Safety Tents and Other Non-Permanent Buildings - Essay Example

In these uncertain and frightening times, there has been a proliferation of defensive devices to provide terrirism protection. There are two main advantages to safely containing an explosion: protection of innocent bystanders and preservation of evidence relating to terrorist acts. This paper will focus on shelters that protect people from explosions, bullets and harmful chemicals. It will discuss the physical properties of such shelters, the mechanics of their protective properties and material types, focusing largely on Kevlar. The paper will also illustrate the specific types of shelters already in use, including military applications. These shelters take numerous forms, including a traditional tentlike structure. One of the main advantages of these protective structures is that they are incredibly strong in relation to the weight of their components. Therefore, they can be rapidly deployed by two to four people. Kevlar’s superiority stems from its minimal “vibration transfer” (Kayak Terapad). It can be molded and shaped, yet maintains its structural integrity. Therefore, it enhances the user’s safety in numerous stress and impact scenarios. Government/Military Uses One of the military uses for such shelters is the Chemical Biological Protected Shelter System (CBPSS) (Business Wire 1997). They are intended for battlefield use against biological or chemical weapons assault. A company called Chemfab has developed the Kevlar-based fabric. The shelter also reduces lingering air contamination following a chemical or ballistic explosion. Homeland Security is using such a device in dirty bomb control. This variation is called a Universal Containment System, and it was developed by Vanguard Response Sytems in Canada (Popular Mechanics 2004). The ballistic resistant tent contains a foam that suppresses the detonation blast. At present, the system can only suppress a bomb the size of a book bag. The technology will be developed to contain a truck bomb, like the one deployed at the World Trade Center in 1993. A similar application is called the Chemical Biological Explosives Containment System (CBECS). It consists of a seven foot inflatable tent that contains a water-based foam, which not only contains the explosion, but it also puts out any chemically-based fires that may ignite (Patent Storm 2007). The whole structure can cover an explosive device, which is then deployed relatively safely (DOD Tech Match). These tents are now being made for the general public by Zumro, Inc. The Chemical/Biological Counterterrorism Team of the Army conceived the tents in partnership with Zumro (DOD Tech Match). The disadvantage of the foam is twofold: water must be added to the system, and the foam tends to obscure forensic evidence from the explosion (Patent Storm 2007). A similar tent is manufactured by Vanguard Respose Systems, under the name The Universal Containment System (Patent Storm 2007). NASA employs Kevlar shields in spacecraft, specifically a “multishock bumper dust shield with four ceramic fabric bumpers” (Osegueda, et.al. 2008). Spectra (a material discussed later) and Kevlar are both used to shield space capsule walls from rupture (Katza et.al. 2008). These shields were tested by shooting high-powered lasers at them. Commercial Uses Taking a page from NASA’s book, a blast resistant material made from ceramic will stand up to a missile moving at over twice the speed of sound (Free Patents), making it virtually bulletproof. The ceramic is interlayered with extremely durable fabric, whose fibers’ tensile stamina is estimated at 425,000 pounds per square inch (Free Patents). Tents and other temporary structures can be built from this ceramic fabric. If you want protection against a nuclear blast, Kevlar has a solution. A Kevlar-reinforced plastic fabric surrounding a polyvinyl foam core are the essential elements of this shelter (Free Patents). This structure protects those within not only from a nearby blast, but from fallout as well. If it stands up to an atom bomb, it will definitely withstand ballistic impact, “biological agents” (Free Patents) and chemical threats. This shelter can be put together in mere minutes. Kevlar Ballistic Panels are used by civilians to create “architectural armor systems” (ArmorCo) for doors and safety/panic rooms, among many other uses. They provide a safeguard against bullets and bombs. This fabric is used in combination with thermoplastic film (ArmorCo). The layers of the panel are bonded with thermo formable adhesive film. The manufacturer claims that bullets fired at such materials are “caught” (ArmorCo). \This ability to absorb the energy of a bullet means that any projectile does not display a boomerang effect, endangering anyone who happens to be in the vicinity. \These panels protect up to a National Institute of Justive Level IV threat level (ArmorCo). These panels are made from a “3000 denier aramid fabric, laminated in a prescribed number of layers, using a thermo formable adhesive film” (ArmorCo). Bullets shot from a 44 Magnum five times failed to pierce this fabric. DuPont, the original patent holder for Kevlar, has invented a StormRoom™ (DuPont). Kevlar has five times the strength of steel, and the walls of the StormRoom are almost penetration-proof (DuPont). This unique room stands up to tornadoes and hurricanes--up to and including Category 5 forces. The walls, which are wrapped in Styrofoam, were tested by shooting 12-foot two by fours with air guns at the walls at 100 miles per hour (Dunbar-Gates 2006). Kevlar Substitutes Since Kevlar was invented in 1965, many alternatives and hybrids have been tested. In terms of ehcmical composition, there is even a Kevlar near-clone, called Twaron (Wikipedia). Some have proven superior in strength, density and/or deployment. The main Kevlar competitor is a fabric called Spectra, which is about half the weight of Kevlar. This attribute makes for easier layering. Spectra is twice as strong as Kevlar (ten times the strength of steel). It can stop weapons fire more quickly and over a greater surface area. Wetness and chemical exposure do not impair its functioning (Vermeeren date unknown). Ballistic panels can also be made out of Spectra (ArmorCo). Spectra’s “extended chain polyethylene” composition and light weight makes it ideal for portable ballistic protection (Patent Storm 2007). Fiberglass that repels bullets has been available for some time. It can be seen in many banks nowadays. It consists of woven fabric treated with a “thermoset polyester resin and compressed into rigid flat sheets” (Pacific Bulletproof). Scientists at the Engineering and Sciences Research Council have invented compounds that exude resin when their structural intefrity is compromised. The resin creates a kind of "scab" (similar to the way the human body does) that repairs any surface breaches (Technorati). Advantages of Kevlar Shelters and Ballistic Panels According to ArmorCo, ballistic panels resist abrasion, can be shaped and formed with heat, resist both fire and moisture and do not produce static. One of the main advantages of making a shelter of Kevlar or similar material is that it does not weigh very much, which allows soldiers to carry the preassembled units for long distanes prior to deployment. One of the most remarkable properties of Kevlar is that it can be joined with common adhesives, such as Gorilla Glue, Elmer’s Pro Pond or even automobile windshield glue (ArmorCo). Mechanics and Shortcomings of Kevlar Protection The exact mechanics of Kevlar protection is unknown. Scientists believe that Kevlar’s molecular structure is like a spider web. If a number of Kevlar layers are woven together, they act as a net that breaks as a projectile works its way through it, slowing down and eventually stopping the projectile (Vermeeren date unknown). Unfortunately, with the advent of higher speed and more powerful weaponry, Kevlar is sometimes not strong enough to stop certain explosive charges. One could always add layers, but in certain applications, this is not practical. Kevlar can be molded with other materials, such as plastics, to give it enough rigidity to form a wall or a tent. This new material is called Kevlar Fiber Reinforced Plastics (KFRP). The type of plastic used is polyvinyl butyral (PVB). This fabric has compared favourably to shatterproof plastic in laboratory testing (Tomotaka et.al. 2004). Another way that Kevlar can be reinforced is by bonding it to supplementary protective fabrics, forming a superior hybrid. Accessories for Enhanced Containment Blast valves are necessary to regulate pressure flow, so that excessive pressure does not explode or implode a protective structure. At the time of a blast, certain contaminants can escape if essential valves are not closed in a timely manner. Potential breaches must be completely contained. Theree should be as few openings in a protective structure as possible (Army/Navy/Air Force 