workers underneath the six-storey structure fled for their lives after the fifth , fourth and third floors crashed down on to the rest of the building - sending a huge cloud of dust into the air .
the terrifying incident is just yards from where an underground cable fire ripped through holborn on april 1 bringing parts of central london to a standstill and costing local firms £ 40million .
he was the only casualty among 30 workers on site at the time .