Back in the mid 1980's I worked for a tab house in New York City. As all the directors were chain-smokers, puffing was allowed at the desks of all employees.
One employee in particular was a real nicotine fiend--he couldn't work without a fag in his mouth. However, he continually reported that his keyboard was bad. We would swap it out for a new one every few months, and it would work fine, until it didn't.
I decided to disassemble one of his keyboards to see if there was anything he was doing that affected the keyboards. When I had it partway disassembled I turned it upside down, and a fine grey mist floated down onto the workbench. Our colleague had been exhaling at the keyboard constantly during work hours, and the grey mist was cigarette ash that had been filtered in his lungs before settling into the keyboard. Smoking at workstations was banned and all then cleared itself up.