Many chemicals behave in somewhat predictable ways when spilled. The way a spill of gases or liquids will disperse can be "modeled." The chemical spill will tend to dissipate upwards, and to the sides and endpoint of the plume. The rate of upward dissipation depends on whether the chemical is a buoyant gas that rises, or if it is a heavy gas that tends to sink. A spill of a heavy gas will tend to travel further along the surface of the ground while a buoyant gas will tend to rise up and away from the spill site. Much of the strategy for handling a chemical spill will be to stop the source of more spilling, to cover or absorb the spilled liquids, if any, and to wait for the spilled chemicals to dissipate below unhealthful or flammable concentrations.