Thursday, April 7, 2016

It’s a bird, it’s a plane, it’s a giant fan?

If you live on Mercer Island, use the Interstate 90 Trail or spend time at Aubrey Davis Park, you might have noticed an unusual sight on Tuesday, April 5 as six new fans arrived at the Mercer Island Tunnel. Contractor crews working for WSDOT and Sound Transit used giant cranes to off-load the 10,000 pound fans from flatbed trucks parked on West Mercer Way into the Mercer Island Tunnel building located in Aubrey Davis Park.

Contractor crews lift one of the 10,000 pound fans into the Mercer Island Tunnel ventilation building.
The building is located under the tennis courts at Aubrey Davis Park.

Not all fans are created equal
We have two types of fans inside the Mercer Island Tunnel: supply fans which bring in clean air from the outside, and exhaust fans which take dirty air out of the tunnel. The six fans delivered today are supply fans and will work in conjunction with the large metal pieces and trusses that crews lifted into the ceiling and installed during this spring’s eastbound weekend work. Together these pieces will work together to better clear exhaust or smoke from the tunnel in an incident. Similar metal pieces and trusses will be installed westbound during the project’s next weekend detours weekend detours scheduled for May 20-23 and June 3-6.

Contractor crews wait to unload fans on Mercer Island. These are three of the six fans
that were delivered to the Mercer Island Tunnel on April 5.

Why do we need new fans inside the Mercer Island Tunnel?
In order to add all-day carpool lanes on I-90 by squeezing in a fourth lane in both directions, contractor crews need to upgrade the tunnel’s fire detection and ventilation systems, which includes fire sprinklers and hydrants, cameras and other items that help to keep drivers safe in the event of fire or other incidents inside the tunnels. While our maintenance crews do a great job keeping these systems in working order, it’s time to give things a much-needed upgrade. The last time we made any big changes to the tunnel systems was about 25 years ago when I-90 was rebuilt. As the years go by it’s tougher to get replacement parts for these aging systems, not to mention keep up with the advances in technology that have happened since then.

All of this work will wrap up by mid-2017 to allow Sound Transit to begin construction for the East Link light rail project across I-90.