Wet and dry chemical extinguishing systems both start when a fire is detected, but they operate differently based on the hazard they protect. Dry chemical systems are typically used for flammable liquid/gas or industrial hazards. They activate from automatic detection (heat/flame) or manual pull station, release nitrogen or stored pressure to push dry chemical powder through piping, and discharge through nozzles. The powder interrupts the chemical chain reaction and smothers the fire. Many systems include alarms, shutdowns, and sometimes a short time delay.

Wet chemical systems are most common in commercial kitchens. When a fusible link melts or detection activates, the system releases wet chemical agent through nozzles into the cooking appliances and hood duct. The agent cools the fire and reacts with hot grease (saponification) to form a soapy layer that prevents re-ignition, while also shutting off fuel and power to appliances.