Deluge (spray) systems, as the name implies, deliver large quantities of water over specific areas in a relatively short period of time. These systems are used to protect against rapidly growing and spreading fires, typically involving flammable liquids and solvents etc.
Deluge systems are like automatic sprinkler systems with the exception that all nozzles (sprinkler heads) are open and will discharge water simultaneously when a control valve opens. These systems are designed to protect areas where fire is likely to spread rapidly and/or where cooling of surrounding equipment is necessary.