Class K Extinguishers

Fire extinguishers for the protection of cooking media fires (vegetable or animal oils and fats) traditionally required a minimum 40-B rated sodium bicarbonate or potassium bicarbonate dry chemical extinguisher as specified for extra (high) hazard requirements of NFPA 10. The evolution of high efficiency cooking appliances and the change to hotter-burning vegetable shortening has created a more severe fire hazard and has prompted the creation of a new classification of fire, Class K. Testing by Underwriters Laboratories has shown that wet chemical extinguishers with a K classification have several times the extinguishing capability of a 40-B rated sodium bicarbonate or potassium bicarbonate extinguisher in controlling cooking fires.

The Class K extinguisher offers improved fire control for this type of hazard by:

(1) Creating a foam blanket by saponifying (converting into a soap) the hot cooking oils.

(2) Cooling both the appliance and the hot cooking oils.

(3) Offering improved visibility during fire fighting.

(4) Minimizing splash hazard.

(5) Providing easier clean-up than when using dry chemical agents.

Accordingly, the Fire Equipment Manufacturers’ Association, Inc. [FEMA] recommends that all Class B extinguishers used to protect cooking appliances/kitchens be replaced by the owners with Class K extinguishers as soon as possible. The travel distance of 30 feet as previously described in NFPA 10 is still recommended.

Class K Rating Tests

Class K rated fire extinguishers are rated for their ability to fight fire in commercial cooking environments. The newest version of the UL Standard 300, Standard for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas, is more restrictive than previous tests in commercial cooking media. The fuel used must be new vegetable shortening or oil with an anti-foaming agent and an auto-ignition temperature of 685 degrees Fahrenheit (362.7 degrees Celsius) or higher. Tests are performed on four types of cooking appliances: fryers, ranges, griddles, and woks. Manufacturers of hood extinguishing systems are now using the potassium-based liquid agents (potassium acetate, potassium carbonate, and potassium citrate) for installation in commercial kitchens because sodium bicarbonate is no longer used.

Class K Extinguisher Distribution Factors

In the working environment of commercial cooking occupancies, fire is always present. Employees in such areas are charged with the responsibility to maintain appropriate cooking temperatures to ensure safety. Because employees are in various levels of training for their jobs and because there is potential of fire hazards occurring in an assembly area (dining room), NFPA 10 has assigned a more restrictive distance requirement. In areas where Class K fires are likely, the maximum travel distance from the hazard to the extinguisher is reduced to 30 feet (10 m).

In addition to proper selection and distribution, effective use of fire extinguishers requires that they be readily visible and accessible. Proper placement of extinguishers should provide the following:

(1) Extinguishers should be visible and well marked.

(2) Extinguishers should not be blocked by storage or equipment.

(3) Extinguishers should be near points of egress or ingress.

(4) Extinguishers should be near normal paths of travel.

(5) Extinguishers should be placed so that all personnel can access it.

(6) Extinguishers with a gross weight not exceeding 40 pounds (18 kg) should be installed so that the top of the extinguisher is not more than 5 feet (1.5 m above the floor.

(7) Extinguishers with a gross weight greater than 40 pounds (18 kg), except wheeled types, should be installed so that the top of the extinguisher is not more than 3 ½ feet (1 m) above the floor.

(8) The clearance between the bottom of the extinguisher and the floor should never be less than 4 inches (100 mm).

 Attacking Class K Fires

Class K (cooking media) fires are particularly difficult to extinguish because of their tendency to reignite after the fire has been extinguished. It has been discovered that although a Class K fire may have been extinguished properly with a dry chemical, the fuel changes chemically and reaches auto-reignition at a lower temperature. For this reason, only an extinguisher with a Class K rating is recommended for use on this type of fire. The initial attack on a Class K fire with an appropriately marked Class K extinguisher is similar to other types of attack. Begin application from a distance of 10-12 feet (3.1 to 4 m) away from the burning material, hold the application wand at the edge of the flames, and coat the surface of the material with a side-to-side sweep. Continue to apply agent until the fire extinguisher is completely empty. Extinguishment takes place through cooling the fuel. It is the innate cooling quality of the agent, along with its ability to form soapy foam (saponification) that prevents the fuel from reaching a lower reignition temperature.