Localized Suppression Systems for the Kitchen

According to the U.S. Fire Administration Publication, A Profile of Fire in the United States: 1992-2001, the kitchen is the area of the home, where most fires originate. Approximately 25% of all fires in one- and two- family dwellings and 48% of all fires in apartments originate in the kitchen. Further, analysis indicates that cooking is the leading cause of residential fires, the leading cause of residential fire injuries and the third highest cause of residential fire deaths. The data also shows that a majority of the cooking fires involve the stove or range top.

This study is focused on limiting the hazard development from a typical kitchen fire, such as a grease fire on a stove, by using "active" fire protection systems that are inexpensive and easy to retrofit into existing homes. The target value per retro-fit was chosen to be $200 or less. The project has several phases as detailed below.

Kitchen Fire Hazard Characterization

An understanding of the fire hazard in terms of engineering units was required to determine how effective a standardized test may be in evaluating a potential solution for mitigating the adverse effects of kitchen fires. The fires were measured in terms of heat release rate (kW), heat flux (kW/m2) and duration. Several different types of cooking oil were heated to auto-ignition in a 250 mm (10 in) diameter, stainless steel frying pan. Canola, corn, olive, peanut, sunflower and vegetable oils were compared with heptane. Corn oil was chosen as the fuel for the fire suppression experiments since it had one of the highest peak heat releases after ignition, approximately 80 kW. For comparison, the peak heat release rate of the heptane pan fire was approximately 35 kW, hence heptane would not be representative of a cooking oil fire for use in standardized tests.

Active Fire Protection Systems Identification

Active fire protection systems have moving parts and are intended to control, suppress, or extinguish the fire. Three types of active systems were considered: 1) a dry chemical system installed under the exhaust hood above the range, 2) a wet chemical system installed under the exhaust hood above the range, and 3) a single automatic fire sprinkler installed in the kitchen.

Of course the best situation is a fully sprinklered residence in accordance with National Fire Protection Association (NFPA) Standards 13, 13D, or 13R. Systems of this type are out of the scope of this study due to the relatively high cost of retrofitting.

Localized Suppression System Experiments and Results

Full-scale kitchen experiments were conducted in several kitchens in an abandoned apartment building. The experiments were conducted to investigate the effectiveness of dry chemical and wet chemical kitchen hood fire extinguishing systems and single residential sprinklers. Under laboratory conditions, these technologies have demonstrated the ability to control or extinguish a stove-top fire. In the series of field experiments both self contained systems, one a wet chemical and one a dry chemical, were quite effective in extinguishing the cooking oil fire.

The concept of a single low flow residential sprinkler was tested and was found to control both the cooking oil fire and an appliance fire on the counter top. Fire control was achieved despite shielding by the cabinets and fire extension to the cabinets and walls, prior to sprinkler activation. Both a pendent (10 gpm) and a sidewall configuration (14 gpm) were tested. If the sprinkler can be supplied by the existing domestic water supply system, retrofit costs would be kept to a minimum.

Conclusions

None of these solutions are perfect. The inexpensive (< $200) self contained systems as well as the single sprinkler do not de-energize the stove. In other words they do not turn off the electricity or the gas. There are UL listed systems that provide suppression agents and also de-energize the appliance, but the installed cost is on the order of $1000.

For the single sprinkler, the challenge for the homeowner/installer will be determining that sufficient water pressure and flow are available to provide an adequate supply to the sprinkler.