Our last article focused on Fire Sprinkler System types and how the different types are best used in particular structures or situations. The same variation is true for fire suppression systems used in special hazard applications. Here we will review the different technologies and their purposes.
Foam-Water
A foam-water fire sprinkler system is a special application system which discharges a mixture of water and low-, medium-, or high-expansion foam concentrate. This results in a foam spray from the sprinkler. This is usually used with special hazard occupancies associated with high challenge fires, such as flammable liquids and airport hangars. The foam-water application can be used in wet, dry, pre-action or deluge system.
Water Spray
Water spray systems are operationally identical to deluge systems, but the piping and discharge nozzle spray patters are designed to protect a uniquely configured hazard, usually being three-dimensional components or equipment. The nozzles are selected for a specific spray pattern to conform to the three-dimensional nature of the hazard. Some typical spray patterns are oval, fan, full circle, and narrow jet. Examples of hazards protected by water spray systems are electrical transformers containing oil for cooling or turbo-generator bearings. Water spray systems can also be used on the surfaces of tanks containing flammable liquids or gases (such as hydrogen). In this case, the water spray is intended to cool the tank and its contents to prevent tank rupture and fire spread.
Water Mist
A water mist system works by creating a heat absorbent vapor. This type of system is used when water damage is a concern or where water supplies are limited. By using a mist, an equal volume of water will create a larger total surface area exposed to the fire. The larger total surface area better facilitates the transfer of heat, thus allowing more water droplets to turn to steam more quickly. A water mist, which absorbs more heat than water per unit time, due to exposed surface area, will more effectively cool the room, thus reducing the temperature of the flame. NFPA 750 defines water mist as a water spray with a droplet size of “less than 1000 microns at the minimum operation pressure of the discharge nozzle.” Water mist systems use a compressed gas as an atomizing medium, which is pumped through the sprinkler pipe. Instead of compressed gas, some systems us a high-pressure pump to pressurize the water so it atomizes as it exits the sprinkler nozzle. Water mist systems can operate with the same functionality as deluge, wet pipe, dry pipe, or pre-action systems.
Clean Agent (Gaseous Fire Suppression)
NFPA 2001 defines clean agent as, “Electrically nonconductive, volatile, or gaseous fire extinguishant that does not leave a residue upon evaporation.” Clean agents are used when protecting high dollar, mission critical assets that would be destroyed by water, such as IT systems, data storage rooms, and manufacturing equipment, or irreplaceable items like intellectual property, art, and antiques. There are three ways clean agents can extinguish a fire: reduction of heat, reduction or isolation of oxygen, and inhibiting the chain reaction of the heat and oxygen.
Clean agent fire protection systems are comprised of the agent, agent storage containers, agent release valves, fire detectors, fire detection system (wiring control panel, actuation signaling), agent delivery piping, and agent dispersion nozzles. Less typically, the agent may be delivered by means of solid propellant gas generators that produce either inert or chemically active gas. Clean agents are applied with either total flooding or local application. Total flooding systems apply an extinguishing agent to a three dimensional enclosed space in order to achieve a concentration of the agent (volume percent of the agent in air) adequate to extinguish the fire. These types of systems may be operated automatically by detection and related controls or manually by the operation of a system actuator. Local application systems apply an extinguishing agent directly onto a fire (usually a two dimensional area), or into the three dimensional region immediately surrounding the substance or object on fire. The main difference in local application from total flooding design is the absence of physical barriers enclosing the fire space.
Condensed Aerosol
Condensed aerosol fire suppression is one of the most efficient forms of fire suppression. It is a particle-based form of fire extinction similar to gaseous fire suppression or dry chemical fire extinction. The aerosol employs a fire extinguishing agent consisting of very fine solid particles and gaseous matter to extinguish fires. The condensed aerosol microparticles and effluent gases are generated by the exothermic reaction; until discharged from the device, the particles remain in vapor state. They are cooled and “condensed” within the device and discharged as solid particles. Condensed aerosols release finely-divided solids of less than 10 micrometers in diameter, the solid particles have a considerably smaller mass median aerodynamic diameter than those of dry chemical suppression agents, remain airborne significantly longer, and leave much less residue within the protected area. Condensed aerosols are flooding agents and therefore effective regardless of the location and height of the fire. This system does not require a room integrity test as it is flooding the space at room pressure; this will save you money in sealing the room and annual testing.
Dry Chemical
Dry chemical fire extinguishing agents are primarily used for fast knock down of high risk gas and liquids such as dip tanks, paint booths and gas filling stations. The dry chemicals work by preventing the chemical reactions involving heat, fuel, and oxygen (combustion). The substances in dry chemicals can also stop the break-down of fuel in the fire to prevent the creation of highly reactive fragments of molecules.
Wet Chemical
Primarily used in kitchen fire suppression, the wet chemical agent suppresses fire by cooling and reacting chemically to produce a foam layer on the grease. The foam seals combustible vapors, stopping the flames from re-igniting.
Fire Extinguishers
Fire Extinguishers may not be a part of the fire sprinkler system, but they are an integral part of your fire safety system. If the proper fire extinguisher is used correctly and promptly, more than 90% of fires are extinguishable. Most work environments are required by OSHA to have an emergency action plan, functioning extinguishers, and trained extinguisher operators. OSHA requirements vary, but safety does not – be safe, provide fire extinguishers and fire extinguisher training to your staff.
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