建築學問題 新樓

That's is called buffer floor or refuge floor
The purpose is to isolate the floor area to avoid further spread of fire.

Every building should be divided into compartments by walls and floors to inhibit the spread of fire. Compartment walls, compartment floors, separations and lobbies should be constructed such as all joints are completed filled with non-combustible material to prevent the passage of smoke or flame. No compartment should exceed the following volume:
max compartment volume = 7000m3 where the compartment floor is above basement level but not exceeding 30m in height measured in accordance with Building (Planning) Regulation 23(1)
max compartment volume = 3500m3 where the compartment floor is above basement level or exceeding 30m in height measured in accordance with Building (Planning) Regulation 23(1)

2009-06-29 11:13:13 補充：
FIRE RESISTING CONSTRUCTION 1996
Part II, cl. 5
http://www.bd.gov.hk/english/documents/code/e_frc.htm

2009-06-29 11:15:51 補充：
THE PROVISION OF MEANS OF ESCAPE IN CASE OF FIRE 1996
Part II, cl. 21
http://www.bd.gov.hk/english/documents/code/moe_part2.pdf