If you are going to take something apart, it helps to know how it was put together in the first place.

And, when you are talking about a site as complex as Sellafield, you really need to know where to find the right information when you need it.

However, on a site covering six square kilometres, containing hundreds of facilities and with a history stretching back more than half a century, keeping track of the records is a massive logistical challenge in itself.

Since 2005, global records management firm Iron Mountain has been responsible for keeping Sellafield’s mass of files safe, as well as digitising them and developing processes for Sellafield Ltd to access the information it needs from day to day.

"What's involved in it is looking after boxes and boxes and boxes of material," says Phil Shepley, vice-president and general manager, Northern Europe for Iron Mountain.

"You can imagine a site like Sellafield has got this huge legacy of different types of records, drawings and evidence.”

Headquartered in Boston, Iron Mountain operates in 52 countries carrying out similar work for clients in a wide range of sectors from large, long-term infrastructure projects to legal firms, financial institutions, retailers and the pharmaceuticals industry.

It employs 1500 people in the UK and, in June, moved from the Sellafield site to new offices at Hensingham Business Park, near Whitehaven, increasing its workforce there from 36 to 61.

"Increasingly, with all the work going on at Sellafield, the records are now being increasingly used and opened up again," says Phil.

"Effectively they are reverse building the site again. In order to dismantle it as safely as they can, they need to understand how it was put together and the legacy is buried in a lot of the records."

Iron Mountain’s work includes photographing documents and then putting them into a database the relevant people can access, as well as digitising them to order. This is important on a practical level but also to ensure Sellafield can fulfil its various regulatory requirements.

Although, understandably, the exact whereabouts of its warehouses are kept confidential, it has 56 sites across the UK with the biggest containing five million boxes.

"We've got some very, very large warehouses and we are able to keep those nice and secure," says Phil.

"That's our business, whether it's 10,000 boxes or a million boxes."

Although it may sound simple, if laborious, to photograph tens of thousands of documents, their nature means staff have to be carefully vetted with a rigorous quality control process in place to ensure the images are an accurate representation of the original and the records are kept in a precise and ordered way.

"It needs to be 100 per cent right when people are going to rely on it in a very sensitive situation,” says Phil.

Over the years Sellafield has also kept records on everything from paper to magnetic tape, to VHS, Betamax and floppy discs - all of which Iron Mountain specialises in converting into modern digital records.

At the same time, it has to constantly adapt to changes in technology and digital record keeping and second guess how people may access the information over the next century.

"Just because it's a PDF today, when you open a computer in 50 years' time - and who knows if you'll even be using a computer in 50 years time - it might not understand how to use that file," says Phil.

"How do you keep the data current? That's a really interesting challenge.”

No matter how the technology changes, he says the key to overcoming the challenge is having a long-term relationship with the site so the two organisations can keep on evolving together even though the work may well involve two or three generations of employees.

"When you can join data up into a continuous stream from paper through to tape ingestion and through to modern digital survey forms, but actually it's the same type of data but just from a different starting point spanning decades it really helps paint an accurate picture people can rely on.”