Radiant heat concerns
Another aspect of the ASTM E119 and UL 263 test requirement apparently waived for the test was the confirmation the glazing has sustained the fire endurance test without passage of flame or gases hot enough to ignite cotton waste during the testing period. This portion of the test would be impractical under lab conditions using a water cur tain since the cotton waste is positioned approximately 25 mm (1 in.) from the glass surface. However, the significance of a potential ignition of the cotton waste is its indication of radiant heat transmission.
Fire-resistive glazing relies on the use of one or more interlayers of a reactive intumescent material to literally shield the non-fire-side glass surface. It is not uncommon for unexposed fire-resistive glass surfaces to remain cool enough to be safely touched during the test procedure. This shield serves to block temperature rise as well as the transmission of radiant energy waves that can potentially cause the spontaneous combustion of surrounding building materials and pose an extreme danger to building occupants.
Davidson calls on the experience of firefighters in addressing the potential danger of relying on water curtains by noting, “the fire service eventually realized that a water curtain does not stop fire spread. Heat is transmitted to other objects by conduction, convection, direct flame impingement and radiation. The water curtains may be able to effect convection to some degree depending on the size of the fire, but they do not stop radiated heat because the water is not opaque.”
It is understandable architects, engineers, and building officials lacking real world firefighting experience may overlook the invisible danger of radiant heat transmission. However, the threat of radiant heat to occupants eager to flee from fire through glazed corridors, stairway enclosures, or occupancy separations remains real. The sole reliance on a water curtain seems to be courting disaster.
In December 2012, the ICC-ES Evaluation Committee once again invited public comment of the reinstatement of AC 385 in light of the pros and cons voiced in the preceding public comment period. However, this time the committee was seeking comment on several proposed modifications to AC 385. The most important of which was the prohibition of horizontal muntins because they can block the contiguous flow of water over the glass surface, and the clear assertion the system is an alternative to a fire-resistance-rated wall assembly and not a fire-resistance-rated fire barrier assembly itself. The committee also proposed the insertion of the following new section:
Special-purpose sprinklers with fixed glazed assemblies are an alternative to a fire-resistance-rated wall assembly requiring approval by the code official. The registered design professional shall provide the code official with documentation outlining the basis of compliance with the criteria specified by the IBC for a code modification in accordance with Section 104.10 or for an alternative method of construction in accordance with Section 104.11.
However, neither this proposed addition to AC 385, nor IBC Sections 104.10 and 104.11 for that matter, require the design professional or the building official to confirm the practical difficulty serving as the basis for alternative construction. Further, the additional AC 385 section does not address allowable occupancy types or limit changes to occupancy types in the future.
Conclusion
The need to backtrack through AC 385 as the result of a reinstatement request calls into question the wisdom applied during the initial ICC-ES review process. The overriding lesson to be learned through this controversy—no matter how it is resolved—is the incentive and desire to circumvent building codes and test requirements for the sake of expediency, cost savings, aesthetic vision, and any number of other factors is ever-present.
The need for a balanced approached to most circumstances is often seen as good advice to be applied in daily life. This knowledge stems from insights handed down from one generation to the next. When public safety is at stake, it becomes even more important to consider not only the systems, but also the impact human error can have on the materials and construction methods we employ to create safe environments. When it comes to fire protection, having a fully tested Plan A and Plan B just makes sense.
Jeff Griffiths, CSI, is the director of business development for SaftiFirst. With over 25 years of experience within the glass and glazing industry, he has worked with both sloped and vertical glazing systems incorporating wood, aluminum, and steel structural components along with various glass products. From 1985 to 1992, Griffiths oversaw the manufacturing of SaftiFirst’s earliest generation of fire-resistive glazing systems. He currently serves on Glass Association of North America’s (GANA’s) Fire-rated Glazing Council Educational Committee, Window and Door Manufacturers’ (WDMA’s) Interior Products Code Committee, and ASTM Committee E60 on Sustainability. Griffiths can be reached via e-mail at jeffg@safti.com.
