On Saturday, October 6, 2012, the plant maintenance employees used housekeeping connections on the new dust collection system to vacuum dust and debris in the pre-mix room. A US Ink maintenance employee reported in an interview that upon arrival on his Saturday, although the mixing tanks were shut down the night before, the dust collection system had run all night, a departure from the initial design intent of automatic start-up and shutdown, in sync with the mixing tanks.23 At the end of housekeeping activities, a maintenance employee manually shut down the dust collection system. Although the maintenance employee reported the dust collection system equipment malfunction to his superiors and to the electrical contractor that wired the dust collection system, US Ink/Sun Chemical Corporation management took no action to immediately investigate the failure or to shut down the ink mixing operation until the malfunction was corrected.24 Employees restarted the mixing tanks and the dust