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Sunday
May152011

TFE-8

Application, Use, & Limitations of Semi & Fixed Fire Protection Systems

     For the FLBSS, there are five {5} frequently seen fire protection systems that must be understood. They are; 1] Foam Chambers, 2] Catenary systems, 3] Subsurface injection systems, 4] Fixed Foam Monitors, and 5] Foam/water sprinkler systems. Each one has its own unique attributes, a competent operating history, is fast responding, can be an automated, and uses Foam concentrate with water for suppression, extinguishment, cooling, and security.

     Foam chambers, as shown in the drawings, are fixed devices evenly spaced along the top edge of the storage tank and can be positioned for seal fires, or full surface tank fires. Their piping is proportional to the volume of finished Foam needed to be supplied, at the proper rate, for the diameter of the tank involved. Multiple chambers increase in number with tank diameter regardless of the proportioning system supplying the chambers. Foam chambers are commonly seen on; open and closed floating roofs and cone roof storage tanks. On cone roof tanks, chambers are usually plumbed through the top edge section of the tank “course” just below the weaker roof to shell joint. The major failure of these systems has been in the supply systems and not the actual chamber. The supply piping and chamber can best be thought of as a fixed nozzle and hand-line. If you cannot supply the water and Foam concentrate, all the hose in the world will not extinguish the fire. Initial operations upon arrival should be to support continuous flow to the chambers. Engine Company pump operations can be a major factor in the successful continued function of these devices.

     “Catenary” systems by definition infer “gentle application” of finished Foam to a seal area or full surface tank fire. This system involves fixed plumbing attached to an application hose on open top floating roofs via the man-way ladder assembly. The hose{s} can be directed towards any area needing Foam protection. This system performs best with volatile products. The excess slack in the supply hose near the ladder allows roof movement without tensioning the Foam supply line. The fixed piping follows the edge of the floating roof around the perimeter, and from tank roof ladder to the ground. The flexible hose section extends out connecting the ladder piping to the roof edge system.

     Subsurface injection systems require high fuel tolerance Foam for effective operation. Here, a High-Back-Pressure Foam maker delivers finished Foam into the bottom of the tank wall, {above the water level to prevent Foam dilution} after passing through the maker. This finished Foam then rises through the product to the surface area. When properly functioning, finished Foam spreads to all areas of the surface smothering and extinguishing the fire. With this system two elements are critical, fuel tolerance and roof type. The Foam solution used must be able to resist molecular breakdown from exposure to the fuel while floating upwards through the fuels body towards the surface. The product characteristics will dictate which Foam is appropriate. Generally, fluoro-protein type Foams work best with this type of system. Secondly, roof type is important. Floating roofs offer zero tolerance between the product and inner roof barrier. This is done to eliminate VOC’s {Volatile Organic Concentrations} found in flammables. These have come under the environmental microscope and as such, are not allowed access to the atmosphere. These roof types inhibit the proper Foam bubble formation and surface spread from sub-surface injection systems. The configuration of the tanks roof structure will dictate whether a sub-surface injection system will operate correctly.

     Fixed Foam monitors are essentially fixed Foam deck guns arranged in a pattern that will cover a designated area with the appropriate rate and flow of finished Foam. They can be totally fixed or oscillating depending on the hazard position. These also can be automated devices, activating when fire is detected. These too have a substantial record of success, failing only from supply problems or the initial ignitions blast. Loading racks for smaller tanks frequently use oscillating monitors.

     For horizontal tanks, enclosed areas, interior buildings, and even some exposures, finished Foam water sprinkler systems are superior. The drawings demonstrate some common plumbing configurations for various structures. While these devices have specialty sprinkler heads for directional spread, Fire Marshal standards also come into play. These systems are designed by Foam professionals in conjunction with Fire Marshal coordination. Head spacing, supply line sizes, and pump delivery is designed for each hazard location. While aerial coverage is complete, ground fires underneath tanks may be concealed from sprinkler systems.

                    Haz Mat Mike

 

 

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