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May 2022


Journal/Book: Brit. J. industr. Med. 1953 10 142.. 1953;

Abstract: From the Microbiological Research Department (Ministry of Supply) Porton Wilts (RECEIVED FOR PUBLICATION MARCH II 1953) Summary A simple device is described which when fitted to the front of an impinger divides the total aerosol sample into two particle-size fractions by means of size-selective impingement into liquid. The cut-off between the two fractions is set at 4 to simulate nasal penetration. The curve of efficiency of impingement of particles into the liquid against particle size shows that the pre-impinger has a very high efficiency in relation to its jet velocity. This is due to a double impingement process an the liquid surface. The particle intake efficiency at various wind speeds is given in detail and is shown to be good for particles smaller than 30 . Empirical equations are given to show the relation between cut-off size intake hole diameter and jet velocity so that the cut-off may be set to any other desired figure in the range 22 1/2 to 8 . Internal losses were evaluated and shown to be small. Streamlines of flow into and around the device were investigated by means of smoke filaments in a wind tunnel. It is concluded that the particle retention of the pre-impinger is similar to that of the nasal passages while the material in the backing impinger is similar to that reaching the lungs. The pre-impinger appears to have some important advantages over other devices for selective sampling such as dry impaction systems elutriators and settling chambers. ___MH

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