Exit signs containing radioactive tritium gas require recycling or hazardous waste disposal. Tritium is the naturally occurring radioactive isotope of hydrogen. When combined with a light-emitting compound, tritium causes exit signs to glow. It is the only radioactive isotope of hydrogen. An isotope is a different form of an element. It has the same number of protons in the nucleus but a different number of neutrons. The nucleus of a tritium atom consists of one proton and two neutrons.
In addition to naturally occurring solar radiation in the atmosphere, tritium can be accelerator-produced and used in nuclear reactors as a fission product in nuclear weapons. The US Department of Energy (DOE) monitors the production and use of tritium. Although tritium does emit radiation, the emission is weak and cannot travel far or penetrate human skin. According to the US Nuclear Regulatory Commission (NRC), unwanted tritium exit signs “pose little or no threat to public health and safety or security,” but they are solid waste.