There’s an old expression: Good enough just isn’t good enough. For writers of the standard building codes, that expression is pretty accurate. Each time the code is reviewed, it is a sure bet that there will be changes. Some of those changes lighten up restrictions to take into account significant technology improvements. More often, restrictions become tighter in an attempt to eliminate recognized potential errors in system design or installation that can cost the lives of building occupants and/or first responders.

Certainly, the latter is the case regarding changes in the code section concerning perimeter fire protection in mid- and high-rise buildings. While there was only one change in this section, allowing the perimeter void installation to conform to the new ASTM E2307 test method, that single change had quite an impact.

Two code references are of particular importance in perimeter fire containment. It is worth digging up a copy of the International Building Code (IBC) code book—old or new version—to highlight the important sections.

The first code reference is in section 704.9. In this section, the code writers try to protect against the vertical spread of fire on the exterior of a building. The code requires three-foot or greater vertical spandrel girders, or at least 30” horizontal protrusions such as balconies, on buildings more than three stories high when not equipped with an automatic sprinkler system.

Next, consider Section 713.4, Exterior Curtain Wall/Floor Intersection, which focuses on maintaining the integrity of the floor slab. This section requires filling the void (safing area) between the floor slab and the exterior curtain wall, which must be done to protect against the interior spread of fire between the floor slab edge and the curtain wall. The void is to be sealed with an approved system or materials to prevent passage of flame and hot gasses, and must maintain the same fire resistance rating as the floor assembly. A change in this section of the code adds that the installed material can either meet the requirements of ASTM E119 or it can be a system “installed in accordance with ASTM E2307,” a recently adopted two-story fire test.

Now, as is so often the case, an important caveat emerges from practical application of the code.

Section 704.9, Vertical Separation of Openings, provides that separating devices such as spandrel girders or exterior protrusions are not required for buildings that are three stories or fewer in height, or that are equipped throughout with automatic sprinkler systems.

On the surface, Section 704.9 language eliminates the need for spandrel panels in sprinkled buildings. However, the code language does not eliminate Section 713.4. Taken in connection with Section 713.4, it is clear that the assembly of the spandrel area along with the perimeter void must be protected and must remain in place to provide at least the same fire-rated performance as the floor slab.

Without a tested assembly to ensure that the curtain wall structure will not be compromised in event of a fire, there can be no assurance that the protection in the perimeter void will remain in place. If the curtain wall gives way, perimeter void protection fails.

This has already been proved in a testing environment. Mineral wool safing was installed between a floor slab and an unprotected glass curtain wall. Just five minutes into the test, the curtain wall glass failed, allowing the safing insulation to dislodge.1 In other words, even though the void between the curtain wall and the floor slab edge was filled to meet the intent of the code requirement, the assembly failed to meet the fire-rated expectations of the building codes.

Breach of a floor barrier in a five-minute span calls into question the exceptions stated in the current code under Section 704.9. Is it really reasonable to expect fire department response time to be better just because a building is less than three stories tall?

Prudent readers of the code will recognize that properly protected spandrel panels at the curtain wall/floor slab intersection are essential for truly meeting code requirements. Assemblies tested to ASTM E2307 meet those requirements. There are no exceptions.

References:

American Society for Testing Materials, “ASTM E2307-04—Standard Test Method for Determining Fire Resistance of Perimeter Fire Barrier Systems Using the Intermediate-Scale Multi-story Test Apparatus,” Volume 04.07, Building Seals and Sealants, Fire Standards: Dimension Stone, 2005. International Code Council, International Building Code, Section 704.9, “Vertical Separation of Openings” and Section 713.4 “Exterior Curtain Wall/Floor Intersection,” IBC 2006. Loss Prevention Council, “Fire Spread in Multi-Storey Buildings with Glazed Curtain Wall Facades,” LPR 11:1999. Shriver, James C., and Cordts, Brandon, “Clarifying Curtain Wall Firestop Standards,” Technical White Paper, 2001. www.fcia.org, Firestop Contractors International Association website, 2006. www.firestop.org, International Firestop Council website, 2006. www.afscc.org, Alliance for Fire and Smoke Containment and Control website, 2006.