The cover on the rebar is generally 50mm but I have seen columns where the cover has been reduced to 35mm. I have seen normal pcc units rejected by Network Rail due to too little rebar cover, and it resulted in a major contract delay. I finished up very experienced in use of a cover meter.In these columns the rebar may have had sufficient cover to protect it until the concrete broke away , or it the heat may have effect the rebar and blow the concrete away.
While the above comments are looking at the columns another pres released photo seems to indicate very little damage to the decking on another floor although the underside must have been effect by the flames
While my experience was in construction I have seen ,many years ago, some work for a chemical plant testing the steel members ,with intumesant paint , surrounding it in fire resistant boarding ,different thicknesses, and other means to reduce the risk of serious fire damage. They also considered the wind effect of the building design to see if they could reduce the risk of fire spreading. Looking now it seems that wind effect we often feel inside an open multi story car park would assist in the fire spreading rapidly.