Medium- and High-expansion Foam System Design Chapter 5 Page 166

Objectives Determine appropriate situations for the use of low-expansion, medium-expansion, 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 Perform a calculation of a high-expansion 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

Local Application Medium- And High-Expansion Foam Systems The majority of medium- and high-expansion 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 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 medium-expansion 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 Figure 5-2. Sectional view of a flammable liquid pump protected by a high-expansion foam system

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 low- expansion 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 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 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 high-expansion foam