RESTAURANT GREASE DUCT FIRES
BY JOSEPH GROSSO
Fires occurring in restaurant grease ducts can be difficult to extinguish. Accumulated grease inside of ducts can ignite, with a resultant hot fire that is shielded from attack by the fire department but can spread from the duct and ignite surrounding materials. These fires are physically taxing for operating units and tactically complex for the officer in command. Among the factors that can add to the complexity of this type of fire are the following:
The type of structure in which the restaurant is located. Restaurants can be found in a structure of any size and any class of building construction, ranging from the small frame building to the high-rise hotel.
The configuration of the structure and the severity of the smoke condition. They further complicate the size-up of a grease duct fire.
The time of day. It can have an impact on the severity of the fire, particularly by delaying the determination of the fire`s location. Incoming units responding to such a fire during business hours, for example, can obtain vital information easier than units responding to fires occurring after hours.
OPERATIONS
The first-arriving engine company should not commit the first line until it has been determined which structure is involved. Grease ducts that exit the restaurant and are carried to the roof area via exterior ductwork can create smoke conditions over exposures that can make it difficult to identify the structure involved. This is especially true when a number of restaurants are located on the same block. Another factor affecting the determination of the involved structure may be the absence of any appreciable smoke at the street entrance to the restaurant.
Information relayed from the first arriving units to the officer in command is vital. When the involved building is identified, the first line should be stretched to the kitchen area. The first arriving ladder company should immediately shut down the kitchen duct exhaust fans. The fan control usually is located in the kitchen area near the kitchen entrance door. Fan controls also can be found at the roof level in many grease ducts run up the exterior.
Two major questions then must be answered:
1. Is the duct fire confined to the interior of the duct, or has the duct fire communicated to surrounding combustible structural members?
2. Does the duct run exit the restaurant and continue to the roof via an exterior duct, or is the grease duct carried to the roof via an interior (possibly noncompliant) combustible shaft?
OPERATION OF HOSELINES
When a fire is in a grease duct that exits the restaurant and is carried to the roof via an exterior duct, the officer in command should consider placing the second line at the roof termination point. The objective is to cool the interior of the duct as quickly as possible. The second line must be closely coordinated with the first line in the kitchen area. The second line would be operated only long enough to extinguish fire emanating from the duct termination point and rapidly cool the duct`s interior. Water runoff from the second line will exit in the kitchen area, presenting hazards to members operating the initial line in the kitchen. For this reason, coordination and control of these two lines are paramount.
The first line will be operated in the kitchen duct via clean-out openings or access holes made by the ladder company. Kitchen ceilings must be pulled to determine if the duct fire has extended to combustible ceiling members.
When a grease duct is carried up the interior of the structure and is located in a combustible shaft, the officer in command should immediately call for additional ladder companies. Access must be gained to all floors through which the duct passes. Ceilings and walls surrounding the interior duct run must be opened. This operation is physically demanding and may be complicated by floor layout, a heavy smoke condition, and difficult forcible entry. Again, the fastest way to place water into the duct above the kitchen area is from the roof termination point. Cooling the interior of the duct from above may prevent or at least minimize extension to the surrounding structural members.
ADDITIONAL CONSIDERATIONS
Placing the second line at the roof termination point is a viable decision by the officer in command. However, some conditions will demand that the second line be placed on the floor above, such as when the fire is in a frame building where rapid extension is possible or when occupants are trapped above the fire. The protection of life and prevention of fire extension should still be the main objectives.
Restaurants located in the basements of buildings of ordinary construction may have additional kitchens with attendant grease ducts located in the cellar.
Ducts in restaurants located in large multiple dwellings may have their ductwork run through combustible ceiling spaces before exiting to the exterior on the side or rear of the building. This is especially true when the restaurant occupies only a portion of the grade floor.
In high-rise hotels, restaurants may be located at grade level as well as on the upper stories. In such cases, a common main duct may carry the exhaust from various intermediary ducts to the roof termination point. The building engineer must be consulted to determine the duct run as well as whether it would be possible to close any fire dampers that may be present.
When available, the duct diagram, sometimes required to be posted in the kitchen, can be used to determine the run of the grease duct.
When a fire occurs in a grease duct, always check the entire run of the duct for extension. Elbows at the horizontal runs can accumulate large amounts of combustible grease. These accumulations can smolder even when located some distance from the original fire. Water should be applied in the duct from above to complete the extinguishing process. Also consider the accumulation of water and the stress it will place on the duct.
Various methods may be used to stretch hoselines to the roof termination point–a rear fire escape, if available; rope stretches; and interior stairs. In addition, portable or aerial ladders may be used. If an aerial ladder is used to stretch a line to the roof, the line must be removed from the aerial once sufficient hose is placed on the roof and secured to a substantial object at roof level and another means of egress is secured for firefighters on the roof. The line is removed from the aerial to allow the ladder company to use the ladder for venting, access, or removal of endangered occupants. In structures with standpipe systems, the hose to the roof may be connected to the top-floor standpipe outlet or, in some cases, to a roof hose manifold.
In recent years, the concept of having multiple fast-food restaurants that share the same ductwork in the same building has been introduced. In such cases, fire extension within the entire restaurant system is a distinct possibility.
As is true for most fire operations, the keys to quickly containing a grease duct fire are proper size-up by the officer in command and the natural aggressiveness of the firefighting units. n
JOSEPH GROSSO, a 33-year veteran of the fire service, has been chief of Battalion 9, midtown Manhattan, of the City of New York (NY) Fire Department, since 1986. He has a bachelor`s degree in fire science from John Jay College.
