Foam Systems
WILLIAM HICKS MSc, CFEI, CFPS, IAAI-CFI, MIFireE, EFO, CFOD, F-IAFI Associate Professor Eastern Kentucky University William.Hicks@eku.edu
Objectives Classify high, medium, and lowexpansion foams, given their respective expansion ratios Determine whether a liquid is flammable or combustible Know the advantages and disadvantages of the currently available varieties of low-expansion foams
Objectives (con t.) Design and calculate a surface or subsurface low-expansion foam system for the exposed fuel surface within a flammable or combustible liquid storage tank Design and calculate a low-expansion foam seal protection system for a floating roof tank
Objectives (con t.) Design and calculate a low-expansion foam dike protection system for a tank farm Design and calculate a low-expansion foam system for an aircraft hangar Perform a detailed layout of a lowexpansion foam system, designed in accordance with NFPA 11
Objectives Determine appropriate situations for the use of low-expansion, mediumexpansion, and high-expansion foam Discuss the differences in the application and the methods of extinguishment for low-expansion, medium-expansion, and high-expansion foam
Objectives (con t.) Perform a calculation of a highexpansion foam system to determine the rate of discharge and number of high-expansion foam generators required Lay out a high-expansion foam system, showing foam fences, generator locations, and piping locations
Components of Foam All foams contain three components Air, contained within foam bubbles Water, delivered at a specified density in gallons per minute per square foot of applied area Foam concentrate, injected into the water stream at a specific predetermined percentage Fire-fighting foam: mixture of the foam solution with air
Expansion Ratio Expansion ratio: measure volume of the foam produced after air is added to the foam solution and compare that volume to the original volume prior to air addition
Expansion Ratio Classifies Foam based on Expansion Ratio Low Expansion = up to 20:1 typical - 8 : 1 Medium Expansion = 20:1 200:1 typical -100 : 1 High Expansion = 200:1 1000:1 typical -500 : 1
Types of Foam Protein foam: contains protein-based animal additives Fluoroprotein foam: contains fluorochemical additives to improve flow Film-forming fluoroprotein foam: uses fluorinated surfactants to produce a fluid aqueous film for suppressing hydrocarbon fuel vapors
Types of Foam (con t.) Aqueous film-forming foam (AFFF): a synthetic foam that forms a thin aqueous film that separates the foam from the fuel Alcohol-resistant foam: for the protection of alcohol-based fires Chemical foams: depends on the initiation of a chemical reaction within the foam solution to create air bubbles in the foam
Proportioning Methods Foam proportioner: ensures delivery of the precise ratio of foam concentrate to a foam solution Venturi proportioner: uses the negative pressure created by water flowing past an open orifice to draw foam concentrate into the water stream
Proportioning Methods
Aspirating Foam Maker
Proportioning Methods (con t.) Pressure proportioner: draws a portion of the incoming water stream to pressurize the tank holding the foam concentrate Balanced pressure proportioner: uses an atmospheric foam concentrate tank, a pump to pressurize the concentrate and force it toward the proportioner
Types of Foam Systems Mobile and Portable Apparatus Semi-fixed Systems Automatic Fixed Foam Systems Subsurface injection Surface application Seal protection for floating roof tanks Dike protection
Applications for Low-, Medium-, and High- Expansion Foams
Subsurface Injection Low-Expansion Foam Systems Subsurface injection: foam is discharged below the surface of a flammable or combustible liquid A low-expansion foam is used for this application Design Method for Subsurface Injection
Subsurface Injection Low-Expansion Foam Systems
Ex. 4-1: Subsurface Injection
Ex. 4-1: Subsurface Injection
Table 4-1 28
Table 4.2 29
Table 4.3 30
Table 4.4 31
Surface Application Low-Expansion Foam Systems Surface application: rolls a thin blanket of foam over the surface area of the fuel Design Method for Surface Application Type I discharge outlet: delivers foam onto the liquid surface in a gentle fashion Type II discharge outlet: applies foam less gently than a Type I outlet, but submergence and agitation are kept to a minimum
Surface Application Low-Expansion Foam Systems (con t.)
