Dimensional analysis and experimental data on the erosion of various granular media by air are used in constructing a formula which describes the variation of the threshold velocity of movement for grains in a fluid in terms of particle size, density and cohesion, and of fluid density and viscosity.

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A knowledge of the air movement around a worker in a low-speed airflow is important in a number of areas: containment testing of fume cupboards; testing of personal dust samplers; testing of LEV effectiveness; and measurement of worker exposure. Measurements of velocity vectors around the upper torsos of manikins and a human in low-speed airflows have been made using a laser Doppler anemometer. Both heated and unheated manikins, as well as a 'breathing' manikin were used. The results show that quite distinctive flow patterns develop with heated and unheated bodies. Comparison of the flows around two- and three-dimensional manikins with that around a human shows that only a three-dimensional heated manikin gives good results. The unheated breathing manikin gave results which were unrepresentative of the real situation. A suitable manikin for use in sampling or testing in low-speed airflows would have a heated, rounded, three-dimensional body of reasonably human dimensions and would be non-breathing and clothed.

A mechanism is proposed whereby dust is removed from a flat deposit by an airflow; it involves the interaction of the laminar sub-layer of the boundary layer with individual particles. Results of experiments on an isolated deposit are presented to show how the mass of dust removed with the airflow velocity and with time. Results obtained with a continuous deposit show that erosion varies not only with time but also with distance along the deposit; this suggests that saltation of larger grains may be taking place.

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The possibility is investigated that dust can be raised from a deposit over which a shock wave passes by the reflection of shock waves from the underlying surface. It is shown that dust is raised as a result of the rapid flow behind the shock rather than as a result of pressure waves passing through the layer. Dust-cloud profiles fit the ballistic trajectories of individual particles having an initial vertical velocity of about 4.5 m s-1.

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