What type of sprinkler system operates with sprinklers that are open all the time?

The deluge system is designed to operate with all sprinklers open, which allows water to flow simultaneously from multiple sprinkler heads when activated. This type of system is typically used in high-hazard areas where rapid fire spread is a concern, such as storage facilities for flammable materials.

In a deluge system, the water supply is released by a fire detection system or manually activated, leading to an automatic release of water from all connected sprinkler heads at once, promoting immediate and widespread application of water to a fire. This is distinct from wet systems, which hold water under pressure in the pipes and only activate individual sprinklers, or dry systems, which contain pressurized air instead of water until a sprinkler head is triggered. Pre-action systems also hold water under pressure but require a preliminary detection event to fill the system with water, making them different from the simultaneous discharge characteristic of deluge systems.

The nature of a deluge system makes it particularly effective in situations where a rapid response to large-scale fires is critical, underscoring why this option is the correct choice.