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CLASS 2 - GASES
Note: The
following description is not intended to be a definitive technical description of what is
termed a dangerous goods under the New Zealand Standard 5433:1999 - Transport of Dangerous
Goods on Land or The United Nations Recommendations on the Transport of Dangerous Goods.
Compressed gases may include any of the other
hazards and have a separate class for a number of reasons. First, a compressed gas has a
physical hazard due to the increased pressure under which the chemical is maintained. Also
since gases are fluids and therefore highly mobile, they have the property of being able
to extend their hazards over a wide area very quickly. In addition, this spread of hazard
can take place in three dimensions as compared to a liquid's usual two.
Compressed gases
include:
- Oxygen, Nitrogen, Compressed Air
- Acetylene, methane, propane,
- Anyhydrous hydrogen chloride
- Chlorine, Ammonia, Nitrogen Oxide
Since gases may have additional hazards, they are
further subdivided into 3 divisions. These are identified by one of 3 labels:
| Flammable gases present
a particularly dangerous hazard. Given the correct conditions, in a confined space they
may even explode. Since they burn, they can cause other normally non-hazards materials to
burn as well. The main category of flammable
gases is hydrocarbon gases such as methane, acetylene and so on. Some gases can be
liquefied under pressure (propane for example), this means that the given cylinder
contains a large volume of gas. |
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It is important to recognise that flammable gases
require oxygen to actually burn. The gas must mix
with the oxygen. In order to begin burning something must be used to ignite the gas,
usually high temperature. These are the features which must be carefully controlled in
order to be able to handle flammable gases safely.
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Some gases are neither
toxic, nor are they flammable. These have two principal hazards, they are compressed as
described above and they have the capability of displacing oxygen from a confined space.
Without oxygen, people very quickly become unconscious and will die within 3 or 4 minutes.
Some division 2.2 gases have the additional
hazard of being oxidizers. A classic example is of course oxygen itself. Oxygen makes up
20% of the atmosphere but only a small increase in oxygen contain will increase the
liklihood of a fire or other chemical reaction and increase the intensity of that fire
should it occur. |
| Toxic (poisonous) gases
are particularly dangerous to health since they mix readily with air and can easily enter
the body's systems via the lungs. Of course,
some gases are more toxic than others. Some are so toxic that they are lethal in small
concentrations even when they are absorbed via the skin, these gases are not transported
commercially within New Zealand. There are other chemicals which are extremely toxic such
as chlorine used for water treatment or hydrogen sulphide. |
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