The crash happened at about noon Thursday as the trooper and others were at the scene of a previous collision on northbound I-5 south of the Interstate 405 interchange.
A semi truck approaching the collision scene lost control and wiped out a series of jersey barriers, ending up sideways across the shoulder amid a jumble of broken concrete chunks.
A mechanic working at the scene sustained minor injuries when he was struck by debris from the impacts. The state trooper was only a few feet away and was nearly struck by the out-of-control semi tractor.
The semi driver was not injured.
Traffic was backed up on I-5 as the Washington State Patrol cleared the crash scene.