1990). There are two main types of blast valve—one that is activated by remote control and one that is activated by the actual blast pressure itself. Remote control blast valve uses sensors to to detect the heat pulse that preceeds an explosion. They are problematic, in that they often do not close in time to provide complete containment (Army/Navy/Air Force 1990). The “self-acting blast actuated” (Army/Navy/Air Force 1990) valves only take milliseconds to close, but that can sometimes be too long to contain all contaminants. This type of valve needs to be optimized to close at both extreme positive and negative pressures. An optimum valve of this type will close without any lag time, will be reliable, have very few moving parts that can malfunction, be durable and easy to maintain. The problem of excessive closure times can be solved by multiplying the “activating pressure-force-to-moving-mass ratio” (Army/Navy/Air Force 1990) and by creating valves that close more quickly. Blast valves must be protected from debris striking them, perhaps by a Kevlar-like material. Plenums can be used to mitigate excessive pressure caused by “jetting” (Army/Navy/Air Force 1990). Plenums can manifest as chambers, or be composed of ducts. Plenums are useful when contaminants are present. Poppet valves can also be used to prevent contaminant leakage (Army/Navy/Air Force 1990). As newer, lighter, more effective ballistic protection is developed, Kevlar is falling out of favor. It is still widely used, but since Spectra and other materials are more effective, they most likely supplant Kevlar. The personal protective shelter may well be the wave of the future. Citation List "About Ballistic Panels." http://www.armorco.com/shop/custom.asp?recid=4 (accessed December 23, 2008). "Airplane Heal Thyself? Self-Repairing Aircraft Could Improve Air Safety." http://technorati.com/posts/1XkdH4orRoSIOaYRvPn7TH1uh9nyWJJd2ult78pZviw%3D. (accessed December 23, 2008). Army, Navy and Air Force. "Structure to Resist the Effects of Accidental Explosions." 1990.http://www.ddesb.pentagon.mil/tm51300.htm (accessed December 23, 2008). "Ceramic bullet-proof fabric." http://www.freepatentsonline.com/5824940.html (accessed December 23, 2008). "ChemFab Corporation to supply chemical warfare shelters for U.S. Army.” Business Wire (1997), http://www.articles.com/p/articles/mi_m0EIN/is_1997_Jan_28/ai_19060667 /pg_1. (accessed December 24, 2008). "Container for containing an explosion." http://www.patentstorm.us/patents/7204183/ description.html (accessed December 23, 2008). "Dirty bomb damage control.” Popular Mechanics 181. 10 (2004), 26, http://0- find.galegroup.com.catalog.oaklandlibrary.org:80/itx/start.do?prodId=EAIM. (accessed December 24, 2008). Dunbar-Gates, Melissa. "Fabric Saving Lives." 2006.http://www.todaysthv.com/news/ news.aspx?storyid=23925 (accessed December 23, 2008). "DuPont StormRoom with Kevlar." http://www2.dupont.com/Stormroom/en_US/products /Products_subpages/proven_by_science.html (accessed December 23, 2008). Katz, S., E. Grossman, I. Gouzman, M. Murat, E. Wiesel and H. D. Wagner. "Response of composite materials to hypervelocity impact.” International Journal of Impact Engineering 35. 12 (2008), 1606-1611, linkinghub.elsevier.com/retrieve/pii /S0734743X08001395. (accessed December 23, 2008). "Kayak Terapad." http://kayak.terapad.com/index.cfm?fa=contentGeneric.dwzhg eznpaxpagiz&pageId=237755 (accessed December 23, 2008). Osegueda, Roberto A., Cesar J. Carrasco, Miguel Orozco, John Eftis, Edward Reynolds, and Ted G. Sholar. "Contour Dust Shield Performance.” Journal of Aerospace Engineering 14. 4 (2001), 147, http://0-find.galegroup.com.catalog.oaklandlibrary.org:80/itx/start.do? prodId=EAIM. (accessed December 24, 2008). "Pacific Bulletproof Co.." http://www.pacificbulletproof.com/products/bullet-resistant- fiberglass/index.html?k=Ballistic%20Panels&se=Adwords&p=0.60 (accessed December 23, 2008). "Success Stories." http://www.dodtechmatch.com/DOD/SuccessStories/View.aspx?id=60196 (accessed December 23, 2008). Tomotaka, Homae, K. Hideaki, S. Toshihiko, F. Koshiro and T. Osami. "Planar Plate Impact Experiments of Kevlar Fiber Reinforced Plastics.” Technical Report 6864. (2004), 11P, sciencelinks.jp/j-east/article/200518/000020051805A0562431.php . (accessed December 24, 2008). Vermeeren, Peter. "Spectra and Kevlar - Not a Fashion Statement." http://ezinearticles.com/?Spectra-and-Kevlar---Not-a-Fashion-Statement&id=550156 (accessed December 23, 2008). Read More