A real blast
The options in fire-rated glass have expanded greatly in recent years. Architects and designers were once limited to traditional wired glass in relatively small sizes; today they can choose from a range of glazing that offers superior fire protection and the chance to incorporate entire walls of glass without compromising safety.
This is no small feat. To achieve a fire rating of more than 20 minutes, heated glass is subjected to a mandatory hose stream test as specified in test standards such as the National Fire Protection Association’s Standards on Fire Test for Window and Glass Block Assemblies. While some have questioned the ongoing necessity of the hose stream test, the NFPA standards clearly state: “The hose stream test provides a method for evaluating the integrity of constructions and assemblies and for eliminating inadequate materials or constructions. The cooling, impact, and erosion effects of the hose stream provide important tests of the integrity of the specimen being evaluated.”
Architects, glaziers and building code officials should be aware of the importance of the hose stream test, because one manufacturer now sells a 60-minute “fire-rated” product that does not and cannot pass the mandatory hose stream test.
To the unsuspecting eye, a 45- or 60-minute fire-rated label on the glass that says “… without hose stream …” might not raise suspicions, unless you know that the hose stream is a mandatory procedure required by North American test standards. To selectively decide what portions of required test procedures one chooses to complete can be dangerous.
Fire glass testing
The hose stream test is part of a series of tests that begins with heat testing of the glass. Manufacturers seeking a fire rating take their products to an independent testing facility, such as Underwriters’ Laboratories. The lab installs multiple pieces of the glass in a frame and wall assembly, which is then placed in a large furnace. A fire is ignited on one side of the window assembly, with temperatures attempting to replicate a real world fire. Following a standard time/temperature curve, at five minutes temperatures approach 1,000 degrees Fahrenheit, and nearly 2,000 F at 180 minutes. The length of time the glass remains intact in the furnace will correspond to the final fire rating it receives, ranging from 20 minutes to three hours.
The goal of this testing is to determine how long the glass can remain in place and be expected to act as a barrier to a real life fire. If glass fails under the intense heat and vacates the frame, the flames and deadly smoke will be free to travel throughout a building.
If glass successfully survives the fire test and the manufacturer is seeking a rating greater than 20 minutes, the glass is immediately put through a second type of test. While the glass and framing system is still hot from the furnace, it is sprayed with water from a fire hose at a pressure of at least 30 pounds per square inch.
Most glass cannot tolerate drastic temperature differences such as this. If one area of the glass and framing system is hot while another is cool, it creates stress on the glass, known as thermal shock. Since part of the glass is expanding and part is contracting at the same time, the glass will shatter and vacate the frame.
The hose stream test is a critical way to measure how glass will respond to temperature differences. The glass must remain intact in order to pass and offer protection.
Interestingly, it doesn’t have to be a fire hose to prove the point. One manufacturer tested a 20-minute rated product with a simple garden hose. While the hot glass was able to withstand approximately 1,500 F, it quickly shattered when the light spray was applied.
Continuing need for hose stream test
In the case of a real world fire, there’s a good chance glass and framing systems that have been exposed to flames also will be subjected to water from a fire hose, sprinklers or fire extinguishers. If the glass can’t withstand thermal shock, it will fall out of the frame, leaving an opening for fire or smoke to spread.
In the United States, all fire-rated glazing products with ratings greater than 20 minutes are required to pass the hose stream test. Canada requires the hose stream test for all ratings. Building and fire codes are clear on why the hose stream test is critical, and in recent years, proposals to eliminate the test have been soundly defeated.
Last year, the manufacturer marketing a product that cannot pass the hose stream test sought to eliminate the test requirements from two portions of the fire-rated glass test standards in the International Code Councils’ building safety and fire prevention codes. The ICC’s Fire Safety Code Development Committee, comprising code officials, fire marshals and other experts, rejected these proposals after careful review of the issues presented in open public hearings. In its rejection of one of the proposals, the committee stated that removal of the hose stream test requirement “… would reduce the level of life safety which the code has generally required and provided.” In its decision on the other proposal, the committee noted that the issue has been debated a number of times and that “it has always been defeated.” (See 2006 ICC Public Hearing Results, FS121-06/07 and FS107-06/07). By its actions, the ICC has repeatedly validated the importance of the required hose stream test for life and property safety.
When choosing fire-rated glazing materials, it is critical to make sure that the product in question meets or exceeds all the testing standards. Otherwise, you might be taking a serious risk or increasing your liability. For openings with fire ratings of greater than 20 minutes, always insist on glass that has passed the mandatory hose stream test, and beware of products that acknowledge they have not passed the required test. There’s no need to compromise when life and property safety could be at stake.