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Restaurant Suppression Issues – Kitchen Suppression Systems

June 4, 2012

Kitchen extinguishing systemIn the past, dry chemical extinguishing agents were used to extinguish kitchen fires. This was mainly because of issues with dumping water on burning oil or grease. The dry chemical agents suppressed fire through a process known as saponification. The process consisted of a chemical reaction between the extinguishing agent and the burning material’s surface. The result is a thin foam barrier or “blanket” across the burning surface which eliminated oxygen. It worked great for a while, and the systems were also reliable and cost-effective to install.

In the late 1980s, there were several reports of restaurant fires showing that the fire systems were not able to keep the fire out even though they were designed and installed correctly. At the same time, in order to reduce fat and cholesterol content of food, many restaurants were switching from animal fat-based frying and cooking oils to vegetable-based oils.

The insurance companies approached Underwriters Laboratory (UL) to find out why extinguishing systems were now failing to protect.  The main discovery was that cooking with vegetable oils results in higher cooking temperatures: while auto-ignition temperature of most animal fat-based cooking oils is around 550° F, auto-ignition temperature of vegetable oils is above 685° F. It was also demonstrated that although the manufactured systems did put the fire out, due to much higher cooking oil flashpoints they did not keep the fire out; once ignited the oils continued to re-ignite even at lower temperatures the longer the oil was in use.

As a result Underwriters Laboratory developed UL300, Standard for Safety for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas. This new system is not only creating saponification but also provides cooling.

To complement pre-engineered wet chemical extinguishing systems portable class K fire extinguishers were also created. The extinguishing agents used in these types of extinguishers include potassium carbonate and potassium acetate mixed with 40-60% water by weight. This combination is proven to help cool the cooking oils and to create saponification. The addition of water discharge significantly aids in increasing and prolonging the foam blanket generated by the wet chemical agent. The longer retention of the foam blanket allows the hot oils to cool well below the auto-ignition temperature.

Statistics prove commercial kitchen pre-engineered fire suppression systems to be 95% reliable in successfully suppressing kitchen cooking hazard fires. If this is the case, one might wonder why a portable extinguisher is still needed. It is mostly because the extinguisher can be utilized in the event of grease spills that would cause fire to spread outside the hazard area of protection, and also to have an extinguisher available in the event of a system failure.

After 1994 all pre-engineered extinguishing systems in commercial kitchens installed were required to be UL300 compliant.


Here is a test question:

What are some obvious signs for an Authority Having Jurisdiction (AHJ), inspector, or restaurant owner to look for in determining that a system installation is NOT UL300 Listed.

1. System cylinders contain dry chemical agent that is identified on the manufacturer’s label

2. System uses a single nozzle to protect multiple appliances

3.  System has only one agent cylinder

4. System was manufactured before November 21st, 1994.



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Read Part 1, Part 2 & Part 3 of this series.


Article by: Cristina Pellett, Field Representative 


Source: The National Association of Fire Equipment Distributors


Learn about WSRB commercial property and kitchen inspections

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