LNG is a cryogen, and is kept in its liquid state at very low temperatures. The gamma-ray spectrometer operated until 1 June 1980, when its cryogen was exhausted. Industry practice is to store LNG as a boiling cryogen. It is recommended that Cryogen Safety Gloves be used by the worker. A number of medical supply companies have developed cryogen delivery systems for cryosurgery. In recent years, with no cryogen, NEOWISE typically makes approximately 0.15 million asteroid observations annually.