The science behind LPG

Can’t tell your butane from your propane, or pick a hydrocarbon out of a crowd? Explore the science behind LPG with our top 10 technical facts – no lab coat required.

1. ‘LPG’ stands for liquefied petroleum gas

Let’s start with the basics. The common acronym you hear used when referring to bottled gas is LPG. This stands for ‘liquefied petroleum gas’ – so called because when this gas is stored under pressure in a cylinder or tank, it becomes liquid.

When you use LPG for your home and commercial appliances, it’s slowly released from a valve at the top of the bottle as a vapour. As the vapour is released from the cylinder, LPG liquid in the cylinder transforms into gas.

It’s this clever characteristic that allows plenty of energy to be stored in a single container, ready for use for cooking, heating, barbecuing and more.

2. LPG is made during oil refining or natural gas production

LPG is produced during the refining of oil and gas products, or is extracted during the natural gas production process.

Instead of burning off or otherwise destroying this useful by-product, LPG is captured and stored so it can be used as a fuel by homes and businesses alike.

3. LPG is a hydrocarbon gas

LPG belongs to a category of fuels known as hydrocarbon gases. And here’s the interesting part – LPG isn’t one single gas, but a mixture of several of them. The common factor amongst all LPG gases is their ability to be compressed into liquid at relatively low pressures.

4. LPG can be propane, butane or more

So, what are the different types of hydrocarbon gas that fall into the liquefied petroleum gas category? The two most common types of LPG are propane (C3H8) and butane (C4H10).

There are also two types of butane – ‘n’ and ‘iso’.

Other hydrocarbon gases which are classified as LPG include propylene, ethylene, butylene and isobutylene.

LPG mixtures can also contain very small amounts of ethane and methane.

5. LPG vapour is heavier than air

When LPG vapour leaks from its cylinder or tank, it can accumulate at ground level. That’s because its molecular weight is heavier than air, causing it to sink.

6. LPG can expand and contract

Gas bottles are fitted with safety relief valves

Another feature of LPG is that, like all liquids and gases, it expands with increases in temperature.

A hot day will result in the LPG pressure inside a container increasing. To cater for these characteristics, there are Australian standards that set maximum fill levels for cylinders and tanks to ensure the liquid has spare room inside its container to safely expand.

That’s why a gas bottle will never be filled to the full capacity it’s able to hold. 

7. LPG cylinders and gas bottles are specially built

LPG cylinders are designed and manufactured specifically to contain pressurised gas.

They’re fitted with safety relief valves to vent the excess pressure which will occur if the container is overfilled, or exposed to extreme heat such as a fire.

Gas bottles must be stored upright to ensure that the safety relief valve is at the top of the cylinder, and so that vapour rather than liquid is released if the valve leaks or vents.

Gas cylinders are also regulated by standards which relate to their manufacture, use and testing. The materials used, and the standards that apply, are all intended to ensure a high level of safety.

8. LPG can have a yellow flame or blue flame

As a flammable gas, LPG burns when mixed with the right quantities of air and an ignition source. It’s this feature which makes it so handy for cooking and heating – and potentially dangerous if there is a leak.

A handy tip to note is that the colour of your LPG flame is a good indicator of how well your burner is working. A blue-tipped flame is ideal, and tells you there’s enough oxygen for complete combustion – and that means no wasted gas or harmful carbon monoxide.

However, if your LPG flame is yellow, red or there are sooty black tips, it’s a sign of incomplete combustion. This can be a serious safety hazard, so it’s important to get your appliance and burners serviced as soon possible.

Learn about our gas safety and appliance service

9. LPG in its natural state has no odour

Contrary to what you might expect, LPG in its natural state has no odour or colour. An odourant called ethyl mercaptan is added to LPG so that if there’s any leaks, you’ll be able to spot that distinctive gas smell. It’s all in the name of using gas safely.       

10. LPG is not natural gas

Finally, it’s important to distinguish between LPG and natural gas.

Many people mistakenly think that LPG and natural gas are interchangeable – but in fact, they have different chemical make ups, with natural gas composed predominantly of methane.

They also have different densities and pressures, and require different amounts of air for complete combustion, so you can’t substitute one for the other.

If you’re looking for gas to power your home or business, make sure you understand the difference and organise a gas supply that suits your existing appliances.

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