Gas bottles come in many sizes and are for holding Liquid Petroleum Gas or LPG for short. LPG is a combination of Butane and Propane. These are fuel gases that are in the liquid state under pressure. Butane is for warmer areas and Propane is for colder area as it boils at a lower temperature.
In some countries the liquid is sold as a mixture part Butane part Propane.
The beauty of it is that the liquid contains a lot of energy.
The liquid LPG is fairly safe and available. We have plenty of it at the moment. Its used in many places and for many uses like cigarette lighters, canisters for camp cookers and lights. Trades use it for warming flooring products and roofing applications. A bigger use is water heating and industrial processes. Restaurants and homes that do not have natural gas will have bottle gas.
It is often used on yachts for cooking and water heating.
Bottle gas comes in sizes of 2kg, 3kg, 5kg, 9kg, 15kg and 45kg in the portable sizes and much larger for stationary sizes and bottles are filled in situ down to 45kg. Others are bottle swapped or filled at gas stations. Bottle filling at 45kg is much cheaper than smaller sizes.
An average house can use bottle gas at the 9kg size and run through 2-3 bottles per year for cooking only. Bottles for homes for water heating are replaced or filled in situ regularly using an automatic switch over valve. The empty bottle is swapped out for a full one.
Bottles have fairly stringent rules about their location and permits and certificates are required for amounts over 100kg on an individual site.
A gas fitter must be used for gas installations in buildings, boats and caravans with a gas certificate. Gas bottles sited inside building have to comply with special rules. The appliances that operate on LPG bottle gas are set up specially for the particular gas in the bottle. Piping from the bottle is mostly copper.