When you enter a condominium or commercial building you will often see wet sprinkler heads located in the walls or hanging from the ceiling. These water suppression systems will extinguish fires involving wood components, couches (polyurethane foam) and other plastic materials, and are effective at controlling or extinguishing fires. But how do we control fires involving grease or other flammable chemicals, like paint?
We are taught at an early age not to throw water on a grease or chemical fire. Why not? Because adding water to grease or certain chemicals creates a larger number of fine particles, thus increasing the size and surface area of the fire. To suppress a grease fire in a residential application, placing a lid over the fire will cut off the oxygen supply and extinguish the fire. However, in a commercial situation, where simply putting a lid over the fire may not be practical, using dry chemicals to extinguish the fire is the only other option.
How do Dry Chemical Suppression Systems Work?
Dry chemical fire suppression systems are mechanical systems that operate with fusible links connected to a pulley system. A dry chemical system usually has a mechanical linkage that allows the dry chemical (usually a mixture of monoammonium phosphate and ammonium sulfate) to reach the suppression heads. It can be activated in two ways: by pulling a tab manually at a pull station, or by the melting of a fusible link. In a system with a nitrogen and dry chemical tank, once the fire melts the link the tension in the cable becomes slack, allowing a mechanical lever to puncture the nitrogen tank. The nitrogen then travels into the dry chemical tank essentially forcing the dry chemical through the fire suppression heads located near the fire.
Considerations and Care of a Dry Fire Suppression System
As spraying water on a grease fire will only spread the fire, and putting a lid on the container may not be sufficient in a commercial kitchen, dry chemical systems are an important tool for the suppression of fire in restaurants. These fusible links are typically located right above the stove top with the pulley system travelling through the ventilation hood. If the ventilation system is poorly maintained, grease can accumulate on all parts of the suppression system, including the fusible links, and in the pulley elbows. As such, while the fusible links might melt if a fire occurs, the cable can get hung up in the pulley, and the system can fail to operate. As a result, this allows the fire time and, more importantly, oxygen to grow.
Not surprisingly, not only is choosing the right fire suppression system for the environment important, but so is the proper care and maintenance of these systems. NFPA 17, Dry Chemical Extinguishing Systems, indicates that these systems should be inspected by the owner monthly to ensure the systems are in their proper location, manual actuators are not obstructed, tamper seals in intact, certification tag is in place, and that there is no physical damage. NFPA 17 also indicates that dry chemical stored in pressure systems shall be examined every 6 years, and the system should be inspected semiannually or as per the manufacturer’s instructions.