Issue link: https://www.e-digitaleditions.com/i/1081695
March/April 2019 I 59 In the Figure 3 scenario, the assembly is anchored to the test furnace. During the testing process, the firestop collars expand through a process called intumescence (i.e., heat applied to the firestop material that causes it to expand rapidly). In so doing, they close off the openings and prevent the fire from spreading. Intumescent products are common in the industry, particularly well-suited for combustible materials, and also frequently used on noncombustible materials as well. The hose stream test (Figure 4) immediately follows the fire test and is designed to evaluate the structural integrity of the assembly. This is by far the most difficult segment of the test to pass. The red-hot assembly is blasted with a stream of cold water from a 64 mm (2-1/2 in.) diameter hose discharged at high pressure. Not only does the assembly need to withstand the force of the water pressure, it also needs to withstand the strong internal forces developed from the thermal shock of rapid cooling. UL 1479 prescribes the pressure and duration of the hose-stream exposure, which depends on the hourly rating being tested and the size of the assembly. Firefighters should particularly be aware of the hose stream test as it gives an indication of whether a structure will withstand the back-draft effect. The FIGURE 4: The hose stream test immediately follows the fire test. Aluminum cable conductors typically melt at 649°C (1,200°F) and many plastics ignite at temperatures significantly below 538°C (1,000°F), which is within two or three minutes of the start of a fire! thermal shock and force of applying a cold, high-pressure stream of water to a red-hot assembly is a good measure of system integrity. To pass the hose stream test, the firestop system must prevent the passage of water to the unexposed side. It is important to remember that a building fire is a dynamic event. As pressure levels change and heat becomes more intense, surrounding structures and elements can fail, thereby stressing the firestop. A good measurement of system integrity is established by the thermal shock of the cold high-pressure water stream to the red-hot