The industrial environment, its evaluation and control : Syllabus for short courses for industrial hygiene engineers and chemists presented at Occupational Health Field Headquarters, Cincinnati, Ohio.

  • United States. Public Health Service. Division of Special Health Services
Date:
1958]
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Licence: Public Domain Mark

Credit: The industrial environment, its evaluation and control : Syllabus for short courses for industrial hygiene engineers and chemists presented at Occupational Health Field Headquarters, Cincinnati, Ohio. Source: Wellcome Collection.

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    chemical analysis the binder can be removed prior to sampling by firing the filter in a furnace just below the sintering temperature of the glass. de A ney iheiesctin wd & in filtration has been the molecular or Milli- pore(R) filter(18) which is a thin (150 n) sheet composed of mixed cellu- lose esters. It can be manufactured in’a variety of pore sizes and resist- ances and with great uniformity. A significant advantage of this filter is that the penetration into the filter, even by the smallest particles, is very slight (10-20 microns). When a portion of the filter with collected sample on it is placed on a microscope slide and moistened with immersion oil of the same index of refraction as the filter (the filter becomes transparent) the parbisfes can be seen all in one plane, an important factor in microscopy 19), The filter is readily soluble in organic solvents such as acetone and ethyl acekaye and therefore can be used to collect sam-— ples for electron microscopy « Because of the uniformity of the membrane it is possible to make accurate and reproducible measurements of light re- flected from the collecting surface and thus sometimes eliminate the neces- sity of a tedious chemical analysis 21), If chemical analysis is desired, the high purity of the filter is an advantage while its small size and slight affinity for water makes accurate weighing possible. ee. Tubes of volatile or soluble crystals, such as salicylic acid, sugar, naphthalene, etc., have been used as methods of dust collection by drawing the contaminated gases through them\4,22), The dust is recovered either by volatilization or solution of the crystals of sufficient purity that no residue is left with the dust collected. The efficiency of the filter depends on the size of the crystals, the depth of the bed, and other factors. When soluble crystals are used gases containing appreciable amounts of water cannot be sampled. Dust collected in this manner is adapt- able to chemical, weight, or particle size analysis. f. Alundum thimbles and sintered glass filters are manufactured in a variety of porosities. They have considerably higher resistance to airflow than comparable paper filters but can be used for high temperature sam- pling 22), There is little variation in weight due to adsorption of water and hence they can be weighed more accurately than filter paper. In addi- tion, the collected sample may be recovered almost completely by brushing the inside of the thimble or it may be treated chemically and dissolved right in the filter. Impactors When a high velocity, dust-laden stream of air strikes a flat surface at right angles, the sudden change in direction of airflow and the momentum of the dust particles result in the separation of the dust from the air. The air passes on, leaving the particles adhering to the surface. The perform- ance of instruments based on this principle has been studied both experi- eee and a ypebikor ee and the parameters involved clearly de- fined\23,24,25), Generally speaking, these instruments are efficient only for particles larger than 0.5 m in diameter since the momentum of the smaller particles is not sufficient to cause them to impinge on the collecting plate, instead they follow the flow lines of the gas stream.