5.03 Intervening Stairs

Reference: 2007 C.B.C. Sections 1020.1 and 707

C.B.C Section 1020.1 Exception # 1 states:  In all occupancies, other than Group H and I occupancies, a stairway is not required to be enclosed when the stairway serves an occupant load of less than 10 and the stairway complies with either Item 1.1 or 1.2. In all cases, the maximum number of connecting open stories shall not exceed two.
1.1. The stairway is open to not more than one story above the story at the level of exit discharge; or
1.2. The stairway is open to not more than one story below the story at the level of exit discharge.

The code is quite clear in this section. An unenclosed intervening stair is only permitted between one adjacent floor. This does not mean that the floors under consideration cannot have access to more than one floor. They can, but must comply with shaft enclosures as outlined in section 707 of the C.B.C.
C.B.C Section 707.2 states that openings through floor/ceiling assembly shall be protected by a shaft enclosure unless if exception 2.1 applies:  Where the area of the floor opening between stories does not exceed twice the horizontal projected area of the escalator or stairway and the opening is protected by a draft curtain and closely spaced sprinklers in accordance with NFPA 13. In other than group B and M, this application is limited to openings that do not connect more than four stories .

NOTE: In a sprinklered building N.F.P.A 13, 2002 edition, Section 8.14.4.1 requires: Where moving stairways, stairways, staircases, or similar floor openings are unenclosed, the floor openings involved will be protected by closely spaced sprinklers in combination with draft stops.

The draft stops shall be located immediately adjacent to the opening, shall be at least 18 in. deep and will be of noncombustible or limited-combustible material that will stay in place before and during sprinkler operation. Sprinklers shall be spaced not more than 6ft. apart and placed 6 to 12 inches from the draft stop on the side away from the opening. Where sprinklers are closer than 6ft., cross baffles shall be provided.
The reason for providing sprinkler and draft stops protection for small vertical openings is that small floor openings tend to behave much the same as a chimney, allowing rapid vertical movement of hot gases from the fire. (This phenomenon does not exist in large openings). Closely spaced sprinklers combined with draft stops are effective to gain control of the fire and prevent activation of sprinklers on the upper levels, by cooling the convective air stream.
Additionally, in buildings with engineered smoke control systems, an analysis of the effects of the opening between floors, prepared by a qualified engineer, must be submitted with the plans. If changes to the smoke control/life safety system are required, those changes must be addressed with the appropriate submittals.