Nozzles placed under the cooker canopies and over each risk propel a water-based agent with a chemical foam type mix over the risk. This is usually triggered by a heat link (a thermal link fixed to a wire which breaks and then releases the valve) or a manual pull switch.
Other systems are triggered from automatic fire detection and back to a fire extinguisher panel. The detection and most equipment in this area needs to be stainless steel to avoid corrosion and the damage/effects of heat.
The agent is usually situated near the risk in a box. This is basically a large fire extinguisher. Pipework from the nozzles terminate at this point and a valve operates the release. Once the system is triggered the agent is propelled from this valve/cylinder to the nozzles.
The agent is a water-based chemical which acts like a foam extinguisher. This is to ensure any flammable liquids are covered by the foam to avoid a boil over from any oven/fryer that may be still switched on, and stops the oil from re-igniting.
Watermist systems can be used for kitchens and can be a more cost-effective solution to Ansul systems and other water chemical systems. However, careful design is needed and approval from insurers.