As the two previous articles in this series presented, the means-of-egress system (exit access, exit and exit discharge) and its means-of-egress components (doors, corridors, stairs and elevators) combine to establish a path through “safe” evacuation zones from any occupied place in a building to the safety of a public way. Additionally, to help protect all occupants during a fire and to limit the spread of fire and smoke, the other parts of the building (structural system, exterior walls, floor-ceiling assemblies, roof assemblies, etc.) must be addressed as well. Coupled with fire suppression, it’s the fire- and smoke-resistance features that actually make these safe zones safe.
The 2015 International Building Code’s section 701.1 summarizes a basic understanding of this fire- and/or smoke-resistance goal: “[T]he materials, systems and assemblies used for structural fire resistance and fire-resistance-rated construction separation of adjacent spaces [are imposed] to safeguard against the spread of fire and smoke within a building and the spread of fire to or from buildings.”
The IBC has established parameters that determine the requirements for fire- and/or smoke-resistance ratings of construction, penetrations, joint systems and opening protectives. Regarding the requirements for fire-resistance ratings of penetrations (IBC 714), the article in this series titled “Penetration Firestopping” covered this wide-ranging topic in depth, so repeating that information here is unnecessary. The requirements for fire-resistance ratings of joint systems (IBC 715) and opening protectives (IBC 716) are such extensive topics that they will be addressed in their own future articles.
But to address the requirements for fire-resistance ratings of construction (building elements, components or assemblies), the IBC established that its parameters are determined in one of three ways: those that pass the tests defined in the American Standards for Testing and Materials’ ASTM E119, those that pass the tests defined in Underwriter Laboratories’ UL 263 and those that comply with the IBC’s Section 703.3. This article focuses on fire-resistance ratings of construction and presents them in two segments: testing methods and construction requirements.
Fire-Resistance Testing Methods
As noted above, the three basic testing methods for determining the construction’s fire-resistance ratings are ASTM E119, UL 263 and IBC 703.3. These methods, formulated by three independent agencies (ASTM, UL and IBC), are further defined as follows:
- ASTM E119—Standard Test Methods for Fire Tests of Building Construction and Materials: This fire test was developed for evaluating walls, floors and roofs under a fire by measuring the duration and transmission of heat and hot gases through the test specimen, as well as the specimen’s ability to carry its loads.
- UL 263—Standard for Fire Tests of Building Construction and Materials: This fire test was developed for evaluating structural material (bearing walls, beams, columns, slabs, etc.) for floors and roofs under a fire event. It measures the duration and transmission of heat and hot gases through the test specimen that are hot enough to “ignite cotton waste” in the specimen, as well as measuring its ability to carry its loads.
- IBC 703.3—Methods for Determining Fire-Resistance: The basic takeaway from this testing method is that it nevertheless relies on the fire exposure and criteria specified in the above two methods. Notwithstanding that fact, the construction’s fire-resistance rating per IBC 703.3 is allowed to employ any of six procedures: (1) “fire-resistive designs documented in approved sources,” (2) “prescriptive designs…as prescribed in Section 721,” (3) “calculations in accordance with Section 722,” (4) “engineering analysis” per test procedures defined by ASTM E119 or UL 263, (5) “alternative protection methods as allowed by Section 104.11” (which, in part, is when approved by the local building official as meeting the intent of the code) and (6) “fire-resistive designs certified by an approved agency” (the ASTM, UL, FM, OSU, etc.).
Fire-Resistance Construction Requirements
The IBC addresses fire-resistance construction—representing the building’s elements, components and assemblies—in 22 separate topics. Because each topic is far too extensive to fully explore here, this article only touches on the salient issues.
Fire-Resistance Ratings and Fire Tests (IBC 703)
This section’s requirements are as follows. Interior walls that have a “non-symmetrical profile” shall be tested at the least-fire-resistive side or from both sides, and any material in the wall that was not part of the test must have a report proving that the wall’s fire resistance is not reduced. Under the prescriptive fire-resistance method noted in this chapter’s Section 721, the fire-resistance method shall be established without an automatic fire sprinkler or other suppression system being part of the test. Noncombustibility tests for elementary materials shall be per ASTM E 136, and tests for composite materials with no greater than a 50 flame-spread index (FSI) per ASTM E 84 or UL 723 shall be accepted as being noncombustible. Fire-resistance-rated glazing shall be permitted if it meets ASTM E119 or UL 263, complies with Section 707, and bears an official mark. Also, permanent markings shall be applied to all fire or smoke barriers inside all accessible concealed floor, floor-ceiling or attic spaces.
Protection of Structural Members (IBC 704)
The primary issue of this topic is that the fire-resistive protection for structural members is typically required, and the ratings shall conform to Table 601’s Fire-Resistance Rating Requirements. The secondary issues of this topic are as follows.
