Hoffmeisterite compount 239 was an oxidizing explosive. It was used to bind free oxygen in a confined space for fire-fighting appliations and for providing oxygen-free environments for industrial processes. Except in cases of extreme emergency, this compound was not to be used in habitable spaces. In 2367, this explosive was stored on aboard the Federation starship USS Enterprise-D.
In that year, Hoffmeisterite compound 239 was on a list of explosives that Lieutenant Commander Data and Counselor Deanna Troi searched through in an attempt to find one that could produce enough energy to release the USS Enterprise-D and an alien ship from the Tyken's Rift. (TNG: "Night Terrors")