The Science of Aged Hides in Small Rooms

As a part of my Nosework Challenges Series 1 class coming out in February, I’ve been working on a weeks worth of advanced aging lectures.  This is an excerpt from one of those lectures…

Aged hides in a small room give us a new challenge.  Odor permeates the room in every nook and cranny.  Small rooms are actually easier to run with less aging because the odor tends to stay close to source.  In a trial you could very well find yourself searching a hide that is possibly up to 6 hours old….  But let’s play with the aging window and really push the boundaries.  Of course with time, aging reaches a plateau and the search area is fully saturated with scent.  Essentially, the odor molecules in the air stabilize and you hit a maximum saturation.  This really depends on a number of factors including the vapor pressure of the oil you are using, the temperature and the ventilation in the search area.  (I wonder what my dad would think if he knew that I use my Chemical Engineering degree to apply it to dog training!  Somehow I can picture his facial expression…  part exasperation and part humor I’m sure!)

Let’s discuss Vapor Pressure…  I’m going to get a little technical so please bear with me…  hopefully I can make this plain English!  However I think it’s important to discuss because it gives us an idea how advanced aging works in a closed room, and how scent saturation occurs.

From Wikipedia:

“Vapor pressure or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of particles to escape from the liquid (or a solid). A substance with a high vapor pressure at normal temperatures is often referred to as volatile. The pressure exhibited by vapor present above a liquid surface is known as vapor pressure. As the temperature of a liquid increases, the kinetic energy of its molecules also increases. As the kinetic energy of the molecules increases, the number of molecules transitioning into a vapor also increases, thereby increasing the vapor pressure.”

Picture attribution: "Vapor pressure" by HellTchi - Own work. Licensed under CC BY-SA 3.0 via Commons -

So in plain English…  Oils are volatile…  our dogs are actually smelling the oil that has turned from liquid to gas.  Essential oils have a high vapor pressure.  That means that it takes a high air pressure to keep the oil from evaporating…  so when the temperatures are normal to higher, there will actually be more scent in the air because more of the oil has evaporated.  At normal air pressure, scent of these volatile substances evaporates and the dog can easily capture the scent.

When a door is closed, over time, the air fills with scent molecules and the system essentially stabilizes.  Of course the “system”…  meaning the room, never really seals, so scent will continue to evaporate from the Qtip.  However, because this process is continuous, the room essentially for all intents and purposes becomes saturated with scent.

Now picture this, you open the door and the dog has to search through a sea of scent.  There is really very little definition left to the scent cone so this makes the task rather challenging.  In competition, you will probably never search a fully saturated room, however you WILL encounter small spaces where the door has been closed and the hide has been aged.  Therefore, it makes sense to train for this scenario!

Here’s a graph of the relationship between vapor pressure and temperature…  this is water…  This is why it feels so humid when you are near the water in the heat!  This means that the hotter it is, the more pressure is required to keep the water in liquid form.

Picture attribution: ATMS 101 Summer 2003

What does this mean for small enclosed areas?  This means that the hotter the search temperatures are, the more scent will be in the air.

What about the time factor?  It takes time to reach saturation.

So what is saturation???  Saturation is when the number of particles in the air stabilizes versus the particles in liquid form (meaning the oil on the Qtip).  So with aging, we reach equilibrium at an unknown point of time.  Therefore, if we place a hide, close up a room and let it sit for a long, long time…  we have essentially created a very challenging puzzle for our dog.

Happy Sniffing!!

© Stacy Barnett 2015