Seattle City Light Investigating Utility Pole Collapse

SEATTLE, WA — The line of 26 utility poles that collapsed along East Marginal Way in Tukwila and Seattle on Friday were inspected in 2016, according to Seattle City Light. But Friday's windy, rainy weather may have played a role in downing the poles, according to one theory.

Seattle City Light said on Monday it will hire a third party to investigate what caused the poles to fall over. A third-party contractor inspected the Marginal Way poles in 2016. Some were identified for replacement in coming years, but none of them were identified as "posing a public safety hazard," the utility said Monday.

Around 4 p.m. Friday, a line of poles fell along a one-mile stretch adjacent to Boeing Field. One of the poles fell on an SUV being driven by Tom and Linda Cook of Des Moines. They came away with just minor injuries, but were trapped in a scary situation for more than an hour as fire crews worked to free them.

"To ensure full accountability and impartiality, we will contract with a third party to assist in a thorough investigation," a Seattle City Light blog post read. "The process will include reviewing previous inspection records, inspecting the damaged poles and equipment, which have been collected and transported to a City Light facility, as well as obtaining and reviewing any available video from the vicinity. At this time, we do not have an estimate for how long this investigation will take to complete."

University of Washington meteorologist Cliff Mass went back to look at weather conditions around the time the poles collapsed. He found that there was a strong weather pattern with heavy rain and winds moving through the area.

"Embedded within the front there was a narrow band of convection — a line of cumulonimbus clouds with heavier rain in which the winds were accelerated," Mass wrote on his blog.

A weather station at Boeing Field near where the poles fell measured winds at 33 MPH at the time of the incident, Mass said, and that's likely not strong enough to topple utility poles. It's possible that the winds were stronger near where the poles fell — but there isn't a weather station in that exact area to know for sure.

One possible factor is geography. The poles fell in a flat area with high hills to the east and west: south Beacon Hill and West Seattle/White Center. The terrain may have accelerated air flowing out of the storm system, Mass said.

"Boeing Field is in a valley with a sharp rise up to West Seattle to the south-southwest of East Marginal Way. Could the interaction of the strong outflow winds from the convective line with the topographic feature accelerated the winds?"

The utility pole collapse knocked out power to thousands in Tukwila and surrounding areas. By Saturday afternoon, Seattle City Light had removed the broken poles and reopened East Marginal Way.