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Scent Theory Understanding Human Scent No matter how hard we try to stay clean by showering, washing our hair, or changing into clean clothes, each of us has an odor or scent that is ours and ours alone. Human Scent Skin cells contain our genetic make-up. Medications and changes in our age and health affect our body’s chemical structure. Other human chemicals such as pheromones, hormones, adrenaline, etc., all affect our scent. Trained dogs can detect skin cancer and oncoming epileptic seizures. Skin glands secrete by-products of everything we consume on the surface of our skin, which also carries residue of the soap we use, lotions, laundry detergent and everything we use in our daily lives. Skin structure and secretions differ between races: for example, Caucasian and Black people have more sweat glands than Asians. Skins cells carry scent emitted from: Eccrine Sweat Glands – regulate body temperature and respond to emotions. More concentrated in feet, hands and forehead. Skins Cells Apocrine Sweat Glands –activated by emotions and tend to give off more odor than Eccrine Glands. These glands also secrete Pheromones and Adrenaline. Located at the base of hair follicles in the arm pits and groin. Sweat – clear liquid consisting of water, sodium, calcium, chloride, potassium, bicarbonate, urea and other body secretions such as amino acids. Sebaceous Glands – located at the base of hair follicles on your scalp, face and upper torso. They open directly to the skin and emit fatty oils, called sebum, that spread over the skin. Bacterial Buddies –such as mites, fungus, yeasts and viruses can never be completely removed by washing. We are constantly shedding our outside skin layer. Skin cells or “rafts” are shed at a rate of approximately 40,000 per minute or roughly 57 million per day. Rafts are also expelled every time we exhale. Shedding Our body temperature is usually warmer than the surrounding air, so as heat rises, each of us are enveloped in a thermal wind that travels upwards at approximately 1.5 miles per hour. As the air rises around us, it carries skin rafts upwards until they clear the tops of our head, where they are caught by atmospheric winds. As rafts are caught by atmospheric winds, the heavier rafts fall close to the source getting caught in anything that will catch and hold rafts. Lighter rafts will travel and land further away. Skin Rafts Each skin cell or “raft” contains bacteria that start feeding on the cell as soon as it leaves the body. This bacteria emits a vaporous gas or “scent”. Rafts continue to produce scent as long as moisture and nutrients from the skin cell last. Once skin rafts fall away from us, many things affect the life span of the bacteria living on it. Temperature – Too hot or to cold… bacteria can only thrive in perfect temperatures. Humidity - Each skin raft is about 80% water, which is necessary for bacteria to grow. Humidity in the air also affects bacterial growth. Raft Life Span Light – Ultra-violet light from the sun can kill bacteria and heat from the sun can dry up necessary moisture. Chemicals – Residues from items such as soap or laundry detergent also affect bacterial growth. Skin rafts that have dried out, may be re-hydrated again when dew forms or with a light rain or mist. The moisture can reactivate bacterial growth. As the ground warms in the morning, heat rises up carrying scent with it and the scent becomes airborne again. Scent Cone or Scent Plume Scent hugs the ground and gradually spreads out in a cone shape from the subject. Scent Cone Steady breezes carry scent longer distances, especially in flat, open country. Gentle breezes produce a wider scent cone. The stronger the wind, the narrower the scent cone will be. Stronger winds and gusts carry skin rafts farther and disperse them higher in the atmosphere, making it harder to find the subject. On days with a steady breeze, a trained air scent dog should be able to pick up and move in on airborne scent from 200 or 300 feet away from source. Open Fields With light breezes or still winds, you should still be able to work your area in a loose grid (wider sweeps). Your dog should be able to move in from 100 feet or more from source. Shifting winds make searching difficult because you may start your dog downwind and, later, the wind direction shifts. In these cases, the best idea is to remain with your original search plan or pattern. The wind may continue to shift and, trying to keep up with it, may leave you wandering around your assigned search area. Areas with light brush may have a combination of open areas and wooded areas. Vegetation is not thick enough to block or change how scent moves. Dogs should be able to work light brush areas about the same as open fields. With a nice breeze, you will be able to work the area in a loose grid (wider sweeps). Brush Areas with