ON THE IMPACTION OF AIRBORNE COARSE DUST INTO THE EYES OF HUMAN SUBJECTS

Abstract

Fly-dust has been defined as airborne coarse dust which can be troublesome on impact with the skin or eyes. It has been experienced by workers in many industries, including coal mining, but there appears to be no evidence in the literature of serious attempts to characterize the problem within a scientific framework. This paper describes part of a programme of research which has been carried out to rectify this situation and deals with the impaction of dust into the eyes of human subjects. It is known from the results of laboratory wind-tunnel experiments on human subjects (published separately) that the threshold for a given level of sensation due to impacting dust onto the facial skin of a given subject follows a unique relationship between dust concentration and the dimensionless combination of particle dia., air velocity and human head dia. (known as the Stokes number) which describes the inertia-controlled transport of particles near the subject's face. Starting from the assumption that the same sort of threshold relationship exists for the triggering of protective eyelid blinking by the impact of dust particles and taking the hypothetical case of a single burst of dust released upstream of the subject, it is argued theoretically that there is a well-defined upper limit to the size of particles which can actually strike the eye-ball and that this limit is not strongly dependent on air velocity. The results of limited-objective experiments at selected locations in coal mines with human volunteer subjects support this view. It is hoped that the work, of which the present investigation was part, will allow characterization of the nature of the fly-dust problem so that methods can be sought for the appropriate monitoring and control of the working environment.