A 90-minute power outage in Langley Thursday morning by a falling tree was a reminder that the flow of electricity remains vulnerable on Whidbey Island even during the summer.

According to Puget Sound Energy, a tree near the Island County Fairgrounds fell on power lines just outside Langley city limits on Langley Road at about 8:30 a.m. Thursday. About 1,400 customers, including all customers in Langley, lost power in the incident.

Tim Bader, a spokesman for PSE, said the tree fall — which occurred on a near windless morning — did minor damage to the lines. Power was back on by 10 a.m.

For the past five years, PSE has been doing nearly constant work on its lines to ensure the lights on Whidbey Island stay on, Bader said. The majority of the effort has been directed toward foiling outages caused by falling trees and tree limbs. Though the company has consistently insisted that burying power lines would be too expensive, it has taken a number of other steps.

Last year, Bader said, about 34 percent of the 169 outages on Whidbey Island were caused by falling trees and limbs. PSE undertook a tree trimming program in 1999 to remove branches and trees maintenance crews found to be threatening power lines. Over the years, PSE subcontractors have trimmed the trees along 120 miles of roads and rights-of way.

Additionally, PSE has installed tree wire along 13 island roads. The wire does not short out when it is impacted or bent by trees or limbs. The wires hit by the tree outside Langley Thursday were not tree wire, thus shorted out.

Bader said PSE’s plans for undergrounding power lines are limited to new housing developments in most cases. He said the presence of other underground utilities — including telephone wires buried by Whidbey Telephone Company decades ago — precludes PSE from doing the same in many locations.

Outages that do not involve tree or limb falls are typically caused by auto accidents, equipment failures and animals, Bader said.

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