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5-9 Principles And Practices Of Foam OperationsPrinciples and Practices of Foam Operations Foam Fire Streams Initially used for industrial and airport fire protection Types of foam Chemical Mechanical Foam Components Foam concentrate Raw foam liquid at rest in storage container Foam proportioner Device that introduces foam concentrate into the water stream to make the foam solution Foam solution The mixture of foam concentrate and water Foam Completed product after air is introduced Class A For normal combustible materials Biodegradable Corrosive Super cleaning ability Used for Maximum absorption Vertical surfaces Or when a combination of both are needed Class B For flammable liquids Two types for Class B fuels Hydrocarbon fuels Petroleum based and float on water Polar solvent fuels Liquids that are miscible in water or fuels that absorb water Regular Protein Foams Derived from naturally occurring sources of protein Rarely used today Very good heat stability and resists burn back Not as mobile or fluid on the fuel surface as other types of low-expansion Fluoroprotein Foam A combination protein-based and synthetic- based foam Has fluorochemical surfactants similar to those for AFFF Provides strong "security blanket" for long- term vapor suppression Can be formulated to be alcohol resistant by adding ammonia AFFF Nearly completely synthetic Has an air-/vapor-excluding film Fast-moving foam blanket that drains water, releasing more film Ability to "heal" when foam blanket is disturbed Alcohol-resistant AFFFs are available from most foam manufacturers FFFP Fluoroprotein foam with aqueous film- forming foam (AFFF) capabilities High-expansion Foams Special-purpose foams Detergent based Low water content Minimize water damage Used in concealed spaces Used in fire-extinguishing systems How Foam Works Separating Creates barrier between fuel and fire Cooling Lowers the temperature of the fuel and adjacent surfaces Suppressing Prevents release of flammable vapors Proportioning Class A Normally mixed at ratios of 0.2% to 1% Class B Mixed at 1%-3% for hydrocarbons Mixed at 3%-6% for polar solvents Proportioning Methods Induction (eduction) Uses the pressure energy in fire stream to induct (draft) foam concentrate Injection Uses an external pump or head pressure to force foam concentrate into the fire stream at the correct ratio Proportioning Methods Batch mixing Foam concentrate poured directly into a tank of water Most simple method Premixing Premeasured portions of water and foam concentrate are mixed in a container In-line Eductors Most common Works off of the Venturi principle Operational Rules Must control flow through the system Pressure at outlet must not exceed 65%-70% of eductor inlet pressure Foam concentration is only correct at rated eductor inlet pressures Operational Rules Thoroughly flush after each use Metering valves must be set to match foam concentrate and burning fuel Inlet to the eductor must not be more than 6 feet above the surface of the foam concentrate Foam Nozzle Eductors Operate on the same principles as the in-line eductor Major disadvantage Foam concentrate must be located near the nozzle Self-educting Master Stream Foam Nozzles For flows in excess of 350 gpm Designed to operate at lower pressures May be used with a jet ratio controller Apparatus-mounted Low Energy Systems Majority of systems can be used for Class A and Class B concentrates Installed In-line Eductors Operate on the same principles as the portable in-line eductor Can be supplied by pick-up tubes out of 5- gallon buckets or by on-board foam tanks Around-the-pump Proportioners One of the most common Consists of a small return (bypass) water line connected from the discharge side of the pump back to the intake side of the pump An in-line eductor is positioned on this bypass line Around-the-pump Proportioners Valve just off the discharge controls flow of water through the bypass line When valve is open, small amount of water discharged from pump is directed through the bypass piping Water passing through the eductor draws concentrate into the bypass piping Around-the-pump Proportioners Resulting foam solution supplied back to the intake side of the pump It is then pumped to the discharge and into the hoseline Around-the-pump Proportioners Major disadvantage of older types Cannot take advantage of incoming pressure Inlet pressures >10 psi will prevent concentrate from entering the intake Can only be used when operating from the apparatus water tank Bypass-type Balanced Pressure Proportioners Foam concentrate line connected to each pump discharge outlet Supplies foam concentrate to outlet at same pressure the fire pump is supplying water to that discharge Bypass-type Balanced Pressure Proportioners Pump discharge are jointly monitored by a hydraulic pressure control valve Concentrate supplied is delivered by size of stream, relating to the overall discharge outlet size Bypass-type Balanced Pressure Proportioners Primary advantage Can monitor demand and adjust accordingly Disadvantage Can cause agitation of the stream Variable-flow Variable-rate Direct Injection Systems Injects concentrate directly into the water stream Amount delivered into the stream is based on flow, not pressure Advantages Primary -Accurately adjust to changes within its design limits Also used with high energy foam systems Disadvantage Must be installed within the piping before any discharge manifolds Variable-flow Variable-rate Direct Injection Systems Variable-flow Demand-type Balanced Pressure Proportioners Basically a Venturi-type system within the water line Advantages Concentrate flow and pressure match demand Does not recirculate the concentrate back to the foam tank(s) Does not require flushing after use Variable-flow Demand-type Balanced Pressure Proportioners Disadvantages Discharge ratio controllers reduce discharge area Pressure drops across discharges are greater than on regular pumps Batch Mixing Simplest means Amount mixed is based on tank size Disadvantages Contaminates the water tank and pump Does not allow for continuous operation High Energy Foam Systems Compressed Air Foam Systems Compressed air introduced into foam solution before discharge into hoseline Turbulence of air and solution in the pipe/hoseline creates a finished foam Used with Class A foams High Energy Foam Systems Advantages Greater reach Uniform, durable bubbles Adheres to surfaces Hoselines are lighter Disadvantages Expensive Hose reaction can be erratic Additional training is necessary Foam Application Devices Handline nozzles Solid bore Fog Air-aspirating Master stream foam nozzles Medium/high-expansion foam generating devices Associated with total flooding applications Foam Storage Pails Barrels Apparatus tanks Expansion Ratios Low expansion Up to 50:1 Medium expansion 50:1 to 300:1 High expansion 300:1 to around 1250:1 Operational Symptom: Failure to generate foam or generating poor quality foam Possible cause Failure to match eductor and nozzle flow No foam is in the pick-up tube Possible corrective action Check manufacturer's recommendations and specifications for eductor and nozzle Operational Possible cause Air leaks at fittings that cause loss of suction Possible corrective action Inspect and tighten all fittings Remove defective components from operation Operational Possible cause Dirty or clogged foam passages from improper cleaning Possible corrective action Clean all proportioning equipment components after each use Operational Possible cause Partially closed nozzle control that results in a higher nozzle pressure Possible corrective action Open nozzle control completely Operational Possible cause Too long a hose lay on the discharge side of the eductor Possible corrective action Reduce hose lay to recommended length Operational Possible cause Kinked hose Possible corrective action Unkink hose Troubleshooting Possible cause Nozzle too far above eductor causing excessive elevation pressure Possible corrective action Lower nozzle Reposition hose configuration Troubleshooting Possible cause Mixing different types of foam concentrates Possible corrective action Use foam only as recommended