Document JJRz2DXMYZa1ezVkRQ90m6Rwa

2 encountered is designated as chrysotile and ties of the mineral serpentine, in which it ; mind that silicosis (and presumably asbeslv, taking from 5 to 15 and even 20 or 25 shed. This rate of progress is influenced silica which the lungs receive, and this doson three variables--the amount of silica in dust in the air, and the length of exposure, might be included as a fourth variable; of the variations in susceptibility in those gbt well be assumed that similar variables rence of asbestosis.'-: os is mined or fabricated1 in North America o be present the clear-cut clinical picturo in communities with ' a true silicosis hazard, . communities. It may-be'that some of the >o recent origin for 'the:typical effects of a manifest, but this would riot apply to the he fabricating plants:; service of the Metropolitan Life Insurance wing investigation'1 during the period from 1931, which included: litions in asbestos mines and mills in Canada along the Atlantic Seaboard in the United jns of asbestos workers, including X-ray ,aust systems designed to eliminate asbestos g plants only are included in this study and ort as plants A, B, C, D, and E. This is a lore extensive study of the asbestos industry i DUST STUDIES 9 of sampling.--Both the impinger (1) and 2) were used for theirhUectionof air samples' levels and in close proximity to the workmen. ;>parntus aro adapted for this work, as they set up and adjustfed-Ter the taking of the level, and are cxtreirielyTefficient. the dust by aspirating1 the air and then surface covered by a''liqUitl iri a container. Lied water, containing 50 percent alcohol to . ` * ' | | j ij 3 January 4,1935 prevent the solution of some of the dusts, particularly any silica which might be present. The impinger was actuated by an electri cally driven rotary pump and the rate of air sampled was measured by means of a resistance type of flow meter with an inclined manome ter for measuring the pressure difference. Each sample represents the dust collected from a volume of 100 cubic feet of air. The electric precipitator is designed upon the Cottrell precipitator principle used for recovering dusts and fumes commercially. This principle depends on electrifying the dust particles by making them pass through an electrostatic field and thus causing them to settle out upon a sheet of celluloid. The electrostatic field is set up by means of a transformer operating from the lighting lines on 120 volts, alternating current. Air is drawn through the apparatus by a small rotary fan, run by a motor, the quantity being measured by a flow meter. Samples of dust brushed from beams and pipe lines near the ceiling also were secured for chemical analysis. All samples were shipped to the industrial hygiene laboratory of the Metropolitan Co., and the dust counts were made according to the methods accepted by the United States Bureau of Mines and the United States Public Health Service (1). Particles in size up to 360 microns in the greatest diameter were counted. Chemical analyses were made for total (free and combined) silica according to the accepted standard method of Hillebrand (3). In the first plant studied (A) only particles 10 microns and under in size were counted. It has been demonstrated repeatedly that no silica particles exceeding 10 microns (a micron equals one-millionth part of a meter or one-thousandth part of a millimeter) in greatest diameter enter the lung tissu ; for this reason, the larger particles usually are not considered when determining dust counts. Later, as it appeared from some of the published articles (4) (English) that asbestos particles much larger in size were found in lung tissue, it was decided to count all particles and make differential counts of all those 10 microns and under.1 Total particles per cubic foot and the corresponding weight of the dust in milligrams were obtained. Since no relationship between the dust counts and the corresponding woights was found, the weights are not included in the tabulations in tliis report. ' Table 1 shows by plants and by departments the maximum and minimum dust counts in million particles per cubic foot of air. Although the counts in plant A are of particles 10 microns and under, 1 Ramplea collected by both the impinger and the electric precipitator were coacted. In addition, microphotographs of these dost particles were enlarged by being projected upon a screen with a lantern* * de projector, the enlarged particles beiDg measured with a ruler. Knowing the entire enlargement (by actual measurement), it was easy to calculate the original particle else (5). By the use of Bozen's (0) ogaiithmic probability paper, the logarithms of the function to be measured (In this case microns) art P otted as ordinates against the probability of occurrence os abscissae.