Propane

Photo by Michael Fötsch

Commercial Propane is sometimes supplied as a mixture of propane and other Liquifed Petroleum Gases (LPG) such as butane, butylene and propylene. Autogas, in most parts of Australia, is a mixture of LPG gases including propane. LPG mixtures can be used as hot air balloon fuel provided adequate fuel pressure can be obtained.

General Properties of Propane

• Propane is a colourless, odourless and non-toxic gas. It is supplied commercially with an added odorant (usually ethylmercaptan) to assist detection by smell.
• Propane boils at -42 degrees Celsius. At 15 degrees Celsius it has a storage pressure of 635 kPa.
• Propane is stored as a liquid under pressure and will expand approximately 270 times to a vapour at normal temperatures and pressure when released.
• When the propane changes to a vapour it is possible to see the initial leak by the cooling effect of the leak, which causes condensation, and even freezing of the water vapour in the air. Not being able to see the effects of the leak after a short distance does not mean that the gas is not present in a potentially explosive mixture.
• Propane is heavier than air, and may flow along the ground or through drains and will sink to the lowest level of the surroundings.
• The flammability range of the gas is 1.6% to 9.5% by volume in air. A small proportion of the gas can therefore give rise to a flammable mixture.
• Propane and other LPG gases are excellent solvents of petroleum and rubber products. Propane and other LPG gases are generally non-corrosive to steel and copper alloys. Precautions against corrosion may be necessary if aluminium or aluminium alloys are used.

Chemical Properties

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• A propane molecule consists of three carbon and 8 hydrogen atoms C₃H₈
• When propane burns completely the products of combustion are water and carbon dioxide (Propane:C₃H₈ + 5O₂ -> 3CO₂ + 4H₂O)
• When propane an incorrect fuel air mixture exists and combustion is not complete carbon monoxide (CO) may also be a product of combustion
• Propane has a heating value of approximately 50 Mj / kg
• Propane vapour is heavier than air. It has a specific gravity of 1.52
• Propane liquid is lighter than water. It has a specific gravity of 0.51. One litre of propane liquid weights 0.51 kg.

Safety

• Propane has a wide flammability range, 1.6% to 9.5% by volume in air. This means take even a small leak can create a large volume of combustible mixture. For example, a 100ml liquid leak will expand to 27 litres of vapour which could mix with between 284 and 1684 litres of air to form a flammable mixture. Even small small leaks need to be treated very seriously.
• Propane boils at -42 degrees Celsius, cold enough to cause severe cold burns to any exposed flesh that it comes into contact with. It is very important that personal protective equipment including gloves, googles and a long sleeve shirt be worn whenever you are working in any environment where there could be a propane leak.
• Even though propane is not toxic it has caused deaths through asphixiation. Being heavier than air it tends to collect in low lying areas. Avoid entering drains or pits anywhere near where there has been a propane leak.

Refuelling Procedures

1. Vehicles should be pointed into the wind, and the refueller must ensure that they are not blocked in.
2. LPG, by its rapid vaporisation and consequent lowering of temperature can cause severe frost burns. Protective clothing such as gloves, goggles and a long sleeved shirt should be worn when there is any possibility of contact with liquid LPG.
3. Before filling commences, the area shall be checked to ensure that there are no sources of ignition, i.e. smoking, naked lights or flames, running car engines, or mobile phones within 10 metres of the connections at either end of the transfer hose.
4. A check should be made to ensure that the test stamp on the cylinder is within the required ten-year test period. A cylinder, which does not have a current test inspection stamp, must not be filled.
5. A check should also be made for apparent damage or corrosion to the cylinder, and all valves and / or controls checked to ensure that they are in good working order with no leakage.
6. Cylinders must not be tilted during refuelling.
7. It is very important that cylinders are not overfilled, and that a vapour space is left at the top of the cylinder. This is achieved by closing the cylinder valve immediately LPG flows from the bleeder valve.

Procedure in case of a Propane Leak

1. Shut off any electrical equipment and leave off until vapour hazard is removed.
2. If available, use the outside “EMERGENCY STOP” handles or buttons.
3. No smoking or naked lights within 70 metres.
4. Move people away from the area. Move upwind.
5. Stop leaks if possible.
6. If possible, separate the leaking container and position so that only gas escapes.
7. Spray water to disperse the gas cloud.
8. Prevent spillage where practical from spreading or entering underground drains by banking with sand or earth.
9. Do not start engines and / or operate electrical equipment in the area.
10. Inform the fire brigade, police and gas supplier.