Are Two 2-Hour Fire Rated Shutters Equivalent to a 4-Hour Shutter Using ASTM E119?

Abstract

Performance-based design is commonly applied to projects that have difficulties in complying with prescriptive fire codes in the Far East. There are procedures for evaluating fire resisting construction and structural elements with fire resistance ratings lower than the values specified in the fire codes. The equal temperature-time exposure concept or t-equivalent rule is commonly applied to support the argument. This paper will discuss whether installing two fire shutters each of a 2-hour fire resistance period is equivalent to one 4-hour shutter. The standard temperature-time curve under ASTM E119 was applied to show they are not equivalent and to illustrate the inadequacy. Further, there are concerns in applying such an approach for bigger fires as the radiative heat flux acting on the construction element is not included. Fire hazard assessment on fire resisting construction with lower ratings under postflashover fires should be evaluated with caution. Full-scale burning tests with bigger fires are suggested as a means to support the argument or demonstrate that the equal temperature-time concept would work as expected.