Surface Application Low-Expansion Foam Systems (con t.)
Ex. 4-2: Surface Application
Ex. 4-2: Surface Injection
Table 4.3 37
Table 4.4 38
Table 4.5 39
Table 4-6 40
Table 4-7 41
End Part 1 42
Seal Protection for Floating Roof Tanks Floating roof: tank roof that floats on the surface of a flammable or combustible liquid Seal protection: filling or covering the seal area with low-expansion foam
Seal Protection for Floating Roof Tanks (con t.) Sectional view of a floating roof tank with above-seal lowexpansion foam protection using a foam dam
External Floating Roof Tank http://www.hghouston.com/images/roof
Types of Seals for Floating Roof Tanks Source: Figure 5.3.5.4.5 NFPA 11 Source: Figure 5.3 C & D NFPA 11
Design Procedure for Floating Roof Tank Seal Protection Low-expansion foam protection of floating roof tank seals uses following methodology Calculate foam distribution area Determine application rate and discharge time Calculate foam discharge rate and concentrate quantity Determine spacing of discharge outlets Determine number of discharge devices
Design Procedure for Floating Roof Tank Seal Protection (con t.) Methodology (con t.) Determine supplementary hose demand and concentrate quantity Calculate supplementary hose demand foam quantity Hydraulically calculate the system
Dike Protection Low-Expansion Foam Systems Tank farm: an enclosure containing tanks that store flammable or combustible liquids, surrounded by a containment dike Dike protection systems: dike area is flooded with foam that floats on top of a flammable liquid that spills within the containment dike
Dike Protection Low-Expansion Foam Systems (con t.) Plan and sectional view of a dike protection system with low-expansion foam protection (part 1)
Dike Protection Low-Expansion Foam Systems (con t.) Figure 4-18. Plan and sectional view of a dike protection system with low-expansion foam protection (part 2)
Formula to Calculate Dyke protection A dike measuring 300 feet by 300 feet surrounds a tank farm. Assume a fuel with a flash point less than 100 F and assume the use of fixed discharge devices. Draw a 6% AFFF low expansion foam system, and calculate the minimum amount of low expansion foam concentrate that would be required for the protection of the dike area. Also determine the minimum amount of foam solution required, and the minimum amount of water that must be available for this design. 56
1. Calculate dike area. A = (L) (W) = (300) (300) A = 90,000 square feet 2. Application rate = 0.10 gpm/square foot for fixed discharge on outlets Discharge time = 30 minutes (assume flash point less than 100 F) 57
3. Calculate foam discharge rate and concentrate quantity, using 6% AFFF foam concentrate. D = (A) (R) = (90,000) (0.10) D = 9000 gpm Q = (A) (R) (T) (%) Q = (90,000) (0.10) (30) (0.06) Q = 16,200 gallons 6% AFFF concentrate 58
4. Determine number of foam discharge devices required. N = 2L+W 30 N= 600 + 600 / 30=40 Devices 59
Low-Expansion Foam Systems for Aircraft Hangars Low-expansion foam systems smother flammable liquid pool fires on the floor and also effectively coats the aircraft skin Group I Aircraft Hangars Group II Aircraft Hangars Group III Aircraft Hangars Aircraft Hangar Foam System Design
Ex. 4-5: Aircraft Hangar Low-Expansion Foam System Application
Ex. 4-5: Aircraft Hangar Low-Expansion Foam System Application (con t.)
Ex. 4-5: Aircraft Hangar Low-Expansion Foam System Application (con t.)
