Refers to the standard safety tactic of having one team of two firefighters enter a hazardous zone (IDLH), while at least two others stand by outside in case the first two need rescue thus requiring a minimum of four firefighters on scene prior to starting interior attack. Also refers to the buddy system" in which firefighters never enter or leave a burning structure alone.

U.S. classification system for fire resistance of building construction types, including definitions for: "resistive" Type I, "limited combustible" Type II, "ordinary" Type III, heavy timber Type IV and "wood frame construction" Type V (i.e. made entirely of wood).