A place to ask questions and add to probative and informative discussions associated with the various aspects of the field of fire investigation. -- FORUM RULES---BE CIVIL AND NO NAME CALLING, NO BELITTLING, NO BERATING, NO DENIGRATING others. Postings in violation of these rules can be removed or editted to remove the offending remarks at the discretion of the moderators and/or site administrator.
Re: Accelerant sampling timeline
Posted by:
John Lentini (IP Logged)
Date: June 14, 2017 01:05PM
There are far too many variables for a rule of thumb. It depends on the amount of IL used, the substrate, the amount and type of debris that's covering the location of the ILR, the temperature of the fire and the ambient temperature afterward. When poured on synthetic carpet, the carpet can melt and entrap the ILR indefinitely. Same for plastic containers. They never give up the ILR unless they are completely consumed.
Carbonized substrates tend to hold ILR for a very long time due to adsorption of the same kind that happens in the lab when the samples are analyzed.
My rule of thumb was always to collect as much as I could and test it no matter how long since the fire. You have to remember that the detection limit for ILR is incredibly low, as low as 1/500 of a drop (0.1uL). So always collect a comparison sample. You wouldn't want to have a positive sample that means nothing, would you? That's what will happen if the lab finds ILR but there is no comparison sample.
The best location is in the middle of the pattern, not at the edges, as was conventional wisdom for many years.
John J. Lentini, CFI
Scientific Fire Analysis
Islamorada, FL
www.firescientist.com
scientific.fire@yahoo.com