The accidental release of large amounts of toxins into the environment. The effects suffered by people in the area are determined by the toxicity of the chemical, its speed in spreading, its composition (liquid, solid, or gaseous), and the spill site, especially its proximity to a water supply or buildings. The major effect may be due to the chemical itself or to a resulting fire or explosion. The catastrophic release of chemicals may overwhelm, at least temporarily, local or regional health care resources.