Critique of Milstein Hall: Fire Safety

Jonathan Ochshorn

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Fire safety contents: 1. introduction | 2. floor area limit | 3. fire barrier | 4. crit room egress | 5. Sibley egress | 6. mezzanine | 7. Rand occupancy | 8. conclusions | 9. summary and appeal | 10. variance application

6. Questionable mezzanine designation

Milstein Hall at Cornell contains what appear to be three floors, all interconnected with an opening through which passes an unenclosed egress stair (Figure 1).1 Building codes are designed to limit the spread of fires from one floor to another floor by requiring that continuous horizontal assemblies separate each floor—this is one of the most elemental forms of compartmentation used to control the spread of fire within a building. Where openings need to be made between floors—for example, to create stairs or elevators, or to allow vertical ducts—building codes stipulate that shafts be constructed around such floor penetrations to preserve the integrity of the building's compartmentation. This, of course, is an enormous constraint on the implementation of architectural concepts that would create interpenetrating or continuous spaces that extend beyond the limits of a single floor. Yet we are all aware of precisely such multi-story rooms or areas: open stairs or escalators between floors, balconies overlooking larger rooms, atriums, and so on.

view of so-called mezzanine from Milstein crit space

Figure 1. Milstein Hall's interconnected spaces—crit space below, lobby/bridge in the middle, and studios above—can all be seen in this image. Photo by Jonathan Ochshorn, 2011.

These exceptions to the fundamental rule requiring compartmentation of floors are precisely that: they are exceptions that have been embedded in building codes where other means to preserve the safety of multi-story spaces have been deemed adequate.2 These exceptions appear in the Code section dealing with "shaft enclosures" (Section 707 in the 2002 Building Code of NYS), and list numerous instances where shaft enclosures are not required. The most important of these exceptions are as follows:

  1. Openings without shaft enclosures can be made connecting no more than four floors in an individual residence.

  2. Openings without shaft enclosures can be made in sprinklered buildings for stairs or escalators that are not part of a means of egress (various requirements govern the implementation of such openings, which can connect an unlimited number of stories in Occupancy Groups B or M, but more than four floors in other Occupancy Groups).

  3. Openings without shaft enclosures can connect any two stories if the opening is not used as part of a means of egress (and is not open to a corridor in Occupancy Group I or R, or open to any corridor on a nonsprinklered floor, or used in Occupancy Group I-2 or I-3, or not separated from some other opening serving another floor).

  4. Openings without shaft enclosures are also permitted for certain egress stairways connecting no more than two floors, where such openings are not open to any other floors.

  5. Openings without shaft enclosures can be made in spaces defined as atriums. There is a whole section of the Code specifying the requirements for atriums (Section 404); these requirements include serious smoke control measures, and fire-rated separation from most spaces outside the atrium unless a maximum of three such non-separated floors are included in the smoke control calculations for the atrium itself.

Using these exceptions, architects can carve out space within their buildings transcending the limits of floor-to-floor compartmentation. However, such spatial options are not unlimited, and they must conform to the specified requirements. I had assumed that Milstein Hall, having three stories interconnected by a spatially-complex opening that allows fire and smoke to move throughout all three interconnected floors, would be in violation of these fundamental requirements: Examining the five major exceptions listed above, it appears that only an atrium design would permit this spatial configuration (three interconnected stories containing a means of egress). The first exception is only for residences; the second is only for stairs that are not part of a means of egress; the third only permits two stories to be connected and only when no means of egress is not placed within the opening; and the fourth—not even found in the applicable 2002 Building Code of NYS—is in any case only for openings connecting no more than two stories.

Milstein Hall was not designed as an atrium, so it was puzzling to me how such an interconnected opening could be allowed. I asked Gary Wilhelm, the Project Director for Milstein Hall, how such an interconnected opening was possible, since the interconnected spaces were clearly not designed as an atrium. He explained that, contrary to appearances, the building only has two stories with no basement: what appears as the basement is actually the first floor; what appears as the first floor is actually a mezzanine; and only the second floor is really what it appears to be—the second floor. Mezzanines must be no more than one-third the floor area of the room or space they are in, and the first-floor lobby of Milstein did appear to be no bigger than one-third the floor area of the crit space under the dome to which it is connected.

However, while the interconnected openings in Milstein Hall appear at first glance to meet the "letter" of the Building Code, they may well be noncompliant.

schematic sections through Milstein's mezzanine

Figure 2. Schematic sections through Milstein Hall: Case I, with wall "A" forming a large lower level, permits a mezzanine between the two floors; Case II, with a smaller lower level space, cannot support such a mezzanine.

Comparing Case I and Case II in Figure 2, one can see that the entire rationale for allowing an unenclosed egress stair from the second floor to the mezzanine lobby depends on the relative area of the space defined by what I have schematically called wall "A." If wall "A" is placed in such a way that the area of the space it forms is at least three times bigger than that of the lobby (Case I), then the lobby can be counted as a mezzanine, and the egress stair is then technically within an unenclosed opening connecting only two stories, thereby conforming with exception 8 or exception 9 in Section 1005.3.2 of the 2002 New York State Building Code.

