1990 Disaster
In 1990, while under construction, the original bridge sank because of a series of human errors and decisions. The process started because the bridge needed resurfacing and was to be widened by means of cantilevered additions in order to meet the necessary lane-width specifications of the Interstate Highway System. The Washington State Department of Transportation (WSDOT) decided to use hydrodemolition (high-pressure water) to remove unwanted material (the sidewalks on the bridge deck). Water from this hydrodemolition was considered contaminated under environmental law and could not be allowed to flow into Lake Washington. Engineers then analyzed the pontoons of the bridge, and realized that they were over-engineered and the water could be stored temporarily in the pontoons. The watertight doors for the pontoons were therefore removed.
A large storm on November 22, 23, and 24, 1990 (the Thanksgiving holiday weekend), filled some of the pontoons with rain and lake water. On November 24, workers noticed that the bridge was about to sink, and started pumping out some of the pontoons. However, on November 25, 2,790 ft (850 m) of the bridge sank, dumping the contaminated water into the lake along with tons of bridge material. The bridge sank when one pontoon filled and dragged the rest down because they were cabled together and there was no way to separate the sections under load. Fortunately, no one was hurt or killed, since the bridge was closed for renovation and the sinking took some time. All of the sinking was captured on film and shown on live TV.
Read more about this topic: Lacey V. Murrow Memorial Bridge