The tragic influx of severe flooding throughout the US in the past twelve months – firstly in North Carolina, and more recently occurring in Texas – has resulted in a great deal of coverage focusing on rescue and recovery efforts. Perhaps one of the most intriguing and useful tools which rescue personnel are deploying in Texas right now are Human Remains Detection (HRD) dogs.
You may be wondering if it is possible for a dog to smell a body under the surface of the water, especially if there is a lot of water and the body could be trapped under debris. The short answer is: Yes.
HRD dogs can be specially trained to identify bodies of drowning victims, even when they are deep under the surface. How is this possible, you ask? In the following article, we will explain exactly what these dogs are smelling, and how these incredible animals are able to recover the bodies of individuals who may otherwise have never been found.
What is odor?
Smells… what we think of when we put our nose to a rose and breathe in. The emotions that we feel when we breathe in through our nose and detect that delectable bakery is cooking in the oven. We all know of smells since smelling is one of our senses, and we use our sense of smell to promote survival.
When it comes to detection dogs, smelling becomes quite a bit more complex. The target odors that dogs are taught to find are most frequently volatile organic compounds. This means that they are molecules which are:
Volatile. These molecules have a high vapor pressure, which basically means that they readily evaporate.1
Organic. These molecules are carbon based, which is an element serving as the basis for living organisms.
Compound. These molecules contain two or more elements which have been chemically joined.2
So basically, the molecules which we are asking our dogs to find are gaseous substances which have the ability to move rapidly due to their low molecular weight, and propensity to evaporate even at normal temperatures. Volatile organic compounds (VOCs) are typically very small molecules with a high rate of movement in most regular environments.
The target odors which HRD dogs are tasked with finding are considered biogenic VOCs, meaning that they are emitted by plants, animals or microorganism. Biogenic VOCs are the result of metabolic processes or decomposition.3 HRD dogs are essentially searching for the VOC profile created by human decomposition. A VOC profile refers to the precise combination of VOCs necessary to make up a particular target odor. Since the decomposition process begins immediately after death and continues until post-skeletonization4, there is often a lengthy period of time where a relevant VOC profile is present.
The second important thing to understand about odor profiles is that pretty much everything has one. The biological processes occurring in living (and deceased) subjects creates an odor profile, which wafts away from that subject in a cone shape. This is often referred to as a “scent cone”. As the odor molecules move away from the subject, they tend to spread out, eventually moving in various ways depending on their environment.
How does odor move in water?
You probably didn’t click on this article so you could enjoy a science lecture – but unfortunately this topic is all about the science. In order to understand how exactly dogs are able to locate victims underwater, it is imperative to first understand how odor molecules move in the water.
As previously mentioned, HRD dogs are searching for VOC profiles. Since these molecules are most happy to evaporate, they are not generally soluble in water.5 When an object emitting VOCs is underwater, it continues emitting these VOCs, which rapidly move away from the object and spread out. Since the molecular weight of water is greater than the molecular weight of gas, these volatile molecules rise to the surface and into the air. The force of running water can have a significant impact on where these molecules end up, since the force of the water’s movement can cause them to reach the air at a distance from the original object. If the water is mostly stationary, the molecules tend not to travel nearly as far.
What do HRD dogs smell?
HRD dogs are trained to locate the smell of human decomposition. These dogs can recognize the VOC profile specific to human decomposition while ignoring irrelevant odors. Since the decomposition process produces a lot of gases, there are a great deal of relevant VOCs.
The decomposition process differs in water than on air. Decomposition in water generally occurs more slowly6, which can mean less odor available for the dogs in the very beginning stages of decomposition but more odor available for longer as the decomposition process progresses.
When a victim drowns and the decomposition process begins, VOCs are released into the water. These VOCs travel through the water until they reach air, where they are able to be identified by an HRD dog. If the water is flowing or moving, these VOCs will travel some distance from the victim. The movement of the water, as well as other factors such as temperature, will determine how far away these VOCs are carried before they reach air. HRD dogs will then identify these VOCs are relevant target odors and communicate their presence to their handler through a TFR (trained final response).
Water HRD can be difficult and very confusing for dogs who have only ever trained on land. Typically, when training on land, an HRD dog is expected to get as close to source as possible. Oftentimes, this means being only a few inches away from target odor. These dogs are expected to work through the odor pool, searching for the area containing the highest concentration of target odor. When working water deployments, however, an HRD dog will never be that close to source. Since HRD dogs are typically expected to work through the larger, less concentrated odor pool into a very high concentration of odor, dogs who have not trained specifically for water deployments will be unlikely to indicate.
Photo credit: NC Trooper's Association
What does a typical water deployment look like?
Water search and rescue missions take place in a boat – typically one which is large enough to safely hold the HRD dog, their handler, law enforcement or any other individuals involved in the deployment – but not any larger. These boats are typically not very tall and are able to move at variable speeds through the water while also providing good directional control.
The HRD dog-handler team will be provided a search area, where they will travel to. Once there, they will travel at a slower pace through the water and the handler will closely monitor their dog’s body language. Although water HRD dogs are not physically moving around, they are still working just as hard as if they were searching on land.
The handler will observe the dog for a change of behavior which signifies that target odor may be present. A lot can happen to the movement of VOCs once they hit the water’s surface, which can mean that they are rapidly available and then unavailable, or that they are discernible at a distance from source, or that other factors (such as physical obstructions) catch them or alter their movement patterns.
Since the amount of available odor can range from barely there to plentiful, a handler must be very attuned to their dog’s body language cues. Once a change of behavior (COB) is recognized, the dog will either indicate (implying that the strongest source of odor is in that exact spot), or simply continue demonstrating a COB (which typically occurs in cases where odor is sparse or rapidly changing). It is then up to the handler to communicate what they are seeing. Oftentimes imaging will be used in conjunction with the dog to identify if an object appears to be under the surface of the water.
Once it is probable that a victim has been located, efforts will be made to retrieve the body – after which further identification and investigation can take place.
HRD dogs are truly an incredible asset to society. They can locate evidence barely visible to the naked eye, find victims in some of the most well-hidden locations, and even let their handler know when a body is trapped deep under the water’s surface. Although nothing will ever make up for the tragedy caused by lives lost in recent flooding events, the HRD dog-handler teams deploying in these locations can provide closure to loved ones who otherwise may spend the rest of their lives wondering. HRD dogs don’t simply find victims – they commence the healing process which affected families need to move forward.
References
1. Speight, J.G. High Vapor Pressure. In: Abraham, M.A. Encyclopedia of Sustainable Technologies. Elsevier. 2017.
2. National Cancer Institute. Compound. NCI Dictionaries. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/compound
3. Epping, R. & Koch, M. On-Site Detection of Volatile Organic Compounds (VOCs). Molecules. 2023; 28(4): 1598. https://doi.org/10.3390/molecules28041598
4. Goff, M.L. Early Postmortem Changes and Stages of Decomposition. In: Amendt, J., Goff, M., Campobasso, C., Grassberger, M. (eds) Current Concepts in Forensic Entomology. Springer, Dordrecht. 2009. https://doi.org/10.1007/978-1-4020-9684-6_1
5. Gorgenyi, M., Dewulf, J., Van Langenhove, H., & Kiraly, Z. Solubiliyt of Volatile Organic Compounds in Aqueous Ammonia Solution. Chemosphere. 2005; 59 (8): 1083-1090. https://doi.org/10.1016/j.chemosphere.2004.12.012
6. Caruso J. L. . Decomposition Changes in Bodies Recovered from Water. Academic forensic pathology. 2016; 6(1), 19–27. https://doi.org/10.23907/2016.003