Update on yesterday's post re: the Madrid fire
Manel of Hispalibertas commented,

Fausta, lo más probable es que se trate de reflejos obtenidos del edificio de enfrente. Los bomberos han calculado que la temperatura en esa planta estaría entre 300 y 400 grados centígrados (572-752 Fahrenheit), lo que resulta mortal para nadie sin equipo adecuado.
Fausta, the most probably thing is that it was a reflexion from the building across. The firemen have calculated that [by that time] the temperature in that floor would have been between 300-400C (572-752F), which would be lethal to anyone without adequate equipment

I agree with the theory of a darkened building's windows reflecting from across the street. Anyone working in an area where the buildings have mirror-glass windows has seen the effect, which at times can be quite disconcerting.

Additionally, in an office building the greatest hazard is paper. Offices generate huge amounts of paper. Paper combusts at 451F (as Ray Bradbury can tell you), but before it bursts into flames it produces a smoldering smokey fire that would have obscured from outside view any figures standing in a room, and killed anyone in there.