Description of the Request:
With tactical military vehicles being exposed to significant threat levels, the safety of interior materials, including seat construction, is undergoing intense scrutiny as of late. Traditional materials for interior tactical vehicle applications, as well as seats, traditionally evolve from the commercial market. Although many of these materials are made with fire retardant components, the level of fire resistance and ultimate performance under fire is not adequate to the exposure that tactical vehicles regularly experience.
In most cases, it is important to consider materials designed for use in aerospace and mass transit vehicles in order to achieve the degree of fire resistance required to offer a significantly higher level of protection and survivability for military personnel. This paper will touch on some basic considerations and offer alternative materials to consider.
However, there are many materials to choose from with varying performance characteristics for each. Adequate choice of flame retardant materials and appropriate construction will depend on the ultimate performance criteria established for the final seat construction. This is best achieved through a close collaboration with sales engineers from material suppliers such as Polymer Technologies, Inc.
Traditional seating materials consist of a multi-layered or homogeneous seat, either molded or contour, cut from a series of commercial grade polyurethane foams. These foams have high resiliency and are designed as excellent cushions and used across a broad spectrum of automotive, truck, and commercial seating. Military seat cushions utilizing this same construction with polyurethane foam may or may not be manufactured with fire retardant additives. Even commercial grade cushions that are manufactured with fire retardant materials are still highly flammable and not readily self-extinguishing.
The challenge in evaluating these traditional materials is that many tests for flammability are not severe and laboratory performance does not directly relate to actual performance in a fire. Many traditional cushioning materials that pass tests such as FMVSS-302, UL 94 HBF, or CAL 117 would still burn readily in a seat configuration exposed to an actual fire. In addition to the threat posed by burning and molten plastic foam, the resulting smoke is black and noxious, and as a result can quickly compromise breathing in a confined area such as a vehicle cabin.
Cushioning for Enhanced Survivability Seat Constructions:
When contemplating a cushioning material that is safer and enhances survivability for tactical vehicles, consideration should be given to seating materials developed and used for both mass transit and aerospace applications. A cost-effective approach would be to consider graphite or melamine-loaded polyurethane foams, which exhibit significant fire resistance and would be considered a flame retardant seating material exhibiting significantly improved performance over traditional seating products. The density of these modified fire retardant polyurethane foams range from 3 ½ lbs. per cubic foot to 6 lbs. per cubic foot, which would be 2 to 3 times the weight of traditional polyurethane cushioning materials. This increased weight is necessary because these products are highly filled and highly fire retardant.
In both mass transit and aerospace applications, weight is a critical consideration to seat construction since weight is a premium in these applications. Due to this, POLYDAMP® Melamine Foam (PMF) is used as a core material. PMF weighs between .4 to .6 lbs. per cubic foot, and is 15 times lighter than the highly filled and combustion modified polyurethane foams. Therefore, a composite construction that utilizes PMF as a core with thinner increments of traditional fire retardant modified urethane foam as top surface are effective in maintaining low weight with enhanced foam resistance and improved survivability.
The highly filled and combustion modified urethanes noted above are traditionally cut to shape and assembled into a required seat profile. Alternatively, there are moldable grades of polyurethane foams, which may also use a core of PMF for weight reduction. Polymer Technologies' POLYFORM® Molded Foams, and specifically a UL94 V-0 compliant High Resilient (PLDM-V0) grade, are an ideal choice for concise seat designs while also offering opportunities to efficiently integrate blast mitigation materials and other components of seat assembly. The actual construction of the seat can take many forms depending on weight requirements, thickness profile, and covering materials. The details of specific seat designs may be supported by contacting your Polymer Technologies' Sales Representative.
There are many types of covering fabrics that are designed to be non-flammable and would enhance the overall fire resistance of seat construction. These materials have varying performance characteristics depending on the application, and can even be produced utilizing Kevlar fiber for increased durability and resistance to cuts and tears, or Nomex felts which may be employed as flame barriers under traditional wool/acrylic blended fabrics.
In tactical vehicle seating, blast mitigation may be of interest. Foamed aluminum with a POLYDAMP® polyurea coating on both sides is an excellent construction material for the bottom of the seat as it supports the seat cushion. Foamed aluminum has excellent blast mitigation properties and the urea coating adds a substantial level of impact resistance and protection from fragmentation to the foamed aluminum. These types of panels can be supplied by Polymer Technologies and easily fabricated into a seat cushion support or insert molded within a POLYFORM® Molded Foam tool.
We appreciate your interest in the subject of flame retardant seating as well as blast mitigation concepts for seats. Polymer Technologies would like the opportunity to work with you on your specific application and in developing specific seat construction elements to meet any specific design goals you have established.
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