At the time of construction, and indeed for many years afterwards, it was considered that the main cables of a suspension bridge would last for the lifetime of the structure. However, by the 1990s, a number of major American suspension bridges were showing signs of deterioration in their main cables. Alerted by the American experience, the main cables of the Forth Bridge and then the Severn Bridge were carefully examined. These inspections revealed that some corrosion of the wires was taking place.
The cables have now been sealed in a membrane and a system has been installed to continually force dry air into the cables to halt further corrosion. Subsequent inspections have confirmed that these remedial measures are working satisfactorily. At the time of writing, the situation appears to have stabilised and, although the condition of the cables is considered unlikely to deteriorate further, periodic and targeted examinations are scheduled at approximately five year intervals in the future.