Specific gravity is not the only factor that determines how quickly a gas will diffuse or disperse. Temperature and pressure also affect it. Remember that an increase in temperature makes a gas diffuse more rapidly. A decrease in temperature slows down the rate of diffusion. A decrease in pressure speeds it up.
Any flammable gas can explode under certain conditions.
In order for a flammable gas to explode, there must be enough of the gas in the air, enough oxygen, and a source of ignition. Figures representing the higher and lower limits of the explosive range are expressed in percentages. The amount of oxygen that must be present for an explosion to occur is also expressed as a percentage. The explosive range of methane, for example, is 5 to 15 percent in the presence of at least 12.1 percent oxygen. Solubility is the ability of a gas to be dissolved in water.