heavy brush can be found in thick woods or un-mowed fields. Tall grasses are harder for dogs to work, as there is little air flow slightly above the ground (where the dog’s nose is located). On hot, still days, in heavy vegetation, the scent stays close to the source. It will be necessary to work the area in a tighter grid (closer sweeps). Forests can vary from open woods, where deadfall and dense underbrush has been cleared, to thick woods, where no clearing has taken place and dense underbrush has grown up under the trees. Woods Open woods are basically worked the same way as light brush. With a nice breeze, you will be able to work the area in a loose grid (wider sweeps). Thick woods are worked the same way as dense brush, work the area in a tighter grid (closer sweeps). Working thick woods at night should be done carefully to avoid unseen hazards. A river, creek or drainage search during the day should be conducted along ridge lines or hilltops on the downwind side whenever possible. This will cover the waterway and the slopes as well. Since cool air falls, an evening search should be conducted in the waterway itself. Waterways Waterways can also act as a funnel, where scent flows downwind. If your dog is alerting or showing interest with his nose in the air and unable to locate source, work your dog upwind to where the source may be located. When doing HRD searches in waterways, here again, if your dog is alerting or showing interest in the water, work your dog upstream to where the source may be located. As SAR canine handlers, we are always aware of which direction the wind is coming from so we can work our dogs in the most effective manner. Wind Wind basically has the same effect on scent as it does on smoke, dust or some other lighter-thanair substance. One of the best ways of determining how wind will affect scent is by watching smoke as it is swirled around by the wind. Another good method is to imagine water rushing in the same direction the wind is blowing and picture in your mind how that water would react as it reaches obstacles. Water and wind will always take the path of least resistance. Gentle breezes carry scent long distances, especially in flat, open country. Gusty, strong winds disperse scent, making it harder to locate the source. If you have a NNW wind, wind is coming from the NNW direction. Winds are identified by the compass point or direction they are coming from. Wind To determine wind direction (and possibly wind speed), some handlers may hold out a small length of flagging tape, some pull a few blades of grass and throw them in the air, some use a puffer bottle with scent-free talc or powder, many just turn around until the wind is hitting them in the face. Some handlers carry a wind meter that accurately measures wind speed and air temperature. No matter what method you use, remember to test the wind at your dog’s nose level. Vegetation and terrain will also affect wind speed and direction down where your dog’s nose is located. How wind moves and how human scent travels are greatly affected by local terrain and vegetation. Terrain Upslope Winds: Morning sunshine heats the sides of hills and mountains, carrying human scent uphill. On hilltops, mountain tops and along ridges, winds are stronger due to upflowing air and converging winds from opposite slopes. In the mornings, work your SAR dog on hilltops, mountain tops or along ridges to take advantage of upslope winds. Down-slope Winds: Evening around sunset, at night or under heavy daytime cloud cover, air cools and flows to the bottom of valleys, carrying human scent downhill. In the evening, work your SAR dog in valleys. Up-valley winds form when valley walls are cooler than the valley floor. The “Venturi Effect” happens when air is forced through a narrow opening such as a mountain pass, accelerating the wind speed. Valleys Down-valley winds result from air moving down-slope in the evenings or at night. As the down-slope winds converge at the valley floor, winds move down the valley, which can be stronger on clear nights. During morning and daytime hours, land heats up faster than water. When the warm air over land rises, the cool air over the water moves in towards land. These are called Lake or Sea Breezes. When working a water HRD problem, dogs may be worked from the shoreline. Lake/Land Breezes During evening or early night, land cools faster than water. In the evenings, warm air over the water rises and cool air from the land moves in towards the water. These Land Breezes are strongest along shore and weaken further inland. When working your SAR dog on land areas with water, working shorelines may be best in the evenings. Rising warm air creates a void that pulls in other air from the surface to fill it. The resulting air movement is called convection current. Thermal Turbulence As warm air rises, it mixes with cooler air at higher