LPG (Liquefied Petroleum Gas), commonly known as Cooking Gas in Nigeria because of its prominent use in cooking, is a mixture of two flammable but non-toxic gases known as propane and butane.

LPG in its natural form is odorless. Its distinctive smell is introduced during production using an odourant which helps people detect any potentially dangerous gas leaks that might otherwise go undetected. 

LPG is naturally in vapour form, however, when compressed to 274 times its normal form, it turns to liquid. This allows it take relatively less space for storage.

LPG remains liquid inside a storage tank/cylinder, as the storage vessel is designed to withstand the pressure. When a cylinder is full, it is usually filled at 80% liquid, with the remaining 20% allowed for expansion and vapour. 

When slowly released from the cylinder valve, it turns back to gas vapour rich in energy which can be burned to release heat for applications like cooking, heating, or powering of machines like generators and car engines. 

LPG as Liquid

As liquid, LPG is colouress and odourless. It looks a lot like water.

Unlike water which turns into vapour/steam at 100*c, LPG boils at -42*c becoming vapour.

It remains liquid inside a cylinder because of its stored pressure, turning only to vapour when the gas valve  is opened. 

LPG as Vapour 

Majority of domestic LPG applications in cooking, heating, etc is with LPG in its vapour form. 

When released from the cylinder valve, vapour LPG expands to 270 times the volume of its liquid form (i.e. 1 liter of liquid LPG equals 270 liters of gaseous LPG) 

LPG gas vapour is heavier than air. When released, it will sink and collect to the lowest point of any area such as ducts, drains, etc. In the event of an accidental release in a sealed structure, it will collect on the floor and rise vertically as more gas is added, creating an extremely hazardous situation. Vapour LPG will however dissipate with the slightest movement of air. 

Explosive limit of LPG is between 2.15% and 9.6% mix of air and LPG. This means that for LPG to ignite, its LPG/air mixture must be between 2.15% and 9.6% of LPG, in addition to the presence of an ignition source such as a naked flame, spark or hot metal.