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Haz Mat "Specialist Course"
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Saturday
Mar052011

TFE-3

     Tank Components

     The FLBSS {Flammable Liquid Bulk Storage Specialist} must be familiar with the design, and understand the purpose of all tank farm “Tank” Components. Specialists must know tank materials, construction methods, and how they will react to fire and spill conditions under the applicable standards at the time of erection. Roof materials and whether or not seals are contacting tank walls, is also essential knowledge for the FLBSS. Incident venting and pressure relief valves must also be thoroughly understood. Tank valves, piping, piping supports, and gauges must be mastered by the FLBSS. Lastly, the FLBSS must understand the use of overfill devices, secondary containment, and fire protection systems for each of the tanks on-site.

     Tank shell materials are obviously shipped to a field site and erected by weld-ments, hence the term “erection” for the actual fabrication of a bulk storage tank on-site. Fire-ground or spill mitigation decisions should be based on the standard used during initial tank erection. Since many tanks were erected before 1987, the 1988 standards shall be referenced throughout the “tank farm series”. When pre-planning additions or upgrades to your facility, be sure to use the revised API 650 {American Petroleum Institute} standard. Depending on the steel used, product that will be held, style and height of the tank, the various steel “courses” {tank wall sections} compositions will range between 0.5 to 1.75 inches. All tank materials have minimum and maximum thickness per API 650. Generally, the tank courses will decrease in thickness as they rise in wall elevation, as this assists in the walls folding inward into the tank during a full scale surface tank fire. Varying exceptions that are allowed on all properly erected tanks must be between these two extremes. The ultimate responsibility remains with the tank erection purchaser. The manufacturer shall advise the purchaser of the specifications he used to fabricate the tank plates according to the API standard.

     Roofing materials when constructed by a method other than floating should range between 3/16” to 0.180 plate, or 7-gauge sheet. Floating roof materials may be thinner per design, but structural joist members must subscribe to a minimum of 3/16” stock. Frangible roof to shell joints {for cone roofs} follow a mathematical formula that prevents them from exceeding a known strength. The end result, assures the roof-to-shell joint will always be weaker than the shell-to-bottom joint. For gasket roofs, seals should be designed to comply with the overall concept for the roof standard as “all roof and supporting structures shall be designed to support dead load, plus a uniform live load of not less than 25 lbs. per square foot of projected area”.

     Tank piping and supports also infers relief valves, gauging devices, overfill devices and tank valves. Basically any “appliance” a hazardous product may flow through. These also have secondary standards applicable for each individual task, under ASTM {American Standard Testing Materials} A671, 105, 181, and 350. Included for all are schematic drawings showing the high detail and intense requirements needed for roof and tank course construction.    

     Secondary confinement methods figure closely with primary fire protection systems as both techniques enable a facility to “confine” the spill or fire to their property. Both methods allow fire suppression forces time to deploy the primary weapon, firefighting Foam. All parameters standardized for safe implementation of Foam practices are listed in NFPA 11 {National Fire Protection Association}. Even this impressive document realizes consultation for each individualized installation must revert back to the real “masters of disasters”, the Foam application manufacturer design Team. Here is where expertise and experience mesh together to form a “safety first” bond. Generally most bulk storage tanks require one or more fixed Foam chambers permanently affixed near the top edge of the storage tank. Size of tank and hazardous contents, dictate the number of these Foam chambers. They must be powered by a fail-safe system that discharges Foam solution to them. This can be supplemented by additional resources from the fire department, but they are designed to be “stand-alone systems”. Other primary systems include semi-protection, and subsurface injection models. These also, are stand-alone operations. Secondary containment methods for spills and fires include the use of fixed “Berm” or “Dam” barriers. Semi-permanent Foam application systems may be staged within these areas. The following schematics demonstrate the common configuration for common commodities. In coming posts, we will look into primary and secondary spill confinement measures.

                                                                                                        Haz Mat Mike

 



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