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Sunday
Apr032011

TFE-5

Fire factors & Risk Assessment for Tank Farms

     Risk assessment factors for tank farm fires or spills are those items which must be taken into account because they will have a direct impact on the successful conclusion to your emergency operation. For the FLBSS {Flammable Liquid Bulk Storage Specialist}, there are six {6} basic factors that must be evaluated to successfully mitigate the confinement of a spill or fight a tank fire. Seeing as how tank fires top the list of destruction compared to un-ignited spillage we will confine our discussion to firefighting. Section 12-2.2.2through 12-2.2.4, in NFPA 472 {National Fire Protection Association} deals specifically with this feature for the Flammable Liquid Bulk Storage Specialist {FLBSS}.

     What type of tank are you dealing with? See tank drawings. Horizontal Tanks differ in approach than do verticals. Does the roof float, or is it conical and affixed to the tank walls? If floating, is it covered also? What is the possibility as fire exposure continues, of the roof sinking or blowing off?  If either happens, how will you handle it? If the tank walls should let go, are your forces outside of the confinement dike? When dealing with any assessment firefighter life safety should be priority one and will aid you in making these decisions. If answers to these questions place lives in imminent danger they are probably the wrong choice. Increasing the size of a fire or losing additional product is not worth a fire-fighters life. The scene will need remediation so the overall size becomes a non-issue against the loss of a life.

     What is the product involved? If it is a petroleum product, is it light, medium, or heavy grade. Light petroleum’s such as finished gasoline have been refined to the point where off gassed constituents during combustion do not develop “heat waves” that migrate toward the tank bottom the longer the fire burns. See post on boil-over. Heavy products like naphtha or asphalt will not allow this “heat wave” to descend to the bottom of the tank due to the materials thickness. Medium grade products such as certain mid-grade oils can accelerate the movement of the “heat wave”. This is why medium grade products have been removed from bulk storage tanks. Is the product corrosive in nature? Will the FLBSS need chemical protective clothing or firefighting gear? Which becomes the greater hazard, the radiant heat from the fire or the corrosivity from the product?

     How much product is within the storage tank? If it is full, is “Slop-over” a possibility? See “Slop-over” post. If not, will exterior tank wall cooling be necessary before Foam application begins? This technique is needed in less than full tank situations to cool the interior environment preventing excessive Foam burn-back and exhausting your Foam supplies before extinguishment occurs. Also, this aids in preventing the actual wall “courses” from collapsing into the tank and possibly releasing burning liquid, or superheating the water layer at the tank bottom. This of course, would move your operation towards the “boil-over” phenomenon. Do you have the water supply available for additional exterior tank wall cooling? Are the monitors or hand-lines to be used in place? If so, will they be manned? The answers to these assessments will be based on your available resources on-site.

     What is the nature of the incident to resources available? Is this a seal fire, full surface fire, partial surface fire, or an overfill situation. Different incidents will dictate different resources needed. Generally, seal fires are easily extinguished by “catenary” systems before they become full surface fires. This means tactical options may be implemented with restricted resources. Does tank spacing threaten adjacent tanks? Are there multiple tanks within the same dike confinement area? Can these exposures evolve into a multiple tank fire?

     Lastly, are there fixed, semi-fixed, or Fire Department protection systems present for this incident? Mandated fixed or semi-fixed systems by API 650 commonly extinguish most small fires before general plant evacuation begins. Have these systems been maintained, and are they operational? If Fire Department operations are the primary method of choice, do they still have the man-power? Is equipment available for the size of this event? Is it in service at the present time?  By using this risk assessment procedure, the FLBSS will be able to pre-plan his evaluation of various events that could occur and understand the extent of operations within his resources. Shortages in resources for major events must be brought to the attention of Tank Farm management.

                                       Haz Mat Mike



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