This is taken from the London Evening Standard:

Alarm as BBC faces eviction

THE Luftwaffe couldn’t drive the BBC out of Broadcasting House but it seems health and safety concerns can. Hundreds of staff will have to go into temporary accommodation this autumn while essential tests are carried out on the new Broadcasting House, where rebuilding work is coming to an end.

Power supplies, fire alarms, heating and cooling, lifts and other “life systems” must be tested for 10 weeks from September 14 and include a “high risk” period in November when all occupants must vacate the premises.

Which will be an unbelievably costly exercise. Why could the tests not take place with people in situ? Because apparently fire alarms will sound continually.

I imagine this is a requirement of all 'new' builds the only difference here is that unlike most other BBC sites the migration from the old to the new will not happen. In other cases all the tests will have been carried out prior to the move to new premises.