What is LPG? Composition, properties and uses of liquefied petroleum gas

The gas cylinder in your kitchen, the 45kg cylinder at a restaurant and the mini gas canister you take camping all hold the same fuel: LPG. So what is LPG, why is it stored as a liquid in steel cylinders, and what should you keep in mind to use it safely? This article gives a short, easy-to-follow explanation for users, dealers and new shop owners.

What is LPG?

LPG stands for Liquefied Petroleum Gas. It is a mixture of light hydrocarbons, mainly propane (C₃H₈) and butane (C₄H₁₀), obtained from crude oil refining or separated from natural gas. At normal temperature and pressure, LPG is a gas; when compressed at moderate pressure, it turns into a liquid and its volume shrinks many times over (often quoted as about 250 times). This is why a compact cylinder can hold enough fuel for several weeks of use.

In Vietnam, LPG is usually just called “gas”. It should not be confused with natural gas (CNG, LNG — mainly methane), which has quite different properties and is stored in a different way.

Composition: how do propane and butane differ?

• Propane vaporises at a very low temperature (about −42°C) and has a higher vapour pressure in the cylinder, so it still gives a good flame in cold weather.
• Butane vaporises at about 0°C and has a lower pressure, making it suitable for mini gas canisters and portable stoves.

Household cylinder gas is usually a propane – butane mixture, with the ratio depending on the supplier and the season. Mini canister gas is mainly butane — learn more about our clean butane mini gas range.

Key properties of LPG you should know

• Heavier than air: when it leaks, gas sinks and collects near the floor, under the stove and in drains — so never place cylinders in a basement or an enclosed low-lying spot.
• Colourless and almost odourless: commercial gas has a distinctive odorant added so users can notice leaks. See how to check for gas leaks at home.
• Expands strongly with temperature: liquid LPG expands when heated, so cylinders are only filled to the permitted level and always keep a vapour space at the top. Do not keep cylinders near heat sources or in strong sunlight.
• High calorific value, clean burning: a blue flame with less soot and smoke than charcoal or firewood when the stove is properly adjusted.
• Flammable within a certain concentration range when mixed with air — which is why you must ventilate and avoid sparks whenever you suspect a leak.

How is LPG stored and transported?

LPG is filled into pressure-rated steel cylinders fitted with a shut-off valve and a safety valve. Cylinders must be manufactured, pressure tested and inspected according to current standards and regulations; throughout their service life, they must also undergo periodic inspection. Common sizes:

• 12kg LPG cylinders — households and small eateries.
• 45kg LPG cylinders — restaurants, canteens and production facilities.
• 220 – 250g mini gas canisters — portable stoves, hotpot and grilling.

Cylinder quality determines the safety of the whole distribution chain. See LPG cylinder pressure testing and how to tell a compliant LPG cylinder.

Uses of LPG

• Households: cooking and gas water heaters.
• Restaurants and commercial kitchens: high-pressure burners, stockpot stoves and ovens — usually running on 45kg cylinders or a cylinder manifold.
• Industry: drying, heating, metal cutting, ceramic kilns and fuel for forklifts.
• Agriculture: drying farm produce and heating livestock barns.
• Portable and outdoor use: mini gas stoves, blowtorches and lighters.

Frequently asked questions

Written by the VietnhatGas technical and sales team — a batch manufacturer of LPG cylinders. This content is for reference; regulations and standards may change, so please check the current texts.