We have all heard the phrase， “time is money.” For industrial facilities， it has never been more true. Unexpected downtime in factories can be extremely costly， as loss of output has a direct， negative impact on revenue. Furthermore， an unexpected factory shutdown can cause loss of work in progress （WIP）， wasted resources， and potential future losses if a restarted production line does not immediately produce output that meets specifications.1 Some production facilities take days to stabilize after a restart， before the output product qualifies for release. If the downtime is due to a catastrophic failure， there could be consequential environmental pollution， collateral damage， legal ramifications， injuries， and even loss of life.

　　In discrete manufacturing， individual items are assembled or fabricated on production lines. This can include anything from cell phones to automobiles. Certainly some of these lines move very quickly so uptime is critical.

　　Downtime in public facilities can cause different， but similarly detrimental consequences. An airport that shuts down when its lighting system fails would be extremely disruptive to thousands of people.