The Electrostatic Precipitator (ESP) that removes particulate matter from the flue gas going up Unit three's chimney is not activated, resulting in a dirty plume of black smoke. This plume can last for eight hours or so before the unit becomes operational and the amount of visible smoke is greatly reduced.

Note that all units were in operation at this time. Their emissions are not visible in the light of dusk with the overcast sky, but can become visible given the right weather conditions.