This is Why … Campfire Smoke Follows You Around

They said someday you’ll find

All who love are blind

When your heart’s on fire

You must realize

Smoke gets in your eyes

Jerome Kern and Otto Harbach, 1933

(“Watching the Campfire” by Mr Moss is licensed under CC BY 2.0)

Despite legions of campers swearing to the contrary, campfire smoke does NOT actually follow you around like your friend’s labrador retriever who really, really, really wants that wiener you just roasted. Of course, if there was no wind, if there were no complex air currents generated by the mixing of hot and cold air, and if you were the only person near the fire, then perhaps you could claim otherwise. But, in any realistic campfire scenario, the airflow is dictated by a large number of variables and where you happen to be sitting is likely the least important factor of them all.

For argument’s sake, let’s assume that we had the perfect evening. There is no wind and the air is moving in the simplified path shown in the sketch below. Denser cool air is drawn in towards the fire at ground level as the warmer, less dense air moves upward in a process called convection. In this scenario, the smoke travels directly upward with the heated air, unless there is a local disruption to these convection currents.

Now, if we add in just one person near the campfire, this could create a local obstruction at ground level:

The camper blocks cool air from flowing in toward the base of the fire at that point in the circle. Like a large boulder in a quickly moving stream, this person is an obstruction to the flow. The disrupted airflow could lead to the smoke swirling around in the region between the fire and the camper, like eddy currents or vortices downstream from the boulder. If she moves to another spot around the circle, the same disrupted airflow and eddies go with her, hence the feeling that the smoke is following her.

This is the same principle by which obstructions are diagnosed in blood vessels with Doppler ultrasound: regular blood flow becomes turbulent with vortices and eddies behind obstructions. The resulting colour Doppler image clearly shows these regions of anomalous flow.



Doppler image suggests 50‐60% blockage (yellow arrow) that was confirmed by angiography (black arrow).
Image from Journal of Neuroimaging, Volume: 28, Issue: 6, Pages: 683-687, First published: 19 June 2018, DOI: (10.1111/jon.12532)

But for the effect of these eddies and vortices to be so pronounced with smoke, there would have to be no other people around the campfire and no wind. You would likely need to be relatively close to the fire as well. So, in reality, campfire smoke doesn’t really follow you around, it just seems like it does. This is a classic example of confirmation basis, a phenomenon observed as long ago as the time of Sir Francis Bacon (1561 – 1626), who said:

“And such is the way of all superstitions,
whether in astrology, dreams, omens, divine judgments, or the like; wherein men, having a delight in
such vanities, mark the events where they are fulfilled,
but where they fail, although this happened much
oftener, neglect and pass them by”

Novum organum by Francis Bacon, 1620

It does make sense. After all, it is super annoying when it swirls in your face and makes your eyes water, so we remember these instances vividly. We don’t, however, tend to notice or remember all the times that the smoke was swirling in the face of your friend with the moochy labrador retriever.

To prevent smoke from swirling in front of you at the campfire, several survivalist references suggest that you build your fire with a large object nearby, such as a rock, a pile of sand, or firewood. This object will create a bigger disruption in airflow and, in theory, the smoke will swirl in front of the wood pile rather than your face. Again, however, this effect will only be observable with very specific circumstances. Let’s just call me skeptical on this one. Rather than going to great lengths to ensure there is a smoke-attracting decoy near the fire in case you have the perfect evening, why not look at it as an opportunity to do some fun experiments on confirmation bias instead?

References

Comparison of Carotid Doppler Ultrasound to Other Angiographic Modalities in the Measurement of Carotid Artery Stenosis 2018 Matthew Boyko, Hayrapet Kalashyan, et al Journal of Neuroimaging 28(6) Pages 683-687 https://doi-org.subzero.lib.uoguelph.ca/10.1111/jon.12532

Confirmation Bias: A Ubiquitous Phenomenon in Many Guises, Raymond S. Nickerson 1998 Review of General Psychology Vol. 2, No. 2, 175-220 PDF available at: nickersonConfirmationBias.pdf (ucsd.edu)

In Burtt, E. A. (Ed.), The English philosophers from Bacon to Mill (pp. 24-123). New York: Random House, published in 1939

Basic Wilderness Survival Skills, Bradford Angier and Lamar Underwood, The Lyons Press, Guilford, Conneticut, 2002; page 65

The Family Guide to Survival (Skills That Can Save Your Life and the Lives of Your Family), Alan Corson, Balboa Press, Bloomington, IN, 2013; page 137

Backpacker – The Magazine of Wilderness Travel, Volume 24, Issue 147, Number 1 (February 1996, page 85)

Published by joanneomeara

Professor, Department of Physics, University of Guelph

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