LPG is a blend of Butane and Propane readily liquefied under moderate pressure. LPG vapour is heavier than air; thus it normally settles down in low-lying places. Since LPG has only a faint scent, a mercaptan odorant is added to help in its detection. In the event of an LPG leak, the vapourisation of liquid cools the atmosphere and condenses the water vapour contained in it to form a whitish fog, which is easy to observe. LPG in fairly large concentrations displaces oxygen leading to a nauseous or suffocating feeling.
Today's LPG or cooking gas prices in 4 metro cities can be found here