Evaporative Weathering
Definition
The preferential loss of volatile components (benzene, toluene, C5-C7 alkanes) from an ignitable liquid residue during and after a fire, altering the GC-MS pattern relative to the fresh product. Heavily weathered gasoline may be misclassified as medium petroleum distillate.
- Process
- Preferential loss of volatile ILR components
- Components lost first
- Benzene, toluene, C5-C7 alkanes
- When it occurs
- During and after a fire
- Misclassification risk
- Weathered gasoline read as medium petroleum distillate
Common questions
Why do lighter hydrocarbon components evaporate faster during weathering?+
Volatile compounds such as benzene and toluene have lower boiling points and higher vapor pressures than heavier hydrocarbons, so fire heat and prolonged exposure drive them off the sample first, shifting the remaining chromatographic profile toward heavier compounds.
How do analysts avoid misclassifying a heavily weathered gasoline sample?+
They rely on target compound ratios and diagnostic patterns from ASTM E1618 that remain relatively stable despite weathering, such as certain alkylbenzene and branched alkane ratios, rather than relying solely on the overall boiling-point range that weathering distorts.
Does evaporative weathering affect all ignitable liquid classes equally?+
No, lighter petroleum distillate classes such as gasoline show more dramatic pattern shifts because they contain a larger volatile fraction, while heavier products like kerosene or diesel change proportionally less since more of their composition is already less volatile.
Related terms
- ASTM E1618
- Standard Test Method for Ignitable Liquid Residues in Extracts from Fire Debris Samples by Gas Chromatography-Mass Spectrometry. The active analytical standard defining...
- Carbon Disulfide (CS2)
- The standard elution solvent for activated charcoal strips in ASTM E1412 passive headspace analysis. Selected for its low UV absorption, minimal GC-FID...
- Extracted Ion Profile (EIP)
- A GC-MS chromatographic display plotting only ions of a specified m/z value against retention time, effectively filtering out all compounds that do...
- Ignitable Liquid Reference Collection (ILRC)
- A database of GC-MS chromatographic data for over 1,100 ignitable liquid products maintained by the National Centre for Forensic Science at the...
- Light Petroleum Distillate (LPD)
- The ASTM E1618 ignitable liquid class covering C4-C9 aliphatic products (charcoal lighter fluid, camping fuel, some paint thinners). The class most frequently...
- Passive Headspace Concentration
- The ASTM E1412 method in which an activated charcoal strip is suspended in a sealed container above heated fire debris (60-80°C, 16...
- Total Ion Chromatogram (TIC)
- A GC-MS chromatographic output plotting the summed intensity of all detected ions at each retention time. Provides the full-pattern overview of a...
- Tropylium Cation (M/z 91)
- The C7H7+ fragment ion produced by rearrangement of alkylbenzenes in the EI ion source of a mass spectrometer. The diagnostic ion for...
- Unresolved Complex Mixture (UCM)
- The broad hump of hundreds of co-eluting cycloalkane and isoalkane compounds in the TIC of heavy petroleum products (diesel, heavy fuel oil,...