Document VjYnK0GxKVaZKyD6kRZZQBBRj

* Industrial Hygiene Digest August. Kurt 771 Correction for Anlsokinetlc Sampling cf Gas-Borne Dual Partlclos. S. Badsioch. J, Inal. Fuel 33, 106-110 (MarT i960). - A representative sample of dust can be obtained from a dual-laden gas trc.m only If sampling la isokinetic. An expression is given for the effect of isokinetic samplin' upon the relative quantity of dust entering the sample nozzle. Two methods for calcub;iu.. the dust concentration are considered and a criterion ia provided for deciding, under ihv particular sampling conditions, which method gives the closer approximation to the true ' ennevntration. Procedures are given for determining the true concentration and si** t: *. .lia; from a sample collected onisoklneticaUy, Errors arising from . > .' .,v.*ty, irrespective of the value of the gas velocity, arc small providing tl .method of circulation ia employed. "" APC'A t t 772 Some Statistical Aspects of Dust Counting. J, R. Ashford, Brit. J, Appl. Phya, U_, 11-21 (Jan. I960), The author uses statistical methods to analyze errors arising in the counting .u.d `siting, by optical microseopo, of thermal precipitator samples of air-borne dusts. TUv samples were taken in coal mines as part of the National Coal Board's Pneumoconiosis , i, Research program. The method of evaluating samples is described and the main anurr. .. error are stated. These are: (1) sampling variation in the number of particles within the area counted; (2) the basic error of the counter as indicated by repeated counts of tbr *aim- "" traverse by thv same counter, due to the difficulty in deciding whether a particle is withii. .. given size-range and of marking off particles counted; and (3) differences between obvr\, ;.. To separate these 3 types of error the logarithms of the numbers of particles counted wc used: this Is stated to be accuptod practice since both variability and personal error incn>.,. ) l with ihv number counted. Tin* logarithm of the number of particles recorded by a given ub* server at a given time is therefore treated as being the sum of 3 independent terms, namcly the logarithm of the average count, the logarithm of the observer's error factor at the limn, and the random error. The results show that at any given time a particular observer h,i a characteristic average counting error which with fees experienced counters varies with rin.*, By contrast, the basic counting error, between repeat counts of the same traverse, by the same, experienced, observer, shows little variation between observers continuously engaged 77 in counting slides. Basie counting errors arise from: (1) failure to count all particles in in appropriate size range, and counting some twice; and (2) allocating some of those counted iu the wrong siie-range. Of these, the latter is normally the more important, and sincu the number in a given range normolly falls steeply with increasing size this latter can couse over* estimates in the count in any range. -- Cond, from Bull. Hyp. 773 Particle Size Analysis for the Chemical Engineer. L. Cohen. Chcm, 4 Process Eng, 40, 3ts3-3d6 (Nov, 1959). For the chemical enyinuer who is intorested in using particle size analysis for ' * I routine prov.us* control or to uituin design dnli,, this article summarizes the application* of particle xizo distribution, the various lypei of instruments available, and tl.oiacfor* in i t! volved in the choice of an mxrr/imeut, Somu ctnr-mont* arc made on the limitation* of the various instruments, not as a critical review bur u a brief fjuiJc for the uninitiated to this rather controversial field. The choice f an inutrumum must be made in the light of all rxet. " involved, the choice of an instrument for size an,tl}*ix is vtry wide unci it is net posuihU :* i pick out any one instrument bring ihu best in all respects and in all circumstances. -- A PC A Alrti. 7?4 Dust Control in Class Mawnfnct.irjnu. E. V', Wilson. Cia^s 1ml. 4!, 252-20), (Apr, 19(0). Major courses of dust in the gl;.as industry nriglnatu in the material handling operations prior in mixing, in mining, and it; >iubsvquml handling of the mixed botch, in* eluding dusting in the lank itself. Since control of dust ia so difficult after it has become f t l 1 | J