Grâce à la liberté dans les communications, des groupes d’hommes de même nature pourront se réunir et fonder des communautés. Les nations seront dépassées.
Friedrich Nietzsche (Fragments posthumes XIII-883)

Détection olfactive - articles

Comment les chiens "voient-ils" avec leur nez

Non seulement nous ne sommes pas toujours en train d'utiliser notre odorat, explique Alexandra Horowitz, mais lorsque nous l'utilisons, c'est souvent parce qu'on sent une bonne ou une mauvaise odeur: il s'agit rarement d'une simple source d'information. Les odeurs que nous percevons la plupart du temps sont soit agréables soit répugnantes, très peu ont un caractère aussi neutre que notre vision... de même que nous voyons le monde, le chien le sent.

Il y a deux conduits aériens dans la truffe (entre 2.000 et 3.000 millions de capteurs, contre 6 millions chez l'homme) : l'un pour respirer, l'autre pour sentir le monde environnant, percevoir les mouvements, ou encore faire la différence entre amitié et hostilité. Plus impressionnant encore, le nez du chien l'aide à voir des choses qui ne sont plus ou pas encore visibles: il détecte ce qui a eu lieu plus tôt (la voiture garée à un emplacement il y a quelques minutes) et ce qui n'est pas encore arrivé (une personne qui va apparaître au coin de la rue).

Nous sommes peut-être capables de remarquer que quelqu'un a ajouté une cuillère de sucre à notre café, mais le chien peut détecter cette cuillère de sucre dans l'équivalent de deux piscines olympiques.

Mais l'être humain aussi a du flair ! 
Très instructif "De la molécule à l'odeur".

Forensic Science International 209 (2011) 133–142, Lauryn E. DeGreeff, Allison M. Curran, Kenneth G. Furton
Human scent can be collected by either contact or non-contact sampling mode. The most frequently used human scent evidence collection device known as the Scent Transfer Unit (STU-100) is a dynamic sampling device and is often used in a non-contact mode. A customized human scent collection chamber was utilized in combination with controlled odor mimic permeation systems containing five standard human scent volatiles to optimize the flow rate, collection material and geometry of the absorbent material. The scent collection method which yielded the greatest amount of volatile organic compounds (VOCs) detected included the use of a single layer of Johnson and Johnson gauze/multiple layers of Dukal gauze with the STU-100 on the lowest flow rate setting. The correlation of the resulting VOC profiles demonstrate that collection of standard VOCs in controlled conditions yielded reproducible VOC profiles on all materials studied with the exception of polyester. Finally, the method was tested using actual human subjects under optimized set of conditions.

Collection and identification of human remains volatiles by non-contact, dynamic airflow sampling and SPME-GC/MS using various sorbent materials
Lauryn E. De-Greeff et Kenneth G. Furton - , in Anal Bioanal Chem (2011) 401:1295–1307

Individual human scent as a forensic identifier using mantrailing  - Forensic Science International, Vol 282, January 2018, pp. 111-121 LeifWoidtke, JanDreßler, CarstenBabian

Individual scent article allows mantrailers to differentiate an odour trail.
Saliva as well as DNA extracted from whole blood are sufficient as a key stimulus.
Mantrailing appears as a reliable and useful tool for law enforcement authorities.
Specially trained dogs have long been used by law enforcement agencies to help in criminal investigations and in searching for missing persons. Still, it is unclear which components of human scent released into the environment contribute to successful searches of individuals. In this study, saliva and axillary sweat samples were taken from a total of 190 people. Additionally, DNA was extracted from whole blood of seven different people and used as an odour sample as well. Overall 675 tests (trails) were performed during a period of 18 months. The ability to track individuals with the odour samples mentioned above was examined with seven dogs, four of which were specially-trained dogs (mantrailer) from the Saxony Police. Results indicated that specially-trained police dogs can track a person with an average success rate of 82% and correctly identify the absence of an odour track with an average success rate of 97% under various conditions. Private rescue dogs were less successful with an average success rate of 65% and 75% respectively. These data suggest that the potential error rate of a well-trained handler team is low and can be a useful tool for law enforcement personnel. Saliva, as a reference odour source, was found to be particularly suitable for the search. The results of the study suggest that the components contained in axillary sweat, saliva and DNA extracted from whole blood are sufficient, serving as a key stimulus for individualized searches.
In this study mantrailer dogs were tested under real police operating conditions. With a scent article from a person, they could follow the individual human scent trail of that person statistically highly significantly. Furthermore, they differentiate highly significantly between the presence and the absence of an odour trace using a scent article containing human scent. The best results were achieved with scent articles using saliva and sweat as an odour source. Additionally, highly significant results were obtained with scent articles from wet DNA samples. These findings may provide valuable information for the practical work of dog handlers for selecting suitable scent articles. The study shows that the success rate was higher depending on training method and operational experience level of the teams and for this reason only well-trained and certificated teams should be used in criminal proceedings. It has been shown that well-trained mantrailing-dogs can be in principle a reliable and useful tool for law enforcement authorities.

