Data Centres are dusty places! Dust/particulate can find its way in from outside environment, on feet, and when doors are left open, etc. Dust/particulate can also be produced, in vast quantities from within the data centre. Aluminium, iron and zinc oxide are often present. Belt residue from the ACU drive belts, is present, where belt drives are used. The use of unsuitable materials, can also cause dust. IT Cleaning Ltd, found rubber being used to block airflow, as you can see this rubber had broken down in the airflow and was causing particles to be shed.
“What you can see in the picture, was found on, and around the rubber. I assume the smaller particles have become airborne, and contaminated some close by equipment”. Stephen Yates