I was called into a Data Centre last week, to investigate the cause of a strange dust. I was told, the fronts of a row of racks, and equipment had yellow dust deposited on them! I had seen this all before; at one of our broadcasting customers. So, I headed directly for the nearest down flow ACU. Sure enough; I found what I was expecting. An engineer working on the water supply for the ACU, had removed the pipe covering, (you know that silver stuff that covers the copper pipe). They had left the discarded covering, on the slab, directly in the ACU airflow. This covering is made of Phenolic material, which is very friable. This foam breaks down in the airflow, into dust (particulate) contamination, and will very quickly contaminate equipment like servers, switches externally and internally. Always make sure your engineers clean up after themselves!!!