Scale effects on propagation rate of laboratory crib fires

Abstract

This paper presents results of a laboratory-scale propagating flame model in which crib fires are used. The model permits establishment of a steady-state condition for the free burning of solid fuels in the form of wood cribs. The principal objectives are to evaluate quantitatively the effects of the properties of fuel and fuel bed on the many attributes of fire behavior and to establish relationships of the variables in terms of several dimensionless groups. A dimensionless relationship of flame dimensions and modified Froude number is presented for data from a propagating flame model and is in close agreement with findings of other investigators using stationary flame models. Scale effects are also given for the fuel and fuel bed variables on burning time, propagating rate, and burning rate of laboratory crib fires. The work led to the following conclusions: (1) Laboratory crib fires may be used to represent line fires; (2) scaling of fuel size to the 1.5 power for burning time is valid for loosely packed fuel beds; (3) same dimensionless groups may be used for correlation of data from propagating flame models and from stationary flame models. Plans for future investigation include the use of crib fires to determine the effects of fuel spacing, wind, and slope on the burning characteristics.