Reading Smoke, Part 1
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.
To start, let’s go 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?
Two key terms are often used to describe smoke velocity: “turbulent smoke” and “laminar smoke.” Laminar smoke is slower-moving and indicates that the compartment and its contents are still absorbing heat. Turbulent smoke, in contrast, is fast, erratic, and “angry,” often chugging and swirling. This suggests the compartment and its contents have absorbed as much heat as they can handle, and without intervention, flashover is imminent. Since turbulent smoke indicates an imminent catastrophic fire event, recognizing the difference between turbulent and laminar smoke is one of the most crucial observations a firefighter can make.
Although not all encompassing, this article aimed to explain what smoke is and expound on one of its four attributes - velocity. Reading Smoke, Part 2 will discuss the other three attributes, while Part 3 will give a systematic approach to reading smoke.
I’d be remiss if I did not give credit to the subject matter experts, David Dodson and Rob Backer. It is through attending their training lectures, and reading their published articles, that I have learned this essential skill. If you’re interested in diving deeper, I encourage you to research their work.
For this month’s drill, utilize structure fire videos on YouTube to examine and discuss the smoke as it pertains to velocity. Some questions to get the discussion started could be:
• Is the smoke laminar or turbulent?
• Where do you predict the seat of the fire is located?
• What parts of the building are potentially involved?
Iowa Firefighter Association training articles are archived at: bit.ly/IowaFirefighter
Cole Kleinwolterink is a member of the Waukee Fire Department, Granger Fire Department, and Fire Science instructor at Des Moines Area Community College. Feel free to reach out to him at kleinwolterinkc@gmail.com with any questions, comments or inquiries.