Defense Technology

Aluminum Mesh Explosion Suppression Systems

Issue: The presence of motor gasoline (MOGAS) in exposed tanks aboard U.S. Navy ships and small boats is a continuing safety concern within the Navy. U.S. Navy ships and small boats need an effective and operationally suitable means of suppressing explosions in MOGAS fuel tanks. Discussion: During the past two decades, a number of products have claimed to significantly reduce explosive overpressure in flammable gases and liquids, thereby reducing the risk of vapor detonation or deflagration. These products are typically manufactured from expanded aluminum alloy or stainless steel mesh or a form of reticulated polyether foam. Previous testing has shown that these materials reduce combustion overpressures in four ways: by the total amount of heat absorption (related to specific weight of the mesh material), by the rate of heat absorption (related to the surface area of the mesh material), by the amount of heat release of the combustion reaction (related to quenching controlled by cell geometry of the mesh material), by the rate of heat release (related to flame propagation speed controlled by cell geometry of the mesh material). The Naval Surface Warfare Center, Port Hueneme Division has funded MTTC to evaluate the effectiveness and suitability of expanded aluminum mesh explosion suppression products for afloat fuel tank applications. This evaluation includes both comprehensive laboratory testing and live fire ballistic testing. Key aspects of the testing program include: Mesh material characterization, chemical analysis and measurement Corrosion testing in typical Navy fuels Both clean and water-contaminated F-76 (Diesel), JP-5 (Aviation), MOGAS (Small boats) Live fire testing using representative Navy tanks and realistic threat ammunition Steel 55-gallon drums and plastic 6-gallon outboard motor fuel tanks Russian 12.7 mm armor piercing incendiary and U.S. 25 mm semi-armor piercing high explosive incendiary tracer ammunition Five vendors of aluminum mesh products responded to NSWC’s Sources Sought Announcement. MTTC procured these materials and submitted them to testing at commercial and academic facilities. MTTC will present quantitative results to the Navy for review and a decision on shipboard application. The following general criteria were established: Chemical and physical attributes: Data must be sufficient to enable product comparison and procurement by description, rather than brand name; Susceptibility to corrosion: If the metal mesh material corrodes, decomposes or otherwise disperses in such a way as to contaminate the fuel, fuel system or other shipboard components, it will not be approved for shipboard use, regardless of its ballistic effectiveness; Ballistic Testing: The desired outcome is the elimination of catastrophic explosions in these fuel tanks. During previous testing, there were definitive differences in maximum pressure and the degree of container damage depending on whether or not mesh material was installed. All mesh samples will be tested in comparison to baseline shots conducted without mesh material. Status: Initial material characterizaton and corrosion testing was completed by the University of Kentucky College of Engineering and KTA-Tator, Inc of Pittsburgh, PA. MTTC has received final reports from both. Live fire ballistic testing was completed on 3 October 2003 by the U. S. Army’s Aberdeen Test Center (ATC), Aberdeen, MD. In September 2005, UK began work to model how the physical properties of aluminum mesh, such as thickness, strand width and cell geometry, affect the performance of the mesh in terms of shock wave propagation. This numerical simulation work, using two-dimensional Computational Fluid Dynamics (CFD) techniques, was completed in February 2006. The data from this simulation work predicted that the aluminum mesh could have a dramatic effect in reducing the temperature of an ignited vapor mixture, and also predicted a measurable pressure drop as a shock wave passes through a flat layer of the mesh. During the summer of 2006, UK conducted follow-on experimental work using relatively rudimentary explosive charges. UK's data revealed that a layer of aluminum mesh as thin as 2cm could reduce shock wave overpressure by an order of magnitude. In late October, UK submitted a proposal for follow-on work using more sophisticated and powerful explosive charges that will produce more consistent and repeatable effects. Work was completed in May 2008 and a final report is in progress. Point of Contact:  Rick Southard   •  Phone:  (502) 638-4486   •  Email:  rsouthard@mttc.org