Control Swab (Background)
Definition
A swab collected from an uncontaminated surface outside the outer cordon of a blast scene, processed identically to scene swabs, to establish the baseline chemical matrix of the environment. Essential for distinguishing blast residue from environmental contamination in the analytical interpretation.
- Location
- Outside the outer cordon of a blast scene
- Purpose
- Establishes baseline chemical matrix
- Processing
- Identical to scene swabs
Common questions
Why must a background swab be processed identically to the scene swabs?+
Any comparison between the two assumes they went through the same extraction and analytical conditions, so a procedural difference could create an apparent chemical difference that has nothing to do with the blast.
What does it mean if the background swab shows the same compounds as a scene swab?+
It undermines confidence that the compound detected at the scene is genuine blast residue rather than something already present in the environment before the explosion occurred.
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