December 2024

You may not enjoy reading books, but reading smoke is a must for all firefighters. Assessing smoke and its interaction with building construction is a crucial part of the size-up that every firefighter should conduct upon arrival. With practice, this skill can be honed to take only seconds.

Before we begin, I’d like to acknowledge subject matter experts David Dodson and Rob Backer. Much of the information in this article comes from attending their training sessions and studying their published work. For those interested in exploring further, I highly recommend looking into their contributions to this essential skill. 

With that, let's get started by going back to the Firefighter 1 textbook and review what smoke actually is. Smoke is produced when a substance undergoes pyrolysis or combustion, creating a mixture of solid particles, liquid aerosols, and gases. Understanding each of these components individually helps build a clearer picture. The solids found in smoke include carbon (soot), ash, dust, and fibers. Aerosols, or suspended liquids, contain water and various hydrocarbons (eg. oil). These oil droplets can have an auto-ignition temperature at 460o Fahrenheit, but don’t ignite because the environment is too rich to allow it. Additionally, smoke contains numerous gases, including carbon monoxide, hydrogen cyanide, acrolein, and benzene.

Why is this knowledge important? Simply put, smoke is fuel. Given the right temperature and oxygen mixture, smoke can ignite, completing the combustion process. This means that hot smoke is highly flammable and heavily influences fire behavior. The ability to "read smoke" helps firefighters anticipate how a fire will behave inside a structure.

When reading smoke, firefighters focus on four key attributes: velocity, color, density, and volume. While each attribute can give the firefighter insight into the fire behavior inside the building, when it comes to reading smoke it is often stated that, “velocity is king.” 

Let’s define velocity in terms of smoke. Velocity refers to the speed and flow characteristics of smoke.

The speed of smoke movement reflects the pressure inside the building, which is created by heat and/or volume. When pressure is caused by volume, the smoke slows down and balances with outside airflow upon venting out the structure. Heat-pressurized smoke on the other hand will rise then gradually slow as it cools when it vents out the building. With this understanding, we can conclude that turbulent smoke is typically seen closer to the seat of the fire making velocity a reliable indicator of fire location. However, when using smoke velocity to locate a fire, it’s crucial to compare openings of the same size (e.g. windows to windows). While videos are ideal for illustrating this concept, examine the picture in this article - 

Where do you see laminar smoke? 

Where do you see turbulent smoke? 

Where does the velocity of the smoke suggest the fire might be located?