DRY air was blown into the full length of the Forth Road Bridge's corroded main cables for the first time yesterday after installation of a new system to reduce humidity was completed. However, officials have told The Scotsman that even if the £11 million project halts corrosion as expected, the bridge may yet suffer a further loss of strength if already-corroded wires snap.

They also said a planned inspection to check on progress might be delayed from 2011-12 should humidity inside the 2ft cables fall slower than forecast. Corrosion of the cables' 11,618 individual steel wires led to initial fears it would force a lorry ban on the bridge by 2013. Further checks on the cables pushed that date back to around 2020, as The Scotsman revealed last year.

THE threat to the Forth road bridge from corrosion is receding, new checks on its main cables are expected to show. The news would further postpone potential curbs on traffic – but also call into question the need for a new bridge costing as much as £1.6 billion.

Bridge chiefs told The Scotsman yesterday that dry air being pumped into the cables to halt the corrosion is coming out dry, indicating the process is stabilising the deterioration. They are now increasingly confident an impending inspection of the cables which hold up the bridge will show no further deterioration. That would stave off traffic restrictions such as a lorry ban, which it was thought could be required as early as 2017. The threat prompted ministers to approve a new bridge beside the Queensferry crossing, which is due to be completed by the end of 2016 in case that worst-case scenario came to pass.

The inspection – the first since 2008 – is due to start in April, with results expected in November. It is also the first check since dehumidification work – blowing dry air into the cables – started in 2009. Inspections are also under way on the main cables’ anchorages at either end of the bridge – the last part of the cables still to be checked.

COSTLY and difficult repairs to a key part of the Forth Road Bridge appear to have been averted after an inspection found the main cable’s anchorages to be “sound”, The Scotsman has learned. It is understood that the concrete plugs which anchor the cable underground were not found to have significant corrosion – unlike cable sections elsewhere on the bridge.

The findings, which are due to be reported to the bridge authority next month, would prevent a further major headache for officials, who last week revealed corrosion of the main part of the cable had been slowed by blowing dry air through it, or “de-humidification”. A former convener of the Forth Estuary Transport Authority (Feta), which runs the bridge, said serious corrosion of the anchorages would have required the cable to be replaced.