Combustion and arson Flashcards
What is gunshot residue (GSR)?
GSR, also known as firearm discharge residue (FDR), cartridge discharge residue (CDR), or gunfire residue (GFR), consists of particles from the primer, gunpowder, projectile, and cartridge case deposited on a shooter’s hands, face, and clothing.
What is the most common source of GSR particles?
The primer, which contains percussive explosives such as lead azide, lead styphnate, tetracene, barium, and antimony compounds.
What factors affect the spread of GSR?
Distance from the firearm, type of ammunition, environmental conditions, and movement after firing.
How long does GSR typically remain on a shooter’s hands?
Approximately 6 hours before it degrades or is removed.
What are some ways GSR can be lost or removed from surfaces?
Washing hands, changing clothes, environmental exposure, and secondary transfer.
What are some alternative sources of GSR-like particles?
Occupational exposure (e.g., welding, fireworks, brake dust) and environmental contamination.
How is GSR collected from a suspect’s hands or clothing?
Using adhesive stubs (SEM stubs) or swabs to lift residue particles.
Why is it important to collect GSR evidence quickly?
GSR is fragile and easily lost, so collection should be done within 6 hours after discharge.
What are some common methods used to detect GSR?
Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectrometry (EDS), Atomic Absorption Spectroscopy (AAS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
How does SEM/EDS help in GSR analysis?
SEM/EDS identifies and characterizes GSR particles based on size, shape, and elemental composition.
What is the typical shape
Spherical
What are PbBaSb particles, and why are they significant?
These are GSR particles containing Lead (Pb), Barium (Ba), and Antimony (Sb), which are considered highly characteristic of firearm discharge
What factors can cause false-negative results in GSR analysis?
Washing hands, wearing gloves, using lead-free ammunition, or firing a rifle/shotgun that does not deposit GSR on hands.
What is the difference between inorganic and organic GSR (OGSR)?
Inorganic GSR (IGSR) consists of primer metals like Pb, Ba, and Sb, while OGSR includes organic compounds from propellants, such as diphenylamine (DPA) and nitroglycerin.
What is the advantage of analyzing both IGSR and OGSR?
It provides more comprehensive evidence and increases detection reliability.
What is the ASTM E1588-20 standard?
It is the forensic standard for analyzing GSR particles using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM/EDS).
How are samples collected under ASTM E1588-20?
Using SEM stubs with a conductive carbon tape to collect residue from hands, clothing, or surfaces.
What is a challenge in detecting GSR using ASTM E1588-20?
Differentiating GSR from environmental contaminants with similar composition.
How does ASTM E1588-20 handle sample preservation?
Samples must be collected and stored in airtight, contamination-free conditions.
How can forensic scientists ensure reliability in GSR detection?
By using strict sample collection protocols, proper controls, and validated analytical methods.
