Based on the number of inquiries the GA receives, we believe that a large segment of the population does not understand that fire ratings are actually based on tests conducted under highly controlled laboratory conditions; nor is it generally understood what “hourly” fire resistance ratings mean.
Fire protection engineers and other fire-testing experts understand that fire resistance ratings are derived from tests run in a laboratory setting. However, based on the number of inquiries we receive at the association and what we have come to understand to be the perception of the public in general, we believe that a large segment of the population does not understand that fire ratings are actually based on tests conducted under highly controlled laboratory conditions; nor is it generally understood what “hourly” fire resistance ratings mean. The purpose of this article is to explain the meaning of the ratings for fire resistive systems, such as one, two, three, and four hours, that are usually incorporated into model and jurisdictional building codes where appropriate.
Most of the fire resistance rated walls or partitions constructed with gypsum board systems in the U.S. and Canada contain “type X” gypsum wallboard (or perhaps an improved variation with a proprietary trade name). Type X gypsum wallboard is manufactured in accordance with ASTM Standard C 36. ASTM C 36 is being phased out and will be replaced shortly by another standard, ASTM C 1396. ASTM C 36/1396 contains a provision that type X gypsum wallboard must meet specific criteria in order to “pass” a test defined in another ASTM Standard, E 119, “Standard Test Method for Fire Tests of Building Construction and Materials.” It is this widely accepted test method that is used to determine the hourly fire resistance ratings for systems constructed of gypsum board (as well as other materials).