[Fire] Resistance is [Not] Futile

 By David Hohenstern | Mon, October 10, 2016 | Meet the Blogger | More Posts by David Hohenstern

 By David Hohenstern | Mon, October 10, 2016 | Meet the Blogger | More Posts by David Hohenstern



Among the many challenges faced by commercial building designers, as though pulling unique new buildings from the imaginative ether is not enough, is fire code compliance. There are many factors to consider: construction type(s), fire separation distances, required hourly ratings, sheathings, air and water barriers, interior finishes, exterior finishes, etc., and, oh by the way, the curveballs thrown by the energy code. Building products manufacturers can make things easier by fully vetting product offerings and transparently offering performance data on product testing. Nichiha tries to do that, and since we know our products best, we keep an eye on the codes and testing standards to make sure that we cover our bases to stay current, and, hopefully, ahead of the curve[ball] (sticking with the baseball metaphors).

Let’s talk a little bit about a few of the fire testing standards in the International Building Code (IBC) that pertain to exterior wall claddings, and, in one case, interior wall coverings as well. This list is not comprehensive, there are more, but three is a baseball-related number (also a “magic number” but this is a totally random reference not related to baseball), so that’s how many we’ll throw at you. ASTM E84, ASTM E119, and NFPA 285 provide useful data about how building products respond to fire and can help architects design with confidence about fire safety. My goal here is to provide a little insight into the standards themselves while also pointing out how they are tied into the IBC.

ASTM E 84

This test standard measures both flame spread and smoke development, appearing at least 30 times in the 2015 IBC. Data generated for a particular test sample is given as indexes for Flame Spread and Smoke Developed. These are measures of flame propagation over the sample surface over time, and, likewise, as the name makes plain, the smoke-developed index represents the amount of smoke generated by the sample versus time. The test apparatus itself is about 25 feet in length and the tested material runs 24 feet (by 20 inches wide) within the test tunnel. Windows built into the apparatus allow the operator to track progress of the flame spread. The sample is exposed to controlled air flow and, of course, a direct flame from gas burners at one end of the chamber. The samples are tested in a “ceiling” position. With the room darkened, the operator notes how far the test sample carries the flame down the chamber during a maximum ten-minute period. A photometer system mounted in the vent pipe at the opposite/exhaust end measures the density of the smoke.*1

Although E84 data is applicable to both exterior and interior building materials, and specific performance requirements under the standard for certain materials, such as foam plastics, are provided for in the code, a key breakdown and classification system is given in Section 803 (Interior) Wall and Ceiling Finishes. A Class A rated material in accordance with E84 data shall have a flame spread index between zero and 25 and a smoke developed index ranging from zero to 450. Class B finish materials have a flame spread between 26 and 75 with smoke developed still capped at 450. Lastly, Class C performers have a flame spread between 76 and 200, while smoke developed can again be no greater than 450.*2

ASTM E 119

Entitled, Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119 is another fundamental standard for fire resistance with 27 references in the IBC, mostly within Chapter 7. The tests are used in the code to establish the fire-resistance rating of building materials and assemblies and is introduced in Section 703. The IBC defines fire-resistance rating as “the period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both…”*2 Section 705, Exterior Walls points back to Tables 601 and 602, which provide required hourly-ratings for structural frames, bearing interior and exterior walls, nonbearing interior and exterior walls and partitions, floors, and roofs. The 0 to 3 hour ratings are, of course, determined, at least in part, by ASTM E 119 data.

The E 119 standard is quite complex and is intended to test building components and assemblies in a manner representative to their actual use in the built environment. Thus, the test incorporates various approaches and procedures for evaluating loadbearing walls and partitions, non-loadbearing walls and partitions, loaded columns, floors, roofs, etc., and the size and dimensions of the specimens are specified within the procedures. We’ll focus in on the exterior wall portions here, so, as an example, the size of the specimen for tests of load-bearing and non-loadbearing walls is greater than 100 square feet.
Test specimens are exposed to a controlled, standard fire at specific temperatures throughout a pre-set period of time. For walls, the test measures the transmission of heat, transmission of hot gasses through the specimen, and, when load bearing is included, “the load carrying ability of the test specimen during the test exposure.”*3 The test-specimens-to-be are protected and conditioned prior to testing to ensure consistent results by preventing variations in such things as moisture content. The test fire is controlled according to a standard time-temperature curve: 1000°F @ 5 minutes, 1300°F @ 10 minutes, 1550°F @at 30 minutes, 1700°F @ 1 hour, 1850°F @ 2 hours, 2000°F @ 4 hours, and 2300°F @ 8 hours or more.

At least nine thermocouples measure the furnace temperatures and nine more are placed strategically on unexposed surfaces of the wall specimens. Specimen temps are recorded every 30 seconds or less. For tests of one hour or more, a hose stream test may be conducted at the conclusion of the fire exposure to subject the sample to the water’s “impact, erosion, and cooling effects.” Conditions of acceptance (ie passing results) are listed out for each specimen type.

NFPA 285

NFPA 285 garners a lot of attention and focus these days and is perhaps an MVP candidate (one, last baseball analogy) for fire standards. It is the Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Nonload-Bearing Wall Assemblies Containing Combustible Components. NFPA 285 is used in the code to allow for the use of combustible materials in non-combustible construction. This is vital to the implementation of the energy code because it enables the use of foam plastic insulation in/on exterior wall assemblies, the key word with NFPA 285, as it is an assembly test. A two story test structure with a 78” x 30” window opening at the burn room is used to test vertical and lateral fire propagation for a particular combination of assembly components. The obvious goal is to prevent a fire that has broken out in one room from escaping out the window and spreading.

But now that we’ve gotten to perhaps the most fun test featured in this blog entry, I’m going to end the episode with a cliffhanger and leave you in anticipation of my follow-up. We are planning a new round of NFPA 285 testing of Nichiha panels, so my next entry will cover that experience in a more personal, story-like fashion while also covering the particulars of the test itself and what the results will mean for Nichiha and our customers.

*1. ASTM International, Designation: E84 – 14, Standard Test Method for Surface Burning Characteristics of Building Materials
*2. International Code Council, 2015 International Building Code
*3. ASTM International, Designation: E119 – 12a, Standard Test Methods for Fire Tests of Building Construction and Materials

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Comments


Is there a UL Design for a one-hour fire-rated exterior wall when using the Nichiha panels yet?

Julie Michael

Hello, Seeing all these Baseball analogies, i must draw conclusion that you are a Cubs fan.  :o)
Joke aside, I find this information on fire testing very well explained.
Thank you.

Alejandro Camalda

Hi Julie,

Thank you for reading my blog post and your interest in Nichiha. While we have not developed a Nichiha-specific UL-rated assembly, U 356 is an example listing that generically lists finish/cladding options, including fiber cement. We do have multiple 1-hour rated assembly test reports under ASTM E-119. These, as well as all our other fire-related test summaries are available at http://www.nichiha.com/resources/product-testing.

Regards,
David

BlogEditor

Hi Alejandro,
Thanks for reading and your kind comments! Although I did pull for the Cubs in the World Series, I live in Georgia and am a life-long Braves fan. I happened to be in Chicago the night of Game 3 and rode the L up to Wrigley and experienced a bit of the electric atmosphere.

-David

BlogEditor

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