LPG marketed in India confirms to Indian Standard Specification IS-4576. Some of the important properties and their bearings are :

LIQUID DENSITY

LP gases in the liqud state are nearly half as heavy as water. Specific gravities range from 0.55 - 0.58. Knowledge of this property helps us in calculating the safe quantities that can be filled in a given container whose volume is known. An LPG container should be filled in such a way that there will be a 5% ullage left at the design temperature, otherwise, as temperature rises excessive pressures are likely to be encountered leading to bursting of cylinders.

CO-EFFICIENT OF EXPANSION OF LIQUID

Approximately 12 times that of water. This property in conjunction with liquid density should be taken into consideration for arriving at safe filling capacities of containers.

VAPOUR SPECIFIC GRAVITY

LPG vapour is nearly 1 1/2 times to 2 times as heavy as air. This would mean that any escaping vapour of LPG would tend to settle down. Hence, there should be adequate ground level ventilation where LPG cylinders are stored.

For this very reason LPG cylinder installations should not be undertaken in cellars or basements which have no ventilation at ground level. Also, cylinders installation should not be within 1 meter of drain opening.

VAPOUR PRESSURE

The vapour of LPG in equilibrium with its liquid exerts a pressure called the vapour pressure and the magnitude of this pressure is dependent on the ambient temperature and not on the quantity of the contents. Vapour pressure increases rapidly with temperature. Boiling point of a liquid is that temperature at which the vapour pressure of the liquid equals atmospheric pressure. Since boiling point of LPG is below 0 deg. C the pressure inside a cylinder is always higher than the atmospheric pressure for temperatures above 0 deg C and hence, this is the reason that gas gushes out of a cylinder when the valve is opened.

Hence, an external equipment i.e. pressure regulator is needed for obtaining gas at a constant pressure for use in appliances irrespective of the ambient temperature.

Combustible gases will only ignite with air  when mixed with it in certain proportion. As a combustible gas is gradually mixed with air in increasing proportions, a concentration is reached at which the mixture just becomes explosive i.e. ignitable. This is called the " Lower Explosive Limit"

As concentration of the gas is further increased,  a point is reached at which the mixture ceases to be ignitable, and the concentration of the gas just before this point is called the "Upper Explosive Limit"