Tritium represents one of hydrogen's isotopes. It is radioactive, having a nucleus formed of one proton and two neutrons, while the most abundant isotope of hydrogen, protium, has no neutrons. The half life of the tritium atom is somewhere around 12 years, and the decay reaction results in a helium atom plus in the emission of an electron and an electron neutrino. Though it is radioactive, this beta-decay does not pose danger to biological entities, as it cannot penetrate skin; however, when inhaled and ingested, it can result in poisoning.

The tritium isotope is commonly used in civilian and military nuclear power plants, and it is discharged in large quantities, so it could pose danger to the surrounding population. According to the Health Protection Agency in the UK, this could double the number of people subjected to tritium residues and the risk of cancer, as a result.

Though the studies show that the cancer risk is still low, even amongst nuclear workers that suffer frequent exposure to radioactive material, Mark Little, from the Imperial College of London, says that the evidence that tritium raises the security risk is proof enough to initiate a change in tritium disposal.

Tritium is mostly used in the nuclear weapons manufacturing industry and has the role of initiating the nuclear chain reaction. It is also a key component of the atomic H-bomb, and a waste product of the energetic reaction. During the initiating stage of detonation of a nuclear weapon, a few grams of a mix of tritium-deuterium gas is injected in the hallow spaces inside the fissile material. Heat and compression, provided by the early stages of the nuclear fusion, start a nuclear fission reaction between tritium-deuterium gas, that creates more heat and compression in order to assist the nuclear fission reaction. Virtually, the two nuclear reactions take place at the same time, assisting each other. The presence of the fusion material also helps the nuclear fission reaction to hold for a longer period of time.

The dumping of high amounts of tritium began in the middle of the 20th century, in multiple locations near nuclear power plants, such as Savannah River in the U.S., or Marcoule in France. Cases of exposure to the radioactive material have been documented in other facilities around the U.K. and Russia.

Tritium is not highly radioactive; but, being widely dispersed in the environment, it rises the risk from 1 to 2, meaning that the maximum level of radiation a person must be subjected needs recalculation.

Tritium gas is currently used in certain illuminating devices, as phosphorus can easily be made to glow, by the electrons emitted by the radioactive material. These device, known as 'trasers', are used to make self-powered lighting key-chains, exit signs, and watches. The military experiments make use of the similar properties of the radioactive radium in order to make gun sights for fire arms, but has recently been replaced by tritium, since exposure to the radium has greatly increased the risk of getting bone cancer.