Type C Interferent (E1618)
Definition
ASTM E1618 designation for a substrate whose pyrolysis products can produce a chromatographic pattern meeting the criteria for an ignitable liquid category. Requires explicit comparison sample analysis and documentation before a positive identification opinion can be issued.
- Standard
- ASTM E1618
- Cause
- Substrate pyrolysis products matching an ignitable liquid pattern
- Required step
- Comparison sample analysis and documentation
- Effect
- Blocks a positive ID opinion until interferent is ruled out
Common questions
Why can a burned carpet or synthetic material mimic an ignitable liquid in GC-MS data?+
Many polymers and adhesives pyrolyse into hydrocarbon fragments that fall in the same retention-time and mass-spectral pattern as a petroleum distillate class, so the raw chromatogram alone cannot distinguish accelerant residue from the substrate's own combustion products.
What does an analyst do once a Type C interferent is suspected?+
They obtain an unburned or minimally burned comparison sample of the same substrate material, pyrolyse or burn it under comparable conditions, and compare its pattern against the fire debris extract before issuing any identification opinion.
Related terms
- 4-Vinylcyclohexene (4-VCH)
- A pyrolysis product of styrene-butadiene rubber (SBR) carpet backing, appearing at m/z 108 in the GC-MS. Elevated m/z 108 in a fire...
- Alkene Triplet Pattern
- The GC-MS signature of polypropylene pyrolysis: a repeating triplet of n-alkane, 1-alkene (terminal double bond), and diene peaks at each carbon number...
- Background Subtraction
- The analytical practice of comparing fire debris EIPs against comparison sample EIPs from unburned substrate of the same type. Features present in...
- Comparison (Control) Sample
- A sample of unburned substrate collected from the same room or proximate unburned area as the fire debris sample, of the same...
- Principal Component Analysis (PCA)
- A multivariate statistical method used in fire debris research to reduce chromatographic data matrices to principal components that capture major variance. Used...
- Pyrolysis
- The thermal decomposition of cellulose in paper at approximately 150 to 300 degrees Celsius, disrupting glycosidic bonds and releasing water and carbon...
- Substrate Interferent
- A pyrolysis product from building or furnishing material that produces a GC-MS chromatographic pattern overlapping with or resembling an ignitable liquid category...
- SWGFEX Type C Interferent List
- A documented list maintained by the Scientific Working Group for Fire and Explosion Investigation (and continued by OSAC) of substrates known to...
- 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,...