Weathering (Evaporative)
Definition
The preferential loss of low-boiling components from an ignitable liquid by evaporation. Shifts the GC-MS pattern toward heavier components and can cause a weathered gasoline pattern to resemble a medium petroleum distillate, requiring careful application of E1618 aromatic-fraction criteria for correct classification.
- Effect on GC-MS
- Shifts pattern toward heavier components
- Common confusion
- Weathered gasoline can resemble a medium petroleum distillate
- Governing standard
- ASTM E1618 aromatic-fraction criteria
- Relevant to
- Fire debris ignitable-liquid classification
Common questions
How do analysts avoid misclassifying weathered gasoline as a distillate?+
They apply the E1618 target-compound and aromatic-fraction criteria rather than relying on overall chromatogram shape, since ratios among diagnostic alkylbenzenes and polynuclear aromatics survive weathering even when the light-end profile does not.
Is evaporative weathering the same process indoors and outdoors?+
The chemistry is the same, but the degree of weathering varies with fire duration, ventilation, substrate absorption, and time between the fire and sample collection, so two samples of the same original liquid can weather to different degrees.
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...
- DB-5 Column
- A gas chromatography capillary column with a 5% phenyl-95% dimethylpolysiloxane stationary phase, the standard column for fire debris GC-MS analysis. Provides adequate...
- 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
- In fire debris analysis, any flammable liquid that could serve as an accelerant. E1618 classifies ignitable liquids into eight categories based on...
- Isoparaffinic Products
- An E1618 category of ignitable liquid dominated by branched-chain (isoparaffinic) alkanes with minimal aromatic or n-alkane content. Examples include Isopar solvents and...
- OSAC (Fire and Explosion)
- Organisation of Scientific Area Committees, Fire and Explosion Investigation Subcommittee, under NIST. Develops and publishes standards and needs statements for fire investigation...
- Passive Headspace Concentration (PHC)
- ASTM E1412 extraction method. The sealed evidence container is heated at 60-80°C; volatilised hydrocarbons adsorb onto an activated charcoal strip suspended in...
- SWGFEX
- Scientific Working Group for Fire and Explosion Investigation. A US-based multidisciplinary body that developed best practice guides for fire debris collection, canine...
- 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,...