When columns and other primary structural members are required to have fire resistance, they shall have complete encasement on all sides for their full height and at connections to other structural members. When secondary structural members are required to have fire resistance, most shall be protected by “individual encasement protection,” and the structural bolts, rivets and so on for structural connections shall have at least one inch of fire-protection coverage.
The thickness of fire-resistive protection of masonry reinforcement (rebar, etc.) shall be measured from the outside face of the reinforcement, with the exception that stirrups and spiral reinforcement ties can penetrate no more than half an inch into the protection.
Fire-resistive protection of structural members shall not be penetrated or embedded by utility-service equipment such as pipes, wires, conduits, duct and so on. Fire-resistive protection of structural members subject to vehicle or other impacts (other than concrete columns or those in a parking garage) shall be protected by at least five-foot-tall noncombustible jackets or corner guards, and exterior load-bearing structural members shall be in accordance with Tables 601 and 602. But the bottom flange of lintels, shelf angles and plates needn’t have fire-resistive protection for those structural members that span no more than 6'4" or those that aren’t part of the primary structural frame.
Sprayed fire-resistant materials (SFRMs) shall be per the manufacturer’s installation instructions for substrate temperatures and surface conditions, as well as for SFRM mixing, curing and so on. Surfaces receiving SFRM shall be free of conditions that prevent adhesion (dirt, oil, grease, loose scale, etc.), but primed, painted, or encapsulated steel that allows SFRM adhesion is permitted.
Exterior Walls (IBC 705)
For buildings on the same lot, the fire-restive requirements shall be considered to have an imaginary property line between them, with Table 602’s required minimum distances applying from the building face to this imaginary line. Exterior walls must meet the fire-resistive ratings defined in Tables 601 and 602; those with a fire-separation distance greater than 10 feet shall be rated for exposure to fire on the inside of the wall, and those 10 feet or less shall be rated for exposure to fire on both sides of the wall.
Door and window openings, of course, are allowed in exterior walls that are fire rated, but they must meet the requirements defined for two possible scenarios: unprotected and protected. Protected openings are those that have automatically dropping fire shutters, an automatic water-deluge system or fire-rated assemblies such as rated frames with rated doors and/or fire-rated glass (per IBC 716). A little-known code requirement is the vertical separation of openings (IBC 705.8.5): openings in the same floor must be at least five feet apart, and openings in adjacent stories must be at least three feet apart, with the exterior wall area between them being a minimum of one-hour construction (and rated for exposure to fire on both sides).
Unprotected openings are typically limited in percentages as described in Table 705.8, which lists requirements for eight fire-separation distances. For example: exterior walls set within a fire-separation distance less than three feet are not allowed to have any openings (unprotected or protected); in all use groups (other than H), unlimited unprotected openings are allowed on the first floor above grade if its exterior wall has a fire-separation distance of more than 15 feet. Sprinklered buildings with a fire-separation distance of 20 feet or more have no area limits on exterior-wall openings, and sprinklered or nonsprinklered, protected or unprotected buildings with a fire separation of 30 feet or more have no area limits on exterior-wall openings.
Furthermore, projections of cornices, eave overhangs, exterior balconies and so on that are beyond the exterior wall shall be set at the minimum fire-separation distances defined in Table 705.2 and Section 1406. Exterior exit stairways and ramps as well as exterior egress balconies shall comply with Sections 1021 Egress Balconies and 1027 Exterior Exit Stairways and Ramps. Plus, combustible projections shall be fire rated no less than one hour.
Fire Walls (IBC 706)
The basic concept and benefit of a “fire wall” is that the code deems it to effectively separate a larger whole building into separate smaller buildings. This function is most useful for large buildings in the more combustible construction categories (Types 2 through 5), in that a building too large to meet the code’s maximum-area restrictions can be considered an assemblage of smaller buildings when fire walls are added.
But its large benefit is coupled with numerous requirements, in that a fire wall shall a) be considered a “party wall” and shall not have any openings if they’re located on a property line used for two separate buildings; b) be designed and built such that if the structure collapses on either side during a fire, it shall remain standing; c) have a fire-resistance rating as defined in Table 706.4,which for typical data center use groups is two hours for type S-2; three hours for B, S-1, H-3 and H-5; and four hours for H-1 and H-2; d) be continuous horizontally and also extend out to horizontal projections such as roof overhangs and balconies; e) be continuous vertically, from the foundation up to 30 inches above the roofs on each side typically, but it can terminate at the underside of noncombustible roof sheathing, deck or slab, provided certain conditions are met. Moreover, the fire wall shall f) have its intersecting exterior walls constructed with a one-hour fire-resistive rating and any openings for at least four feet to each side of the fire wall constructed with three-quarter-hour protection, and g) have no openings in adjacent walls or roofs (such as exterior windows, doors, roof access, etc.) located within 4' of a fire wall.
