In 2000 NFPA, section 8.2.5.5 states that unenclosed floor openings forming a communicating space between floors is permitted if it meets the following requirements:
1) Doesn’t connect more than 3 stories
2) Lowest or next to lowest story is street floor
3) Entire floor area of the communicating space is open and unobstructed such that a fire in any part of the space will be readily obvious
4) If sprinklered, communicating space is separated from remainder of building by smoke barrier
5) Space has ordinary hazard and sprinklered
6) Egress capacity is sufficient to provide for all occupants to simultaneously egress the communicating space
7) Occupants not in communicating space has access to no less than one exit without entering communicating space