After a century of service to sailors and locals, the first class optic lens of the Gibb's Hill Lighthouse is being replaced.

The lighthouse, which is one of the oldest in the Western Hemisphere, will be re-lit on May 1 ? the anniversary of the day it was first opened in 1846.

Marine and Ports assistant director Mike Dolding said it was the first time that the lens, called a first class optic, had been removed since 1904 when it was installed.

"When it was installed it was cutting edge design, but the problem is not with the lens, it is with the balls that ran on mercury," he said.

Due to the complicated nature of the procedure, a team of specialists had to be flown to the Island to attack the task of changing the lens.

"The mercury was removed and it will be replaced with a mechanical track, which the lens revolves around," said Mr. Dolding.

"The old mercury system required very little maintenance, but the mercury is highly toxic."

The decision to replace the mercury driven revolver with the mechanical track was made after Hurricane Fabian, when about two gallons of the mercury spilled, he added.

When there are high winds, the lighthouse "sways like a reed", he said. The mercury needed to be replaced and the insurance company decided it was a good idea to replace the antiquated system at the same time.

"The existing optic lens has to be removed," said Mr. Dolding.

But the team on the Island is up to the job. James Woodward, owner of The Lighthouse Consultant company, said almost all lighthouses in the United States have had the old style mercury driven bearings removed and replaced with the mechanical device.

"The mercury device was designed by a Frenchman, Augustine Fresnal, in the 1820s, but it was not used until the 1890s," said Mr. Woodward, who did similar work for the US Coast Guard.

"In 1973, men working on lighthouses in the US had mercury poisoning and the Government decided to replace all of them.

"Trinity House, (a lighthouse maintenance team) in the UK, continue to use the mercury."

Mr. Woodward said not only is there a risk that the mercury will spill out but the heavy metal clean-up is also very expensive.

"In the US, the clean up cost for a quart of mercury is $180,000 ? it costs too much, it's not worth it, "he said.

Mr. Woodward, a lampist, said that he and his team had a combined experience of over 60 years.

"Frank Blaha also worked in the Coast Guard for 20 years and he had experience with working with lens," he said.

"Jim Dunlap is a retired Coast Guard officer, who specialised in the Aid to Navigation department, and completely pulled down the lens in the Ponce Inlet lighthouse and rebuilt it.

"Kurt Fosburg assisted me with the removal and rebuilding of a lens in Marquette, Michigan.

"It is a specialised technique and he (Kurt) showed natural ability has been working with me ever since."

Mr. Woodward will remove the 25 pieces of the lens and then they will be fit back to the mechanical tracking system.