In a recent Q&A on the FacilityCare website, consultant Brad Keyes answered a question about dust on sprinkler heads.
Q: I just had a survey and received a finding for dust on some of the sprinkler heads. I understand that foreign material is not permitted, but minute amounts of dust??
A: Dust is a foreign material, and foreign material is not permitted on sprinkler heads. I support the finding, since how much dust is too much? If you allow just a little dust, then at what point is it too much dust? Besides, any foreign material, including dust, can change the reaction time of a sprinkler head.
Inside One of Healthcare's Most Ambitious Hospital Projects 
Trauma-Informed Design Transforms Boston Homeless Shelter
Disinfectant Contact Time: The Case for Biofilm Disruption
Texas HHSC Reaches Construction Milestone for Panhandle State Hospital in Amarillo
Mon General Succumbs to Phishing Cyberattack