Fire Scene Evidence Collection Guide
Soil/Grass
Detailed Procedure:
Soil and grass are typically sampled:
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As trace evidence recovered from a substrate, such as a tire or a suspect's footwear
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For comparison to questioned trace evidence as a possible source
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For ignitable liquid residue testing
If a sample is being collected for ignitable liquid residue testing, select a soil sampling area that contains some or all of the following characteristics:
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Within an area of ignitable liquid indicators, such as a suspected pour pattern
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In an area where ignitable liquid may collect, such as the lowest point on the grade
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Edge of a burn pattern or suspected pour pattern
Soil samples that may contain ignitable liquid residue should be refrigerated or frozen as soon as possible and then left refrigerated or frozen until they are submitted for testing so that soil decomposition does not break down any ignitable liquid residues that may be present.
To collect soil and/or grass:
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Select a productive sampling area.
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Photograph the soil or soil particles in place.
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Wear new, unused, clean latex or nitrile gloves.
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If you are digging soil from the ground, use a new or properly cleaned trowel or other suitable tool. Sample the top 2 to 4 inches of topsoil, including surface material. Soil that may contain ignitable liquid residue must be collected in an airtight container. If not confined in an airtight container, the ignitable liquid vapors may evaporate. Therefore, place the soil in a new, clean, unused metal paint can. Do not pack down the soil. Leave 1/3 headspace in the can for vapors.
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If you are collecting particles from a substrate, collect the entire item if possible and secure it in an appropriate container that will not allow soil particles to escape. If you cannot collect the entire item, using a new or properly cleaned brush, gently brush the soil particles onto a new, clean sheet of white paper. Then, either pharmacy-fold this paper and place it in an evidence envelope or funnel the particles into a glass jar with a screw-type lid.
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If needed, collect a comparison sample from a location not within the ignitable liquid pattern in a separate container using new gloves and a new or properly cleaned tool. A comparison sample for ignitable liquids testing will help the laboratory exclude compounds occurring naturally in the soil.
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Clean the lip of the can using a new or properly cleaned screwdriver or other suitable tool.
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Tightly close the can by gently tapping it with a rubber mallet to seal it. Do not dent the can because it may compromise the seal.
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Seal the container(s) with evidence tape, and initial and date the tape.
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Label each container with identifying information, including case number, date, exhibit number, a brief description including recovery location, and your name.
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Store the item(s) in a secure location, such as a locked evidence van or your vehicle, until you are able to transport it to the laboratory.
Testing for ignitable liquid residues in soil samples is very time sensitive. Samples should be sent to the laboratory ASAP. Soil samples should be refrigerated or frozen as soon as possible and kept refrigerated/frozen until the sample can be sent to the laboratory for testing. This will keep bacteria that are naturally occurring in soil from degrading common ignitable liquids. If needed, consult your forensic laboratory for guidance.
Laboratory examination of soil:
Soil particles can be examined for microscopic characteristics and makeup. Questioned soil particles may be able to be compared to a known soil source in an attempt to determine the origin of the questioned particles.
Soil can be tested for ignitable liquids using gas chromatography mass spectrometry. This test can determine the classification of the ignitable liquid.
Source:
Crime Scene and Evidence Collection Handbook. Bureau of Alcohol, Tobacco, Firearms and Explosives, 2005.
interFIRE. "Evidence Sampling for Ignitable Liquids Testing." Online Training Module, 2013: