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Pre-Engineered Chemical Extinguishing Systems by Kerry Bell and Kenneth W. Zastrow Each day new restaurants are opened featuring unique food preparation or marketing approaches intended to attract customers. In offering distinctive food products to customers, many of these restaurants use special food preparation techniques -- such as cooking in full view of customers, cooking with specialty oils, or cooking with specialty fuels such as mesquite wood. Unnoticed in the backdrop of food preparation, however, many restaurants have a common safety feature which is generally unappreciated by customers unless a fire occurs during food preparation. This common safety feature is a fire suppression system. Although a variety of fire suppression systems, including sprinklers and carbon dioxide, exist for the protection of restaurant cooking operations, many restaurants incorporate a pre-engineered dry chemical or wet chemical fire extinguishing system. These systems are intended to provide protection for cooking appliances and associated ventilation equipment considered to be a potentially significant fire risk. System Components and Uses Pre-engineered dry and wet chemical fire extinguisher systems generally consist of an extinguishing agent, expellant gas storage tank(s), manual and/or automatic control hardware, piping or tubing to deliver the agent, and nozzles to effectively disperse the agent onto the fire area. The installation requirements for a pre-engineered fire extinguishing system are specified by the system equipment manufacturer. Construction specifications, including the quantity of extinguishing agent, pipe size and length limitations, maximum number and type of fittings, and nozzle type and installation locations are outlined int he manufacturer's installation, operation and maintenance manual. Additional system design engineering is not necessary provided the fire extinguishing system is installed in accordance with the limitations specified in the manual. Dry and wet chemical extinguishing systems are intended for use in situations where prompt extinguishment is required and sources for re-ignition are not present. Dry chemical extinguishing systems utilize sodium bicarbonate, potassium bicarbonate or ammonium phosphate as an extinguishing agent. Wet chemical extinguishing systems utilize a variety or proprietary chemical compositions for extinguishing agents. Underwriters Laboratories Inc. (UL) issued the first UL Listing for a dry chemical fire extinguishing system unit in the mid 1950s. Subsequently, the National Fire Protection Association (NFPA) adopted the Standard for Dry Chemical Extinguishing Systems, ANSI/NFPA 17, which specifies installation system units are UL Listed for use in a variety of fire suppression applications, including:
Pre-engineered dry chemical extinguishing system units utilize two basic methods to achieve fire suppression -- total flooding and local application. Either method, or a combination of both methods, may be utilized depending on the end-use application. With total flooding, the dry chemical is discharged into an enclosed space. This enables the extinguishing system to build up the necessary concentration of dry chemical within a short period of time so that extinguishment can be achieved. Since the extinguishing mechanism is relatively short term, these systems are intended to be used where re-ignition sources do not exist. Local application protection is different form total flooding in that the dry chemical is applied directly onto the surface of the fire source. Applying a dry chemical locally to a fire is effective only in those applications where the fire risk is isolated from other fire risks, or where all fire risks are protected simultaneously. Local application protection is only effective in those situations where re-ignition sources do not exist. Pre-engineered wet chemical fire extinguishing systems have been UL Listed and used to provide protection for commercial cooking areas since 1968. In 1984, the NFPA published the first edition of the Standard for Wet Chemical Extinguishing Systems, NFPA 17A. Consistent with current use, the scope of NFPA 17A covers the installation, operation, inspection, and maintenance of pre-engineered wet chemical extinguishing systems intended for the fire protection of commercial cooking areas. Wet chemical extinguishing system units are UL Listed to provide fire protection for commercial cooking areas only. As such, wet chemical extinguishing systems generally achieve fire suppression by way of local application of the agent to the fire source. Standards for Safety Due to the increased usage and expanded application of dry and wet chemical extinguishing system units, UL initiated an effort in the late 1980s to develop Standards for Safety covering product construction and performance requirements for these units. The initial phase in the development of these Standards included a meeting of UL's Industry Advisory Conference (IAC) for extinguishing system equipment to discuss the proposed safety requirements developed by UL. A draft of these requirements was circulated to a variety of organizations and interested individuals for review and comment. Those involved included the appropriate UL Engineering Councils concerned government agencies, extinguishing system equipment manufacturers, consumers, jurisdictional