Ep. Three – Shelby the Dog and the case of Carbon Monoxide


Dogs are amazing creatures. Not only are they cute, loyal and great companions, they also have an incredible sense of smell. Some say they’re able to smell a pinch of sugar in a million gallons of water. So the idea of a dog smelling carbon monoxide isn’t that far fetched, right? Let’s find out on this episode of A Reasonable Breakdown.

Part One – The Nose Knows

The story posted on Facebook goes like this: Shelby the dog saved her family of four after her keen sense of smell alerted her to a carbon monoxide leak. She then woke each family member and led them all outside to saftey. This is such a heartwarming story and it’s exactly the kind of post that gets shared all over social media. Everyone loves a good dog rescue, but is it true? Let’s find out.

This story has 2 main elements that I want to expore. The first is just how good is a dog’s nose and second what exactly is carbon monoxide?

Let’s dive a little deeper into these incredible animals and just how acute their sense of smell is.

Humans have roughly 6 million olfactory receptors in our noses. A dog, however, can have up to 300 million of these olfactory receptors. So, what exactly does that mean? According to the book, Inside of a Dog, by Alexandra Horowitz, a dog-cognition researcher at Barnard College, humans can probably tell if a cup of coffee has a teaspoon of sugar in it. A dog on the other hand can detect a teaspoon of sugar in a million gallons of water. That’s equivilent to two Olympic size swimming pools.

Scientists agree that a dog’s sense of smell is far superior to ours, and not by a little bit, but by orders of magnitude better – it’s 10,000 to 100,000 times as acute. So, let’s look at it another way, literally. James Walker, former director of the Sensory Research Institute at Florida State University says that if we assume that dog’s are just 10,000 times better at smelling, if we translate that to vision, what we humans can see at a third of a mile, a dog could see more than 3,000 miles away and still see as well.

It’s not just the fact that a dog can have hundreds of millions of olfactory receptors, it’s also how their brains and noses are wired together. Brent Craven, bioengineer at Pennsylvania State University, modeled the airflow and odor transport using high-res MRI scans of a lab cadaver’s nose. Brent and his team found that when airflow enters a dog’s nostril it splits into two different flow paths, one for olfaction and one for respiration. The air we humans smell goes in and out with the air we breathe, in dogs though Craven’s team found that about 12% of the inspired air gets routed to a recessed area in the back of the nose dedicated just to olfaction. They have a dedicated section just for smell! It’s incredible.

It gets better. This separation of smell and respiration also allows dogs to sniff more or less continuously. A study done at the University of Oslo in Norway found that a hunting dog holding its head high into the wind sniffed in a continuous stream of air for up to 40 seconds. But that’s not all. Did you know that dogs can also wiggle their nostrils independently? This helps dogs determine which nostril an odor arrived in and that aids in them locating the source of a smell.

If it wasn’t apparent before, it should be now, that dogs are simply incredible animals with such an amazing ability to sniff out scents in parts per trillion. Carbon monoxide should be easy to sniff out, then, right?

Part Two – The Invisible Killer

What exactly is carbon monoxide? In the simplest terms it is a gas that consits of one carbon atom and one oxygen atom. Carbon monoxide is known as an oxocarbon because it is a chemical compound that only has carbon and oxygen. A common oxocarbon is carbon dioxide, which is something we produce when we breathe.

Now, carbon monoxide has a slew of interesting properties. It is colorless, tasteless, flammable, and probably the most important property, at least to this story, carbon monoxide is odorless.

But it can’t be odorless to dogs, right? They can track scents through heavily wooded areas and even detect certain cancers in humans. Carbon monoxide is only odorless to us measly humans. That’s probably what that means.

Unfortunately, odorless is odorless. It is impossible to smell carbon monoxide, whether you’re a dog, a cat, a human or a machine. Carbon monoxide does not emit an odor, the chemical make up has no properties what-so-ever that can produce a smell. In fact even carbon monoxide detectors work by noticing the changes in a chemical solution or even a gel that reacts when it comes into contact with carbon monoxide. But there’s simply no smell. So, right here and now, this story is false. Dogs, no matter how good they can detect the most minute amount of a scent, cannot smell something that doesn’t have an odor.

Now, I do want to touch on something that I found absolutely mind blowing about dogs during my research for this story, which I think is part of the reason people can believe that a dog can smell the most impossible of things.

When I think about cancer, I don’t think about the cells or the mass or tumor or anything physical. What I mostly think about is the person and what they’re going through or their families. However, things are happening that we can’t see and it sometimes can maybe seem like these cancer cells don’t have the same physical properties such as an odor. According to a study though, published from Ben-Gurion University of the Negev in Israel, and I apologize profusely if I did not pronounce that correctly, this study titled, Canine Scent Detection of Volatile Elements, Characteristic of Malignant Cells, in Cell Cultures, which i will link to in the description of the podcast, it concludes that not only can dogs pick out all of the target specimens of breast cancer cell cultures they were trained to, but they could also detect other cultures of cells that they weren’t trained to find, meaning that cancer cells have a unique odor pattern that is common to different types of cancer.

It turns out certain cancers do in fact have an odor!

In another paper titled Lung Cancer diagnosis by trained dogs, published in Dec 2017 by the Oxford University Press, it describes a clinical trial where well-trained dogs were able detect the presence of lung cancer in exhaled gas samples. Now again I will link that study in the description of the podcast so you can read these on your own time if you wish.

I only bring up cancer because sometimes I think that dogs are capable of truly impossible things, like detecting lung cancer or breast cancer and that in turn can lead me to believe that dogs could smell something like carbon monoxide. In the end though, dogs are only able to smell what has an odor, even if it does seem impossible.

My final thought on this story is this – dogs cannot smell carbon monoxide, however dogs are affected by carbon monoxide poisoning faster than humans, so it is possible that Shelby the dog alerterd her owners in time for them to get to safety, but it wasn’t because Shelby could smell carbon monoxide.

Thank you for listening to this episode of A Reasonable Breakdown.

Link to episode:


Additional references:

The Secret of a Dog’s Sniffer

Article on NOVA’s website about dogs