A commercial deep fryer holds a large volume of oil at a temperature well above its own ignition point. When it catches, the fire is Class F, and it behaves unlike any other fire in the building.
Water makes it worse: it flashes to steam beneath the oil and throws burning oil out of the vessel. Dry powder leaves the oil hot enough to reignite. The wet chemical agent instead reacts with the oil to form a soapy layer that seals it from the air and holds it while the oil cools below its ignition temperature.
What a kitchen system covers
Where a wet chemical system belongs
Restaurant and hotel kitchens with deep fryers, ranges, griddles or woks.
Canteens and central kitchens in factories, schools and hospitals.
Food court and kiosk cooking lines under a common extract hood.
Any commercial cooking appliance sitting under an extract canopy with a duct behind it.
What the system covers
- Nozzles positioned over each appliance, sized and aimed to the appliance type rather than spaced evenly.
- Nozzle coverage inside the extract hood plenum and up into the duct, where grease accumulates and fire travels.
- A detection line above the cooking surface, normally fusible links that release the system automatically.
- A manual pull station on the escape route, so a person leaving can trigger the system.
- Automatic gas shut off and appliance power isolation on discharge, so the heat source stops with the fire.
Servicing and the grease problem
- Systems are inspected on a scheduled interval, with the nozzles checked for grease blockage and the fusible links replaced periodically.
- Grease build up in the hood and duct is the most common reason a kitchen fire spreads beyond the appliance, and it is also what blocks the nozzles that should have stopped it.
- We inspect the hood and duct condition as part of the service visit and report where cleaning is falling behind, because a well maintained system above a filthy duct is not protection.
- After any discharge the system is stripped, cleaned, recharged and recommissioned before the kitchen reopens.
Common questions
Why can we not just keep extinguishers in the kitchen?
You should have them, for the fires that are not the fryer. But a portable extinguisher requires a person to be present, willing to approach a burning oil vessel, and to use the right type.
A wet chemical system operates automatically, discharges into the hood and duct where a person cannot reach, and shuts off the gas at the same time.
Does the system shut off the gas automatically?
That is part of a correctly installed system. On discharge, a mechanical gas valve closes and appliance power is isolated, so the fuel and the heat stop along with the fire.
If your existing system does not do this, it is worth raising, because it is a common shortfall on older installations.
How often does it need servicing?
Kitchen systems are serviced on a scheduled interval and, in practice, need attention more often than most fixed systems because of the grease environment.
We set the interval against how hard the kitchen runs rather than applying one figure to every site.
Can you install into a kitchen that is already operating?
Yes. The work is planned around service hours, usually overnight or on a closure day, and the hood is handed back clean and operational.
We will tell you honestly how many nights it needs after seeing the appliance line and the duct route.
Want this scoped for your building?
Hello Trimy Fire Tech, I would like to discuss wet chemical systems for our premises.