That incidence shook up a lot of construction workers who worked at refineries!
A friend has a son, who is a police officer. He went to the range for his continual qualifications. Came home showered and went to his local airport to board a plane to go on vacation.
This was before the 9/11 thing. This young man had a baseball hat on and a moustashe. That sets off a profile. They took his carry on and ran swabs on it. That picked up the residual gun powder even after his showering. They had him over in a private area and cops were called in. Two of the cops were fellow cops, and they started laughing as they jokingly handcuffed him. Then they explained what had happened as they were on the range with him. They were covered with the unseen residue! Then the young cop finally got on his plane!
Talk about screwed up profiling!
Or just drop rounds all over, until the dogs give up on all the false alarms. Or just sprinkle the powder near the factory gates and parking lots. That kind of thing.