From introduction: 'The importance of documented case studies or histories of wildfires (Alexander 1982) has been repeatedly emphasized by both fire managers and fire researchers (e.g., Schaefer 1961; Luke and McArthur 1978). For example, at the 4th Conference on Fire and Forest Meteorology, Chandler (1976) noted that 'Time and time again case histories have proven their values as training aids and as sources of research data.' We strongly support this notion and have endeavored to reflect it in out individual work area in fire research and fire management, respectively (Alexander et al. 1983; Lanoville and Schmidt 1985; De Groot and Alexander 1986). The idea of relying on wildfires as a possible source of fire behavior data is especially pertinent to empirically-based schemes of quantitative fire behavior prediction such as employed in the Canadian (Alexander and others 1984; Lawson et al. 1985; Canadian Forestry Service 1987; Stocks 1986) and Australian (McArthur 1977; Luke and McArthur 1978; Cheney 1981, 1985) systems of forest fire danger rating; this fact is certainly significant at the extreme end of the fire intensity scale where experimental fires (e.g., Stocks 1987) are rather difficult to arrange. The purpose of this paper is to present a wildfire case study which exemplifies the basic premise that fire suppression personnel are often in the best position to record a few simple, yet 'key' aspects of a fire's chronology. This opportunistic approach to documenting certain features of fire behavior is illustrated with an example of a free-burning, high-intensity crown fire (HY-36-81) which occurred near the town of Hay River, Northwest Territories (N.W.T) (Fig. 1) in July 1981. The fire management terminology used here follow Merrill and Alexander (1987). Mountain Daylight Time (MDT) used throughout the paper.'