SDI and FSI may sound like acronyms for exploring the stratosphere, such as the Strategic Defense Initiative (aka “Star Wars”) and the Frontier Spaceflight Institute. But for mission-critical data centers, they’re simply earthbound code requirements for the flame-spread index (FSI) and the smoke-developed index (SDI) that govern a building’s exposed materials and finishes. The 2015 International Building Code (IBC) generally addresses these two indexes in its Chapter 14 Exterior Walls and Chapter 8 Interior Finishes, and the 2015 NFPA 101 Life Safety Code (herein called the NFPA) addresses them in its Chapter 10 Interior Finishes, Contents, and Furnishings.
Regarding FSI’s and SDI’s governance for exterior walls and interior finishes, the IBC and NFPA separate them into three basic finish ratings—Class A, B and C—with these definitions:
- Class A has 0–25 flame spread and 0–450 smoke development.
- Class B has 26–75 flame spread and 0–450 smoke development.
- Class C has 76–200 flame spread and 0–450 smoke development.
During my research for this article, I saw a reference to Class D and Class E flame-spread ratings, but neither the IBC nor the NFPA mentions them. Like every code requirement I’ve explored, all locally adopted codes (such as the IBC, NFPA 101, 2010 ADA, ANSI, etc.) are mandatory, and for any conflicting requirements between codes, the more stringent should be applied.
Additionally, although Class B and even Class C finish ratings will be code compliant for many conditions, I always recommend citing in the permit set the lowest condition allowed but then constructing to the highest safety standard available, herein being Class A finish.
IBC’s Chapter 14 addresses flame-spread index (FSI) and smoke-developed index (SDI) requirements for exterior walls, but mostly for the surface burning characteristics of specific components. These components include combustible water-resistive barriers per Section 1403.5; polypropylene siding per Section 1404.12; combustible exterior-wall coverings per Section 1406.2, which references minimum fire separation distances per Table 1406.2.1.1.2; metal composite materials (MCMs) per Section 1407.10.1; and high-pressure decorative compact laminates (HPLs) per Section 1409.9 and .10.
Rather than adding numerous FSI and SDI conditions to its code, the IBC instead limits the spread of fire and smoke at exterior walls (and its opening protectives) through its extensive fire-resistance requirements. Primary examples are the IBC’s fire-resistance ratings for each major building element (such as its exterior walls) and its open-space requirements around the building. Secondary examples appear in Section 1406.2, which says, (1) “Combustible exterior wall coverings shall not exceed 10 percent of exterior wall surface area...where the fire separation distance is 5 feet (1,524 mm) or less”; (2) “Combustible exterior wall coverings shall be limited to 40 feet (12,192 mm) in height above the grade plane”; and (3) combustible exterior wall materials may require ignition resistance and/or need to comply with the minimum fire separation distances.
Given such measures as noted above to help prevent the spread of fire from building to building, establishing further metrics to protect the outside of a building is unnecessary to protect the occupants within. So the IBC (and NFPA) say little regarding FSI and SDI requirements for exterior walls. Interior finishes, however, are a different matter. The spread of fire and smoke within a building has a major impact on the welfare of its occupants. So, to reduce the spread of fire and smoke, the IBC (and NFPA) focuses primarily on ensuring a low FSI and SDI for the interior materials and finishes. The IBC separates the protections needed for interior finishes into three main components: (a) interior wall and ceiling finishes, (b) interior floor finish and floor coverings, and (c) decorative materials and trim.
In addition, the IBC also includes FSI and SDI requirements for other components (such as for combustible materials in Construction Types 1 and 2, for insulation, and for acoustic ceiling systems), but mostly addresses them in depth elsewhere in the code. The NFPA, however, has a section explicitly addressing interior furnishings, discussed below as item (d), and the IBC has extensive FSI and SDI notations regarding penetration firestopping systems, discussed below as item (e).
(a) Interior Wall and Ceiling Finishes
For a building’s exposed interior wall and ceiling finishes to be code compliant (per the IBC’s Table 803.11: Interior Wall and Ceiling Finish Requirements by Occupancy and per the NFPA’s Chapter 10 Interior Finish, Contents, and Furnishings), they must meet their assigned designation of Class A, B or C.
- The IBC defines the required interior wall and ceiling finish classifications first by occupancy group (data centers typically fall into Use Groups S, B and sometimes H), then by sprinklered versus nonsprinklered, then by the type of space (exit stairways and exit passageways, corridors and exit accesses, and rooms and enclosed spaces).
- Regarding the FSI and SDI testing methods for interior walls and ceiling finishes, the IBC typically references ASTM E 84, UL 723 and NFPA 286, whereas the NFPA typically references ASTM E 84, UL 723 and NFPA 255.
