Felix Stein

Re-entrainment of particles from a plane surface.

Abstract We studied the adhesion of spherical glass particles and fly ash to glass and metal substrates using an ultracentrifuge or air at high velocity to achieve particle removal. Adhesion forces increased with increased particle size and ambient air relative humidity, but decreased with increased surface roughness. By properly charging the surface, adhesion could be increased or decreased. Boundary layer theory was used to calculate air drag acting on adhering particles subjected to a high-velocity air stream. Increased time of exposure did not increase particle removal in a centrifugal force field, but it did have this effect with high-velocity air. This result was interpreted on the basis of turbulent eddies penetrating the laminar sublayer to reach adhering particles. Alternately, adhering particles could create turbulance in their immediate vicinity.

The Ratio Between Projected Area Diameter and Equivalent Diameter of Particulates in Pittsburgh Air

Abstract A horizontal elutriator was designed, fabricated, and calibrated with clouds of spherical polyvinyltoluene latex and styrene divinylbenzene particles. It was used to sample Pittsburgh air and deposit particles from 2.0 to 16 microns equivalent diameter on glass slides. By assuming a parabolic velocity profile between plates approaching infinite width, a theory of deposition was developed which agreed well with experimentally determined particle deposits. We measured deposited particle projected area diameter with a calibrated microscope reticle. The ratio between particle projected area diameter (d p) and equivalent diameter (d e) varied from 0.5 to 2.8 for almost all particles, but was as high as 6.5 in extraordinary cases. Stress is placed on the need for specifying d p or d e based on the applications of sizing data.

Physical and Chemical Properties of Respirable Coal Dust from Two United States Mines

This investigation was aimed at establishing procedures for obtaining data relative to the physical and chemical characterization of respirable coal mine dust for utilization in epidemiological studies of incidence of coal workers’ pneumoconiosis in different United States mines. In this paper the dust sampling and analytical procedures are briefly described and results are presented for three samples of approximately 4 grams each collected in each of two United States coal mines representing two different coal seams. Analyses were performed to determine the extent of differences ijn dust properties between (1) samples collected in the same mine and (2) samples collected in each of the two mines.

PHYSICAL AND CHEMICAL CHARACTERISTICS OF “RESPIRABLE” COAL MINE DUST*

The Federal Coal Mine Health and Safety Act of 1969 placed limits on the permissible concentration of airborne “respirable” coal mine dust. The respirable fraction of the total airborne coal mine dust is defined on the basis of initial deposition of inhaled particles in the nonciliated portions of the respiratory tract following inhalation by man. The definition of respirable dust is that of the British Medical Research Council,l as embodied in the British Mining Research Establishment air sampler.‘ The only dust parameter considered in determination of adherence to the law is the weight concentration of dust, expressed as mg/m3. Implementation of regulatory legislation often requires simplification of concepts, but sufficient evidence exists to demonstrate that the effects on health of a given quantity of respirable coal dust may depend on dust properties other than weight concentration, as well as on host factors. Dust particle size, shape, density, specific surface, and chemical composition are among the dust parameters of interest in an epidemiological study of the relationship between coal miners’ pneumoconiosis and records showing exposure of miners to dust. The purpose of the investigation described here is to develop techniques and to collect data using these techniques, relative to properties (other than weight) of respirable coal mine dust. In conjunction with medical records, these data should make it possible to evaluate the biological potential of different coal mine dusts for causing pneumoconiosis. Insight will also be gained into the factors relevant to production of this dust in mines through the correlation of the data with mine operating procedures, including cutting and ventilating practices.

Particle size measurements with phase contrast microscopy

Abstract Identical samples of particulate materials were sized with phase contrast and with bright-field microscopy and the results were compared. The phase microscopy revealed from approximately 30% to 70% more of the small particles than the bright-field microscope. Photomicrographs of polystyrene latex spheres of known sizes were used to determine the accuracy of size measurements with phase contrast of particle sizes close to the limit of resolution. Only with phase contrast is it possible to size accurately particles as small as the theoretical limit of resolution of the objective. With bright-field microscopy the limit of accurate size measurements is highly dependent on the optical properties of the particles.