Fire extinguishing system for hydrocarbon or petrochemical storage tank with floating roof

A method of extinguishing a fire, the method comprising:

• installing a foam supply conduit extending from a remote location to a foam diffuser affixed to an underside a floating roof circumscribed by a vertical wall of a storage tank in which a flammable liquid is stored;
• releasing a foam concentrate into the foam supply conduit from a foam supply in response to detecting the fire;
• discharging the foam from the diffuser into the flammable liquid;
• and
• forming a protective foam blanket between the underside of the floating roof and an upper surface of the flammable liquid to extinguish the fire.

A fire extinguishing system, comprising:

• a storage tank defining a vertical wall
• a flammable liquid stored within the storage tank;
• a floating roof floating on an upper surface of the flammable liquid and circumscribed by the vertical wall, the floating roof movable vertically along the vertical wall in response to a changing level of the flammable liquid within the storage tank;
• a rim seal defined circumferentially between the floating roof and the vertical wall;
• a foam supply at a remote location with respect to the storage tank;
• a foam supply conduit extending to the storage tank from the foam supply at the remote location;
• and
• a foam diffuser fluidly coupled to the foam supply conduit, the foam diffuser submerged in the flammable liquid and affixed to an underside of the floating roof, the foam diffuser including:
• a backflow preventer for preventing flow of the flammable liquid into the foam supply conduit;
• and
• at least one outlet for discharging a foam from the foam supply conduit into the flammable liquid adjacent the underside of the floating roof and an upper surface of the flammable liquid.