Replacing international temperature–time curves with BFD curve

Abstract

From The World Trade Centre Investigation Draft Report by NIST [National Institute of Standards and Technology. World Trade Centre performance study: data collection, preliminary observations and recommendations. FEMA (Federal Energy Management Association), 2002.], one of the recommendations was to “improve the century-old standard for the testing of building components, assembles and systems”. NIST believes that it is essential to complete a comprehensive review that will establish a firm technical basis for future fire-rating requirements. The purpose of this paper is to describe and demonstrate how a single log-normal equation (such as BFD curve [Barnett CR. BFD curve: a new empirical model for fire compartment temperatures. Fire Safety J 2002; 37: 437–63]) can be used to replace international temperature–time curves such as ISO 834, BS 476, ASTM 119, NFPA 251, the external, the hydrocarbon and the Eurocode parametric curve. There are five main reasons for such a replacement. Firstly, BFD curve is a “natural” fire curve that fits the results of actual fire tests closer than previously known fire modelling methods. Secondly, the shape of the curve bears a strong relationship to both the pyrolysis coefficient ( R/ A v. h v 0.5) and the opening factor ( F O2). Thirdly, the shape of the curve is related to the thermal properties of the firecell. Fourthly, contrary to a number of other fire modelling curves, BFD curve does not need the use of a time shift. Finally, it uses a single equation to model the temperature of both the growth and decay phases of a fire in a building whereas a curve such as Eurocode 1 curve requires two equations. Only three factors are required to model a BFD curve: maximum gas temperature, the time at which this maximum temperature occurs, and a shape constant for the curve. Ref. [2] shows how these factors can be derived.