What Is Dust And How Is It Defined?

As dust is fine solids or, in some cases liquids, there needs to be a system of measuring the particulate size and then to categorise the various dusts by size to see to what extent the dust is ingested.

The particulate can be measured by various means but within the metric system of measurements, we use the term micrometer or micron, which is an exceedingly small measurement of one-one thousandth of the millimetre.  The human eye will only see a profusion of dust in the air under certain conditions – predominantly if one is viewing the plume of dust against a blue sky against the light.  This presumes of course, that the dust concerned has a low reflective index and the colour has the greatest contrast with the sky colour as possible.

A lime dust plume is far more visible than cement, which is grey – less of a contrast against the sky’s blue.  Similarly, coal dust will be visible against the sky, whereas a light grey roadway dust will be less visible.

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