In some recent PHA’s for a client I have seen a pattern in some general assumptions that PHA teams should not be making, but often do. It involves the “consequences” for scenarios such as “LOSS of ELECTRICTY”. The catch is that there is a general assumption that with a “LOSS of ELECTRICTY” that everything shuts down. There may be two very critical errors in this assumption:
1) Often times electricity is not the only power source. In my PHA’s each one had a “critical flow” that personnel just assumed would stop with a power outage. When reviewing the P&ID, it was revealed that the feed was done via an air pump. Now granted, the air pump will not run for long after the loss of electricity, but this was a critical flow that MUST be immediately stopped with the loss of agitation. A flow of just 30 seconds after the loss of agitation and cooling water could set up the scenario for an extremely bad situation should the power come back before operators could actually shut down the process.
2) To make matters worse, the FAILSAFE-CLOSED valves the facilities were relying on as a safeguard was held OPEN by plant air. This means that this valve would remain OPEN allowing the critical feed to continue during the time the facility was counting on this valve CLOSING.
Lessons: PHA’s need to specifically review each mode of power or utility. A simple assumption that “everything shuts down” when a utility is lost is just not always correct and could be setting a facility up a serious incident. In the scenario above, what the facilities thought would stop did not and what they thought would close did not. Easy fixes, but something that had been over looked for nearly 25 years.