What is Residual Odor

Residual Odor

Several court cases I have been involved with centered around residual odor prompted me to explain what it is and how you define it. Canine handlers have used residual odor for years to identify an odor plume followed by a K9 to a source, where nothing was found. The judge wanted to know how a canine could smell something not present in one case. In the second case, an expert from the other side was testifying that it is a dead odor, and we should be training our canines to a threshold so the dog would ignore odors that are no longer there.

Residual odor is liberated or separated odor or scent from humans, narcotics, explosives, and cadavers. This separation readily produces vapor and is said to be volatile and to have a high vapor pressure. Hence the name Volatile Organic Compounds (VOC). VOCs can be released by liquid or solid substances and spread out into the air over time. The example I use in court to explain this is how we use dogs to detect human scents. Skin cells readily fall off the human body, carrying with them the unique scent of that person. Even after the person has left the area, a dog can track that scent to where the person is currently walking.

Now that you have more information about VOCs, we should talk about courtroom testimony and how experts try to defuse residual odor and its detection by police canines. Trainers and handlers are relatively unique in that many people do not understand what we do or how we do it. This includes judges and lawyers. Your ability to explain residual odor or scent may be the key to a successful conclusion.

Ted Daus explains it this way in his article “When does drug dog odor become “residual”?

“Odor Is Odor
Now let’s discuss the archenemy of the K-9 handler — the term “residual odor.” Let’s examine the terms residual and odor and how they function together. The term residual means: the quantity remaining after most of something has been removed. Odor is a distinctive smell. Thus, “residual odor” is what remains of a distinctive smell after the original object has been removed. Allow me to simplify that concept: the odor given off by an object — whether or not the object is present — is still just odor. Defense lawyers want to label odor as “residual” because they want to be able to argue that if a dog can alert on a car without drugs actually being in the vehicle, then the dog should not be a tool that law enforcement can use to determine whether there is probable cause for a search of that car.”

Canine experts who often testify against us use several arguments to persuade a judge or jury in residual odor cases. They often say you should be training your dog to a threshold they won’t give a final response for residual odor. The answer is simple; several factors determine odor or scent availability. Packaging, air movement, vapor pressure, and the amount of odor or scent. Weather can also play a role in availability once the VOCs are released. Dogs are trained to detect an odor and follow it to the source. That is their job. When an expert says you should train your dog to a threshold, they imply the dog can tell by smell how much of the product is located at the source. They can’t.

Dead odor is another one; if it is dead, it is not there. 

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