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Experts Tie Pigeon Dung, Bridge Collapse

By MARTIGA LOHN,
AP
Posted: 2007-08-23 15:54:45
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.

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 2008 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
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Recent Comments

1 - 10 of 1744
1744 comments

kcaron1504 10:10:31 AM Aug 25 2007

Cleaning anything off the underside of a bridge that spans a body of water is extremely difficult and expensive as nothing can be allowed to drop into the water, the entire work area must be completely shrouded. EPA

edwardretusaf 01:54:00 PM Aug 24 2007

Open a skeet shooting range on the bridge. Only use real pigeons and not clay birdies. Should make rush hour more interesting.

edwardretusaf 01:51:00 PM Aug 24 2007

Let's spend tens of millions of dollars to study the effects of bird sht not only pigeons but every other bird that nest or lands on that bride. Chalk it up to the state not maintaining or workers not doing what they are paid to do. That what's they should study

dzoeblu1 01:34:35 PM Aug 24 2007

TYPICAL, BLAME IT ON PIDGEON SH IT - THE BLAME SHOULD FALL ON THE STUPID BAST ARDS WHO WERE SUPPOSE TO DO THE MAINTENCE, CLEANING AND INSPECTION OF THE BRIDGE AND APPARENTLY SAID SCREW IT AND DIDNT DO THEIR JOB THAT THEY GET PAID TO DO

Silhearts 01:05:50 PM Aug 24 2007

Peter and Penelope Pigeon could not find section 8 housing so they took up living under the expressway bridge in Minneapolis as a last resort. They had a nice view of the cityscape and the river. They felt that the frequent traffic although noisy, provided the great urban life style they always wanted. When the bridge collapsed Peter was arrested and pointed out in a line up by some old senile senior citizen. Peter admitted his address was Interstate 35 West. The senior citizen said this was the grey pigeon who always was evading the government workers who screened areas under the bridge. Because the government provided the screening and the labor the Pigeons felt their occupancy was a welfare program for their benefit. The Pigeon?s didn?t know they weren?t wanted in that neighborhood. Folks also said Peter?s feather color (medium grey) meant he was an illegal alien. Actually his father was born under a bridge over the Chicago River where he was fed in the park by old seni

Drewbuddie8 11:58:46 AM Aug 24 2007

the bridge had an automatic deicing system? see what salt will do to your car?

sprylynnx 11:53:33 AM Aug 24 2007

Why is everyone so quick to pass judgment without having all the facts? This story did not blame pigeons alone, it is merely taking into account what IMPACT pigeon poop -may have had_ on the structure to see IF it was one of the causes of which there are are most likely many!

And yes, pigeon poop is corrosive -- just take a good look at your stainless steel barbeque grill if you live in an area that has a lot of pigeons!!

stocksshocks 09:57:03 AM Aug 24 2007

Sounds like a load of crap to me, literally and figuratively.

luamor846 09:02:19 AM Aug 24 2007

So sad to see the state trying to blame the pigeon poop on the collapse of this bridge. This really upsets me..where were all the tax dollars of the State of Minnesota going? There is no way that there is 20 years worth of pigeon poop still on that bridge..how about cleaning it? What a sorry excuse for the explanation of a bridge collapse which may have never happened if the State of Minnesota was doing it's job. Now, we have lives lost that could have ultimately been prevented just by the monthly cleaning of a bridge...we have to do better!

weathergirl719 02:45:46 AM Aug 24 2007

Nope its definately time to find another excuse cause the american public is definately not falling for that one. Hey do you really think we are that stupid????I mean really?!? COME ON!!!

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