Testing for Fire Resistance

The fire resistance of assemblies is established in accordance with ASTM Standard E119, which is published by ASTM International. Formerly known as the American Society for Testing and Materials, ASTM International is a widely recognized standards development organization.

ASTM Standard E119 provides the ratings for walls and partitions, floor-ceiling and roof-ceiling assemblies, beams and columns. From this nearly century-old test standard, other test standards have been developed to evaluate the level of performance of through-penetration fire stop, joint and curtain-wall systems as they relate to the desired compartmentalization of buildings. The level of fire resistance is measured in hourly ratings: one, two, three, four and eight hours.

ASTM Standard E136 is employed to determine whether or not a given material is considered combustible. This standard measures a characteristic of the material itself, while the former standards evaluated the performance of the assemblies. The surface flammability and the amount of smoke produced by a given material are evaluated in accordance with ASTM Standard E84.

In establishing the fire resistance of an assembly, three factors are taken into consideration: the ability of the assembly to prevent the passage of flame, the capacity of the assembly to limit the heat transfer from the exposed side to the unexposed side and the assembly's ability to maintain its structural integrity for the classification period. Another consideration is the temperature of the structural steel, which may be used to establish restrained and unrestrained ratings.

Walls are required to be subjected to a hose stream test after a portion of the fire resistance test. The purpose of the hose stream test is to measure the relative integrity of the wall after it has been exposed to a fire. Water from the stream is not permitted to project through the wall assembly.

The walls that are to be tested are built within a steel and concrete yoke or frame. ASTM Standard E119 specifies that the area of the test specimen must be a minimum of 100 square feet, with no dimension measuring less than 9 feet. Typically, the test frames are 10 feet by 10 feet. Once the assembly is built within the frame, the frame is clamped in front of the furnace so that one side of the assembly is exposed to the fire.

The temperature within the furnace throughout the test is regulated in accordance with the standard time-temperature curve prescribed in the ASTM Standard.

Standard Time-Temperature Curve

The temperature on the unexposed side is monitored at a minimum of nine locations using thermocouples, which are temperature sensors that can measure a wide range of temperatures. Five of these locations are defined specifically by the standard. One of the thermocouples must be located exactly in the center of the assembly, while the other four must be positioned in the center of the wall quadrants. The location of the remaining four thermocouples is left to the discretion of the lab conducting the fire test.

The average temperature rise on the unexposed surface is not permitted to exceed 250 degrees F, while no single thermocouple is allowed to exceed a temperature rise of 325 degrees F. Load-bearing walls are tested with a superimposed axial load simulating the maximum load condition. The wall must be able to sustain the superimposed load during the fire endurance and hose stream tests. The relative integrity of the wall after a portion of the fire endurance test is determined by the hose stream test.

A second wall is tested to half, but not more than one hour, of the intended fire resistance rating. The fire is shut off, and the partition removed and immediately hit with a specified pressurized stream of water from a distance of 20 feet for a specified period of time that depends on the fire resistance rating. The test requires that this hose stream must be emitted from a 2-1/2-inch hose with a National Standard playpipe nozzle with a 1-1/8-inch tip. If the water does not project beyond the plane of the wall, then the wall passes the hose stream test.