Dust sampling to simulate the human lung.

There are many difficulties associated with sampling an air-borne dust and with assessing its concentration, especially when the potential danger to the lungs is being considered. This is evident from the fact that such a large number of different dust-sampling instruments have been devised from time to time, no two of which give the same results under all conditions. This multiplicity of instruments is due partly to the fact that there is no fundamental agreement on the appropriate index of concentration to represent the pneumoconiosis hazard of a dust; whether it should be in terms of particle number, surface area, or mass. The relationships between these different units depend very much on the size-distribution of the particles in the dust being considered: different instruments sample particles of different sizes with varying efficiencies. Until recently there has not been any satisfactory quantitative information on the manner in which dust particles penetrate as far as the lung alveoli. It is the purpose of this paper to consider the effect of certain physical parameters of dust particles, e.g. size, density, and shape, on lung deposition. Subsequently, an examination is made of the possibilities of taking dust samples that are representative of the proportional deposition of the different sizes in the lung. Consideration is given to the different units in which concentration may be expressed. In many dust clouds most of the mass occurs in particles too large to penetrate to the lung alveoli. Table 1 gives the size-distribution of a typical coal-dust cloud; the area and mass distributions have been calculated from the number distribution determined with a microscope. This is a coarse dust from the point of view of the lung. When the size distributions of the dust, the shape, and density of particles are taken into account (see Fig. 5) the lung, i.e., alveolar, deposition has been calculated to be: By number .. 30% By area .. 8-4% By mass 3 0% As would be expected, the amount of dust deposited in the lung from a dusty environment depends, among other things, on the size-distribution of the dust. The problem becomes, therefore, -how to develop an instrument which selects dust particles of different sizes, densities, and shapes in the same proportion as they are deposited in the lung, so to give an estimate of the respirable dust. The best information available on alveolar deposition is probably that given by Brown, Cook, Ney, and Hatch (1950). They made over 100 tests with human subjects and sampled the dust breathed in and out through the mouth. Respiration rate was controlled with a Drinker respirator to 15 a minute, the volume per breath varying from 600 to 800 ml. The exhaled dust was partitioned into a number of fractions so that the alveolar fraction could be separated from that coming from different parts of the upper respiratory system. Other investigators have not made this refinement, and with the exception of Wilson and LaMer (1948) have not been able to report more than the retention