News

State Fire Marshal’s Notice – March 2015

Definitions of Control, Comparison, and Exemplar SamplesIt has come to attention of the State Fire Marshal’s Office that there is a misunderstanding related to the use of “Control,” “Comparison,” and “Exemplar” on evidence submitted to the SFMO Forensic Arson Lab. The following is a clarification of these terms and the limits in which they can be used in lab evidence submittal.

Definitions:

Control Sample – a sample of known composition that is analyzed alongside test samples in order to evaluate any bias in the medium. Example: unopened gauze from agency supplies, carpet sample from manufacturer
Exemplar Sample – a typical representative of a test sample that is expected to evaluate any bias in the medium. Example: unburned carpet sample from the fire scene, most likely untouched by ignitable
Comparison Sample – a known reference sample used to compare to a test sample. Example: liquid from or swab of liquid from a labeled charcoal lighter fluid bottle found at the scene

Application:

A control sample is a sample from outside the crime/fire scene and is in its original, manufactured form untouched by its environment.
An exemplar sample is a sample taken from the crime/fire scene that is expected to have no ignitable residue present.
A comparison sample is a sample of a known ignitable liquid at the crime scene collected to be used as a comparison to an ignitable liquid residue found in another sample found at the crime scene.

Although NFPA 921 suggests that controls and/or exemplars be submitted with case evidence, the FAL does NOT require it. You may choose to keep case notes identifying what each item is using your own wording and simply submit the evidence under a general description and item number. Example: Item #1 4×4 gauze with unknown liquid; Item #2 4×4 gauze

*IMPORTANT NOTE – Analysis of a comparison sample to determine similarities between it and the evidence in question is not conducted by the Forensic Arson Laboratory. Due to magnitude of different products available that share the same chemical formulas and since origins cannot be determined with complete certainty, the Forensic Arson Laboratory will not conduct this type of analysis. In addition, analyses performed by the Forensic Arson Laboratory CANNOT determine the origin or manufacturer of an ignitable liquid.

For more information;
SFMO Forensic Arson Laboratory
512-676-6801
http://www.tdi.texas.gov/fire/fmlab.html