levels. Winds increase and flow back down to the ground in spurts or gusts, increasing surface wind speed. This mixing of air is called thermal turbulence. Surface winds are stronger in the afternoon (the hottest part of the day) than at night. When surface temperatures start cooling at night and in early morning hours, the air becomes more stable. These hours of stable air are usually the best times to work your SAR dog. If rising warm air meets a layer of very cold air, a thermal layer may form causing turbulence two or three feet above the surface. This turbulence will keep human skin rafts airborne longer. Mechanical Turbulence slows down surface winds. Winds hitting buildings, rocks, or any stationary object causes the air to divide and flow around the object. Picture how water moves as it hits a rock in a fast flowing stream. Mechanical Turbulence Eddies, or swirling pockets of air, form on the lee side (the side that is sheltered from the wind). There will be areas of turbulence and areas of calm (dead spots). In the calm areas, human scent will settle more quickly. The air traveling around an object will be denser and/or traveling faster than the surrounding air. In this area, human scent will settle slower and tend to travel farther than the particles caught in eddies or surrounding areas. Air flowing over a ridge is influenced by the shape of the ridge, the wind speed and the wind direction. Mechanical Turbulence Higher wind speeds on sharp ridges, bluffs or canyon rims cause turbulence and large rolling eddies, updrafts and downdrafts on the lee side (downwind side). Upslope winds can be felt on the surface of the lee side. Depending on the terrain, dead spots with no air movement can also occur on the lee side of mountains. These chaotic air movements make it more difficult for your SAR dogs to find scent. Surface Winds Mechanical Turbulence (an object on the surface) changes the wind path and direction. Thermal Turbulence (surface heating) causes pressure differences which can increase or decrease wind speed. Both work together to change winds at the surface, which are measured up to 20 feet above the ground or any vegetation. Additional Mechanical Turbulence such as bushes, rocks, gravel, plowed fields, grasses, etc. on the surface can also slow down surface winds due to surface friction. Slide your hand over a sheet of typing paper and then over a sheet of rough sandpaper, and you’ll get the idea of how surface friction works. Human scent tends to flow with surface winds until they eventually land or get caught by objects. Tall buildings act much like canyon walls, causing Urban Canyon Winds. Urban Canyons When wind hits the face of an object (in this case a building) the wind scatters. How the wind reacts depends on the angle of building to the wind (flat or at a corner). Wind streams down the sides of the building and eddies form at the back, or downwind side of the building. Vertical Eddies form when winds converge at the corners of buildings or at the mouth of steep canyons. Whirlwinds and dust devils are examples of vertical eddies. Horizontal eddies are cylindrical air formations that roll along the surface. How air moves within a building affects scenting conditions. Heating and air conditioning systems, for instance, may circulate scent within the room or throughout the entire building. Even with the system shut down, ducts between rooms will continue to move air. Holes and cracks in the walls and ceiling, open windows or doors will also move scent around. When you enter a building, try to determine which way air currents are moving. Exterior walls will also affect scent. The side of the building exposed to the sun will be warmer than the side that is shaded. Scent tends to move to the interior or cooler walls. Buildings Thermals usually occur by the sun heating darker surfaces such as the ground, open areas in woods or parking lots. Darker surfaces do not reflect back many of the suns rays thereby heating them faster than surrounding areas. Thermals This uneven heating causes the air to rise in a column. The rising column of hot air cools as it rises until it reaches the same temperature as the surrounding air. The air then turns downward, flowing around the outside of the hot air column. Think of water spouts in fountains. The water shoots up so high, then collapses and falls back down on the sides. This is the basic principle behind the Chimney Effect. Open meadows in wooded areas form natural chimneys. Chimneys draw cool air from under surrounding shaded areas into the sunny meadow or opening where warm air is rising. Chimney Effect If your SAR dog loses scent in open areas or meadows, the rising air may be carrying the scent too high for your dog’s nose to catch it. As the scent drops back down to the ground, you may be able to cast your dog in the surrounding shady areas and pick up scent again.