The responses of human subjects to the facial impaction of airborne coarse dust.

“Fly-dust” has been defined as airborne coarse dust which can cause irritation on impact with the skin or the eyes. It is known to be a problem to workers in many industries, including coal mining, but very little attempt appears to have been previously made to characterise it within a scientific framework. This work sets out to rectify the situation with respect to the impact of dust onto the skin of the face. The question of impact into the eyes is being considered separately.

Laboratory wind-tunnel experiments on human subjects, using classical psychophysical methods, show that the threshold for a given level of sensation due to impacting dust on the facial skin of a given subject follows a unique relationship between dust mass concentration and the dimensionless combination of particle diameter, air velocity and human head diameter (known as the Stokes number) which describes the inertia-controlled transport of particles near the subject’s face. These results are consistent with a theory based on “impaction pressure”.

The “fly-dust” problem thus characterised, methods can be sought for the appropriate monitoring of the working environment.