Fire protection


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Fire protection SYSTEMS in Buildings

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Fire protection

  2. 2. FIRE PROTECTION SYSTEMSFire protection systems are used in buildings depending upon the type of use of thebuilding. Fire suppression systems are used in conjunction with smokedetectors and fire alarm systems to improve and increase public safety. Suppressionsystems are governed by the codes under the NFPA 13 handbook.Types  Gaseous agents  Wet and dry chemical agents( Foams)  Fire sprinkler systems (wet, dry, pre-action, and deluge)  Gaseous agents:
  3. 3. The system typically consists 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. Gaseous fire suppression is a term to describe the use of inert gases and chemical agents to extinguish a fire. There are four means used by the agents to extinguish a fire. They act on the "fire tetrahedron”  Inhibiting the chain reaction of the above components  Reduction or isolation of fuel  Reduction of heat  Reduction or isolation of oxygenMethods for applying an extinguishing agent :  Total flooding  Local application i. Systems working on a total flooding principle 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. ii. Systems working on a local application principle 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. In the context of automatic extinguishing systems, local application normally does not refer to the use of manually operated wheeled or portable fire extinguishers, although the nature of the agent delivery is similar.  Wet and dry chemical agents( Foams) Fire-fighting foam is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. Depending on the type of foam system, this is done in several ways:
  4. 4.  Foam blankets the fuel surface smothering the fire. The fuel is cooled by the water content of the foam. The foam blanket suppresses the release of flammable vapors that can mix with the air. 1. Class “A” foam : Class A foams were developed in mid-1980s for fighting wildfires. Class A foams lower the surface tension of the water, which assists in the wetting and saturation of Class A fuels with water. This aids fire suppression and can prevent reigniting. Favorable experiences led to its acceptance for fighting other types of class A fires, including structure fires. 2. Class “B” foam : Class B foams are designed for class B fires — flammable liquids (such as nail polish and White Out). The use of class A foam on a class B fire may yield unexpected results, as class A foams are not designed to contain the
  5. 5. explosive vapors produced by flammable liquids. Class B foams have two major subtypes. a) Synthetic foams : Synthetic foams are based on synthetic surfactants. Synthetic foams provide better flow and faster knockdown of flames, but limited post-fire security. Aqueous film forming foams (AFFF) are water-based and frequently contain hydrocarbon-based surfactant such as sodium alkyl sulfate, and fluorosurfactant — such as fluorotelomers,perfluorooctanoic acid (PFOA), or perfluorooctanesulfonic acid (PFOS). They have the ability to spread over the surface of hydrocarbon-based liquids. Alcohol-resistant aqueous film-forming foams (AR-AFFF) are foams resistant to the action of alcohols, able to form a protective film when they are present. b) Protein foams : Protein foams contain natural proteins as the foaming agents. Unlike synthetic foams, protein foams are bio-degradable. They flow and spread slower, but provide a foam blanket that is more heat-resistant and more durable. Protein foams include regular protein foam (P), fluoroprotein foam (FP), film- forming fluoroprotein (FFFP), alcohol-resistant fluoroprotein foam (AR-FP), and alcohol-resistant film-forming fluoroprotein (AR-FFFP). Protein Foam from non-animal sources is preferred because of the possible threats of biological contaminants like prions. Fire sprinkler systems (wet, dry, pre- action, and deluge) A Fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flow rate to a water distribution piping system, onto which fire sprinklers are connected. Although historically only used in factories and large commercial buildings, home and small building systems are now available at a cost-effective price.
  6. 6. SPRINKLING PROCESS :Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb ora two-part metal link held together with fusible alloy. The glass bulb or linkapplies pressure to a pip cap which acts as a plug which prevents water fromflowing until the ambient temperature around the sprinkler reaches the designactivation temperature of the individual sprinkler head. In a standard wet-pipesprinkler system, each sprinkler activates independently when the predeterminedheat level is reached. Because of this, the number of sprinklers that operate islimited to only those near the fire, thereby maximizing the available waterpressure over the point of fire origin.A sprinkler activation will do less damage than a fire department hose stream,which provide approximately 900 liters/min (250 US gallons/min. A sprinkler willusually activate between one and four minutes, whereas the fire departmenttypically takes at least five minutes to arrive at the fire site after receiving analarm, and an additional ten minutes to set up equipment and apply hose
  7. 7. streams to the fire. This additional time can result in a much larger fire, requiringmuch more water to extinguish.