I too work in an industry like that. Driftwood is right, operations will probably have a 12 hour day shift and a 12 hour night shift to keep things running 24/7. The only time a plant shuts down is during a turnaround, which is where key components to the plant have maintenance done on them ie pump / heat exchanger replacement etc... bascially any piece of equipment that requires maintenance that cannot be isolated from the main operatating system of the plant will be done in a turnaround. I could only see typical turnaround for a small plant such as this to be about 1 week...