Latest Minneapolis bridge collapse theory: pigeon poop
Inspectors investigating the I-35 bridge collapse in Minneapolis have a new theory: pigeon poop may be one of the culprits. Seriously:
It is thought the build-up of guano over many years could have speeded up the rusting of the steel beams in the eight-lane bridge, which collapsed into the Mississippi on August 1.
Structural engineers had been aware of the problem since as early as 1987, when inspectors noted a coating of guano on the inside of some of the steel girders.
Pigeon droppings contain ammonia and salt which, when combined with rainwater, can lead to tiny electrochemical reactions that rust the steel. "Over a long term, it might in fact cause structural weaknesses," Neal Langerman, of the American Chemical Society, told Associated Press.
I guess that's possible, given enough pigeons pooping over a long enough period of time, but "death by pigeon poop" seems like an awfully embarrassing way to go.
Apparently, it's also a problem elsewhere:
Workers at the Colorado Department of Transportation spent so much time cleaning pigeon manure off bridges, officials there decided to research new ways to keep the birds away. They're embarking on a two-year research project to keep pigeons and swallows from nesting on their bridges -- pigeons because of their droppings, swallows because the often legally protected birds can get in the way of maintenance.
Patricia Martinek, the agency's environmental research manager, said pigeon dung is more than an eyesore.
"It can be damaging to our structures because it's slightly acidic and it has other compounds in it that can dissolve especially things like concrete," she said.
Pigeon droppings are the focus of the Colorado DOT's research because they tend to build up on structurally important bridge beams.
Who'd-a thunk it?