Investigators: Pigeons may have been a factor in I-35W bridge disaster
In a Minnesota Department of Transportation report based on a Jan. 31, 1989, inspection, agency officials wrote: “There is a coating of pigeon dung on steel with nest and heavy buildup on the inside hollow box sections.” Screens were installed over bridge beam openings to keep pigeons from nesting, but droppings still found their way to other parts of the I-35W structure.
Chemist Neal Langerman, a health and safety expert at the American Chemical Society, explained that ammonia and acids in pigeon waste can turn into a concentrated salt if they aren’t washed away. According to Langerman, who was quoted in a USA Today article, rainwater that falls into the salt can lead to a tiny electrochemical reaction that rusts and corrodes the steel underneath. After years of exposure, Langerman said, structural weaknesses can develop in bridge steel.
A final analysis of what caused the bridge breakup is being written. Minnesota’s legislative leaders have announced that they will launch a joint bipartisan Senate-House investigation of the bridge collapse by examining reports from the past 40 years. The probe, officials said, will not overlap with investigations being conducted by the National Transportation Safety Board or transportation committees in Minnesota’s legislature.
The total cost for the I-35W bridge cleanup and reconstruction is estimated at about $393 million. That’s almost $150 million more than the federal government has pledged. Minnesota Department of Transportation officials have said that the state will seek additional federal assistance on the rebuilding project.
The Aug. 1 failure of the bridge, which spans the Mississippi River near downtown Minneapolis, left 13 dead and injured 100.
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