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? I think this is an unreasonable citation. What do you say?

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 too much dust? Besides, any foreign material, including dust, can change the reaction time of a sprinkler head.

It is similar to a communication cable hanging across a sprinkler pipe… One cable does not seem to make any difference with the added weight on the hanger. But when does it become too much? Since it is not defined, then the answer is one cable is too much.

Keep in mind, when the codes and standards are not definitive, the AHJ gets to decide what is definitive.