Loading Rack Protection A loading rack is the critical point where flammable or combustible liquids are pumped from or to storage tanks to or from a truck or rail car Hazards Associated with Loading Racks Fire Protection Strategy for Loading Racks Loading Rack System Design Procedure
Loading Rack Protection (con t.) Figure 4-29. Truck loading rack-ground sweep nozzles
Hydraulic Calculation of Foam Systems After foam quantity estimates are made Designer draws CAD layout of the system Performs a comprehensive computerized hydraulic calculation of the low-expansion foam system When hydraulically calculating a foam system, perform the calculation both to the supply and to the demand
Local Application Medium- And High-Expansion Foam Systems The majority of medium- and highexpansion foam systems are total flooding systems Foam fills a volume to a specified height For local application systems, NFPA 11 specifies minimum design criteria
Electrical Clearances For Medium- And High-Expansion Foam Systems Because foam contains water, application of foam could transmit electricity Designer must prevent this The proximity of foam components to live electrical components must be coordinated
Electrical Clearances For Medium- And High- Expansion Foam Systems (con t.) For altitudes greater than 3300 feet (1000 m), the clearance is required to be increased at the rate of 1% for each 330 feet (100 m) of altitude above 3300 feet (1000 m) See Table 5-1, Page 168 for electrical clearances
Medium-Expansion Foam The required depth of medium-expansion foam over a protected hazard shall vary as a function of expansion ratio The depth of medium-expansion foam shall be determined by tests The rate of discharge of mediumexpansion foam shall be determined by tests The quantity of medium-expansion foam shall be determined by tests
Applications For High-Expansion Foam Systems For hazards in which smothering of a three-dimensional fire or oxygen deprivation of a three-dimensional fire is primary objective A three-dimensional object requiring high-expansion foam is one that requires foam to be totally flooded and completely covered to an elevation above the highest level of the object requiring protection
Applications For High-Expansion Foam Systems (con t.) Figure 5-2. Sectional view of a flammable liquid pump protected by a high-expansion foam system
Medium- and High-Expansion Ratio Foams
Other Applications For High-Expansion Foam Suppression Systems High-expansion foam systems Primarily for extinguishment of flammable liquid fires Should be specified with some degree of caution with respect to personnel safety
High-Expansion Foam Systems For Robotic Flammable Liquid Rack Storage First consideration: personnel Second consideration: fire protection engineer must determine and solve the performance objectives of the system
High-Expansion Foam Systems For Aircraft Hangars NFPA 409 permits high-expansion foam systems to be specified in lieu of the lowexpansion foam systems Overhead AFFF low-expansion foam systems protect flammable liquid spill fire hazards in aircraft hangars High-expansion foam may be an answer to EPA concerns about low-expansion foam
High-Expansion Foam Systems As Dike Protection Successful use of high-expansion foam has been employed
High-Expansion System Extinguishment Mechanisms High-expansion foam systems are suitable for the protection of Class A ordinary combustibles Class B combustible liquids Extinguishment is accomplished by Smothering Cooling Insulating Penetrating
Design Of Total Flooding High-Expansion Foam Systems Total flooding method: completely filling a room or enclosure volume with a fire protection agent Personnel Considerations for High- Expansion Foam High-Expansion Foam Components Determination of High-Expansion Foam Quantity
Design Of Total Flooding High-Expansion Foam Systems (con t.) Duration of High-Expansion Foam Application (see Table 5-2, Page 181) Discharge Rate Number of Generators Required
Ex. 5-1: High-Expansion Foam
Ex. 5-1: High-Expansion Foam
Summary High-expansion foam systems Primarily for volumetric total flooding of three dimensional objects Use a foam with an expansion ratio of between 200 to 1 and 1000 to 1 Foam is expanded by a high-expansion foam generator that resembles a large fan
Summary (con t.) High-expansion foam extinguishes fire by smothering, cooling, insulating, and penetrating NFPA 11 requires that high-expansion foam be flooded to an elevation exceeding 10% above the highest combustible, or 2 ft. above the hazard, whichever is higher The rate of high-expansion foam discharge must consider foam breakdown that might occur if a sprinkler system is activated above the area protected by highexpansion foam
References Design of Special Hazards and Fire Alarm Systems - 2 nd Edition-Gagnon Fire Protection Systems-2 nd Edition-Jones Fire Protection Handbook-20 th Edition- NFPA NFPA Standard 85
Questions?