The Art of Reading Smoke – Understanding Velocity

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In the ongoing effort to dispel fire service mythology, let’s address what is perhaps the most important observation that you can make in your size-up:  Velocity. Velocity is king in smoke reading. Here’s what it doesn’t tell you:  the size of the fire.  Not quite sure where this came from, but if this is what you were taught, expel it from your understanding immediately.  In truth, the velocity of the smoke is your single best indicator of heat. However, we cannot compartmentalize the explanation into a cute little meme.  Of course it requires further understanding.

There are two terms we will use to describe the velocity of smoke.  When you look up the definition of the word Turbulent, you will see terms like “violent,” “without order,” “fast,” and “not controlled by calm.”  If you research the definition of Laminar, you will find terms like “ordered,” “calm,” “smooth,” and “without turbulence.”  These are the two terms we will use to describe the velocity of smoke that we encounter.  What is the cutoff between the two? That is up to your discretion. Velocity is an observation, and you must decide whether the smoke you see is calm and ordered, or fast and violent.

Put on your third grade science hats for a moment.  Imagine a detached single family residence with a room and contents fire in the incipient stage.  This house will be our box. The box has smaller boxes (rooms) inside of it. (Really, it doesn’t matter if it’s an apartment building, big box warehouse, or a McMansion.  They’re all boxes) Where, within the box, will be the hottest, or where will be encounter the most heat? The seat of the fire, of course. So the smoke will be hottest at the seat of the fire, or more specifically, the smoke will be hottest at the flame tips. Flame tips will always produce turbulent smoke.  It will be turbulent if it is a big fire, it will be turbulent if it is a small fire, and it will be turbulent if it is any size in-between. Got that, meme makers? Flame tips will always produce turbulent smoke, regardless of the size of the fire.

But frequently, we see laminar smoke from our seat in the apparatus when we arrive.  What changes between the flame tips (turbulent) and the exit portal (laminar)? Simply put, the box is capable of absorbing heat. The box, and all its furnishings – every object in the box, really – will absorb heat.  Your box serves as a heat sink, robbing the smoke of its heat (velocity). As soon as the smoke is produced, the box begins to suck the heat out of it. As the heat is removed, so too is the velocity. If you are arriving on scene of an incipient stage fire that is distant from the exit portal (door, window, etc.) that you see, we will visualize laminar smoke that has been robbed of its velocity (heat) as it traveled through the house towards the exit.

So why, then, would we ever encounter turbulent smoke if the fire is distant from the smoke exit portal?  Well, the box has limits to how much heat it can absorb. Let’s use sheetrock as an example. When the walls of the box can no longer absorb any more heat, it will begin reflecting heat.  At this point, that portion of the box is no longer serving as a heat sink. The smoke will not lose any velocity as it travels.  Left unchecked, we will eventually see smoke at the exit portal that is just as hot/turbulent as the smoke at the flame tips. So remember this – turbulent smoke at the exit means that nothing in between the seat of the fire and the exit is absorbing heat.  All objects are either reflecting heat, or they are degrading (pyrolyzing). If you have turbulent smoke, and nothing is serving as a heat sink for you, what do you think comes next? Smoke is fuel. The fuel has all the heat it needs, so what is it missing?  Don’t be the guy who sees smoke as a complication of the fire. Be the guy who sees smoke as an extension of the fire, and mitigate the problem accordingly.

Let’s tie this up by adding the color component that was discussed in the previous article.  That article expounded on the understanding that smoke is filtered as it travels through the box and as it touches objects.  We should expect to see laminar, white smoke during an incipient stage fire that progressively gets faster as the box’s ability to serve as a heat sink is taxed, and we should expect it to get darker as the fire grows in intensity, pyrolyzing more and more of the structure and its furnishings inside that don’t face as many filters as smoke that is more distant to the exit portal.  Reading smoke is not a shortcut. Rather, it is a process that requires a thorough understanding of what smoke is, how it behaves, and how it is influenced by the box and environment. Having that understanding, combined with repetitions in practice, empower you to rapidly read, analyze, decide, and act in a manner that is intellectually aggressive.

Please share this information.  Your ability to share what you know is as powerful as your ability to read the smoke.  Knowing where the fire is, how progressed it is, and how much time you have until “next” happens is a critical component to a successful fire attack.  The fires are getting worse. We have to get smarter. Lives depend on it.

ABOUT THE AUTHOR

Rob Backer is a 16-year veteran of the fire service and currently serves as a Captain for Thornton Fire Department in Thornton, Colorado.  He is an instructor for Dave Dodson’s The Art of Reading Smoke and is available to teach nationally.

robbacker.fdi@gmail.com

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