Your definition should also include the fact that true comparison samples are "unburned" and should not be collected from the area/room of origin. If your sample does not meet the above stated criteria, then it is not considered a true comparison sample by the laboratory and should not be labeled as a comparison sample, but simply just another debris sample.
This is the reason why a comparison sample cannot be collected at every fire scene.
Sharee B. Wells
Forensic and Scientific Testing
Senior Forensic Scientist/Laboratory Director
Swells@fast-lab.com