Chapter 09


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Chapter 09

  1. 1. Wet and Dry Chemical Extinguishing Systems Chapter 9
  2. 2. Learning Objectives <ul><li>Describe the characteristics and types of wet and dry chemical systems </li></ul><ul><li>Discuss the most likely hazards wet and dry chemical systems protect </li></ul><ul><li>Define pre-engineered system </li></ul><ul><li>Discuss the events that lead to the standardization of UL300 </li></ul>
  3. 3. Learning Objectives (continued) <ul><li>List the major components that make up wet and dry chemical systems </li></ul><ul><li>Describe how wet and dry chemical agents control and extinguish fire </li></ul><ul><li>Discuss the various inspection, testing, and maintenance requirements for fixed and dry chemical systems </li></ul>
  4. 4. Introduction <ul><li>Wet and dry chemical systems provide an alternative to water </li></ul><ul><ul><li>Used when water would have no effect, or make the situation worse </li></ul></ul><ul><li>Wet chemical systems most commonly used to extinguish fires in commercial kitchens </li></ul><ul><li>Dry chemical systems extinguish flammable and combustible liquid fires </li></ul><ul><li>Both systems use gas to expel the agent and have a finite amount of agent available </li></ul>
  5. 5. Wet Chemical Extinguishing Systems <ul><li>Protect appliances in commercial kitchens </li></ul><ul><ul><li>Deep fat fryers, ranges, griddles, grills etc. </li></ul></ul><ul><li>Chemicals used are proprietary for the manufacturer </li></ul><ul><li>Water-based; forms a medium for the agent to flow to the hazard </li></ul><ul><li>Saponification decreases or eliminates the fuel vapors by smothering and cooling the fuel </li></ul>
  6. 6. Figure 9-1 Wet chemical extinguishing system protecting a commercial kitchen
  7. 7. Dry Chemical Extinguishing Systems <ul><li>Protect equipment and processes against flammable and combustible liquid fires </li></ul><ul><li>Fine powders that use pressurized gas as the transport medium </li></ul><ul><ul><li>Particles suspend in the gas to facilitate distribution </li></ul></ul><ul><li>Knock down the flame and coat the surface area, cutting off oxygen </li></ul><ul><li>Effective on three-dimensional surface fires </li></ul>
  8. 8. Standards for Wet and Dry Chemical Systems <ul><li>Many wet and dry chemical systems are pre-engineered and adaptable to many situations </li></ul><ul><li>Some hazards require full engineering </li></ul><ul><ul><li>Amount of agent needed is the basis for system design </li></ul></ul><ul><li>NFPA 17 and 17 A are the standards </li></ul><ul><li>UL 300 and UL 1254 provide specific requirements </li></ul>
  9. 9. System Component and Requirements <ul><li>Wet and dry chemical systems use similar types of components </li></ul><ul><li>Main components: </li></ul><ul><ul><li>Agent storage containers </li></ul></ul><ul><ul><li>Expelling gas cartridges </li></ul></ul><ul><ul><li>Piping and fittings </li></ul></ul><ul><ul><li>Nozzles </li></ul></ul><ul><ul><li>Activation devices </li></ul></ul><ul><ul><li>System alarms and indicators </li></ul></ul>
  10. 10. Agent Storage Containers and Gas Cartridges <ul><li>Containers that store wet and dry chemicals are made of non-reactive metal </li></ul><ul><ul><li>Must handle high pressures </li></ul></ul><ul><li>Size depends on amount of agent needed to protect the hazard </li></ul><ul><li>Many manufacturers do not combine wet chemical agent and expelling gas </li></ul><ul><li>Dry chemical containers may be larger </li></ul>
  11. 11. Piping and Fittings <ul><li>Piping and fittings must be made of non-combustible material </li></ul><ul><ul><li>Must be compatible with the agent </li></ul></ul><ul><ul><li>Must be able to handle anticipated pressure </li></ul></ul><ul><ul><li>Usually a metal specifically approved for use with the specific agent and extinguishing system </li></ul></ul><ul><li>Arrangement and size of the pipe and fittings depends on the hazard and the agent </li></ul><ul><li>Fluidization : mixing dry agent and expelling gas </li></ul>
  12. 12. Nozzles <ul><li>Different types made for wet and dry chemical systems </li></ul><ul><ul><li>Require listing for the intended application </li></ul></ul><ul><li>Distribute the extinguishing agent by delivering a specific application pattern </li></ul><ul><li>NFPA 17 and 17 A require the nozzles to be noncombustible </li></ul><ul><ul><li>Should not deform when exposed to fire </li></ul></ul><ul><li>Nozzles on wet systems require in-line strainer </li></ul>
  13. 13. Figure 9-6 Wet chemical system nozzles with blow-off caps
