Mega-tank fire suppression solutions
Vol. 27 No. 3
With industry engineering practices driving open floating roof tank sizes to more than 400 feet (122 meters) in diameter, fire suppression solutions for these mega-tanks that often bear crude oil are becoming more complex. The resources necessary to wage a full-scale manned ground assault to extinguish a full-surface fire for a tank that is 360 feet (110 meters), 420 feet (128 meters), or even larger can outstrip local resources, including manpower, foam stores, hoses and water supply. Most importantly, proper staging distances to effectively project a FootPrint™ of foam into a tank of this size may place response teams in the containment area – an unacceptable risk.
Considering these challenges, Williams Fire & Hazard Control (WF&HC) recently launched the Ambush System – a new fixed / semi-fixed system that can deliver large-volume water / foam applications to better address both rim seal and full-surface fires. The system is secured to the internal rim of a mega-tank. It is the first product of its kind to effectively combine Type II and Type III foam applications for large external floating roof storage tanks.
Extinguishing primary hazards within a tank
Mounted equidistantly along the rim, the four-nozzle configuration of the Ambush System uses three of the nozzles to propel a Type II foam delivery laterally along the inner wall to address the seal area of the tank. The fourth nozzle atop the Ambush System delivers a Type III application to the center of the tank to overcome a full-surface fire event. These attacks may be executed separately or in unison as necessary.
Rim Seal Fires
Rim seal fires, which occur at the internal perimeter of a storage tank (where the floating roof meets the wall), traditionally have been addressed by Type II foam pourers or chambers. These chambers rely on gravity and the molecular weight of the foam to gradually move the application around the foam dam. Seal fires can also be addressed using a manned large-volume monitor-nozzle affixed to the tank rim, enabling the water / foam application to reach across the radius of the tank to overcome the seal fire from the landing area of the tank’s ladder.
Mega-tank diameters prohibit this manned response format, creating an opportunity for the Ambush System to deliver its robust Type II application for rim seal fire extinguishment matching even the largest of tanks.
Full Surface Fires
Full-surface fires engulf the entire surface content of the tank due to a situation such as a sunken roof. These fires often require a Type III application from the ground, where large-volume trailer-mounted monitor packages deliver a water / foam solution from a ground-based staging point that is stationed a safe distance from the involved tank.
In a Type III attack, the water / foam solution is projected from the ground over the top of the tank rim to the center of the tank from a safe staging distance. As tank diameters approach and exceed 400 feet, this ground assault is jeopardized because personnel must move closer to the tank to ensure the foam application effectively reaches the center. Staging distance is inversely related to the diameter of a storage tank; as the tank size increases, staging distances are diminished placing the trajectory point closer to the tank wall in order for the foam solution to project to the tank’s center.
Meeting the challenge of larger and larger tanks
Industrial storage tank fires require large-volume attack capabilities be applied rapidly and safely. As tank diameters exceed already expanded distances, tactics, equipment and resources must adapt to meet the challenge inherent in fire events of their magnitude. The Ambush System is the industry’s first large-volume attack deployed from a rim-mounted system that is equal to the task.
Large-scale storage tank fires can also outpace localized resources, requiring multi-jurisdictional efforts to successfully extinguish them. Response times of even the most experienced command centers can often be too slow, and fighting these complex fires necessitates specialized training, especially for ground-based Type III logistics, which is not generally included in municipal or even industrial firefighter educational programs.
Further, many large-scale storage tanks are located outside small towns, taxing local fire departments or volunteer staff beyond their capabilities. The Ambush System safely minimizes the strain on personnel and loose equipment a mega-tank response can cause.
Protecting personnel and materials in large-scale fires
The Ambush System provides several important benefits for fire protection when dealing with mega tanks, including:
Efficiency in scale of resources required to overcome the challenge related to fire suppression for mega-tank sizes, including water, foam, manpower and loose equipment.
Quicker response times via system activation.
Easy operation with selective response options to address a rim seal or a full-surface fire or both.
Tank rim mounting location results in greater application density due to less wind erosion of the water / foam streams.
A recent full-scale test on an open floating roof tank conducted by WF&HC demonstrates the effectiveness of the Ambush System in extinguishing seal and surface fires. In this test, six units were attached to the rim of a 277-foot tank. When Ambush was fully engaged, the collective flow rate reached 9,000 gallons per minute, equivalent to 1,500 gpm per unit. The application rate for the area covered by the Type II portion of the Ambush System is 0.13 gpm/ft2 (.492 liters per minute/.6096 meters), 25 percent greater than the minimum National Fire Protection Association (NFPA) requirement. The area picked up by the Type III attack equates to 0.22 gpm/ft2 (.832 liters per minute/.6096 meters), which is significantly higher than the NFPA standard.
Attacking tank fires from the top down
While storage tank fires pose a threat to life and property, business interruption due to the loss of a tank can be fiscally significant. Today’s storage tanks can generate billions of dollars in revenue over decades of service, prompting oil and gas industry leaders to consider the potential long-term loss of revenue following a catastrophic fire event involving one of their most precious assets.
As tanks continue to grow in size and asset value, potential incidents such as a rim seal or full-surface fires can challenge even the most robust response plans as never before. Considering these growing demands on localized response resources, the Ambush System and other tank protection innovations provide response performance that is matched to these emerging hazards and offers ownership and response entities the best possible chance for handling such an event.