authorities and others who expressed an interest. Through meetings and written comments, these groups suggested a number of revisions and clarifications. This input provided a degree of assurance that the safety requirements and UL's Listing Mark on these products would be readily accepted. After all comments were considered and resolved, UL published the first editions of two new Standards for Safety in July of 1992. UL 1254, the Standard for Safety for Pre-Engineered Dry Chemical Extinguishing System Units, includes construction and performance requirements for pre-engineered dry chemical extinguishing system units. UL 300, the Standard for Safety for Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas, includes the fire test methodology and associated requirements for dry and wet chemical extinguishing system units intended for use in commercial cooking areas. Construction Requirements The UL investigation of dry and wet chemical extinguishing system units includes an examination of construction features to determine conformance with the applicable requirements in UL 1254. A sampling of these requirements includes the following:
Operational and Performance Tests After the extinguishing system components are reviewed to determine conformance with applicable construction requirements, the operational and performance characteristics of the equipment are evaluated. This evaluation includes tests such as hydrostatic strength, one year leakage, 30 day elevated temperature exposure, 500 cycle operation, mounting device, pneumatic operation, pressure relief, vibration, and pressure gauge performance. Fire Tests An extensive evaluation of the extinguishing system's capability to extinguish various types of fires is conducted. The type of hazards referenced in the manufacturer's installation instructions are used to determine the fire tests UL will conduct in the evaluation of the system equipment. Commercial Cooking Areas - Dry and wet chemical extinguishing system units are investigated for use with each type of cooking appliance referenced in the manufacturer's installation instructions. These tests are conducted in accordance with the appropriate fire test method specified in UL 300. Appliances may include deep fat fryers; griddles; gas or electric radiant charbroilers; lava, pumice or synthetic rock charbroilers; natural charcoal and mesquite wood charbroilers; and upright and chain broilers. Typically, the most difficult fire test to achieve extinguishment involves a deep fat fryer cooking appliance. A commercial gas-fired fryer, which represents the maximum cooking area specified in the manufacturer's instructions, is used for this test. Each type of nozzle intended to be used on deep fat fryers is positioned in a location and orientation considered to be most difficult to achieve extinguishing as permitted by the installation instructions. Each fire test is also conducted with the extinguishing agent storage container pressurized to simulate the minimum operating temperature or fitted with a gas cartridge which has been conditioned to the minimum operating temperature. Having established these conditions, the fryer's safety limit controls are bypassed and the fryer is heated until auto-ignition of the cooking oil occurs. After a two minute freeburn, the extinguishing system unit is actuated. In order to comply with UL 300, the extinguishing system unit shall (1) cause the flame in the appliance to be completely extinguished and (2) not permit re-ignition of the grease for 20 minutes, or cause the temperature of the grease to decrease to at least 60-F below its observed auto-ignition temperature, whichever is longer. Additionally, the extinguishing system unit is evaluated for its ability to extinguish fires occurring in an exhaust hood and duct assembly. The maximum perimeter duct and hood and duct assembly. The maximum perimeter duct and hood size specified in the installation instructions is used. As with the cooking application tests, the extinguishing system agent storage container is installed to provide the lowest extinguishing agent discharge rate. The interior surfaces of the hood, filters and duct are coated with a layer of grease. A deep fat fryer is located under the hood and directly below the duct entrance. Thermocouples are placed at several locations in the duct to monitor temperatures to determine ignition and fire suppression. Ignition of the grease on the surfaces of the hood and duct is initiated by external heat sources. The fire in the duct is permitted to burn freely for at least 30 seconds after a temperature of 1200zF is achieved at a thermocouple located 20 feet downstream form the duct entrance. At this time, the extinguishing system is actuated. To comply with UL 300, the fire shall be suppressed as evidenced by a sharp decrease in temperature measured at the thermocouple. This test is conducted using three separate conditions: (1) duct outlet opened with no exhaust blower operating, (2) duct outlet opened with exhaust blower providing between 500 to 1000 ft/min air velocity, and (30) duct outlet closed immediately before system actuation. Local Application Protection - Flammable Liquids - When investigated for such use, pre-engineered dry chemical extinguishing system units may be used to protect localized flammable liquid fires. These units are generally designed to discharge the extinguishing agent either overhead or