Fire-Protective vs. Fire-Resistive Glazing: Radiant Heat, Tests and Ratings
Learning Objectives - After this course, you should be able to:
- Gain an understanding of the difference between fire-protective and fire- resistive glazing; its application, test standards and the function it is supposed to perform.
- Broaden understanding of current test standards, including the hose-stream test's history and original intention, and what code updates say and not say about the performance of fire-protective glazing
- Evaluate the uses (and misuses) and limitations of widely used fire protective glazing such as traditional wired glass and ceramics, and tempered products.
- Apply knowledge about the most overlooked concern when specifying fire protective rated glazing; the effect of dangerous radiant heat on the safe egress of building occupants in the event of a fire.
In designing safe building structures, architects have three methods for protecting against the loss of life and property due to fire. One is detection, which includes smoke and heat detectors as well as alarms. A second, suppression, encompasses sprinklers and fire extinguishers. The third, compartmentation, is uniquely architectural in nature. This method describes the use of material barriers and design layout to separate zones within a building from each other, preventing the migration of smoke and fire from one area to the next.
While it may seem counterintuitive, glass can be an effective material and system component for compartmental barriers. Properly specified and designed, glazing can successfully protect building occupants from fire, smoke and radiant-heat hazards.
Due to the increasing interest in preventive fire protection and the simultaneous growth in the use of architectural glazing, this subject is especially timely. Architects increasingly seek open, transparent, and communicating buildings, allowing more views and daylight for occupants. To serve this need, fire-resistive glazed partitions, doors and windows have become widely available over the last two decades.
Just as prevalent, however, have been misconceptions and misinformation about the proper specification and application of fire-rated glazing. For that reason, architects and their project teams seek better understanding of the types of fire-protective and fire-resistive glass; their system requirements, standards and codes; and their performance in actual fires. Also important is a good working knowledge of effective uses of fire-rated glazing-and the misuses, too.
Fire-Protective vs. Fire-Resistive Glazing
To help compartmentalize a building design, fire-rated glazing are available. There are a few general types of fire-rated glass, and each product in these categories has its own fire rating, measured by time. The time describes how long the product can meet the fire endurance test for either-fire protective or fire-resistive standards.
One important difference between "protective" and "resistive" glazing concerns radiant heat, a mechanism of fire and heat propagation. It is also a serious life-safety risk, and so is covered in detail below.
Fire-protective performance can be described by means of a Fire-Protection Rating. According to the Glass Association of North America (GANA), this is "the period of time that an opening protective assembly will maintain the ability to confine a fire as determined by tests." The tests include NFPA 252, NFPA 257, UL 9, UL 10c, ASTM E 2010, and ASTM E 2074.
This narrow ability to "confine" a fire is different from Fire-Resistance, which GANA defines as "that property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use." It is described by means of a Fire-Resistance Rating: "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, as determined by tests," including NFPA 251, ASTM E 119, and UL 263 (wall assemblies).
In this context, fire protection means confining fire (smoke, flame and, to some degree, heat) for a period of time. Fire resistance means the qualities of a material that similarly confine fire, smoke and radiant heat, and at the same time maintain that material's structural characteristics.
The critical distinction in the performance of fire-rated glazing is the ability of glass to limit or control radiant heat-the often dangerous heat transmitted from the fire side of a building separation to the non-fire side. At critical intensities, this heat transferred through a construction assembly can cause harm to building occupants and the spontaneous ignition of building materials and contents-again, on the non-fire side.
To compare fire-protective and fire resistive products, the categories-which are significantly different from each other-are described in Section 8 of the Glass Association of North America (GANA) Glazing Manual, titled "Fire Rated Glazing Products."