LPG exists as a gas at normal atmospheric pressure & temperatures, but may be liquefied by the application of moderate pressure. If the pressure is released the liquid will revert back to vapour.
LPG as a liquid is colourless and as a vapour, cannot be seen.
Pure LPG has no distinctive smell so for safety reasons a stenching agent is added during production to give a pungent, unpleasant smell and so aid detection.
LPG is non-toxic but at very high concentrations in air, LPG vapour acts as an anaesthetic and subsequently an asphyxiate by diluting or decreasing the available oxygen.
When LPG is mixed with air, a highly flammable mixture is produced. The flammability range is between 2% to 11% by volume of gas to air. Outside this range any mixture is wither to weak or rich to potentially ignite.
One volume of liquid will produce approximately 250 volume of gas vapour. “A little goes a long way, treat LPG with respect”
LPG vapour is heavier than air. Any escapes will find its way to the lowest level where it can remain and form a flammable mixture. Therefore LPG vessels must be sited away from drains and appliances must not be sited in basements or cellars. Cylinders in boats and ships must be stored in purpose built sealed gas lockers.
LPG is lighter than water and therefore floats on top of it in a similar way to oil and petrol. Therefore LPG vessels must be sited away from drains and gullies.
The pressure LPG exerts on a vessel varies with ambient temperature. The higher the temperature of the liquid the higher the vapour pressure, conversely the lower the temperature the lower the pressure. This means LPG must be protected from heat sources and protective safety distances imposed on the siting and storage of LPG.
Commercial Propane has a vapour pressure of approximately 2bar (30psi) at 15oC (similar to the pressure found in a lorry tyre).
Commercial Butane has a vapour pressure of approximately 2bar (30psi at 15oC (similar to the pressure found in a car tyre).
Because of these characteristics Comercial Butane can be used indoors and Commercial Propane must only be used outdoors.
|Technical Typical Properties
Of Commercial LPG Grades
|Commercial Propane||Commercial Butane|
|Gas: Air ratio for combustion||1:24||1:30|
|Flame temperature in air max. *C||1930||1900|
|Flame Speed cm/sec||44||44|
|Relative Density of liquid at 15.6*C (Water at 0*C = 1.0)||0.51||0.58|
|Litre/tonne at 15.6*C||1975||1742|
|Relative Density of gas at 15.6*C (Air at 15.6*C = 1.0)||1.52||2.01|
|Volumes of gas (litres) per kg of liquid at 15.6*C||537||411|
|Ratio gas: liquid volume at 15.6*C||279||238|
|Boiling Point at 1 atm. *C||-45||-2|
|Vapour Pressure-typical bar g at 0*C / 15.6*C||3.8 / 6.4||0.5 / 1.6|
|Limits of flammability (percentage of gas by vol. In gas-air mixture) Upper / Lower||10 / 2||9 / 1.8|
When LPG is heated it expands very rapidly. In order to allow for expansion LPG cylinders and tanks are only filled by volume to a maximum of 87% of the total volume of the retaining vessel.
The boiling point is the temperature below which LPG will not vaporise to form a gas vapour.
Boiling point of Commercial Propane is approximately – 42oC
Boiling point of Commercial Butane is approximately – 2oC
Commercial Butane can be affected by cold weather resulting in poor pressure and should not be used outdoors in winter months. Commercial Propane is not adversely affected by cold weather in the UK and is an ideal fuel source for heating, cooking and industrial applications. However care must be taken for skin not to come in contact with liquid LPG as cold burns may occur.
LPG in both its liquefied and gaseous state has a very low viscosity and will flow very easily like water, petrol etc. This means they will flow with ease and penetrate any breaks or weakness in the installation. Therefore, special jointing componds must be used for LPG installations and certified for use with the service conditions – such as Clessetite.
LPG is aggressive to certain non-metalic materials like natural rubber and many plastics; therefore equipment and hoses must be suitable for LPG. Clesse use only the best rubber hoses from certified European manufacturers.
The Calorific Value of a fuel is described as “The amount of heat released when a known quantity of fuel is burned”.
Commercial Propane = 95 MJ / m3
Commercial Butane = 121 MJ / m3
Natural Gas = 38 MJ / m3
Because LPG appliances release more heat than Natural Gas, it is important that any gas appliances fuelled by LPG are designed and manufactured for that purpose i.e. they will often require special conversion by qualified persons.
Fuel / Air Mix
Commercial Propane = 23:1
Commercial Butane = 30:1
Natural Gas = 9.6:1
Therefore, it is important that appliances fuelled LPG are provided with adequate ventilation and serviced regularly to ensure that they burn efficiently.