chapter 06
TRANSCRIPT
© 2008 Delmar, Cengage Learning
Specialized Water-Based Fire Protection Systems
Chapter 6
© 2008 Delmar, Cengage Learning
Learning Objectives
• State three reasons to install other types of water-based fire protection systems instead of standard automatic fire sprinkler systems
• Discuss the characteristics and applications for fixed foam systems
• Discuss the characteristics and applications for water spray fixed systems
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Learning Objectives (continued)
• Discuss the characteristics and applications for foam-water sprinkler and foam-water spray systems
• Discuss the characteristics and applications for water mist systems
• Discuss the inspection and test requirements for acceptance of special water-based fire protection systems
• Recognize the possible impairments to special water-based fire protection systems
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Introduction
• Water-based systems that protect special hazards:– Low-, medium-, and high-expansion foam systems– Water spray fixed systems– Foam-water sprinkler and spray systems– Water mist systems
• Provide protection where other systems would be inadequate
• Few major differences between these four types
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Required Installations
• Models codes establish requirements based on occupancy conditions and use
• Model codes permit alternative suppression systems when approved
• Hazard evaluation determines the best system to provide appropriate protection
• Hazard determines the use of a particular type of system– Certain systems more appropriate for some hazards
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Design and Installation Standards
• Water-based protection systems similar in many ways– Different enough to publish separate standards
• Standards do not state where to install these systems
• Design professional determines the type of system that is most appropriate
• Design professional implements the design and installation
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NFPA 11, Standard for Low-, Medium-, and High-Expansion
Foam• Class B foam best for flammable and
combustible liquid fires• Standards for foam combine in NFPA 11• Other NFPA standards establish when foam
systems are needed to protect a hazard
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NFPA 15, Standard for Water Spray Fixed Systems for Fire
Protection• Water spray fixed systems provide specialized
protection to different hazards– Transformers, motors, flammable liquids
• NFPA covers design, installation, inspection, testing, and maintenance of these systems
• Does not apply to systems in NFPA 13, NFPA 750, monitor nozzles, and explosion suppression
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NFPA 16, Standard for the Installation of Foam-Water
Sprinkler and Foam-Water Spray Systems
• Deals with the use of foam• NFPA 16 covers foam-water sprinkler and spray
systems– First published in 1954
• Limited to using low-expansion type foam
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NFPA 750, Standard on Water Mist Fire Protection Systems
• Relatively new standard– First appeared in mid-1990s
• Provides minimum requirements for water mist systems
• Does not establish operational measure or specific guidance on how to extinguish a fire
• Standard states that it is not a design handbook• Design requires verification of its viability
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Types of Specialized Water-Based Fire Protection Systems
• Fixed automatic foam systems protect flammable and combustible liquid hazards
• Foam is an effective agent to meet all objectives– Foam is less dense than fuel or water– Freely flow over liquid surface
• Foam concentrate mixes with water to form a foam solution
• If proportioning incorrectly or used with incompatible equipment, foam will not work
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Figure 6-1 These flammable liquid storage tanks are protected by a foam system that applies the foam onto the surface of the fuel inside the tank.
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Foam Products• Low-expansion foam increases at a 2:1 to 20:1
ratio– Protect outdoor storage tanks, interior flammable
liquids, loading racks, diked areas, etc.
• Medium-expansion foam increases 20:1 to 200:1• High-expansion foam increases 200:1 to 1000:1• Medium- and high-expansion protect ordinary
combustibles, flammable liquids etc.
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Fixed Foam System Components• Proportioning methods:
– Venturi proportioner method– Pressure proportioners– Balanced pressure proportioner
• Foam concentrate tank• Foam generating/distribution equipment
– Subsurface injection– Oscillating monitor nozzles– Foam maker chambers– Foam generators and pumps
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Figure 6-3 Water enters the tank to put pressure on the rubber membrane bladder that in turn pushes the foam concentrate out of the tank.
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Water Spray Fixed Systems
• Fixed piping network with specialized spray nozzles
• Designed to:– Protect specific equipment– Protect structural members surrounding equipment– Function as part of an overall fire protection
installation
• System delivers concentrated, directed water spray pattern onto surface of the hazard
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Water Spray Fixed Systems (continued)
• Require at least one adequate automatic water supply
• Automatic activation is by a device such as heat, flame, gas detectors, etc.
• Automatic nozzles use the same technology as sprinkler heads
• Ultra-high-speed water spray system applies water to the hazard within 100 milliseconds
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Figure 6-5 Water spray nozzles connected to a deluge valve surround this electrical transformer that is protected by fixed water spray system.
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Foam-Water Sprinkler and Foam-Water Spray Systems
• Protect Class B flammable and combustible liquids– Acceptable for use with certain Class A hazards
• Primary design goal is extinguishment– Appropriate for prevention, control, exposure
protection
• Foam and water are companion agents• Pre-primed systems have foam and water in the
piping
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Figure 6-9 Summary of relationship for systems, discharge devices, and foams.
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Water Mist Systems• Discharges fine spray mist of water droplets out of
specialized nozzles– 99% of water mist must be 1000 microns or less– 25,400 microns equal one inch
• Droplets extinguish by cooling, displacing oxygen, blocking radiant heat
• Protect land facilities, marine and offshore facilities• Not appropriate for use with materials that react
with water
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Inspection, Testing, and Maintenance Requirements
• Similar approval, inspection, and test processes as standard fire sprinkler systems
• All systems subject to the same acceptance inspections and tests
• All specialized water-based fire protection systems require flushing– Additional requirement to flush or clean the system
piping
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Figure 6-9 Summary of required inspections and tests for specialized water-based fire protection systems.
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Periodic Inspection, Testing, and Maintenance
• Inspection, testing and maintenance provide a level of confidence in the system
• Maintenance should be in accordance with established intervals in NFPA 25– Depending on conditions, daily to every five years
• Subject to impairments– Lack of proper inspection, maintenance, component
failure, environmental conditions, etc.
• Piping obstructions occur for many reasons
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Summary
• Specialized water-based systems provide protection when sprinkler systems inadequate
• Differences from sprinkler systems:– Specialized spray nozzles and discharge devices– Integration of foam agents with water– Use of specialized components for application
• Different types of foam for different hazards• Water mist systems protect land facilities• Periodic system verification necessary