However, if wall "A" is moved so that the area of the space it forms is less than three times the size of the lobby (case II), then the lobby cannot be called a mezzanine. It then becomes the first floor, and the same openings and egress stair become noncompliant.

This seems entirely irrational, since Case II, with less floor area to house combustible products and a smaller number of occupants than Case I, is nevertheless noncompliant, whereas Case I, with a larger area and therefore more occupants and potentially combustible products, would be deemed compliant.

It seems probable either that the writers of the Code never anticipated that their definition of mezzanine would be exploited in this way, or that other aspects of the mezzanine definition make this geometry noncompliant.

The definition of mezzanine, found in Section 502 of the 2002 Code, states that it must have "a floor area of not more than one-third of the area of the room or space in which the level or levels are located." The key word here is "in." The mezzanine must be "in" the room or space, not outside the room or space with an opening that connects them. Now, one might debate what exactly the meaning of the word "in" is (by analogy to Bill Clinton insisting that a proper interpretation of his testimony concerning sexual relations with a White House intern "depends on what the meaning of the word 'is' is").3 As can be seen in Figure 3, common sense would suggest that the lobby is not "in" the dome. Both the section (Figure 3a) and the composite photo (Figure 3b) show clearly that the concrete structure of the dome creates a distinct "room" or "space" and that the lobby—pictured through the hole in the dome visible at the left of Figure 3b—is completely outside that space.

section and composite photo of Milstein Hall dome and lobby

Figure 3. Both (a) the section through the crit space, under the dome, and the lobby of Milstein Hall, and (b) a composite photo of the crit space, show clearly that the lobby ("mezzanine") is structurally and spatially outside the crit space. Photo by Jonathan Ochshorn, 2011.

It is possible (along the lines advocated by Clinton) to define "in" topologically rather than by recourse to "common sense"; in that case the lobby can indeed be tested as a mezzanine "within" the dome "crit space." In other words, we could draw a continuous contour line through the opening connecting the two spaces and call the resultant figure a single space. But the Code is fairly careful about the prepositions it deploys. If the intent were to allow a mezzanine to have any interconnected relationship to a room or space, other words or phrases could have been chosen instead of "in" or "within." The Code does not describe a mezzanine as being "next to" or "adjacent to" or "connected to" some other room or space: it specifically says that a mezzanine must be "within" a room.

Still, this is admittedly ambiguous. The commentary to the 2009 IBC doesn't really help: "So as not to contribute significantly to a building's inherent fire hazard, a mezzanine is restricted to a maximum of one-third of the area of the room with which it shares a common atmosphere." Here, the phrase "common atmosphere" has two purposes: first, it signals that the mezzanine must be somehow contiguous with the space it is in; second, it excludes any "enclosed portion of a room" in computing "the floor area of the room in which the mezzanine is located." Having a "common atmosphere" appears therefore to be a necessary, but not sufficient condition. The mezzanine must also be "in" the room or space, which again brings us back to the question of what "in" is.

But this much is true: if the lobby space cannot be called a mezzanine, then it counts as a story. In that case, the interconnected openings are noncompliant, as they meet none of the exceptions for shaft enclosures outlined in Section 707.2 of the 2002 Code. And even if the lobby is now granted the status of mezzanine, the crit space under the dome becomes locked into its current geometry forever: it can never be reconfigured, for example, into a series of smaller rooms, since the lobby would then exceed its maximum floor area qua mezzanine and would revert back to being a separate story. The opening connecting what would now be three interconnected stories would be noncompliant.

However, this is precisely what occurred immediately after Milstein Hall was occupied: permanent movable partitions were fabricated and installed in the crit space which had the effect of creating separate and smaller rooms within what was a single space. This immediately calls into question the designation of the ground-floor lobby as a mezzanine (Figure 4). The lobby's floor area is not less than one third the area of smaller spaces that can be configured using the movable partitions (exactly what room the lobby is "in" when the movable partitions are deployed is difficult to determine), so the lobby appears to no longer satisfy the criteria for designation as a mezzanine. In that case, the lobby becomes a "story" rather than a mezzanine, and therefore at least two aspects of the building become noncompliant: a) unprotected floor openings now connect three, rather than two, stories in Milstein Hall; and b) required men's and women's rooms become two stories, rather than a maximum of one story, distant from the main studio floor level.

plans of crit space and lobby, Milstein Hall

Figure 4. Noncompliant mezzanine: Area of ground floor lobby-bridge (left) exceeds one-third the area of crit room space at lower level (right).

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Fire safety contents: 1. introduction | 2. floor area limit | 3. fire barrier | 4. crit room egress | 5. Sibley egress | 6. mezzanine | 7. Rand occupancy | 8. conclusions | 9. summary and appeal

Notes

1 Much of the material on Milstein Hall's questionable mezzanine designation is taken from two of my blog posts from Oct. 10 and Oct, 13, 2011, which can be found here and here (accessed July 23, 2012).

2 For more information on creating "holes" in floors, see: Jonathan Ochshorn, "How are holes (vertical openings) made in floors (per IBC 2009)?", updated Sept. 27, 2011, online here (accessed July 23, 2012).

3 Timothy Noah, "Bill Clinton and the Meaning of 'Is,'" in Slate.com (accessed July 23, 2012).