Lacey V. Murrow Memorial Bridge
The Lacey V. Murrow Memorial Bridge is the second longest floating bridge in the world, at 6,620 feet. It carries the eastbound and carpool lanes of Interstate 90 across Lake Washington from Seattle to Mercer Island, Washington. The original bridge was constructed in 1940 and it sank on November 25, 1990, while it was undergoing refurbishing & repair. The current bridge was built in 1993.
The sinking of the original bridge was an example of human errors and decisions compounding to lead to disaster. The process started because the bridge needed resurfacing and was to be widened by means of cantilevered additions. The state of Washington department of transportation decided to use hydrodemolition: high-pressure water to remove unwanted material. 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 safely be stored temporarily in the pontoons. The watertight doors for the pontoons were therefore removed. A large storm arose on November 22, 23, and 24, 1990. This 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, 850m of the bridge sank, ironically dumping the contaminated water into the lake along with tons of bridge material. The bridge sank because first 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.