Atrium as an EXIT Stair

[Examiner]

Atriums are not something I do every day.

The building is five stories. type II-A with a sprinkler system throughout. The upper levels have a balcony open to the atrium and they connect to two open stairs at each end of the atrium. The Atrium and its balcony is separated from the offices with a 1-hour rated wall. The rated wall has 20-minute doors. I think the wall, which is the fire barrier to separate the Atrium, is to have 45-minute rated doors. The Atrium balcony also has the location of the restrooms. I read the 2006 Section on Atriums and the Commentary and it appears that you can egress through the Atrium but the open stairs in the Atrium cannot be used as the EXIT. Is that a correct interpretation? Is there anything else you see as needing correction?

 

[AegisFPE]

All atria are not created equal, and there are many facets to them.

Section 404.4 requires smoke control per 909 for 3+ story atria, and 909.4.6 references the egress time as a factor in determining the duration of smoke control system operation. In determining the egress time, I think it would be fair to assume that occupants would use the open stairs if they remained in a tenable environment, such as how Section 909.8.1 describes maintaining the smoke layer 6 feet above the walking surface, in addition to other criteria as identified in a rational analysis (per 909.4).

Depending on the configuration of the atrium, there may be no fire scenario that results in untenable conditions at a stair, or maybe one or both open stairs become blocked. Therefore, in addition to the specific performance-based design for the atrium, prescriptive code compliance with Section 1020 should also be evaluated.

Toilet rooms probably have a low occupant load (though this may not hold true for some assembly spaces) such that if early fire detection is achieved and early occupant notification results, the evacuation of occupants from the toilet rooms through the atrium space could be acceptable prior to untenable conditions on the top balcony level.

A Fire Protection Engineer experienced in atrium design should be able to address the applicable criteria for this project on behalf of the design team. You may find some atrium checklists online by looking at sites of other jurisdictions where atria may be more prevalent to see if there are any other apparent discrepancies.

 

[texasbo]

Open stairs in the atria may be used as exit access; in fact, 404.8 specifically addresses such arrangements by limiting exit access travel distance (except at the lowest level) to 200 feet. I have seen few atria that did not include open stairs used as exit access.

As Aegis said, proper design of smoke control is critical.

 

[RJJ]

So if exist travel distance is limited to 200'. The atria could only be used for the floor/floors that have direct access that do not exceed the 200' ?

 

[texasbo]

The portion of the travel distance within the atrium cannot exceed 200'.