By Lars Niven

OFFICIALS AT the Forth Road Bridge are confident the de-humidification system will solve the corrosion problem in the structure’s main support cables.

Bridgemaster Barry Colford said they would not have spent millions of pounds installing the system if they did not believe it would work, but he warned there were no guarantees.

Engineers plan to halt or slow the corrosion by pumping warm air through the cables in an attempt to dry the steel strands.

They are examining a section of one of the cables to update the findings of a study carried out in 2004, which found some of the steel strands had snapped and that many were badly corroded.

Officials at the Forth Estuary Transport Authority (FETA), which maintains the bridge, believe the structure may have lost as much as 8% of its original strength as a result.

They need to update those findings, and over the past few months consultants have opened up a section of the east cable to take a look.

Mr Colford told The Courier he was confident the dehumidifiers will work.

He said, “We wouldn’t be putting this much money into it if we weren’t.

“It is the best chance we have of stopping the corrosion, and we felt that—given the experience of the Japanese and Scandinavian bridges—this was the only option open to us.

“Obviously we wouldn’t spend that amount of money if we didn’t have some confidence, but there are no guarantees.”

Tony Martin, chairman of FETA management board, added, “They have only ever put de- humidification on a bridge when it’s been completely new, and we know it works for that—you don’t get corrosion.

“It’s never been put on one that has already got corrosion on it.”

Mr Colford added, “We know that if you put a piece of galvanised steel, galvanised wire, in an atmosphere of 40% relative humidity, then that piece of steel does not corrode.

“But—and it is a big but— no one has carried out a thorough inspection of a deteriorating cable that’s been dehumidified and then gone in to see whether it actually works.

“The Japanese have been de-humidifying (bridges) for the last 10 years, and now specify de- humidification in all their main cables.”

He continued, “The desktop analysis has told us that it should work.

“We are pretty confident that it will, so we do think this is the answer.”

Mr Colford and his team hope to have a clearer picture of what is going on inside the main cables within a matter of weeks.

He said, “We’ll get an evaluation of the strength of the cable, but it has to be remembered this is only a snapshot.

“We are looking at a very small portion of the cable, but it will be the best evaluation that we can carry out to determine what the strength is before we start dehumidifying.

“Then, once dehumidification has been running for about 18 months, we’ll take another evaluation of the strength and do the same thing to see whether or not we have managed to halt —or at least significantly reduce —the deterioration of the cable.”

Mr Colford said the findings could be ready for FETA’s board meeting in April.