الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Dust ’’count’’ has been successfully used as an index of d us tine ss. lmpinger sampling of the mineral dust coupled with ilcounting” in light field microscopy has been used to monitor work environment in the U. S .11.., while other ”counting” instruments are simil~rly used in other countries. Atmos pheric levels in this work places were compared with the i..C.G. I.H. recommended ”count” permissible limits, computed on basis of the free silica content in dust. The incidence of silicosis there was r,,)duced as a result to the use of these techniques. However, the it counting ” method is far’ from ideal with regards to relevance to health hazard, simplisitY9 reproducibility and unit cost. During the annua~ meeting, the A.C.G.l.H. recommended(1970) the usa of ”mass” permissible limits for I’respirabloil and ”total” mineral dust. Two formulae werJ recommended to compute these limits which were based IT~inly on the studies of the Vermont granite sheds. ”Gross mass” and preferably Us ize-selective” mass sampling havo been recom..rnended for monitoring of work environment; the latter is more relevant to health. Besides \1mass sampling” is simpler, more reprod ucible and less expensive than the ilcounting”. However, the proposed ”mass” limits were developed without the benefit of any ilnew” epidemiological data to permit proper judgment of the adequacy of these standards. hlso, studies in some dusty operations - other than the above referred one - showed that the proposed ”mass!! limits and ”count” limits did not agree as to the degree of hazard. 18 a consequence of this variation, it deemed necessary to test the relation between these two methods in the environ mental assessment of different levels of different types of mineral dust. It has been aimed in this work to study the different ”total” and ”size-selective” mass sampling methods in refolation to ”count” method in sampling and evaluation of different typfCS of mineral dust in different dusty places ( Le. diff er ent levels of dustines?) and under different sampling conditions, in order to establish the relation between ”count” and ”mass” concentrations for mineral dust, and develop conversion equation(s) from one concentration to another. The data developed, when coupled with the medical findings (developed in a parallel medical study) will present the bases for reco~~ending the method(s) of dust sampling believed to be most relevant to health. Sampling was performed in the different dusty operat ions of eight different plants producing and/or handling refractories and ceramics, sand bricks, phosphate ore, hematite ore and cement, which include different types of raw materials containing different proportions of fro”e silica. Besides, dust was sampled - under environmental controlled conditions - from dust clouds produced in a dust chamber and using dust particles passing through 300 mesh sieve of quartz, phosphate, hematite, clay and cement. Levels of dustiness were appraised using M.S.i~. impinger ”count” sampling, M.S.~l. personal sampler with and without 10-MM nylon cyclone, M.S.ll. electrostatic precipitator with and without a locally designed horizontal elutriator, MBE gravi metric dust sampler ancl thermal precipitator sampler (for dust sizing). Density and free-silica content were a-ISo determined in settled dust samples. With a felA! exceptions, concentrations of dust sampled in the different wQrk placos were relatively high. In the dust chamber various concentrations ranging from relatively low to relatively high were sampled. Generally, different degrees of consistency were observed between the results of 11 count”, i’total ma.s s it andlor ”respira bIe mas s 11 concentra t ions in the diff’3rent operations in most of the studied plants. The best consistency was observed where the concentrations of dust were relatively low. In a few operations where dust concentrations Wore high, however, good consistency was also observed. The Uta tal” to ”respirable” ratio was mostly double in most of the plant, while in a few operations this ratio varied from 3 to 5 folds. It has been concluded that dust concentrations obtained by all - or some - of the different sampling instruments used in this study, are affected by : (a) the range of concentration of sampled dust, and (b) the different work and environmental conditions in the work place (e.g. work activity, air vel ocity and air direction etC.Jo Due to these factors, the concentrations of ”res pira ble t1 dust sampled with pers onal sampler (with the IO-I1}I nylon cyclone) were mostly the highest while the concentrat ions obtained by the lVIRE gravimetric dust sampler were, in most cases, the lowest. Statistical testing of the. ”count” versus mass concentrations in relation to dust density (0), geomotric mean of particle size (DD and the parameter (dD2) revealed that the ”count-mass” relation showed the best correlation with the parameter (OD2) follolvcd by the particle size (D). 2 Consequently, the parameter (OD) was used to develop mathematical relations for the conversion of midget ”count” concentrations to ”massl1 concentrations (i’total” and ”respirable”), for each of the sampling instruments used in the study for both field sampling and sampling in the dust chamber, the relation: Y = n X (JD2 where Y = ”massil dust concentration (mg/m3) X = ”count’! dust concentration (m.pop.c.f.) n = constant (repr~senting the slope of the ”ma$s ”countlt relation) These relations l,vere used to develop the t’general” ”count” ”mass” conversion equations for iltotal” and ”respirable’” mineral dust: YT = 0.01 X 6D~ YR = o. 004 X OD2 and where YT and YR are the ”mass” concentrations for ”totall1 and ”respirable;’ dust rospectively.