The 40 year old bridge collapsed, killing 13 people and injuring 100 commuters.
Experts say the build-up of pigeon poo ( Guano ), helped the steel beams to rust faster. Pigeon droppings contain ammonia and acids. If the mess is not washed away, it dries out and turns into a concentrated salt. When water gets in and combines with the salt and ammonia, it creates a small electrochemical reaction, that rusts the steel.
Google…. Bridge collapse pigeon poo USA. Here you will see all sorts of reports on the subject.
This now leads to the steel bridges in UK. Locally in Brighton, Sussex, we have two steel bridges, under the railway on Old Shoreham Road. They are infested with pigeons, that have nested/roosted over many years. The pavement below is covered in mess, creating a slip hazard and also posing a health risk. Pigeon droppings carry all sorts of diseases, including, E-Coli, salmonella, Psittacosis, Ornithosis etc. It is therefore paramount that the pavements are kept clean, to prevent the slip hazard and possible infection.
So, how safe are these steel framework bridges that are very old??? There are all sorts of deterrents that can be used, including netting, spikes, post and wire systems, bioacoustics and low volt electrics. It is down to the owners of the bridges to carry out regular maintenance and surveys!