UNDER THE MICROSCOPE: Richard Hampshire, of Wharfedale Environmental Services, clearance tests an air sample taken from inside a protective tent housing a locomotive Picture: Frank Dwyer

At the time it probably seemed like a good idea for Britain's train manufacturers.

Stop the heat getting out of their steam engine boilers - and the cold getting in - by wrapping them in asbestos blankets. It was a sound insulation material.

It was also used in the manufacture of railway carriages in York - and, as many former York Carriageworks employees have found to their cost, inhaling asbestos dust can have very serious consequences.

Today, dozens of Britain's greatest steam locos - from the Mallard to the Duchess of Hamilton - are proudly on display at the National Railway Museum (NRM) in York.

But how do museum staff prevent any asbestos risk to the hundreds of thousands of visitors who wander round the complex in Leeman Road each year?

Head of museum Andrew Scott says that the vast majority of engines have already had their asbestos lagging removed during refurbishment programmes over the past three decades.

A series of audits of all the rolling stock have pinpointed where the material is still present, and he says only seven locos remain lagged with asbestos. The museum liaises closely with the Health and Safety Executive (HSE) on what to do with them - and in many ways the best thing to do is... nothing. Provided the material is hidden away and undisturbed, it presents no danger whatsoever. Only when dust is raised does it present a deadly threat.

All over Britain, in schools, homes and offices where asbestos was used during construction, this is how the material is treated.

But at the NRM, conservation assistants who clean the locomotives are informed of the correct procedures to follow if they spot anything untoward.

Mr Scott says that, in a couple of instances where asbestos was spotted leaking from cracks at the edge of an engine, immediate steps were taken to seal off the cracks so that there was no danger of dust being raised.

But in a long-term bid to ensure that, within about seven years, all vehicles are free of the material, the museum has a rolling programme, approved by the HSE, of stripping one loco every year under tightly controlled conditions.

One loco, the Boxhill, has been stripped over the past week inside a sort of sealed tent created alongside the museum building, in an area barred to visitors. Specialist licensed contractors wearing special masks and clothing have entered through an air lock into the sealed atmosphere to carry out the stripping work.

The asbestos has to then be put into large, approved bags before being taken away to a landfill tip to be buried underground by the contractors.

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.