Fire Barriers (IBC 707)
Fire barriers, such as fire-rated walls and floor-ceiling assemblies, provide separate fire zones in the building to protect most means-of-egress pathways (such as exit stairways, exit ramps, exit access corridors and horizontal exits), to prevent the spread of fire and smoke through vertical shafts, to often separate atriums and control areas from other parts of the building, and to provide separation of mixed uses.
Fire barriers must have a fire-resistance rating as defined in Table 706.3.10, with data center use groups of S, B and sometimes H ratings being the following: two hours for S-2, B, H-4 and H-5; three hours for S-1; and four hours for H-1 and H-2.
Additional special considerations for fire barriers include the following: they also need continuity, and their supporting construction must also be fire rated with the same rating; hollow vertical spaces must have fire blocking; openings in fire barriers must be protected per the requirements of IBC 716; individual openings in a fire barrier must not exceed 156 square feet, while aggregate openings must not exceed 25% of any single barrier; penetrations into a fire barrier must be constructed with a tested penetration-firestopping system (per IBC 714), and joints must be constructed with a tested joint system (per IBC 715).
Smoke Barriers (IBC 709)
Both horizontal and vertical smoke barriers require a one-hour fire-resistance rating and must be continuous from the top of construction at its start below (foundation, floor or floor/ceiling assembly) to the underside of the construction above (floor/ceiling assembly, roof, deck, etc.). Although continuity typically includes interstitial spaces, such as above drop ceilings and through mechanical plenums, an exception applies if the ceilings or exterior walls are built to prevent the passage of fire and smoke equivalent to the level that the smoke barrier provides.
In addition, several special continuity requirements also apply: smoke barriers enclosing areas of refuge (1009.6.4) and elevator lobbies (405.4.3, 3007.6.2, 3008.6.2) are meant to ensure that these ADA-oriented areas are protected by an effective barrier; penetrations must conform to section 714; fire-resistant joint systems must conform to 715; window and door openings must conform to 716; and ducts and air-transfer openings must conform to 717.
Horizontal Assemblies (IBC 711)
The IBC definition of horizontal assemblies is a “fire-resistance-rated floor (floor-ceiling assembly) or roof assembly of materials designed to restrict the spread of fire in which continuity is maintained.” Similar to the fire-barriers and smoke-barriers sections, horizontal assemblies also have continuity requirements (except for vertical openings as permitted) and supporting-construction requirements (where the structure’s fire resistance is the same as in the horizontal assembly).
Although horizontal assemblies must have a fire-resistance rating of at least what Table 707.3.10 defines, additional special conditions bump up its minimum rating. For example, when horizontal assemblies separate mixed occupancies, they must conform to the requirements of section 508.4; separating fire areas must conform to section 507.3.10; separating smoke compartments must conform to 709; and separating incidental uses must conform to 509.
Vertical Openings (IBC 712)
Vertical openings in a rated floor/ceiling or roof-assembly system are essentially breaches in a continuous fire-resistive system. Typical examples are stairs, elevators, miscellaneous shaft enclosures (mechanical ducts, banked conduits, etc.) and penetrations (plumbing pipes, electrical conduits, etc.).
Since these penetrations are essential to the proper functioning, operations and inhabitation of every data center, the code allows penetrations to be “permitted where protected,” thereby still maintaining the integrity of the penetrated assembly’s fire resistance. Although most vertical openings in Section 712 are addressed as references to other, more in-depth sections of the code, it lists requirements for a few building elements, two of which are the following:
- Two-story openings are permitted if the opening connects no more than two stories, doesn’t penetrate any fire areas or smoke barriers, isn’t open to nonsprinklered corridor on a nonsprinklered floor, and is separated from other vertical openings (floor openings, air-transfer openings, mechanical shafts, etc.).
- Except as required in Section 705.8.6, skylights and other roof penetrations are allowed to be unprotected “provided that the structural integrity of fire-resistance-rated roof assembly is maintained.”
The other protections noted by this code section mostly refer to requirements listed in other sections of the code; examples are shaft enclosures per section 713, penetrations per section 714, joint systems per sections 712 and 715, ducts and transfer openings per 717, atriums per 404, mezzanines per 505, exit-access stairways and ramps per 1019, corridors per 1020, and elevators per Section 713 and Chapter 30.
To help keep all occupants safe during typical occupation and especially while egressing during a fire, limiting the spread of fire and smoke in all parts of the building is critical. This task pertains not only to the extremely important means-of-egress system (exit access, exit and exit discharge) and its means-of-egress components (doors, corridors, stairs and elevators), but also to the other parts of the building (structural system, exterior walls, floor-ceiling assemblies and roof assemblies). Adhering to the proper fire- and/or smoke-resistance requirements will help make the building a safe working environment and provide safe evacuation from any occupied place to the safety of a public way.
Leading article image courtesy of DVA Architects
About the Author
Dean Ventola, RA, NCARB, LEED AP BD+C, is the Director of Construction Administration at DVA Architects in Gaithersburg, MD, a nationally prominent mission-critical data center architect.