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January 2025
Last month, we explored the concept of reading smoke and focused on one critical attribute: velocity. This month, we study the other three attributes—volume, density, and color—to help you sharpen your situational awareness and decision-making on the fireground.
COLOR
Similar to velocity, the color of smoke provides valuable insight into fire behavior. It can indicate the fire’s location, warn of backdraft potential, and signal structural instability.
Black smoke is found closest to the fire, because it signals intense heat during late-stage combustion. As smoke travels from areas of high-pressure to areas of low-pressure, it gets filtered through contact with surfaces. In addition to being filtered by traveling distances, smoke can become filtered through resistance, meaning there are a lot of objects/obstacles. As black smoke is filtered, it will transition into dirty white. Turbulent dirty white smoke still represents a hot fire but is a sign of distance or obstacles between you and the seat of the fire.
Clean, white smoke is typically associated with water vapor or steam. This smoke usually indicates one of two things - early-stage heating or water application. White smoke from shingles can indicate the attic is being heated because the water content in shingles are being heated from the heat inside the attic space below.
Yellow smoke is a warning sign of high sulfur content caused by extreme heat and oxygen starvation. Yellow smoke demands cautious ventilation, as introducing oxygen could trigger a backdraft.
Brown smoke signals the transition from a contents fire to structural involvement, because it is often emitted from pyrolyzing unfinished wood (e.g., wall studs, floor joists, roof trusses, etc.). It’s a key indicator of late-stage heating and impending collapse, especially when seen escaping from gable vents, eaves, or floor seams. Additionally, Rob Backer pointed out in his class, Reading Smoke, that “OSB and laminated veneer lumber weaken with heat and do not need fire to come apart. Thus, brown smoke from structural spaces containing OSB or LVL can indicate that critical strength has been already lost.”
video credit: Coffee Cup Drills on Facebook
DENSITY
The thickness of smoke correlates with its fuel load and the danger it presents.
Dense smoke reduces the tenability of the environment for victims and can increases the likelihood of rapid fire progression because of its “fuel continuity.” In Part 1, we discussed how the smoke overhead is in fact fuel. The denser the smoke, the closer the fuel particles are in the smoke. Thus, thick smoke will spread a fire event (like flashover) farther than less dense smoke. So although we are concerned when we see turbulent smoke because of its potential to turn to flashover, firefighters also need to be cognisant of dense laminar-flowing smoke because it has the potential to ignite due to the continuity of the smoke to the seat of the fire.
video credit: Coffee Cup Drills on Facebook
VOLUME
Smoke volume is a product of incomplete combustion, with its size offering clues to fire behavior and ventilation conditions.
Low-volume smoke indicates a hot, clean-burning fire with sufficient oxygen supply.
High-volume smoke signals a fire in an underventilated environment, generating significant smoke due to low oxygen levels.
When evaluating volume, consider the compartment size. A larger structure requires more smoke to fill it, so heavy smoke production in such spaces suggests a more significant fire.
video credit: Coffee Cup Drills on Facebook
A valuable resource for fire-related videos is the Coffee Cup Drills Facebook page; I encourage you to browse the page to find videos for this month’s drill. As you view the videos as a crew, focus on analyzing and discussing smoke characteristics, including velocity, color, density, and volume. Before starting, be sure to set the expectation with your crew that the purpose of this drill is to study the smoke, not critique the actions of the firefighters in the video. Without setting this expectation, the discussion can quickly shift away from smoke reading, and turn into an critique of the responding firefighters.
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