- Selecting the most commonly cited test for further explanation, that being ASTM E 84, this standard is “intended to provide only comparative measurements of surface flame spread and smoke density measurements with that of select grade red oak and fiber cement board surfaces under specific fire exposure conditions.” And, furthermore, placing a nominal 24-foot-long by 20-inch-wide specimen in a testing tunnel, “This test is conducted with the specimen in the ceiling position with the surface to be evaluated exposed face down to the ignition source…but does not by itself incorporate all factors required for fire-hazard or fire-risk assessment…under actual fire conditions.”
(b) Interior Floor Finish and Floor Coverings
IBC Section 804.1 says, “Interior floor finish and floor covering materials shall comply with Sections 804.2 through 804.4.2,” but it then gives exceptions to “floor finishes and coverings of a traditional type, such as wood, vinyl, linoleum or terrazzo, and resilient floor covering materials that are not comprised of fibers.” The main takeaway here is that materials composed of fibers (such as carpeting, rugs and fabrics) and other nontraditional materials will most likely ignite easier and spread flames quicker than “traditional” floor materials.
- Regarding the FSI and SDI testing methods, IBC Section 804.2 says, “Interior floor finish and floor covering materials required by Section 804.4.2 (which addresses conditions for different Use Groups) to be of Class I or II materials shall be classified in accordance with NFPA 253.” NFPA 101 Section 10.2.7 has similar statements for Class I or II interior floor finishes, and it too references NFPA 253.
- NFPA 253, simply explained, is for “evaluating critical radiant flux of floor coverings in corridors or exitways,” with “radiant flux” being the energy needed to sustain a flame.
(c) Decorative Materials and Trim
IBC Section 806 addresses combustible decorative materials and trim that aren’t decorative vegetation; its main notations are the following:
- Noncombustible materials shall not be limited.
- Combustible decorative materials, such as “curtains, draperies, fabric hangings and similar combustible decorative materials suspended from walls or ceilings shall comply with Section 806.4 (where such draperies, etc. are tested and meet NFPA 701’s Standard Methods of Fire Tests for Flame Propagation of Textiles and Films), and shall not exceed 10 percent of the specific wall or ceiling to which it is attached.”
- Pyroxylin plastic, which sometimes coats or fully constitutes a fabric (e.g., some imitation leather), shall not be used in Use Group A. So even though most data centers are in Use Groups S, B and sometimes H, but seldom in Group A, noting the concerns with using pyroxylin plastic fabrics is nonetheless important.
- Interior trim other than foam plastic shall have minimum FSI and SDI ratings of Class C. Foam plastic trim must comply with 2604.2 Interior Trim, which includes 2604.2.4 Flame Spread.
- Wall bases up to six inches tall shall be tested per Section 804.2 (referencing NFPA 253’s radiant flux) and be not less than Class II.
(d) Furnishings, Contents, Decorations and Treated Finishes
NFPA Section 10.3.1 says, “Where required by the applicable provisions of this Code, draperies, curtains, and other similar loosely hanging furnishings and decorations shall meet the flame propagation performance criteria…of NFPA 701, Standard Methods of Fire Tests for Flame Propagation of Textiles and Films,” whose main notations are the following:
- Sections 10.3.1(1) and (2) contain requirements for upholstered furniture that’s subject to smoldering or ignition from cigarettes.
- Section 10.3.3 requires upholstered furniture to have limited heat-release rates when exposed to a flaming ignition source, unless the building is fully sprinklered.
- Section 10.3.5 prohibits the use of furnishings or decorations of a highly flammable character.
- Section 10.3.6 requires fire-retardant coatings to be maintained.
- Section 10.3.7 requires furnishings and contents made with foamed plastic materials that are unprotected from ignition to conform to UL 1975.
(e) Penetration Firestopping Systems
In addition to the above noted components, the IBC requires that the exposed sealants and finishes for penetration firestopping systems have Class A’s flame-spread index and a smoke-developed index.
As I’ve noted in previous articles in this series, the IBC requires open space around a building and/or rated exterior walls to help prevent fire from spreading from building to building. It also requires rated interior partitions, and it often requires an automatic sprinkler system to help prevent fire from spreading from one interior area to another. In addition to those measures, the code requires limits on the surface burning characteristics of interior finishes as well. Such limits help reduce the spread of fire and help minimize the amounts of deadly smoke, implementing yet another important defense in mission-critical data centers. With most data centers having a large floor plate, seemingly endless corridors, and large rooms filled with rows of electric towers, banks of air handlers or a sea of data racks, adhering to FSI and SDI limits could reduce damage, facilitate safe evacuation and be instrumental in saving lives during a fire.
Leading article image courtesy of DVA Architects
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.