I feel sorry for someone who doesn’t get a response to a sensible question on the forum. So here is my tuppence worth. By zircon particles I assume you mean zircon dust from the refractory coating to a kiln/furnace. If you check EH40/2005 Workplace exposure limits you will see that zirconium compounds have a long-term exposure limit (8-hr TWA reference period) of 5 mg.m-3 or of more interest a short-term exposure limit (15 minute reference period) of 10 mg.m-3 The short term exposure limit is of interest as it indicates that the stuff is a serious hazard and you had better take precautions aimed at lowering any exposure to a minimum (not just to the exposure limit). That is unfortunately the limit of my knowledge but anybody doing a clean-up this area would need some sort of suitable PPE including respiratory protection. There would also have to be other controls in place to stop the dust spreading and to safely dispose of any waste.

Daisy You may also find they are referring to Zircon Sand which sand moulds are made from. I suspect the same precautions referred to above would also be appropriate Try doing a search on Google for foundry sand.