Fire Science
This transition occurs when thermal radiation from the upper hot gas layer causes widespread ignition of exposed combustibles.
What is flashover?
The reason fire debris should be packaged promptly after collection.
What is to minimize loss of volatile compounds and prevent contamination?
The hydrocarbon family characterized by saturated, open-chain molecules with no branching.
What are normal alkanes (n-alkanes)?
This explains why increasing temperature can transfer more analyte from a debris matrix into the headspace.
What is increased volatilization?
This GC parameter describes the time between sample injection and the appearance of an analyte peak.
What is retention time?
This environmental process tends to preferentially remove the more volatile constituents of an ignitable liquid.
What is evaporation (weathering)?
The four elements necessary to sustain flaming combustion.
What are fuel, oxygen (oxidizer), heat, chemical chain reaction?
This type of evidence container is commonly used for collecting debris suspected of containing volatile ignitable liquid residues.
What is a clean, vapor-tight metal evidence can?
This refinery process separates crude oil into fractions primarily according to volatility.
What is fractional distillation?
This sorbent is commonly suspended above fire debris during passive headspace concentration.
What is an activated charcoal (activated carbon) strip?
This term describes the most intense peak in a mass spectrum.
What is the base peak?
This type of interfering chemical profile can arise from thermal decomposition of carpet, wood, plastics, or other substrates.
What is a pyrolysis?
This type of heat transfer can ignite or damage materials without direct flame contact.
Radiation
This type of control helps distinguish compounds originating from the substrate from those associated with a suspected ignitable liquid.
What is a comparison substrate sample?
This petroleum component classification conatains many alkane with contain one or more branches.
isoparaffins
This headspace technique uses a coated fiber to collect volatile compounds without requiring solvent elution.
What is SPME?
This GC oven program feature is commonly used to elute compounds across a broad range of boiling points in one run.
What is a temperature ramp (temperature programming)?
A questioned sample and a reference ignitable liquid have different relative peak intensities but similar diagnostic chemical patterns. Give one reason the two could still be consistent.
What is differential weathering, matrix effects, dilution or extraction-related differences?
This uses the scientific method (hypothesis testing) requiring fire investigators to test competing explanations against the available evidence.
NFPA 921
One reason an investigator should avoid packing an evidence container completely full.
What are maintaining sufficient headspace for vapor sampling and allowing a reliable seal (either)?
This refining process converts larger hydrocarbon molecules into smaller ones and can change the composition of petroleum fractions.
What is cracking?
Unlike headspace sampling, this technique accumulates analytes on a sorbent over an extraction period.
What is passive headspace concentration?
This type of chromatogram displays signal only for selected mass-to-charge ratios.
What is an extracted ion profile/chromatogram (EIP/EIC)?
A chromatogram contains many hydrocarbons. Explain why this observation alone is not enough to identify an ignitable liquid residue.
What is because substrates and pyrolysis products may also contain hydrocarbons, so the overall distribution and diagnostic patterns must be evaluated?
A floor-level burn pattern is observed after a room reaches full-room involvement. Name two processes, other than a liquid pour, that might explain it.
What are ventilation-driven burning, radiant heating, burning/melting furnishings, or falling burning debris? (Any two.)
Two ways that an investigator's own actions could introduce misleading volatile compounds into a debris sample.
What are contamination from tools or gloves, exposure to fuels/solvents, or cross-contamination between samples? (Any two.)
Compared with a straight-chain alkane of the same molecular formula, a highly branched isomer generally has this difference in boiling point.
What is a lower boiling point?
A passive extraction is performed at an excessively high temperature. Identify one possible advantage and one potential disadvantages.
What are increased analyte recovery, but also increased matrix interference, possible sorbent overload, or sample alteration?
Two compounds coelute chromatographically. Explain how mass spectrometry might still help distinguish them.
What is by examining their characteristic ions and fragmentation patterns, provided sufficiently distinctive ions are present?
A laboratory detects compounds consistent with an ignitable liquid. State two conclusions the analyst cannot establish from this chemical finding alone.
What are the fire's cause or manner, whether the liquid was intentionally introduced, the identity of a particular commercial product, or the fire's point of origin? (Any two.)