Wood Char Depth: Interpretation in Fire Investigations

INTRODUCTION Wood char depth patterns have been considered important by fire investigators in most countries where significant use is made of wood as a construction material. This is natural, since post-fire patterns found on wood members are generally more pronounced and extensive than those found on many other construction materials. But the present state of affairs has been such that there is not much agreement on what quantitative interpretation, if any, can be placed on such patterns. In fact, respected specialists have suggested that charring rates are meaningless with respect to fire investigations [1][2]. The standard guide for fire investigators used in the US, NFPA 921 [3], states that: “The investigator is cautioned that no specific time of burning can be determined based solely on the depth of char.” Nonetheless, it then devotes two pages to a discussion on how to measure depth of char and what conceivable deductions might be made from these measurements, although it arrives at no definite conclusions on the latter point.