Bridge collapsed because ... bird droppings

Overload traffic, steel rust and the lost points caused the bridge across the Mississippi River in the United States to break. But now a new culprit has been found: pigeons.

Experts said piles of bird waste scattered across the interconnected federal bridge made the iron bars rust faster. Although investigators still have no official conclusions about the cause of the collapse on August 1, killing 13 people and injuring 100 people, the pigeon is one of many factors that damage the structure. bridge structure.

(Photo: Acc.umu.se) "There was a layer of pigeons covered in iron and bird nests heavy in hollow boxes of the bridge," the investigators wrote in the 1987-1989 report. . In 1996, screens were mounted on barge bars to prevent pigeons from nesting there, but it still did not prevent bird droppings scattered everywhere.

Bird droppings contain ammonia and acid. If not washed, it will dry and solidify into salt. When the rain falls, combined with salt and ammonia, it will create an electrochemical reaction that rusts the steel below.

"Every time there is a layer of mucus there, there is a chemical reaction that happens and gradually leads to erosion and decomposition. Finally over a long period of time it makes the work weak," said Neal Langerman. said the health and security officer at the American Chemical Society.

This problem occurs in many bridges elsewhere. However, chasing the bird out of the bridge requires a complex strategy, including putting a net to block holes in the bridge, attaching spikes to prevent them from landing, and sometimes even shooting or trapping birds.

The problem is that pigeons love bridges and high-rise buildings because their ancestors are cliffs on the precipice, Karen Purcell, Cornell Ornithology's PigeonWatch project leader, said. know. The bridge is a good shelter to avoid enemies and has an ideal surface for nesting and overnight.

MT