horizontally across the fuel surface. Fire tests consist of using a 8 in. (minimum) deep steel pan having the maximum area as reference in the manufacturer's installation instructions. The pans are filled with two inches of heptane to provide a 6 in. freeboard (distance from top of the fuel surface to the top of the pan). The heptane is ignited and allowed to burn freely for at least 30 seconds, after which the extinguishing system is actuated. To comply with UL 1254, the test fire must be completely extinguished. In addition to the extinguishment tests conducted with the nozzles at the maximum height above the heptane surface, extinguishment tests are also conducted with the nozzles located at the minimum height above the heptane surface. For this test, the extinguishing system storage container is pressurized to stimulate the maximum storage temperature and the minimum amount of distribution piping is employed. This condition represents the highest agent flow rate that the extinguishing system will develop. For this test, UL 1254 specifies that the test fire must be extinguished and that no splashing of the heptane is to occur. Open-Face Type Paint Spray Booths - When investigated for such use, pre-engineered dry chemical extinguishing system units may be used to protect open-faced type paint spray booths. These systems are intended to protect Class A or Class B combustibles, or both. Fire tests are conducted using a booth type structure representing the maximum size (length, width and height) referenced in the manufacturer's installation instructions. The test booth is also to include the maximum size open face, commonly referred to as the uncloseable opening. Paint booth protection is generally divided into three areas: (1) work area, (2) plenum area, and (3) exhaust duct. For Class B combustibles, cans filled with heptane are located at the booth corners of the work and plenum areas, at both floor and ceiling levels. Cans with heptane are also located in the duct. After the can are ignited, they are allowed to burn freely for 30 seconds, after which the extinguishing system is actuated. In addition, Class B fire tests are conducted using a 5 square foot pan of heptane within the work area and a 1 foot wide pan of heptane placed on the floor along the length of the uncloseable opening. After the fuel in the test pans is ignited, they are allowed to burn freely for 30 seconds, after which the extinguishing system is actuated. In addition, Class B fire tests are conducted using a 5 square foot pan of heptane within the work area and a 1 foot wide pan of heptane placed on the floor along the length of the uncloseable opening. After the fuel in the test pans is ignited, they are allowed to burn freely for 30 seconds, after which the extinguishing system unit is actuated. For Class A combustibles, tests are conducted using two wood cribs, 12 in. by 12 in., placed within the work area. The cribs are ignited and allowed to burn freely for two minutes, after which the extinguishing system unit is actuated. Each paint spray booth fire test is conducted under conditions of air flow and no air flow. For tests conducted using air flow, the air flow is adjusted to provide an average velocity of 100 ft/min across the uncloseable opening area. For each fire test, UL 1254 specifies that the fires must be completely extinguished. Other Industrial Fire Risks - Pre-engineered dry chemical extinguishing system units may also be suitable to provide protection for automobile service filing areas, off-the-road type vehicles and industrial total flooding applications. The test protocol for industrial use total flooding is similar to that for paint spray booths. Since use in this application is limited to reasonably draft-free enclosures, fire tests are not conducted with air flow. Additionally, since this type of system is intended for installation in enclosures with uncloseable openings not exceeding 5 percent, pan fire tests are not conducted. Fire tests for extinguishing system units intended to protect automobile service filling stations are evaluated similar to local application systems. In lieu of using a pan of heptane, small cans of heptane are located around the perimeter of the protected area to determine the coverage area for each discharge nozzle. Off-the-road vehicle fire tests parallel those conducted for total flooding applications. Installation To determine the extinguishing system will perform as anticipated, UL conducts appropriate fire and performance tests using the installation conditions considered to be most critical, based on the limitations and end use information provided in the manufacturer's manual. The requirements in UL 1254 specify that the manufacturer's installation manual is to include information such as:
Summary Pre-engineered dry and wet chemical extinguishing systems have been used by the fire protection community for many years. Publishing the requirements outlined in UL 1254 and UL 300 provides an opportunity for manufacturers and Authorities Having Jurisdiction to reference the parameters utilized by UL in the investigation and Listing of this equipment. When installed in accordance with the limitations established by the manufacturer and specified in the UL listing, these extinguishing systems provide an acceptable level of fire suppression for a number of unique fire risks. References
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