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It is important to recognize the flammable characteristics inside a floating roof tank. Essentially two potential circumstances lie in wait ...
Under normal conditions, the vapor space within the tank is too rich to burn and will remain dormant with proper vapor exchange via the tank venting system.
However, it has been our experience that given the right conditions this rich vapor will lean out due to any given set of circumstances such as failure of tank venting systems, low-pressure exterior atmospheric conditions, or an abnormal breach in the tank structure.
Even in extreme situations, if ignition does occur at the vents the interior space of the tank MAY remain too rich to burn and a surface fire within the tank will be avoided.
HOWEVER, several incidents Williams Fire & Hazard Control has reponded to domestically and internationally have been due to an adequate open-air exchange leaning out the interior vapor space whereby a fire source at the vent flashes back insde the tank resulting in a devastating combustion of the residual gases.
Our experience is that an internal foam application resulting in a rich foam blanket will reduce vapor yield within the tank, and will inhibit any potential surface fire resulting from secondary ignition sources as outlined above.
MOST NOTABLE: Our Dual-Agent chamber - a COMPLIANCE+ product - follows the foam application with an abundant dry-chemical surge that overwhelms any residual vapor inside the tank, extinguishes the fire at the vents, and prohibits a potential explosve flashback event.
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