The 2011/12 inspection will give further indicators that will increase data but some degree of uncertainty concerning the magnitude of future strength loss is likely to remain, he said in a report to the Forth Estuary Transport Authority's board.
His report comes as the bridge authority prepares to switch on the final section of the dehumidification system designed to dry out the cables and prevent further corrosion. This project is set to be completed on schedule by contractor C Spencer, with drying-out expected to have begun on both main cables by the end of the month.
The report notes that dehumidification of the west cable, which began in March 2008, is producing the expected slow and steady fall in the relative humidity within the cable. However, Colford cautions that there is no guarantee this will prevent further loss of strength.
The report also provides an update on each of the projects listed in the bridge authority's 15-year programme of strengthening and improvement works. Other notable projects include the replacement of approach viaduct bearings, currently out to tender.
