© 2008 Delmar, Cengage Learning Portable Fire Extinguishers Chapter 11

© 2008 Delmar, Cengage Learning Introduction Portable fire extinguishers are intended for use in incipient stage where water is ineffective –Useful if there is quick access, the correct type is available, and person is trained –Has fixed amount of suppression agent –Are clearly labeled and require little training Rapid access to the extinguisher is critical

© 2008 Delmar, Cengage Learning Requirements for Fire Extinguishers Code requirements exist in all of the model codes for fire extinguishers –Requirements center on use and occupancy conditions and processes IFC requires extinguishers installed in almost every new and existing occupancy classification NFPA 10 lists the requirements for fire extinguishers

© 2008 Delmar, Cengage Learning Fire Extinguisher Classification Through the classification system, extinguishing agents matched to fire hazards Classification designated with letters –Class A fires: ordinary combustibles –Class B fires. flammable and combustible liquids and gases –Class C fires: energized electrical equipment –Class D fires: combustible metals –Class K fires: cooking media

© 2008 Delmar, Cengage Learning Fire Extinguisher Ratings Class A and B have a number rating to indicate performance capability of the extinguisher –Expresses how much fire the extinguisher can handle Class A extinguishers are tested using a wood crib on fire, allowing it to burn for a time Class B extinguishers are tested with a flammable liquid fire in a pan –Flammable liquid is usually heptane Class C extinguishers do not receive a rating

© 2008 Delmar, Cengage Learning Figure 11-1 Wood cribbing for Class A extinguisher test

© 2008 Delmar, Cengage Learning Figure 11-3 Class C test for conductivity

© 2008 Delmar, Cengage Learning Types of Fire Extinguishers Pumped, stored pressure, and cartridge pressure categories Many suppression agents: –Water, foam, carbon dioxide, dry chemical, wet chemical, dry powder, halon, clean agents Some agents will not work well with a particular category of extinguisher

© 2008 Delmar, Cengage Learning Pump Extinguishers Require manual operation of a pump mechanism –Creates pressure in the tank to expel extinguishing agent Extinguishing agent is either water or antifreeze solution Easy to operate and fill Backpack type extinguisher has external pump –Mechanism similar to hand-held

© 2008 Delmar, Cengage Learning Stored Pressure Extinguishers Mix pressurized gas and extinguishing agent in the same tank Gas is above the agent and keeps constant pressure on the agent When operated, the pressure of the gas forces the extinguishing agent out of the tank Air or nitrogen frequently used as expelling gas Pressure gauge indicates if pressure is sufficient

© 2008 Delmar, Cengage Learning Cartridge Pressure Extinguishers Similar to stored pressure type, but pressurized gas is in a separate cartridge –Attached to the side of the extinguishing tank Activating the extinguisher punctures the cartridge that expels the gas into the tank Allows for easy maintenance of certain types of agents –Top removes without dumping the agent or losing the gas pressure Good for agents that settle and need stirring

© 2008 Delmar, Cengage Learning Common Fire Extinguisher Agents Same agents used in sprinkler and suppression systems are common in fire extinguishers –Present in smaller amounts

© 2008 Delmar, Cengage Learning Water One of the best agents because it absorbs more heat per pound than any other material Most effective on Class A fires Not effective on some fuels; dangerous to use on others When used in an extinguisher, extinguisher must not be exposed to cold

© 2008 Delmar, Cengage Learning Foam Good agent for Class A but better for Class B fires Foam forms a vapor barrier between the fuel and the atmosphere Agent must discharge through special aspirating nozzle so that air can mix with the agent Two types of foam: –Aqueous film-forming foam –Film-forming fluoroprotein

© 2008 Delmar, Cengage Learning Carbon Dioxide Carbon dioxide gas effective in Class B and C fires; limited use on Class A fires In extinguisher tank, carbon dioxide is a high- pressure liquid state –Expands to a gas when released Depletes the oxygen supply Must be discharged at close range to the fire because air movement carries the gas away Operator must have oxygen supply available to avoid asphyxiation

