The sixth floor of the Ivory Tower is joined to the seventh by four cast spans rather than by the stair. Ivory built them for trolley traffic between the holding cells plus the records room, so each one carries a rated load printed along the rail.
Yenna Rook had written the prisoner route across three of those four spans at the seventh hour. She wrote it that way to keep eleven people off the lower stair, which is the only part of the plan anybody has praised since.
A core fire burns inward, so a building does not shed load in the order any survey expects. The spans went before the floors did, from the tenth hour and nineteen minutes onward, in a sequence Ivory's own structural file had ranked last.
[Structure: spans two and four gone.]
The arithmetic on that floor changed twice inside four minutes, without anybody arriving to help her change it.
