Comparison (Control) Sample
Definition
A sample of unburned substrate collected from the same room or proximate unburned area as the fire debris sample, of the same substrate type. Analysed under identical GC-MS conditions to provide the substrate background chromatogram for subtraction.
- Field
- Fire debris analysis
- Source
- Unburned substrate from the same room or nearby unburned area
- Matched to
- Same substrate type as the fire debris sample
- Purpose
- Background chromatogram for pyrolysis product subtraction
Common questions
Why must the control sample come from the same room as the fire debris?+
Building materials, carpet, and furnishings vary by room, and different substrates pyrolyse to produce different background hydrocarbon patterns, so a control from a different room or a different material type would not reliably represent the background the fire debris sample is being compared against.
What happens if no unburned comparison sample can be collected?+
The examiner has to interpret the fire debris chromatogram without a matched background, relying more heavily on pattern recognition of known ignitable liquid signatures, which increases the risk of misattributing a pyrolysis artefact to an accelerant.
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...
- 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...
- Type C Interferent (E1618)
- ASTM E1618 designation for a substrate whose pyrolysis products can produce a chromatographic pattern meeting the criteria for an ignitable liquid category....
- 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,...