Passive Fire Resistance
The passive fire resistance provided by fire-resistant rated gypsum based assemblies for walls, ceilings, floors, and other building systems, slows or prevents the spread of fire, allows time for evacuation, and limits fire damage. Passive fire protection measures are intended to contain a fire and the spread of fire and smoke for a limited period of time, as determined by the local building code and fire code.
What Does A Fire Resistance Rating Mean?
Fire test results, including fire resistance ratings, enable code officials to compare materials and systems against code requirements to determine compliance. A fire resistance rating is one of many tools used by designers to assess relative fire risk. In addition to fire resistance, other properties of the construction materials to be considered include burning characteristics, fuel load of the space, and the proposed use of the structure or occupancy. All of these features must be considered before an assessment of the actual fire risk can be made. Additional factors such as building location, distance to fire services, and the presence or absence of other fire protection systems are also part of this complex assessment process.
A fire resistance rating alone cannot predict the performance of a system or building in an actual fire. No fire test method that is conducted under laboratory conditions can predict what will happen in a real structure fire as every structure is different – construction quality, fuel load, and other factors make every fire unique. Fire tests are a convenient way of classifying materials and assemblies to establish a ranking of performance among different materials and assemblies so designers can compare and select materials and systems for specific projects.
How is Fire Resistance Measured?
The fire resistance test method used throughout the United States is ASTM E119, Standard Test Method for Fire Tests of Building Construction and Materials. Similar test methods are published by Underwriters Laboratories (UL) and by the National Fire Protection Association (NFPA). The identical test referenced in the Canadian codes is ULC 263 Standard for Fire Tests of Building Construction and Materials.
The Fire Endurance Test subjects a specimen to a prescribed fire until certain conditions are met that indicate the end of the endurance test. This period of time is known as the “resistance period” of the Fire Endurance Test. All fire resistance rated systems, regardless of the materials from which they are built, are tested using this Fire Endurance Test.
In addition, the Hose Stream Test is utilized to ensure the assembly will be able to handle the abuse of a high-pressure firefighting hose and is divided into 1) a “primary” or “standard” method and 2) an “optional program” method. The optional program is referred to as an “exception” in the NFPA version. The standard method states that: “a duplicate specimen [is] subjected to a fire exposure test for a period equal to one half of … the resistance period of the Fire Endurance Test, but not for more than one hour.” The duplicate specimen is then immediately subjected to the impact, cooling, and erosion effect of a stream of water from a fire hose at a pressure and for a duration of time specified in the test method. If no significant amount of water passes through the test specimen, the fire endurance time of the first specimen becomes the fire rating for the system.
The duration of the hose stream exposure is a function of the fire endurance period of the original specimen and is keyed to the fire-resistance rating of the system being tested; i.e., the longer the rating, the longer and more severe the hose stream exposure. The “optional” program, which can only be used if both the testing laboratory and the test sponsor agree, is to administer the hose stream to the same specimen used for the Fire Endurance Test without the need for, and added cost of, constructing and burning a duplicate specimen as required by the standard method.