Workers make their way up the structure known as 'the arch', a 25,000 tonne steel structure that will be 108 metres high, 162 metres long and span 257 metres. Once complete (est. 2017) it will cover the sarcophagus, a steel and concrete shield originally built, over the damaged reactor No. 4, in the aftermath of the 1986 nuclear explosion. As well as covering the damaged reactor the 'arch' will also be used to store contaminated waste from the site. It has a double membrane with an 11 metre gap and it is within this void that the workers are walking.