Radiobiology. In fusion, as in an ordinary (chemical) fire, ignition is the point where the temperature and confinement of heat in the fuel (plasma in the case of fusion) are such that energy released from ongoing reactions is sufficient to maintain the temperature of the system, and no external heating is needed. An ignited fusion plasma produces so much energy from fusion reactions that the plasma is fully heated by fusion reaction products (alpha particles in the case of D-T fusion), and the plasma no longer needs any external source of power to maintain its temperature. (The plasma may, however, still need something to maintain its confinement, this gives us control over the fusion reaction and helps prevent fusion reactors from having meltdown problems like fission reactors.) Ignition may refer to: *Firelighting, the human act of creating a fire for warmth, cooking and other uses *Combustion, exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species *Minimum ignition energy, the minimum amount of energy required to ignite a combustible vapor, gas or dust cloud tocright. An OSH glossary used in safety and health at work which is, adopted by ILO