Black Smoke: What Does It Mean And What Causes It?


If you’ve ever watched a fire and seen thick, angry plumes of smoke rising up to the sky, you may have wondered what makes smoke the color it is and what that means? Black smoke looks the most toxic of all smoke colors but is it? What should you do about this kind of smoke? 

Black smoke is a result of the burning of heavy fuels or synthetic materials. This can mean that the fumes are particularly toxic and shouldn’t be inhaled if you are exposed to them. However, most smoke can be toxic and dangerous to varying degrees.

Let’s take a look at what makes smoke black vs white and what the differences are. We will also look into some more rare colors of smoke and their causes. Here’s what you need to know. 

Also read: House Fire Temperature: How Hot Does It Get?

What Is Smoke?

Smoke is simply a byproduct produced when a fuel burns but is not consumed in its entirety (incomplete combustion).

In coal fire, for example, the smoke particles are what we might think of as “ash”. It depends on the fire and the product being burned and how well it is being burned as to what kind of smoke may be produced.

Thus, smoke tends to be made up of tiny particles of either partially oxidized or fully oxidized or unreacted fuel particles. It can be poisonous if the particles contain toxic elements or compounds and its smoke is very dangerous in the event of a building fire, where it can cause suffocation even if there is no toxic element to it. 

In fact, the majority of who people die in a fire are from smoke inhalation rather than being burned. This is both because the smoke can contain many very toxic chemicals and because the smoke can displace the clean oxygen, leaving nothing to breathe.

That’s an incredible difference and it’s why it’s always good to know as much about smoke as you can so that you can make informed decisions about your health and safety. 

Is Black Smoke More Dangerous?

Though most smoke is dangerous, black smoke is an indicator of heavy fuel burning or manmade materials on fire. These materials produce black smoke that is even more toxic and full of harmful chemicals.

For example, look at this black smoke from heavy fuels burning on the highway:

So, in general, the darker the smoke, the more dangerous and toxic it is.

In fact, for the longest time – the Environmental Protection Agency spent no time at all examining the color of smoke because they said that there was a much more important factor involved in the determination of the potential harm from smoke: opacity. 

Is it Better If You Can See Through The Smoke? (Opacity) 

Yes. The harder it is to see through smoke, the more smoke particles that there are.

This should be fairly obvious and thus, it’s fair to say that there are more polluting particles present and thus, the more opaque (harder to see through) a smoke is, the more dangerous it is likely to be if you get a lungful of it.

In fact, you can measure the opacity of smoke if you want to. Y

ou need something called a “Ringlemann Chart” this compares absolute transparency and absolute opaqueness with the color of the smoke and then you can convert the results into “percentage opacity” which is really a measure of the grey element in the smoke. 

The best advice when it comes to smoke, however, is simple.

You should treat all smoke as potentially harmful to health and whenever possible seek to avoid breathing it in at all. When you must breathe it in, you should seek to minimize the amount of smoke you inhale (for example, by using protective breathing equipment).

What Causes Black Smoke Vs White Smoke vs Grey Smoke?

Black smoke tends to occur when heavy fuels are being burned and you can see black fumes coming off vehicles that burn heavy fuel oils, for example.

However, they are often an indicator that synthetic and manmade materials are on fire – rubber or synthetic building materials are typical examples. Firefighters treat black smoke as an indicator of possible volatility within the fire.

White smoke, on the other hand, tends to indicate that the fire is creating either gas or water vapor and it can be an indicator that the fire has only just started burning or is in the process of going out.

It may also mean that light materials are on fire – think hay or fibers which will normally smoke with a white color.

Grey smoke is different again. In general, it means that the fire has nearly run its course and it is struggling to burn material effectively.

This can be very good news for firefighters, but it is always possible for a fire to spread to some new material – so, it’s not a cause to relax or slow down firefighting efforts either. 

If you are curious about how to read and interpret smoke in a fire from the perspective of a firefighter, this video covers the basics:

What Causes Smoke Of Other Colors

What Makes Smoke Blue?

Firstly, when smoke is seen outdoors, it often takes on the appearance of the background that it appears in front of.

So, in the instance of a dark background – the smoke will often appear blue, this is because of the way the light interacts with the smoke particles which reflect the light from everywhere except the background behind it (where no light is falling) and this has the effect of making it far more visible.

At the same time, this reflection causes the scattering of the light rays and allows them to break into individual colors and the blue rays will scatter farther than those that deliver red or yellow, colors. Thus we tend to perceive the smoke as blue when it’s burning against a black background.

What Makes Smoke Orange?

However, if we then take this smoke and allow it to filter up against a bright blue sky, it’s no longer blue – in fact, it tends to take an orange hue. This is because now the smoke particles are reflecting light in all directions (there’s no absorption on the background) and the scatter pattern is less. 

The background blue also overwhelms any blue in the scatter pattern that is created. This leaves our eyes focusing on the yellow and red rays and when you combine these two colors? You get the orange hue that you see in the sky.

What Makes Smoke White?

Then there are another couple of effects that can affect the color of smoke in the outdoors.

Firstly, the size of the particles in the smoke. Mainly, smoke consists of fairly small particles but as they get larger, the diffraction pattern changes and they no longer scatter the rays within reflected light – thus, smoke with large particles when viewed outdoors tends to appear white.

Is The Smoke Another Color? 

Finally, it’s actually quite straightforward to make smoke outside any color you like – you just add chemicals that burn with a specific hue to the smoke. Photographers do this all the time when they use smoke bombs like the one featured in the YouTube clip below. 

Conclusion

Black smoke: what does it mean and what causes it? Well, as you’ve seen, it might well mean that the fire is consuming heavy fuels, or it might mean that you’ve got a bunch of man-made materials on fire. This isn’t a guide to the toxicity of the smoke (in fact, we’d advise that you treat all smoke as toxic) though it may indicate that black smoke is more toxic than normal.

It’s best not to judge smoke by its color at all. As we’ve seen, the same smoke can appear many different colors based on how it is viewed. Don’t assume that white or grey smoke are better for you than black smoke. 

Related Articles:

Is Diesel Flammable? Yes and No…

How Hot Does Wood Burn? Examined

How Do Firefighters Know When There is a Fire?

Chase

I have been a Firefighter in Northern California since 2012 and a Paramedic since 2008. My site is dedicated to helping answer questions people have about the fire service. I am passionate about helping to share what I have learned and assisting those who are pursuing a career as a firefighter. Thanks for coming to my site!

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