  14. 14. Activation Devices <ul><li>Wet and dry chemical extinguishing systems operate by automatic and manual activation </li></ul><ul><ul><li>Failure of one does not inhibit the other </li></ul></ul><ul><li>Automatic activation by mechanical or electrical sensing device located in the hazard area </li></ul><ul><ul><li>Mechanical device example: fusible link </li></ul></ul><ul><ul><li>Electrical device example: heat detector </li></ul></ul><ul><li>Pull station must be 42- 48 inches above the floor in path of egress </li></ul>
  15. 15. System Alarms and Indicators <ul><li>Upon activation, wet and dry chemical systems must initiate an alarm </li></ul><ul><ul><li>Must tie into building fire alarm system </li></ul></ul><ul><ul><li>If no alarm system is in building, local audible alarm or visual indicator provides notification </li></ul></ul><ul><li>When flowing, dry chemical discharge creates potentially dangerous cloud of powder </li></ul><ul><ul><li>Inhibits breathing and visibility </li></ul></ul><ul><li>Indicators notify when recharging or investigation is needed </li></ul>
  16. 16. Wet and Dry Chemical Agents <ul><li>Wet chemicals are liquid-based </li></ul><ul><li>Dry chemicals are solid particle-based </li></ul><ul><li>Each agent is appropriate for particular applications and conditions </li></ul><ul><li>Design professional must consider: </li></ul><ul><ul><li>Environment </li></ul></ul><ul><ul><li>Type of system </li></ul></ul><ul><ul><li>Amount of agent needed </li></ul></ul>
  17. 17. Wet Chemical Agents <ul><li>Proprietary water-based solutions </li></ul><ul><li>Mixed with: </li></ul><ul><ul><li>Potassium acetate </li></ul></ul><ul><ul><li>Potassium carbonate </li></ul></ul><ul><ul><li>Potassium citrate </li></ul></ul><ul><ul><li>Mixture of the above </li></ul></ul><ul><li>Wet agents are most effective for Class K fires </li></ul><ul><li>May corrode, stain equipment if not cleaned up </li></ul><ul><li>Generally harmless to humans </li></ul>
  18. 18. Dry Chemicals <ul><li>Small solid particles propelled by pressurized gas </li></ul><ul><li>When discharged, chemical covers and smothers the burning material </li></ul><ul><li>Three categories: sodium bicarbonate-based, potassium-based, multipurpose </li></ul><ul><li>Sodium bicarbonate and potassium-based work well on Class B and C fires </li></ul><ul><li>Ammonium phosphate works well on Class A, B and C fires </li></ul>
  19. 19. Types of Fixed Pipe Wet and Dry Extinguishing Systems <ul><li>Two types of fire extinguishing systems: </li></ul><ul><ul><li>Local application systems </li></ul></ul><ul><ul><li>Total flooding systems </li></ul></ul><ul><li>Local application systems necessary when the hazard is exposed and not surrounded </li></ul><ul><ul><li>Can be wet or dry </li></ul></ul><ul><li>Total flooding system protects enclosed hazards or hazards in confined areas </li></ul>
  20. 20. Local Application Systems <ul><li>Protects a specific area, piece of equipment, process or operation </li></ul><ul><li>Use wet or dry extinguishing agents </li></ul><ul><ul><li>Discharge the agent directly onto the hazard </li></ul></ul><ul><ul><li>Smother, cool, extinguish the fire </li></ul></ul><ul><li>Must protect entire hazard </li></ul><ul><ul><li>Hazard must be isolated from other hazards to avoid spreading the fire </li></ul></ul><ul><li>Nozzle placement critical to ensure proper application of the agent </li></ul>
  21. 21. Total Flooding Systems <ul><li>Protect enclosed hazards and areas within a structure </li></ul><ul><li>When discharged, the agent fills entire protected area to disrupt the fire’s chain reaction </li></ul><ul><li>Amount of agent and nozzles needed depend on total volume of area </li></ul><ul><ul><li>Based on manufacturer’s design calculations </li></ul></ul><ul><li>Successful suppression requires adequate sealing or minimal openings in protected area </li></ul>
  22. 22. Other Wet and Dry Chemical Application Methods <ul><li>Hand hose lines can stand alone, supplement other systems </li></ul><ul><li>Installation of hand hose line permissible if approved by governing authority </li></ul><ul><li>When supplementing dry chemical system, hand hose line must have separate chemical supply </li></ul><ul><li>Minimum 30-second dry chemical supply </li></ul><ul><li>Must be accessible and reach the hazard </li></ul>
  23. 23. Wet and Dry Chemical Extinguishing System Operation <ul><li>May be manual or automatic </li></ul><ul><li>Automatic activation: fire must build to a sufficient level to activate the sensing device </li></ul><ul><li>Manual activation: person must make physical connection with releasing device </li></ul><ul><li>Manual or electronic release starts operational sequence: </li></ul><ul><ul><li>Agent flows; associated utilities are controlled; alarm sounds </li></ul></ul>
  24. 24. Figure 9-11 Once the system activates, the cable attached to the gas shut-off valve releases to close the valve.
