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RSSProtective materials
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The human body’s remarkable design can protect against heat and
cold, cushion blows and even repair its own injuries. But our bodies are not fireproof or bulletproof, they cannot protect us against the extremes of temperature and pressure found deep in the ocean or out in space, and they are poorly suited to defend us against injury in high speed accidents.
Humans are believed to have use fire more than million years ago, but people have now developed effective protection against its destructive effects. Fire means intense
heat and temperature, so fire protective materials must be capable of resisting heat for some time without themselves catching fire. Polyvinyl chloride (PVC) for example is used as an insulator in domestic electrical wiring. A composite of silica and alumina, two naturally non inflammable minerals is used in industrial building such as power stations to offer heat protection up to 1200°C.
This composite is also used in airplanes, whose combustible plastic interiors give off as much energy as their equivalent weight in petroleum when they catch fire. Totally fireproof materials can be expensive for example; airplane seat cushions are typically made from flammable polyurethane, but can be made safer by coating them with fire resistant Kevlar.
If the human body is badly designed to withstand fire, it has even less chance where bullets, knives, and bombs are involved. Five times stronger than steel and much lighter, Kevlar has revolutionized body protection. It is fibrous material made from long chains of polymers called polyparaphenylene terephthalamide. Woven together, the fibers knit into a tough protective grid that can withstand knife blows and cuts and some types of gunfire.
It is not always practical for people to wear bulletproof clothing-sometimes it is more convenient to protect them by armoring the vehicles in which they travel. Today, composite materials provide the same protection as antiballistic steel but add much less weight to the vehicle. Armored vehicles are also typically fitted with bulletproof “glass”-a tough sandwich of glass and polycarbonate.
Not everyone needs a defense against petroleum fires or automatic weapons, but everyone is exposed to some risk every day. most helmets consist of a Styrofoam liner and an outer shell made of a plastic or a composite .in an impact, the Styrofoam liner in a cycle helmet is crushed slowly, dissipating the energy of the blow an bringing the wearer’s head to a gradual stop. Meanwhile, the rounded outer shell helps to spread the impact over a larger area, reducing the damage it does in any one place.
Some people have to wear protective materials all the time. Sufferers of a rare genetic condition called xeroderma pigmentosum have skin that lacks natural protection against ultraviolet radiation.
