Public must wait for final review on outage

But HECO's system might not have quit had the mercury switches on two generating units given correct readings of their fluid levels. The false indications triggered the loss of power at Kahe 5 and Kahe 6, among HECO's largest generating units.

HECO says it has replaced the switches with ones less sensitive to earthquakes, a good start in ensuring this problem won't occur again. Though the company cannot predict what would happen in comparable situations, the public expects reliable power generation and HECO should consider atypical events.

According to the report -- prepared by Power Engineers Inc., an Idaho-based consultant, at HECO's request -- the quake probably shook the mercury in switches that sense fluid levels in equipment regulating steam flow to the turbines. The false readings activated relays that locked the turbines to prevent damage, tripping a series of shutdowns that resulted in the outage.

The report also noted that HECO's actions in restoring power were reasonable, though it recommended the company set priorities for getting power to "critical customers," such as hospitals and communication services.

The study is just the first step in a review by the Public Utilities Commission that will include HECO's affiliates on Maui and Hawaii. Customers will have to wait for that evaluation before making their own judgments.