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Experts Tie Pigeon Dung, Bridge Collapse

Posted: 2007-08-23 13:52:09
Filed Under: Nation News
ST. PAUL, Minn. (Aug. 21) - Pounded and strained by heavy traffic and weakened by missing bolts and cracking steel, the failed interstate bridge over the Mississippi River also faced a less obvious enemy: pigeons.

Photo Gallery: Bridge Collapse Probe

Jim Mone, AP

Pigeons gather under the Robert Street bridge Friday in St. Paul, Minn. Investigators are now looking at the impact of pigeon dung on the collapse of the interstate bridge in Minneapolis on Aug. 1.

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Inspectors began documenting the buildup of pigeon dung on the span near downtown Minneapolis two decades ago. Experts say the corrosive guano deposited all over the Interstate 35W span's framework helped the steel beams rust faster.

Although investigators have yet to identify the cause of the bridge's Aug. 1 collapse, which killed at least 13 people and injured about 100, the pigeon problem is one of many factors that dogged the structure.

"There is a coating of pigeon dung on steel with nest and heavy buildup on the inside hollow box sections," inspectors wrote in a 1987-1989 report.

In 1996, screens were installed over openings in the bridge's beams to keep pigeons from nesting there, but that didn't prevent the building of droppings elsewhere.

Pigeon droppings contain ammonia and acids, said chemist Neal Langerman, an officer with the health and safety division of the American Chemical Society. If the dung isn't washed away, it dries out and turns into a concentrated salt. When water gets in and combines with the salt and ammonia, it creates small electrochemical reactions that rust the steel underneath.

"Every time you get a little bit of moisture there, you wind up having a little bit of electrochemistry occurring and you wind up with corrosion," said Langerman. "Over a long term, it might in fact cause structural weaknesses."

Langerman emphasized that he wasn't saying pigeon dung factored into the collapse of the 40-year-old bridge. "Let's let the highway transportation and safety people do their job," he said.

The problem is familiar to bridge inspectors everywhere.

The Colorado Department of Transportation spent so much time cleaning pigeon manure off bridges that it is embarking on a two-year research project looking for ways to keep pigeons away from its spans.

"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," said Patricia Martinek, the agency's environmental research manager.

Pigeon guano isn't just a danger to the bridges.

In the Denver area, the Colorado DOT pays outside environmental specialists to clean bridges wearing full biohazard suits with respirators because of heightened fears about bird flu and other diseases, said Rob Haines, who supervises maintenance there.

Keeping pigeons off bridges usually requires a multi-pronged strategy that can include netting to block holes and surfaces, spikes to keep them from landing, and sometimes poisoning, shooting or trapping the birds, said John Hart, a Grand Rapids, Minn.-based wildlife biologist with the U.S. Department of Agriculture.

The problem is that pigeons are naturally drawn to bridges and tall buildings since they're descended from cliff-dwellers, said Karen Purcell, who heads Project PigeonWatch at the Cornell Lab of Ornithology. Bridges offer shelter from predators and flat surfaces for nesting and roosting.

"It's a nice fit for them," Purcell said.

Meanwhile, the National Transportation Safety Board issued an update on its findings in the collapse Wednesday, saying investigators are looking at whether chemicals used in an automated de-icing system had any corrosive properties.

The state Transportation Department wasn't concerned about the system; in fact, the agency is planning to install a similar system on the replacement bridge, said Khani Sahebjam, a state transportation engineer.

The de-icing elements are inside the concrete deck, Sahebjam said, so he wouldn't expect them to pose a structural problem.

The automated system was triggered by weather conditions and kept the state from having to send crews to spread de-icing chemicals, Sahebjam said.

Copyright 2007 The Associated Press. The information contained in the AP news report may not be published, broadcast, rewritten or otherwise distributed without the prior written authority of The Associated Press. All active hyperlinks have been inserted by AOL.
2007-08-23 09:27:26

Recent Comments

1 - 10 of 620

elizpowell 03:50:10 PM Aug 23 2007

Pigeons!!!!! Please stop Blaming NATURE!!!!!

harleydakotaride 03:49:56 PM Aug 23 2007

I always knew they werent flying straight..........they have been plotting "or should I say ********" there revenge for decades

rkep8600 03:49:48 PM Aug 23 2007

Yah it was Bush's fault...... but CLINTON STARTED IT

Liemslimshady 03:49:35 PM Aug 23 2007

This is part of life when something goes wrong and we try to blame on certain things that could be prevented. I believe what ever we do or try to prevented from happening, the cause of death will come sooner or later

vinnie4health 03:49:28 PM Aug 23 2007

Pigeons my a_ _ . My brother reported that a train bridge was about to fall and was told to keep quite. He went to the newspaper and they had to close off that line on Staten Island.
Bush has sent money every year to repair the bridges and roads, but they decided to put the money in Nature trail, Bike trails etc. every year. So lets blame the pigeons. I wish we had a pigeon................. a stool pigeons that would come out with the truth.

madsarro 03:49:11 PM Aug 23 2007

let michael vick out of jail to organize a pigeon fighting league. the PFL.

ETeeuwe 03:48:55 PM Aug 23 2007

The degradation of the bridges structurals are more likely the result of the acidic urine of the homeless wino's that live under the bridge.

rjhussian 03:48:44 PM Aug 23 2007

Oh, it wasn't faulty or non-existant maintenance. THE PIGEONS did it!!!

golfnpaz 03:48:34 PM Aug 23 2007

madsarro 03:46:06 PM Aug 23 2007

Report This! bush sh*t on the bridge and broke it. it's his fault.


cenasgirllover 03:48:02 PM Aug 23 2007


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