TECHNOLOGY AREA(S): Air Platform, Materials/Processes

ACQUISITION PROGRAM: PMA-261 H-53 Heavy Lift Helicopters

OBJECTIVE: Develop a lightweight fuel tank explosion suppressant that fits within a wide range of aircraft fuel tank geometries, and is easily installed and removed.

DESCRIPTION: The Navy has two Fuel Tank Explosion Suppression (FTES) methods operating within the fleet for air vehicles: On Board Inert Gas Generating System (OBIGGS) and Explosion Suppression Foam (ESF) [Refs 1, 2]. The OBIGGS protects the fuel tanks internally by constantly generating inert gas (typically nitrogen) and supplying it to the fuel tank ullage space to maintain an oxygen depleted environment, thus suppressing an explosion. ESF (urethane foam) protects by filling the fuel tank with reticulated foam and keeps a ballistically-induced or electrical failure-induced flame front and explosion from propagating throughout the fuel tank. Air vehicles use only one of these suppression systems if vulnerability reduction is required due to the platform�s mission environment.

ESF has a few practical limitations in the fleet. Routine maintenance of fuel tanks requires that the ESF be removed until maintenance is complete, at which point the ESF is reinstalled in the fuel tank. ESF is often difficult to remove and reinstall, increasing the amount of time required for routine repairs and time out of service for the air vehicle. The second limitation has to do with the density and volume of ESF. The nominal density of ESF is 1.3 pounds per cubic feet [Ref 1].� ESF can displace up to 2.5 percent of fuel by volume and retain up to 2.5 percent of fuel by volume.

An innovative FTES material to replace ESF, while meeting the explosion suppression performance properties, is needed. The new FTES material must not displace more than one percent fuel volume, and must not retain more than one percent fuel volume in any given fuel tank. The new FTES material must have a uniform nominal density not to exceed 0.9 pounds per cubic foot and should perform with JP-4, JP-5, JP-8, and commercial Jet A fuels (including military additives (i.e., static dissipater additive, corrosion inhibitor/lubricity improver, fuel system icing inhibitor, and may include antioxidant and metal deactivators)) [Ref 11]. No toxicity hazard to personnel who maintain or come in contact with the FTES material can occur [Ref 1]. Material color should be uniform throughout and cannot be blue, orange, yellow, or red. It must be easy to install and remove per SAE AIR 4170B [Ref 2] during routine maintenance for a wide range of complex fuel tank geometries. There should be a 10-year maintenance requirement to check and remove if necessary and a storage life of 3 years. All of the material must be removable during maintenance and no foreign object debris (FOD) can detach from the FTES material. SAE AIR 4170B [Ref 2] provides examples and diagrams of common obstacles that must be taken into account during installation and removal of the new FTES material. These obstacles include valves, pumps, pipes, and fuel inlets.

The developed material will be expected to pass several tests similar to those detailed in MIL-F-87260 [Ref 1]. Uniform density will be tested using a material specimen 3 inches (width) x 4 inches (height) x 10 inches (length). The results will be reported to the nearest 0.1 pounds per cubic foot. Ten locations on the specimen will be randomly chosen and the density will be measured at those locations. Tear resistance will be tested in accordance with ASTM D3574 Test F [Ref 5]. Fuel displacement will be tested at standard conditions using a 1000 mL capacity cylinder filled to the 900 mL mark with approved fuel. The material specimen will be cut to the diameter of the cylinder and to the length of the 900 mL mark of the cylinder. Then the specimen will be submerged in the fuel for 24 hours, to obtain maximum swelling effects. The fuel level of the cylinder will then be measured for fuel displacement. The fuel will be transferred to a second cylinder and measured to determine fuel retention.

PHASE I: Develop a concept for an innovative explosion suppression material that is low density and low volume. Determine technical feasibility through demonstration of the material�s proposed suppression capabilities. Produce plans for prototype development in Phase II.

PHASE II: Develop and demonstrate a prototype FTES capable of meeting desired suppression capabilities and ease of installation and removal on representative air vehicle fuel tanks. Validate, through testing, the ability of the new FTES material to meet the qualification requirements including a uniform density test, tear resistance test, and a fuel displacement test (see Description section above).

PHASE III DUAL USE APPLICATIONS: Complete validation and verification of the FTES material. Transition the technology for implementation on existing Navy air vehicle fuel tanks. Lightweight fuel tank explosion suppression technology can transfer to commercial aviation, automotive and transportation industries, providing protection of tanks containing fuel, hazardous materials, and other liquids.

REFERENCES:

1. MIL-F-87260, Foam Material, Explosion Suppression, Inherently Electrostatically Conductive, For Aircraft Fuel Tanks. (07-FEB-1992). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-F/MIL-F-87260_46748/

2. �Reticulated Polyurethane Foam Explosion Suppression Material For Fuel Systems And Dry Bays.� Society of Automotive Engineers, Inc. (SAE), SAE AIR 4170B. http://standards.sae.org/air4170b/

3. MIL-T-5624, Turbine Fuel, Aviation, Grade JP-4, JP-5, and JP-5/JP-8 ST. (29-SEP-1992). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-T/MIL-T-5624P_30850/

4. MIL-B-83054, Baffle and Inerting Material, Aircraft Fuel Tank. (17-MAY-1998). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-B/MIL-B-83054B_14045/

5. �Standard Methods of Testing Flexible Cellular Materials - Slab, Bonded, and Molded Urethane Foams.� American Society for Testing and Materials International, 1 December 2011, ASTM D3574-86. http://reference.globalspec.com/standard/3845336/astm-d3574-11-standard-test-methods-for-flexible-cellular-materials-mdash-slab-bonded-and-molded-urethane-foams

6. �AC 25.981-1C - Fuel Tank Ignition Source Prevention Guidelines.� Federal Aviation Administration (FAA), September 19, 2008.� https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25.981-1C.pdf

7. �AC 25.981-2A - Fuel Tank Flammability Reduction Means.� Federal Aviation Administration (FAA), September 19, 2008. https://www.faa.gov/documentlibrary/media/advisory_circular/ac_25.981-2a.pdf

8. MIL-DTL-27422F, Tank, Fuel, Crash, Resistant, Aircraft (Non Self-Sealing and Self-Sealing). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-DTL/MIL-DTL-27422F_49706/

9. MIL-DTL-5624, Turbine Fuel, Aviation, Grades JP-4 and JP-5. http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-DTL/MIL-DTL-5624U_5535/

10. MIL-T-5578C, Tank, Fuel, Aircraft, Self-sealing. http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-T/MIL-T-5578C_13565/

11. MIL-DTL-83133E, Turbine Fuel, Aviation, Kerosene Type, JP-8 (NATO F-34), NATO F-35, and JP-8+100 (NATO F-37). http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-DTL/MIL-DTL-83133E_14547/

KEYWORDS: Suppressant; Fire-protection; Explosion Protection; Fuel Tank; Survivability; Low Density