What type of sprinkler system holds water at high pressure and discharges water when triggered by heat?

The correct choice is a wet-pipe sprinkler system. This type of system maintains water under pressure in the pipes at all times. When a fire occurs, the heat from the flames activates the sprinkler heads, allowing the high-pressure water to discharge and extinguish the fire.

Wet-pipe systems are typically the most common type used in buildings because they are simple to maintain, reliable, and effective for many types of environments. They work well in climates where freezing is not a concern since the pipes are always filled with water and ready to activate immediately in response to fire conditions.

Other sprinkler systems serve different purposes. For instance, dry-pipe systems contain pressurized air instead of water in the pipes, which is released when a heat-triggered valve opens. Pre-action systems require both heat detection and a manual or automatic mechanism to fill the pipes with water before it can be discharged, making them more complex. Deluge systems, on the other hand, have open sprinkler heads and are activated by a heat detector, releasing a large volume of water for fire suppression. Each of these systems has specific applications based on building safety needs, but the wet-pipe system is distinguished by its constant water presence, providing immediate response to fire incidents.