Vapour from fire debris is passed through a scrubber containing an oxidising agent such as acidified potassium dichromate absorbed in silica-gel granules to a flame ionisation detector. Commonly used arson accelerants, eg petrol and paraffin, present as constituents are relatively non-reactive and pass to the detector, whereas most of those vapour constituents which are not accelerants, but are detectable and so could otherwise mask the presence of accelerants, eg alpha -pinene from wood, are relatively reactive and are absorbed in the scrubber.
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