Fire Scene Evidence Collection Guide

Ignitable Liquid Residue & Fire Debris

Carpet

Detailed Procedure:

Because they are porous and absorbent, carpet, carpet padding, and the subfloor below the carpet can all be excellent substrates to retain ignitable liquid residue.

To collect carpet for ignitable liquid residue testing:

  1. Select a productive sampling area. Productive sampling areas contain some or all of the following characteristics:

    • Within an area of ignitable liquid indicators, such as a suspected pour pattern

    • In an area where ignitable liquid may collect or pool, such as the lowest point on the floor or at the base of a wall

    • The edge of a burn pattern or suspected pour pattern

    • At junctures with furniture and walls

    • Where the tread meets the riser on a stair

  2. Photograph the carpet in place, including any stains, patterns, or other features noted.

  3. Wear new, unused, clean latex or nitrile gloves.

  4. Use a new or properly cleaned utility knife to cut a strip of carpet and the padding underneath that will fit inside the evidence can.

  5. Lift up the cut carpet and padding. Visually inspect the backs of both materials for staining and note any odors. Photograph any stains.

  6. Chimney roll the carpet and padding together. Allow any excess water to drain. Stand the chimney-rolled carpet and padding up in a new, unused metal paint can. Fill the container no more than 2/3 full, leaving 1/3 headspace for vapors.

  7. You may also elect to sample the subfloor under the carpet. Follow the procedure for sampling that type of flooring.

  8. If it will fit in the same can, add the subfloor to the carpet sample. If the piece is large, break into smaller pieces to fit into the container. If the subfloor will not fit in the same can as the carpet to leave 1/3 headspace, place the subfloor in a second can and note on the evidence label that it was the subfloor and what carpet sample it corresponds to.

  9. Clean the lip of the can using a new or properly cleaned screwdriver or other suitable tool.

  10. Gently tap the top of the lid with a clean rubber mallet to seal it. Do not dent the can because it may compromise the seal.

  11. Seal the can with evidence tape. Initial and date the tape.

  12. If possible, collect a comparison sample of carpet and padding that is not suspected to contain ignitable liquid residue and is not in the room of origin. Comparison samples are especially important when sampling carpet because many carpets and carpet paddings are manufactured using petrochemicals and can share molecular similarities with many ignitable liquids. This sample should be collected in a separate container using a new, unused pair of gloves and a properly cleaned or new tool.

  13. Label the container with identifying information, including case number, date, exhibit number, a brief description including recovery location, and your name.

  14. Store the item in a secure location, such as a locked evidence van or your vehicle, until you are able to transport it to the laboratory.

Laboratory examination of carpet:

Carpet can be tested for ignitable liquids using gas chromatography mass spectrometry. This test can determine the classification of the ignitable liquid. If necessary, carpet can also be examined for class characteristics. Some carpets may be able to be traced to the manufacturer. Carpet fibers can be compared to questioned fibers found elsewhere.

Source:

interFIRE. "Evidence Sampling for Ignitable Liquids Testing." Online Training Module, 2013:

http://www.interfire.org/training/evidencesampling.asp

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