This fades into the kinetic molecular theory of gases, which explains their behaviour, including that gases have no fixed volume, size or shape largely due to the lack of intermolecular forces.  The same lack of bonding explains why gases are not dense and mix well with other gases.

At some stage you would have learned of the atomic theory of matter, including the sub atomic structure of atoms; particles, protons, neutrons and electrons, and eventually the wonders of photons.

Thanks to years of study on gases, we understand a significant amount about gases and their behaviour.  But who knows how much is as yet, left undiscovered?

Through the years, a number of gas laws have been established and can be used for the greater understanding in the behaviour of gases.  Some of the more common gas laws can include Boyle’s, Charles’, Gay-Lussac’s and Avogadro’s laws. The Ideal gas law describes the general behaviour of most gases, and Van der Waal’s ‘real gas law’ accounts for those gases that won’t behave theoretically.

The ideal gas law equation is as follows:  PV = nRT

Let’s have a quick look at those constants:  P demonstrates pressure, measured in kPa or atm; V equals volume, measured in L, n is the number of moles, R is a gas constant, which changes depending on weather the pressure is measured in atm or kPa, and T represents temperature, given in Kelvin (K.)

Mathematically, if one side of the equation increases, so will the other.  The same will apply should one side of the equation decrease. so, if the temperature is increased, either pressure, volume, or a combination of both, will increase.

It's easily seen then, that should a compressed (already highly pressurised gas) within a cylinder (having a fixed volume) can become dangerous as temperature increases.  Should the temperature increase too significantly, such as in the event of a fire, the cylinder will not be able to contain the substance and is likely to rupture or explode ultimately adding to the fire and creating a flying projectile.  The same principle apples when a cylinder is pierced or punctured. The pressure within the cylinder will rapidly disperse from the weakened vessel, creating a flying missile.

Storage requirements of gasses

Being aware of how dangerous gases can potentially be, it is critical that gas cylinders are stored in an appropriate manner.  It is required that all gas cylinders are compliment to the regulations established through Australian Standard AS4332-2004 ‘The storage and handling of gases in cylinders.’

It is crucial, especially for cylinders containing pressurised gases, to be both used and stored only in an upright position, and when in storage the protector cap must be secured over the valve, and the cylinders secured with a strap, cable or non-abrasive coated chain that will not scratch the cylinder.  Ideally, the cylinder should be stored in a customised racking system.

A gas cylinder store complaint to the Australian standards is specifically designed to cater for the risks associated with gases, and to reduce those risks in your workplace.  AS4332-2004 outlines requirements of gas cylinder stores such as:

  • Gas cylinder stores must be constructed from non-combustible material
  • The base of the gas cylinder store must be level.  If drainage is required, the floor must be sloped in a way that doesn’t compromise cylinder stability.
  • Any space between the bases of the gas cylinder store and the ground must be filled with a solid non-combustible material or have at least 2 ends completely open to the air.
  • Any gas cylinder store that is attached to or located within a building must be separated from the rest of the building by one or more walls.  Each of the walls must have a fire-resistance level (FRL) of 240/240/240.
  • The floor above any gas cylinder store in a multistorey building must be constructed of a material having a fire resistance rating of 180/180/180.
  • The walls and roof of gas cylinder stores must be of a non-combustible material.  Where practical the supporting structure must also be of non-combustible material.
  • Bollards and crash barriers must be installed where there is a risk of cylinders being damaged by vehicles in the surrounding area.
  • Ignition sources must be excluded from any gas cylinder store containing flammable gases.
  • The doors of a gas cylinder stores must open outwards or be a ventilated roller door that can be open from inside the store.
  • Any electrical equipment installed in a gas cylinder stores must comply with AS/NZS 3000 and all elect ravel fittings must be installed in a way that prevents them from being damaged by impact from cylinders.
  • Gas cylinder stores must also have gas cylinder restraint bars and chains to prevent the gas bottles from falling over.
  • Gas cylinder stores can be located indoors or outdoors, however the indoor storage of compressed gases must be avoided at all times.

Next Steps

So, who knew there was so much to a single element of life?  Gasses surround every moment of our lives. They are dangerous, almost inconspicuously so.  However, gases aren’t the only dangerous goods that we interact with on a daily basis, and all of them present risk and danger within your environment.  If you are interested in more information on the varying classes of dangerous goods including the ever-evasive gases, download our free eBook by clicking on the image below:

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