© 2008 Delmar, Cengage Learning Dry Chemicals Small solid particles propelled by pressurized gas When discharged, chemical smothers the burning material Not considered dangerous or toxic; do not react with flammable liquids or gases; not conductive Once discharged, create a cloud that limits visibility; may cause respiratory problems May leave a corrosive residue

© 2008 Delmar, Cengage Learning Wet Chemicals Wet chemical agents most effective with Class K fires Water-based solutions that mix with potassium carbonate, potassium acetate, potassium citrate React with fat in the cooking medium or food to develop a soapy foam blanket on the surface –Smothers, cools, and extinguishes the fire Liquid in the agent cools the cooking media adequately to maintain the foam blanket

© 2008 Delmar, Cengage Learning Dry Powders Class D fires present a challenge –Water is not a good choice because it can react with metals to liberate oxygen and fuel the fire Dry powders are one of the most effective agents –No one powder effective on all metals Some agents do not work in an extinguisher –Applied by shovel, scoop or by hand

© 2008 Delmar, Cengage Learning Halon and Other Clean Agents Halon still in use but less available –Gradual fade-out for environmental concerns Leaves no residue; not conductive; more effective than the same amount of CO 2 Halons are somewhat toxic and exposure can cause physical problems –Vertigo, loss of agility, loss of coordination Two types still in use: 1211, 1301 Inert gases generally safe for humans

© 2008 Delmar, Cengage Learning Summary Portable fire extinguishers –Are intended to suppress small incipient fires –Hold a fixed amount of suppression agent, so access should be quick –Must have knowledgeable operator Extinguishing agent must be suitable for the type of fire Three categories of extinguishers: pumped, stored-pressure, cartridge pressure

© 2008 Delmar, Cengage Learning Introduction Smoke and toxic gases can migrate outside of the fire area –Smoke travels along stairways, ducts, corridors, elevator hoistways, etc. Spread of smoke and toxic gases can cause much damage, injuries, and death Passive design approach uses walls, etc., to create barriers Active design approach uses mechanical systems to exhaust the air

© 2008 Delmar, Cengage Learning Figure 12-1 Manually operated smoke and heat vent in stairway

© 2008 Delmar, Cengage Learning Code Required Smoke Control and Smoke Management Code-mandated installation of smoke control limited to certain structures Many structures facilitate quick evacuation –Significantly compartmentalized to inhibit smoke travel Installation of these systems in every structure is unnecessary Requirements exist for occupancies with significant evacuation challenge

© 2008 Delmar, Cengage Learning Smoke Containment, Removal, and Opposed Airflow Basic goal of smoke control is to mitigate the spread of smoke Smoke control techniques can be standalone or integrated into a building-wide approach Systems use 100% outdoor air for positive pressurization –100% exhaust to the outdoors for smoke relief General approaches: containment, removal, opposed airflow

© 2008 Delmar, Cengage Learning Containment by Pressure Differentials Stairway pressurization: prevents or reduces smoke intrusion into egress stairways Floating zone/floor-by-floor pressurization: uses the HVAC system Elevator hoistway pressurization: similar to stairway pressurization Refuge area pressurization: prevents smoke intrusion into refuge areas

© 2008 Delmar, Cengage Learning Figure 12-2 This mechanical fan and duct line supply air to pressurize a stairway

© 2008 Delmar, Cengage Learning Figure 12-3 Air supply grill for stairway pressurization

© 2008 Delmar, Cengage Learning Figure 12-4 Mechanical fan unit for “sandwich effect” pressurization

© 2008 Delmar, Cengage Learning Figure 12-5 Exhaust vent in corridor for “sandwich effect” pressurization

© 2008 Delmar, Cengage Learning Smoke Removal Best suited for large volume spaces, such as atriums, indoor stadiums, and airport terminals Provides vertical cross-flow ventilation from floor to roof Large volume spaces have no barriers –Smoke and toxic gases will rise and spread throughout the area Unpolluted air fed at a slower rate than the exhaust system rate –Fed from a level lower than the fire

© 2008 Delmar, Cengage Learning Figure 12-6 Atrium