A longer sprinkler response time during the critical first moments of fire is possible due to the time required for the water to travel from the control valve to the open sprinkler head. Response time may lag by as much as 1 minute, allowing a larger number of sprinklers to operate. In museum applications, dry-pipe sprinkler do not offer any significant advantage over wet systems. This option involves replacement of the halon protection with a pre-action type sprinkler system. The principle of pre-action is that the piping in the protected area is dry.
Water is held back by an electronic pneumatic valve, controlled by the room's detection system.
Upon detector operation, water is introduced into the piping. When the sprinkler head operates, this water is discharged onto the fire. Advantages include the sprinkler advantages presented under Option 5. Disadvantages include a longer sprinkler response time in fast- developing fires and increased installation and maintenance expenditures due to increased system complexity. Water mist sprinklers will deliver water at exceptionally high pressures, producing a fine, high-efficiency water vapor.