A wet ceiling-only fire protection system for protection of a stored commodity, the system comprising: a demand portion including a plurality of sprinklers disposed above the commodity, each sprinkler having a minimum designed operating pressure, the plurality of sprinklers being interconnected by a network of pipes (20, 22); and a supply portion coupled to the demand portion and configured for pressurizing the demand portion; characterized in that: the plurality of sprinklers is interconnected by a network of pipes (20, 22) filled with water to provide each sprinkler with an initial pressure that is equal to or greater than the minimum designed operating pressure in an unactuated state of the system, wherein the initial pressure is permitted to decrease for a predetermined withholding period; the supply portion pressurizes the demand portion following actuation of at least one sprinkler in response to a fire and expiration of a predetermined withholding period; and an assembly (16, 116) is coupled to the demand portion for determining the expiration of the predetermined withholding period, wherein the assembly (16, 116) includes: a valve having a standby state which prevents fluid communication between the supply portion and the demand portion and an operated state which permits fluid communication between the supply portion and the demand portion; a timing device which initiates countdown of the predetermined withholding period following the actuation of the at least one sprinkler, the timing device being coupled to the valve to transition the valve from the standby state to the operated state upon expiration of the predetermined withholding period. a demand portion including a plurality of sprinklers disposed above the commodity, each sprinkler having a minimum designed operating pressure, the plurality of sprinklers being interconnected by a network of pipes (20, 22); and a supply portion coupled to the demand portion and configured for pressurizing the demand portion; characterized in that: the plurality of sprinklers is interconnected by a network of pipes (20, 22) filled with water to provide each sprinkler with an initial pressure that is equal to or greater than the minimum designed operating pressure in an unactuated state of the system, wherein the initial pressure is permitted to decrease for a predetermined withholding period; the supply portion pressurizes the demand portion following actuation of at least one sprinkler in response to a fire and expiration of a predetermined withholding period; and an assembly (16, 116) is coupled to the demand portion for determining the expiration of the predetermined withholding period, wherein the assembly (16, 116) includes: a valve having a standby state which prevents fluid communication between the supply portion and the demand portion and an operated state which permits fluid communication between the supply portion and the demand portion; a timing device which initiates countdown of the predetermined withholding period following the actuation of the at least one sprinkler, the timing device being coupled to the valve to transition the valve from the standby state to the operated state upon expiration of the predetermined withholding period. the plurality of sprinklers is interconnected by a network of pipes (20, 22) filled with water to provide each sprinkler with an initial pressure that is equal to or greater than the minimum designed operating pressure in an unactuated state of the system, wherein the initial pressure is permitted to decrease for a predetermined withholding period; the supply portion pressurizes the demand portion following actuation of at least one sprinkler in response to a fire and expiration of a predetermined withholding period; and an assembly (16, 116) is coupled to the demand portion for determining the expiration of the predetermined withholding period, wherein the assembly (16, 116) includes: a valve having a standby state which prevents fluid communication between the supply portion and the demand portion and an operated state which permits fluid communication between the supply portion and the demand portion; a timing device which initiates countdown of the predetermined withholding period following the actuation of the at least one sprinkler, the timing device being coupled to the valve to transition the valve from the standby state to the operated state upon expiration of the predetermined withholding period. a valve having a standby state which prevents fluid communication between the supply portion and the demand portion and an operated state which permits fluid communication between the supply portion and the demand portion; a timing device which initiates countdown of the predetermined withholding period following the actuation of the at least one sprinkler, the timing device being coupled to the valve to transition the valve from the standby state to the operated state upon expiration of the predetermined withholding period.