The wet chemical reacts with the burning fat to form a soapy foam layer (saponification), cutting the oil off from the air while cooling it at the same time. Nozzle types and positions are chosen to match the cooking appliances, so every kitchen gets its own design. We take the appliance schedule from the kitchen layout, set nozzle coverage according to the manufacturer's manual and commission the system together with the gas shut-off valve.
ATypes and components
Wet chemical agent cylinder
A potassium salt-based extinguishing liquid stored in stainless steel cylinders, either stored-pressure or cartridge-operated. The number of cylinders depends on the appliances covered and the length of duct.
Appliance, plenum and duct nozzles
Appliance nozzles cover cooking surfaces such as ranges, fryers, grills and woks; plenum nozzles protect the space behind the filters; the duct nozzle covers the exhaust duct entry. Each nozzle's coverage and mounting height are limited by the system listing.
Fusible link detection
Fusible links are fitted along a steel cable inside the hood and separate at a set temperature. When the cable tension is released, the control head opens the cylinder; it needs no electrical power, so it works during a power cut.
Pneumatic detection tubing
Some systems detect fire with a pressurised tube that bursts under heat. The tube is routed over the cooking appliances; when it bursts, the valve opens and agent is sent to the nozzles.
Manual pull station
A pull station on the kitchen exit route lets staff discharge the system as soon as they see a fire, without waiting for detection to operate.
Gas and power shut-off
On discharge, a mechanical or solenoid gas valve closes and electrical power to the cooking appliances is cut. If the heat source stayed on, the oil could re-ignite, so this interlock is an essential part of the system.
BHow it works
- Temperature rises above the appliance and a fusible link or the detection tube operates.
- The control head opens the agent cylinder and wet chemical discharges through the appliance, plenum and duct nozzles.
- At the same time the gas valve closes, power to the appliances is cut and a signal goes to the fire alarm system.
- The agent forms a saponified blanket on the oil, cools it and prevents re-ignition.
CAdvantages
- Agent developed for cooking oil fires and tested to UL 300
- Mechanical detection option that needs no power
- Automatic gas and power shut-off
- Appliances, hood, filters and duct protected together
- Simple clean-up and recharge after discharge
DApplications
- Restaurant and hotel kitchens
- Shopping centre food courts
- Hospital and school kitchens
- Factory and campus canteens
- Airport and catering kitchens
- Fryers on food production lines
EFrequently asked questions
Do we still need a hood system if we have a Class K extinguisher?
Yes. A Class K (Class F in Europe) portable extinguisher supplements the fixed system; it does not replace it. A fire inside the hood or duct cannot be reached with an extinguisher. The standards expect the extinguisher to be used as back-up after the fixed system has discharged.
How often does a kitchen hood system need servicing?
NFPA 17A requires servicing every six months by a qualified technician. Nozzle caps and aiming are checked, the detection line is tested, the gas shut-off is operated and the fusible links are replaced. Grease build-up can affect the detection elements, so hoods and ducts also need regular cleaning.
Does the system need changing if we add a new appliance?
Usually, yes. Nozzles are selected for specific appliance types and positions, so replacing a range with a fryer or moving appliances around breaks the coverage. After any change to the kitchen layout, nozzle positions and agent quantity should be reviewed.