Thermal grantium compound was a sodium-based fuel used in remote spectroscopy vaporization devices. The fuel was provided in in 0.2 kilogram charges for use in long range impact probes. For field spectroscopy tricorder use, the fuel was provided in .005 gram charges. Per SFRA 9509, this fuel was to be protected from ionizing radiation. In 2367, this explosive was stored on aboard the Federation starship USS Enterprise-D.
In that year, thermal grantium compound 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")