High-Q | חטיף 3


חטיף מס '3


Text II (Questions 18-22)

The ancient Greeks were the first to discover the fireproofing and insulating properties of asbestos, but they knew nothing of the mineral’s dangers. When asbestos is inhaled, the fibers can cause asbestosis, a stiffening of lung tissue that contributes to heart disease and lung cancer. Because of this risk, asbestos is being removed from schools, hospitals, and thousands of other buildings around the country. It’s a costly, time-consuming process, as 5 workers in protective gear use their hands to scrape out the substance, which must then be disposed of as a hazardous material. To prevent asbestos fibers from escaping into the air, areas being cleaned must be sealed in airtight tents. Now a new way has been developed to deal with asbestos - by changing its chemical composition so that it is no longer asbestos. Chrysotile asbestos, the most common form of 10 the mineral, is composed of oxygen, hydrogen, silica, and magnesium atoms. The removal formula researchers have devised consists of a powerful acid combined with a fluoride ion, which acts as a catalyst. The formula attacks the silica layer, then the magnesium layer, and basically removes the magnesium from the mineral. The reaction breaks up asbestos’ brittle, spiky fibers, leaving behind clumpy minerals that are not easily airborne. At the 15 completion of a treatment, the chemical composition of the material is not asbestos. Less than 1% of the original asbestos fibers remain after the treatments, which is a level deemed safe by the Environmental Protection Agency. What used to be asbestos has been converted into harmless chemicals like silica oxide and magnesium oxide. These continue to provide fireproofing for buildings, at the same level of protection that was 20 provided when the material was still asbestos. The chemical treatment is applied directly to asbestos-covered pipes or walls in a mix that has the consistency of whipped cream. The application is very gentle, so that asbestos fibers are not stirred up into the air. So few fibers escape, in fact, that a pressurized tent is not necessary. This provides huge cost savings for institutions that want to use the process. 25


18. Asbestos is dangerous for humans because -

(1) it does not provide adequate protection against fibers (2) its fibers can cause a stiffening of lung tissue (3) it is fireproof (4) it forms a powerful acid in the lungs

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