Firestop Sealants are used to seal small openings/gaps through penetrants (such as  pipes, ducts, electrical cables, etc.) passing through walls or floors in buildings.  The purpose of fire sealants is to seal any small openings so as to prevent a fire from traveling from a fire area/compartment to another area/compartment of a building or structure. firestop  like all passive fire products, have a fire rating which indicates the time it will stop fire for.