Mineral fibers limits

Table 8. Exposure Limits for Asbestos Fibers, Synthetic Mineral Fibers (SMF) and Nuisance Dust in the Workplace ...

Minextl R Molded into Limited com- Excellent Moderate Mineral fibers Flexible and Will not resist 100 1700 0.300 0.420 0.420 18... 

Option B corresponds to the existing system in Kiev, where the possible increase in production rate of the melter is currently limited by the capacity of the production line for making mats from mineral fiber. The maximum capaeity of this line is 3 t/h of the melt. But even with this restriction, preheating of the charging materials increases the thermal efficiency of the melter by 50%. 

Acetate and triacetate are essentially unaffected by dilute solutions of weak acids, but strong mineral acids cause serious degradation. The results of exposure of heat-treated and untreated triacetate taffeta fabrics to various chemical reagents have been reported (9). Acetate and triacetate fibers are not affected by the perchloroethylene dry-cleaning solutions normally used in the United States and Canada. Trichloroethylene, employed to a limited extent in the UK and Europe, softens triacetate. 

Physical Dilution. The flame retardant can also act as a thermal sink, increasing the heat capacity of the polymer or reducing the fuel content to a level below the lower limit of flammabiHty. Inert fillers such as glass fibers and microspheres and minerals such as talc act by this mechanism. 

The extent of substitution of magnesium and siUcon by other cations in the chrysotile stmcture is limited by the stmctural strain that would result from replacement with ions having inappropriate radii. In the octahedral layer (bmcite), magnesium can be substituted by several divalent ions, Fe ", Mn, or Ni ". In the tetrahedral layer, siUcon may be replaced by Fe " or Al ", leaving an anionic vacancy. Most of the other elements which are found in vein fiber samples, or in industrial asbestos fibers, are associated with interstitial mineral phases. Typical compositions of bulk chrysotile fibers from different locations are given in Table 3. 

Fiber Organic Solvents Animal, Vegetable, and Peiro Oils Microorg anisms Alkal Orga-ies nic Acids Oxidi- zing Agents Miner- al Acids Temperature Limits ( F)... 

Only one phosphide mineral appears on the list. The tabulation contains twenty-six arsenate species but not a single arsenide. The fibrous minerals recorded reflect the limitations imposed by natural circumstances, and especially the opportunities for elements to be juxtaposed geochemically and able to produce a particular mineral compound. Oxygen containing compounds form by far the most prevalent natural fibers, but simple hydroxide and carbonate compounds are also prominent on the list. There are more oxyhalides and water-containing minerals than pure chloride minerals, al-... 

Regulation. The identification of health risks associated with asbestos fibers, together with the fact that huge quantities of these minerals were used ( 5 x 06 Uyr) m a variety of applications, has prompted strict regulations to limit the maximum exposure of air-borne fibers in workplace environments. 

The degree of the fiber degradation and mineralization of the Seip materials made them difficult to sample and also limited the degree of visual examination that was ethically justifiable without destruction of the textiles. 

In our first study described above (2), a negative balance of -0.02 mg Mn was found on a dietary level of 0.11 mg/day. This figure is small considering levels reported from past studies. However, the diet fed to the subjects was semi-purified, not whole foods. It is believed that retention of the mineral was enhanced by increased physiological needs caused by a manganese depletion from consumption of such a low dietary level. Furthermore, the diet did not contain any phytates and limited amounts of fiber. 

The next stage in the research project will focus upon those location points where significant variation exists, or where the data collected are puzzling. Selection of a limited number of points for the physical and chemical testing would preserve at least part of the evidence and assist in the search for information about the character of the fiber. An array of instrumental analyses would be designed to yield essential data about the textile evidence and its mineralization processes. 

In order that interpretations of prehistoric fabric use and manufacture are soundly based, it is necessary to demonstrate that minerals formed during postburial alteration of a fabric-metal association do, indeed, replace fabric components and duplicate faithfully the shapes of the fibers, yams, and fabrics. The degree of detail to which this duplication occurs must be determined to establish limits to information that can be expected from fabric-pseudomorph study. For example, nodes on barbules of feathers, necessary for feather classification, have not been observed yet, but the mechanism of pseudomorph formation may be found capable of replicating such fine structures and thus prove useful in some archaeological studies. In addition, the relationship between pseu-... 

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