Performance evaluation of the Scent Transfer Unit (STU-100) for organic compound collection and release
- J Forensic Sci. 2006 Jul;51(4):780-9, 
Eckenrode BA, Ramsey SA, Stockham RA, Van Berkel GJ, Asano KG, Wolf DA. 

The Scent Transfer Unit (STU-100) is a portable vacuum that uses airflow through a sterile gauze pad to capture a volatiles profile over evidentiary items for subsequent canine presentation to assist law enforcement personnel. This device was evaluated to determine its ability to trap and release organic compounds at ambient temperature under controlled laboratory conditions. Gas chromatography-mass spectrometry (GC-MS) analyses using a five-component volatiles mixture in methanol injected directly into a capture pad indicated that compound release could be detected initially and 3 days after the time of collection. Additionally, 15 compounds of a 39-component toxic organic gaseous mixture (10-1000 parts per billion by volume [p.p.b.(v)]) were trapped, released, and detected in the headspace of a volatiles capture pad after being exposed to this mixture using the STU-100 with analysis via GC-MS. Component release efficiencies at ambient temperature varied with the analyte; however, typical values of c. 10% were obtained. Desorption at elevated temperatures of reported human odor/scent chemicals and colognes trapped by the STU-100 pads was measured and indicated that the STU-100 has a significant trapping efficiency at ambient temperature. Multivariate statistical analysis of subsequent mass spectral patterns was also performed.


Kenneth G. Furton, Norma Iris Caraballo, Michelle M. Cerreta and Howard K. Holness
Published by the Royal Society 2015
This paper explores the advances made in identifying trace amounts of volatile organic compounds (VOCs) that originate from forensic specimens, such as drugs, explosives, live human scent and the scent of death, as well as the probative value for detecting such odours. The ability to locate and identify the VOCs liberated from or left by forensic substances is of increasing importance to criminal investigations as it can indicate the presence of contraband and/or associate an individual to a particular location or object. Although instruments have improved significantly in recent decades—with sensitivities now rivalling that of biological detectors—it is widely recognized that canines are generally still more superior for the detection of odourants due to their speed, versatility, ruggedness and discriminating power. Through advancements in the detection of VOCs, as well as increased standardization efforts for instruments and canines, the reliability of odour as evidence has continuously improved and is likely to continue to do so. Moreover, several legal cases in which this novel form of evidence has been accepted into US courts of law are discussed. As the development and implementation of best practice guidelines for canines and instruments increase, their reliability in detecting VOCs of interest should continue to improve, expanding the use of odour as an acceptable form of forensic evidence

1. Introduction
Forensic science can be defined as the application of any form of science, in particular analytical chemistry, where ‘the trace, which, by definition, is a pattern, a signal or material transferred during an event (often unknowingly by the actors of the event)’ is analysed and accepted as a form of scientific evidence into a civil or criminal proceeding [1,2]. It is for this reason that knowledge and technology obtained through a sound scientific method should not only meet good scientific practice, but should also comply with the rules of admissibility that are set forth by the relevant courts of law. Overall, science alone may not have the ability to provide definitive solutions, but it can offer increasingly accurate and objective information generating investigative leads, as well as assisting a judge/jury in determining the truth and allowing for justice to be achieved. It is for this reason that there is a necessity for continued scientific advancement with respect to forensic investigations.
For more than a century, fingerprint evidence was recognized as the gold standard in forensic science. It was in 1880 that Henry Faulds of Scotland published his seminal paper proposing the use of fingerprints to identify an individual and, in particular, suggested that the skin-ridge patterns could be used to connect an offender to a crime scene [3]. Simultaneously, another cost-effective, real-time detection tool that was being employed by law enforcement officials, owing to its reliability, versatility and speed, was the use of canines (Canis familiaris) [4].
The use of canines in criminal investigations dates as far back as the use of finger-prints. The English used bloodhounds while searching for Jack the Ripper in 1888 and in 1893 the state Supreme Court of Alabama (US) acknowledged that ‘dogs may be trained to follow the tracks of a human being with considerable certainty and accuracy’ [5]. The courts ruled that the testimony regarding the tracking performance of a canine can be presented to the jury, along with other evidence, as a means to connect the defendant to the crime. Since then, canines have been continuously employed for the detection of humans, drugs, explosives and human remains because of their high selectivity and sensitivity towards locating odours. While the canine’s olfaction system is widely relied upon, the system itself is not completely understood, but it is known that, like humans, canines have receptor cells that can detect a compound(s), and olfactory nerves that carry the signals that are interpreted by the brain, allowing for the identity of the odourant to be determined [6]. Unlike humans, however, the canine olfactory system constitutes a much larger portion of its biology, with 50% of the internal nasal area containing olfactory sensory cells and nearly one-eighth of a canine’s brain being dedicated to olfaction. While the average person has some 5 million olfactory sensory cells, common detection canines, such as German Shepherd dogs, have 220 million olfactory sensory cells, indicating that a canine’s olfactory abilities are at least 44 times greater than that of humans [7]. Moreover, canines have approximately 1300 genes in their olfactory repertoire, which is nearly 20 times more than that of humans, providing them with the ability to be trained on various types of odours with a high degree of sensitivity and discriminating power [8].
Over the years, attempts have been made to develop various forms of technology and instrumentation for on-site detection and screening of VOCs, yet none to date has been capable of replicating the combination of selectivity, sensitivity and field versatility demonstrated by canines, which is why they are currently and widely recognized as the gold standard for the field detection of VOCs [6]. This paper highlights the advancements made in analytical chemistry, specifically focusing on the detection of VOCs released from different forensic specimens, the relevance of these specimens to canines and the increased application of odour as a form of forensic evidence.

