Combustion-by-products/Fire debris analysis (Black carbon/soot, char, ash)
Fire insurance claims, especially due to the increasing wildfires incidents, have risen considerably in the past 18 months. Considering the materials and the conditions that are involved in fires (residential or wildfire) the analysis of fire residues (combustion-by-products) usually covers black carbon/soot, char and ash. Black carbon/soot is similar with carbon black in terms of morphology and size, but black carbon/soot is used in conjunction with “unwanted” products of incomplete combustion of hydrocarbons, as opposed to the “wanted” and controlled process that produces the industrial carbon black. Char is defined in ASTM D 6602 as being composed of particles that are larger than 1µm and may preserve the original cellular morphology of the material that was burnt. The generic term of carbonized material applies to char, ash, and coke/coal. Char is mostly elemental carbon, but it may also contain trace concentrations of mineral components and ash. Ash is also elemental carbon, with trace concentrations of minerals. However, the main difference between ash and char is that ash may not preserve any of the original morphology of the precursor and it may have a higher concentration of inorganic components due to the complete consumption of the organic matrix. As an example, analysis performed by EMSL Analytical of samples collected from homes impacted by wildfires by a composite analysis involving TEM/EDX (the mandatory method for black carbon/soot analysis) and light microscopy, determined the levels of contamination of various locations in homes with wildfires debris; the information could be used for mapping of impacted areas and accurate assessment for cleaning and de-contamination needs.