Apparently, there was some kind of mechanical venting mechanism, presumably meant to whisk away smoke filled air, which was creating a low-pressure area in the lobby. (I don't know enough about fire codes to know if the implied supply of fresh air to a fire is consequential either.) The amount of force needed to open the doors was tremendous. Eventually the back doors (a floor down) were open, although I'm not sure how, or how they were kept from slamming shut.
"New, from the Towering Inferno Construction Company! It's LobbyVacuuSeal technology! Why bother with pesky layoffs and expensive severance packages, when you have LobbyVacuuSeal?"
Quote of the Moment
[The Monrobot Mark XI all-purpose computer] solves many of the technical problems that we in the computer game have been bucking for years [...] Mark XI weighs only three hundred and seventy-five pounds and is therefore completely portable.