  25. 25. Inspection, Testing, and Maintenance <ul><li>Wet and dry chemical systems must undergo acceptance inspections and tests </li></ul><ul><li>Relatively simple for both types of systems </li></ul><ul><ul><li>May be many interconnected systems </li></ul></ul><ul><li>As systems age, periodic inspections, tests, maintenance are required </li></ul><ul><li>Some inspections and tests must be done by specially trained personnel </li></ul>
  26. 26. Visual Inspections <ul><li>Visual inspection confirms equipment is located and installed according to documentation </li></ul><ul><li>Includes verification that: </li></ul><ul><ul><li>Correct nozzle types are installed </li></ul></ul><ul><ul><li>Nozzles are properly oriented and located </li></ul></ul><ul><ul><li>Pipe material, sizes, and length are correct </li></ul></ul><ul><ul><li>Agent type and amount are correct </li></ul></ul><ul><ul><li>Auxiliary equipment is correctly installed </li></ul></ul>
  27. 27. Discharge Test <ul><li>Discharge tests verifies that system nozzles and associated equipment operate correctly </li></ul><ul><li>Balloons or bags capture the agent when discharged </li></ul><ul><li>Capturing and weighing the product more critical to the dry systems than the wet systems </li></ul><ul><li>Gas propellant is usually nitrogen or compressed air </li></ul><ul><ul><li>Avoids corrosion by wet agent </li></ul></ul>
  28. 28. Figure 9-12 Bags tied to the nozzles to collect the wet chemical agent during a discharge test to ensure proper flow to each nozzle
  29. 29. Acceptance Test <ul><li>Confirms proper operation by manual or automatic release </li></ul><ul><li>Activating manual release, automatic detector or fusible link minimizes spread of fire </li></ul><ul><ul><li>Fuel shut off equipment that produces heat </li></ul></ul><ul><ul><li>Electrical supply shut off </li></ul></ul><ul><ul><li>Supply air shut down </li></ul></ul><ul><ul><li>Alarm activation </li></ul></ul><ul><ul><li>Exhaust fan shut down and damper closes </li></ul></ul>
  30. 30. Periodic Inspection, Testing, and Maintenance <ul><li>Many tests performed when commissioning a system are the same tests for inspection </li></ul><ul><ul><li>More frequent and the owner’s responsibility </li></ul></ul><ul><li>Inspection: on a monthly basis, visually inspect for conditions that could cause failure </li></ul><ul><li>Periodic testing determines if system is operating as designed </li></ul><ul><li>Routine maintenance follows manufacturer’s guidelines </li></ul>
  31. 31. Summary <ul><li>Wet and dry chemical systems provide an alternative to water-based systems </li></ul><ul><li>Wet chemical agents are a mixture of water and other chemicals, and are proprietary </li></ul><ul><li>Dry chemical agents coat the surface of the hazard, preventing oxygen from reaching fuel </li></ul><ul><li>Many systems are pre-engineered </li></ul><ul><li>Two types of systems: local application and total flooding systems </li></ul>