Glazing Must Pass Rigorous Tests to Earn a Fire Rating
By Jeff Razwick
As architects and designers incorporate glazing throughout buildings to support daylighting, aesthetic and security goals, ensuring a fire rating is also necessary in certain applications. The growing use of glass for both interior and exterior applications means that in more cases, the glazing must also play a role in building compartmentation.
Properly designed, specified, installed and maintained, fire-rated glazing provides an effective barrier against flames and smoke. To earn a fire protection rating, glazing is subjected to testing requirements specified in the National Fire Protection Association’s (NFPA) 257: Standard on Fire Test for Window and Glass Block Assemblies. These tests help ensure that glass and framing can withstand the intense heat from structural fires and the potential effects of firefighting actions.
Overview of Fire Ratings
Fire-rated glazing for door and window assemblies is rated from 20 minutes to 3 hours. The rating reflects the amount of time the material is anticipated to remain in place to help stop the spread of fire and smoke. While ordinary window glass and tempered glass break at temperatures well below those found in many building fires, fire-rated glazing is available that can withstand temperatures up to approximately 1,800° F or greater (980° C).
Fire ratings are determined by a series of tests conducted by independent testing facilities, such as Underwriters Laboratories. The lab installs samples of the glass and framing in a wall assembly. This assembly is then subjected to specified test standards that include two required elements: a “fire test” and a “hose stream test.”
Fire Test
For the first stage of testing, the wall assembly with glass and framing is placed in a furnace. The temperature inside the furnace is controlled following a standard time-temperature curve specified in NFPA 257, Figure 4.1.1. At five minutes, the temperature in the furnace reaches 1,000° F (583° C). At 30 minutes it rises to 1,550° F (843° C). After one-and-a-half hours it approaches 1,800° F (980° C).
For a given fire rating, the glass and framing must meet several performance criteria specified in NFPA 257 at the conclusion of the fire test. These include:
- “The window assembly shall remain in the wall in which it is installed for the duration of the fire test”
- “No flaming shall occur on the unexposed surface of the assembly”
- “There shall be no separation of the glazing material edges from the glazing frame”
- “There shall be no openings in the window assembly”
Additional performance criteria address limitations on the movement of operable components from their closed positions and limitations on the movement of the overall assembly relative to the wall.
Hose Stream Test
Within two minutes of completion of the fire test, the hot glass and framing is subjected to a hose stream test. The side of the assembly exposed to the heat of the furnace is sprayed with water from a fire hose at pressures and durations specified in NFPA 257, Table 6.2.3.
The purpose of this test is to provide “a method for evaluating the integrity of constructions and assemblies and for eliminating inadequate materials or constructions.” (NFPA 257, B.11.4) The standards further state “the cooling, impact, and erosion effects of the hose stream provide important tests of the integrity of the specimen being evaluated.”
To successfully pass the hose stream test, the glass and framing must remain intact and not separate from the frame, within limits specified in NFPA 257, B.12.
In the United States, the hose stream test is required for all fire ratings of 45 minutes or greater. Canada requires the test for all fire ratings.
The Role of Testing in Life Safety
While the importance of the fire test is generally well understood, some product manufacturers have raised questions about the ongoing need for the hose stream test. NFPA 257, B.11.2 explains that spraying the glass and framing with water “provides a measure of its structural capabilities.” The standard explicitly acknowledges that weights have been used in Europe to test impact, but that the hose stream test provides greater uniformity and accuracy. In addition, the hose stream test evaluates the assembly’s ability to withstand thermal shock, such as might be experienced when hot glass is exposed to cool water from fire sprinklers or fire hoses.
The International Code Council (ICC) has re-affirmed the importance of the hose stream test on a number of occasions. Responding to several proposals by a product manufacturer to lessen or eliminate the test requirements, in 2006 the ICC’s Fire Safety Code Development Committee stated that these actions “…would reduce the level of life safety which the code has generally required and provided.” The Committee went on to note that the issue has been debated a number of times and that “it has always been defeated.” (2006 ICC Public Hearing Results, FS121-06/07 and FS107-06/07). During the recent round of code reviews, the ICC in February 2008 rejected additional proposals to change the hose stream test requirements.
Although NFPA standards are very clear that both the fire test and hose stream test are required, one glazing product on the market is labeled as having 45 and 60-minute fire ratings “without hose stream.” The manufacturer encourages architects and specifiers to seek local exemptions to well established and researched national testing requirements and building codes in order to install the product in their buildings.
Local exemptions for building materials and practices provide code officials with the latitude to make professional judgments based on unique situations. These exemptions are appropriate when a product has at a minimum passed the basic required test standards. Officials also rely on proper testing and listing of products by independent laboratories to determine at a glance if a product is suitable for a given application. Incomplete testing and misleading labels can result in misuse of products and thereby endanger building occupants.
Authorities having jurisdiction (AHJ) need to know that all test requirements for a product have been met, not that only selected portions of tests have been performed. A label indicating a fire rating of 45 or 60 Minutes “without the hose stream” test should send up a red flag.
A good first rule for any openings with fire ratings of greater than 20 minutes is to insist on glass that has passed the mandatory hose stream test, and is labeled in compliance with International Building Code requirements. (see label example) With so much at stake and so many fire-rated glazing options available, there is no need to settle for less than full compliance with the codes.
Jeff Razwick is the Vice President of Business Development for Technical Glass Products (TGP), a Snoqualmie, Washington-based supplier of fire-rated glass and framing systems, along with specialty architectural glass products. www.fireglass.com, 800-426-0279