Deibid has answered for me
Offices were empty because in saturday nights only security personel work. It seems extinction and detection systems failed.
However, if this had happened in working days, the fire would have been detected very quickly, and it would probably have been extinguished inmediately. Obviously moving hundreds of persons to evacuate a building is always risky, so we don't know what would have happened.
Anyway, I still think this time emergency teams and authorities have done their job well.
Fernando