wet and dry chemical system fire extinguishing systems

Training and operational manual

1. Wet and Dry Chemical Extinguishing Systems Chapter 9

2. Learning Objectives Describe the characteristics and types of wet and dry chemical systems Discuss the most likely hazards wet and dry chemical systems protect Define pre-engineered system Discuss the events that lead to the standardization of UL300

3. Learning Objectives (continued) List the major components that make up wet and dry chemical systems Describe how wet and dry chemical agents control and extinguish fire Discuss the various inspection, testing, and maintenance requirements for fixed and dry chemical systems

4. Introduction Wet and dry chemical systems provide an alternative to water Used when water would have no effect, or make the situation worse Wet chemical systems most commonly used to extinguish fires in commercial kitchens Dry chemical systems extinguish flammable and combustible liquid fires Both systems use gas to expel the agent and have a finite amount of agent available

5. Wet Chemical Extinguishing Systems Protect appliances in commercial kitchens Deep fat fryers, ranges, griddles, grills etc. Chemicals used are proprietary for the manufacturer Water-based; forms a medium for the agent to flow to the hazard Saponification decreases or eliminates the fuel vapors by smothering and cooling the fuel

6. Figure 9-1 Wet chemical extinguishing system protecting a commercial kitchen

7. Dry Chemical Extinguishing Systems Protect equipment and processes against flammable and combustible liquid fires Fine powders that use pressurized gas as the transport medium Particles suspend in the gas to facilitate distribution Knock down the flame and coat the surface area, cutting off oxygen Effective on three-dimensional surface fires

8. Standards for Wet and Dry Chemical Systems Many wet and dry chemical systems are pre-engineered and adaptable to many situations Some hazards require full engineering Amount of agent needed is the basis for system design NFPA 17 and 17 A are the standards UL 300 and UL 1254 provide specific requirements

9. System Component and Requirements Wet and dry chemical systems use similar types of components Main components: Agent storage containers Expelling gas cartridges Piping and fittings Nozzles Activation devices System alarms and indicators

10. Agent Storage Containers and Gas Cartridges Containers that store wet and dry chemicals are made of non-reactive metal Must handle high pressures Size depends on amount of agent needed to protect the hazard Many manufacturers do not combine wet chemical agent and expelling gas Dry chemical containers may be larger

11. Piping and Fittings Piping and fittings must be made of non-combustible material Must be compatible with the agent Must be able to handle anticipated pressure Usually a metal specifically approved for use with the specific agent and extinguishing system Arrangement and size of the pipe and fittings depends on the hazard and the agent Fluidization : mixing dry agent and expelling gas

12. Nozzles Different types made for wet and dry chemical systems Require listing for the intended application Distribute the extinguishing agent by delivering a specific application pattern NFPA 17 and 17 A require the nozzles to be noncombustible Should not deform when exposed to fire Nozzles on wet systems require in-line strainer

13. Figure 9-6 Wet chemical system nozzles with blow-off caps

14. Activation Devices Wet and dry chemical extinguishing systems operate by automatic and manual activation Failure of one does not inhibit the other Automatic activation by mechanical or electrical sensing device located in the hazard area Mechanical device example: fusible link Electrical device example: heat detector Pull station must be 42- 48 inches above the floor in path of egress

15. System Alarms and Indicators Upon activation, wet and dry chemical systems must initiate an alarm Must tie into building fire alarm system If no alarm system is in building, local audible alarm or visual indicator provides notification When flowing, dry chemical discharge creates potentially dangerous cloud of powder Inhibits breathing and visibility Indicators notify when recharging or investigation is needed

16. Wet and Dry Chemical Agents Wet chemicals are liquid-based Dry chemicals are solid particle-based Each agent is appropriate for particular applications and conditions Design professional must consider: Environment Type of system Amount of agent needed

17. Wet Chemical Agents Proprietary water-based solutions Mixed with: Potassium acetate Potassium carbonate Potassium citrate Mixture of the above Wet agents are most effective for Class K fires May corrode, stain equipment if not cleaned up Generally harmless to humans

18. Dry Chemicals Small solid particles propelled by pressurized gas When discharged, chemical covers and smothers the burning material Three categories: sodium bicarbonate-based, potassium-based, multipurpose Sodium bicarbonate and potassium-based work well on Class B and C fires Ammonium phosphate works well on Class A, B and C fires

19. Types of Fixed Pipe Wet and Dry Extinguishing Systems Two types of fire extinguishing systems: Local application systems Total flooding systems Local application systems necessary when the hazard is exposed and not surrounded Can be wet or dry Total flooding system protects enclosed hazards or hazards in confined areas

20. Local Application Systems Protects a specific area, piece of equipment, process or operation Use wet or dry extinguishing agents Discharge the agent directly onto the hazard Smother, cool, extinguish the fire Must protect entire hazard Hazard must be isolated from other hazards to avoid spreading the fire Nozzle placement critical to ensure proper application of the agent

21. Total Flooding Systems Protect enclosed hazards and areas within a structure When discharged, the agent fills entire protected area to disrupt the fire’s chain reaction Amount of agent and nozzles needed depend on total volume of area Based on manufacturer’s design calculations Successful suppression requires adequate sealing or minimal openings in protected area

22. Other Wet and Dry Chemical Application Methods Hand hose lines can stand alone, supplement other systems Installation of hand hose line permissible if approved by governing authority When supplementing dry chemical system, hand hose line must have separate chemical supply Minimum 30-second dry chemical supply Must be accessible and reach the hazard

23. Wet and Dry Chemical Extinguishing System Operation May be manual or automatic Automatic activation: fire must build to a sufficient level to activate the sensing device Manual activation: person must make physical connection with releasing device Manual or electronic release starts operational sequence: Agent flows; associated utilities are controlled; alarm sounds

24. Figure 9-11 Once the system activates, the cable attached to the gas shut-off valve releases to close the valve.

25. Inspection, Testing, and Maintenance Wet and dry chemical systems must undergo acceptance inspections and tests Relatively simple for both types of systems May be many interconnected systems As systems age, periodic inspections, tests, maintenance are required Some inspections and tests must be done by specially trained personnel

26. Visual Inspections Visual inspection confirms equipment is located and installed according to documentation Includes verification that: Correct nozzle types are installed Nozzles are properly oriented and located Pipe material, sizes, and length are correct Agent type and amount are correct Auxiliary equipment is correctly installed

27. Discharge Test Discharge tests verifies that system nozzles and associated equipment operate correctly Balloons or bags capture the agent when discharged Capturing and weighing the product more critical to the dry systems than the wet systems Gas propellant is usually nitrogen or compressed air Avoids corrosion by wet agent

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. Acceptance Test Confirms proper operation by manual or automatic release Activating manual release, automatic detector or fusible link minimizes spread of fire Fuel shut off equipment that produces heat Electrical supply shut off Supply air shut down Alarm activation Exhaust fan shut down and damper closes

30. Periodic Inspection, Testing, and Maintenance Many tests performed when commissioning a system are the same tests for inspection More frequent and the owner’s responsibility Inspection: on a monthly basis, visually inspect for conditions that could cause failure Periodic testing determines if system is operating as designed Routine maintenance follows manufacturer’s guidelines

31. Summary Wet and dry chemical systems provide an alternative to water-based systems Wet chemical agents are a mixture of water and other chemicals, and are proprietary Dry chemical agents coat the surface of the hazard, preventing oxygen from reaching fuel Many systems are pre-engineered Two types of systems: local application and total flooding systems