Decomposing Human Blood: Canine Detection Odor Signature and Volatile Organic Compounds 

Rendine M, et al. J Forensic Sci. 2019.

The admissibility of human "odor mortis" discrimination in courts depends on the lack of comprehension of volatile organic compounds (VOCs) during the human decay process and of the lack in standardized procedures in training cadaver dogs. Blood was collected from four young people who died from traffic accidents and analyzed using HS-SPME/GC-MS at different decompositional stages. Two dogs, professionally trained, were tested to exactly locate blood samples, for each time point of the experiment. We found a long list of VOCs which varied from fresh to decomposed blood samples, showing differences in specific compounds. Dog performance showed a positive predictive value between 98.96% and 100% for DOG A, and between 99.47% and 100% for DOG B. Our findings demonstrated that decomposing human blood is a good source of VOCs and a good target for canine training.

Cadaver dogs: Unscientific myth or reliable biological devices?

IreneRiezzo,MargheritaNeri,MarcelloRendine,AlessandroBellifemina, SantinaCantatore, CarmelaFiore, EmanuelaTurillazzi

We aimed to detect the reliability of dogs trained to locate human cadaveric blood.
We adopted an optimized and rigorously controlled experimental design.
The primary detection task was human cadaveric blood at very low concentrations.
Dogs’ discriminative capability among confounding substances was also investigated.
Dogs represent a scientifically unassailable tool in detecting human blood traces.

Abstract :
Dogs are commonly used to detect explosives, narcotics, and other illegal materials. In the forensic setting, cadaver dogs are trained to detect and locate concealed human remains or fluids due to the high sensitivity and selectivity of the canine olfactory system and the relative ease with which dogs can be trained and handled. The need for international and scientifically validated standards has long been outlined by the literature. It is important, therefore, to establish the reliability of the handler/dog team. Our study aimed to detect the real effectiveness of dogs trained to locate human cadaveric blood in very low concentrations, through an optimized and rigorously controlled design which would rule out any possible sources of bias. The study was designed to determine the dogs’ olfactory sensitivity to human cadaveric blood and how this capacity might change as the dilution of blood increases from pure blood to very low concentrations. The further step was to examine the dogs’ ability to discriminate among target (human cadaveric blood) and non-target (confounding substances) odors (discriminative capability). Our results revealed that well trained dogs were able to detect human cadaveric blood samples even when very low concentrations of blood were stored in the tubes, showing high levels of olfactory sensitivity and to discriminate the target odor even when the non-target odor was orders of magnitude higher in concentrations. Although our results are based only on two dogs, the procedure we used may provide a comprehensive answer to the need for a scientifically unassailable tool for quantifying and objectifying the performance of well-trained specific search dogs in detecting human cadaveric blood traces.

09 May 2013
Mary Cablk - The Science of Sniffer Dogs

Blind and double blind training can be very simple, and can be made complex. Let's start with simple. The basics of either (blind or double blind) are the same:
someone besides the handler sets the problem.
anyone who has knowledge about the set (how many hides, where they are) keeps that information to themselves.

