Convenience stairs, loosely defined as any non-egress stairs, are increasingly popular in retail establishments. Most establishments prefer open convenience stairs as opposed to fully enclosed shaft stairs. Because open convenience stairs pose increased fire hazards, they are required to abide by a strict series of code. Here is how open convenience stairs may be permissible with the most allowances.
Building Code Section 708.2 contains sixteen exceptions for convenience stairs that are not shaft enclosures. The only exception allowing open convenience stairs connecting more than two floors is BC 708.2, exception 2. Exception 2 states that a building may have a non-egress, open convenience stair if the building has an automatic sprinkler system. Exception 2 then breaks down into two options of compliance, one of which must be complied with.
Exception 2.1, perhaps the more appealing of the two options, allows for convenience stairs connecting up to four floors. Use groups B (business) and M (mercantile) are permitted to connect more than four floors. To comply with exception 2.1 a convenience stair must have a floor opening with an area not exceeding twice the hozizontal projected area of the stairway. Also, the floor openings must be protected by a draft curtain and closely spaced sprinklers abiding by NFPA 13 as modified by Appendix Q.
For even larger openings, exception 2.2 requires all openings to have protected, noncombustible, automatic shutters that have a fire-resistance rating of no less than 1.5. When a smoke detector is triggered, these shutters must close, completely shutting off the opening. Exception BC 708.2.2 also has requirements for shutter speed and release characteristics.
Other exceptions in BC 708.2 provide options for connecting just two floors with an open convenience stair.
Source: http://www.decodernyc.com/open-convenience-stair-dob/