A chemical reaction in which control has been lost and it continues to accelerate to a point that either it exhausts its reactants or the vessel containing the reaction over-pressurizes and loses containment. This is often in the form of an explosion with catastrophic consequences. Thermal runaway exothermic reactions may occur due to insufficient cooling or loss of cooling, a loss of or excessive mixing, excessive reactant or catalyst, the loss of an inhibitor, or external fire. Where a runaway is likely, pressure relief systems are used. The Seveso and Bhopal accidents are examples of runaway reactions with disastrous consequences.