To explore the feasibility of terminating combustion without the hazardous flame and debris associated with venting, a series of sixteen 5-in.-diam motors was fired. Two techniques were investigated: 1) injection of liquid into the combustion chamber, and 2) explosive discharge of coolants from a canister located inside the chamber. The minimum quantity of water required for reliable termination was found to be less than 0.5 pt. Pressure decay rates between 12,000 and 25,500 psi/sec during water injection were observed. The ability to stop, restart, and again stop burning on command was demonstrated. Explosive quenching by shock-wave disruption of burning, followed by deposition of a subliming heat absorbing salt, is confirmed by experimental observations. Design features of this potentially lightweight and convenient technique are discussed.