(21c) Fire Water Fuel Tank (FWFT) Integrity Under Blast Loads from Vapor Cloud Explosions

Fire water systems employ the use of elevated, gravity-fed fuel tanks to supply diesel fuel to pumps that are used for fire suppression. The integrity of this system is critical to providing firewater in the event of an explosion and/or fire to prevent knock-on effects. Typical fuel tanks are horizontal steel cylinders that can hold 350 gal of diesel fuel or more. The fuel tank assembly has an angle iron steel support structure that elevates the fuel tank above the pump, typically at a height of 6 ft. For the fire water pumps to maintain function, it is imperative that the tanks remain above the pumps and connected to them. If a flammable release and subsequent vapor cloud explosion (VCE) occurs near a fire water pump station, it is important to understand the impact the blast load will have on the fuel tanks.

This empirical study evaluated the blast response of 350 gal, 6 ft elevated diesel fuel tanks filled with an 80% equivalent weight of water to simulate a nearly full fuel tank. A deflagration load generator (DLG) directed blast loads between 1-10 psi and 50-180 psi-ms at a 3x3 array of nearly identical fuel tanks. Each row of 3 tanks were rotated to different orientations with respect to the blast load to investigate the effect of fuel tank orientation with respect to potential explosion sites. Pressure gauges and high-speed video recorded the blast loads and dynamic response of the fuel tanks during testing.

In addition to the empirical study, an analytical Finite Element Analysis (FEA) was conducted using LS-DYNA[1], with the purpose of modeling tank response at the 3 different tank orientations, under the empirical blast loading conditions gathered from the test data. Test video and post-test inspection of the tanks were used to validate FEA modeling techniques which could be used to explore additional parameters, i.e., larger tanks, alternative support structures, or different load regimes to develop a better understanding of safe fuel tank installation in process facilities. This paper documents the DLG test program and the FEA modeling efforts described above.

[1] LSTC, LS-DYNA Keyword User’s Manual, Volumes I and II, Version 971, Livermore Software Technology Center (LSTC), Livermore, CA, 2007