Here's where the difference comes in: if it is a blind problem, someone with knowledge about the solution to the problem may be present and they provide no information to the handler that might bias the outcome. They may stand on the sideline, they may walk along with the team, they may be anywhere nearby. In a double-blind problem all individuals with knowledge of the solution to the set, in whole or in part, are out of the area. In double blind there isn't a way for the handler to recieve any information that would help them solve the problem. There's no ability for bias to occur.

This requires no more people to set up than is needed for any other training, with the exception of when a handler is training by themselves without assistance. A handler cannot self set a blind or double blind problem. Two people can do blind and double blind training. It can be that simple and easy.

When do blind and double blind training problems make sense in training? At some point a dog and handler have to make the leap from working known problems, where the dog is learning it's target odor for example, learning it's trained alert or final response, or figuring out how to follow the track of the subject through turns and over different surfaces. You don't want that leap to be made on a real search.

One approach is to begin with blind problems where a person with knowledge of the solution can step in if needed. Not truly blind when assistance or feedback is given, it is a transitional step. Generally this is done in the early stages of moving away from known problems so that the dog is continued to be rewarded only on its target odors. At some point the handler has to go for it, and work problems without any help. In the words of my colleague Terje Groth Berntsen, Head of the Norwegian People's Aid Global Training Cenre (, "Mary! You have to let the dog fail! How else is it going to learn?!"

Blind problems show where weaknesses are in the team, such as dependencies, and can be used effectively to remedy training issues. The challenge in blind problems is for the knowledgable person to remain neutral. Even when a knowledgable person tries their hardest to remain neutral, it is still possible for them to bias the team inadvertantly. This is why double blind training is necessary to document a team's reliability.

In double blind problems there is no safety net for the team. Because the handler does not know the solution, and there's nobody there who can step in to offer assistance, the dog can leave sources without the handler knowing it, the dog can alert on non-targets, and the dog can be rewarded for false alerting or not rewarded for finds. On the other hand, with nobody around to offer input, the team can show they have proper training - making independent finds, few to no misses, and few if any false alerts. For these reasons double blind problems are highly useful diagnostics of the reliability of a team.

Handlers who work double blind problems and are able to address training issues discovered in doing so, report greater confidence and with good reason - they demonstrate over and over that their dog works independently at what it is trained to do.

One last practical tip on blind and double blind: how is the team assessed? The handler marks alerts in the field with flags, or records their track on a GPS. When the dog is back up in the truck, the handler and problem setter walk the area and count coincident flags. For a track the handler's GPS is downloaded and mapped against the tracklayer's GPS. They can walk the tracklayer's route together as well.

There are more subtleties that go along with all of this, whether known, blind or double blind, and those are for future blogs; what about pool alerts? how far off track can a dog be and still be "on track"? when is a false a false?

My data show that when handlers start working double blind problems their reliablity drops dramatically at first - and then it increases steadily. Be ready to see this happen when you first start working double blinds. With time and continued training using known, blind, and double blinds wisely, the reliability of the team remains high. This is where all canine handlers want to be, and can be. It is that simple.

Témoignant pour la défense dans l'affaire Redwine
Mary Cablk, une chercheuse basée au Nevada qui se concentre sur la détection sensorielle et est un maître-chien de chiens cadavres, a déclaré que les chiens renifleurs devaient être formés à un environnement spécifique et, dans le cas des chiens cadavres, à un niveau de décomposition spécifique. Un chien dressé avec des restes humains frais dans un climat humide ne serait pas fiable pour rechercher des restes humains en décomposition dans une région aride, a déclaré Cablk.

Les chiens cadavres ont besoin d’au moins 16 heures d’entraînement par mois, a déclaré Cablk. Corcoran a témoigné qu'elle entraînait Molly huit heures par semaine. Cablk a également déclaré que les chiens ne devraient pas être entraînés à réagir à l'odeur des cheveux; Corcoran a témoigné que Molly avait été formée pour détecter les cheveux.

Cablk a déclaré que les chiens qui s'entraînent avec des restes humains frais absorbent des substances chimiques différentes de celles des chiens entraînés à détecter des parties du corps en décomposition. Corcoran a témoigné que Molly ne s'était jamais entraînée avec des restes humains ou l'odeur de restes humains en décomposition depuis au moins neuf mois.

Un chien bien entraîné ne trouvera pas seulement une odeur mais localisera le point d'où elle émane. Une odeur résiduelle ne peut rester dans un endroit plus d'une semaine, dit-elle. Elle ne peut pas être quantifiée, et la lumière du soleil et la chaleur peuvent modifier la composition de l’odeur, a-t-elle déclaré.

«Elle ne dure pas éternellement», a déclaré Cablk à propos de l’odeur de restes humains.