One of the most important skills all firemen should possess is the ability to read smoke signals. The ability to read the smoke at any position within the company can help those responding to the incident make better tactical decisions. Smoke can help first responders determine the fire’s location, growth, toxicity, the direction of travel. In the case of a structure fire, it helps us predict hostile fire events like smoke explosions, backdrafts, and flashovers. “Reading smoke can tell us what is happening now and, more importantly, what is going to happen in the future,” said author the author of The Art of Reading Smoke, David W. Dodson. “Watching how fast it is changing can tell if we have seconds or minutes before something happens.”
Types of Smoke Signals
The art of reading smoke must first start with what comprises the emission. Smoke is made up of particulates, aerosols, and gases, and has four attributes:
- Smoke Volume
- Smoke Velocity
- Smoke Density
- Smoke Color
Smoke Volume can provide a useful indication of the location and indicates the amount of fuels off-gassing within an area. The measure of volume is important but unfortunately, it elucidates nothing much other than location. There can be large volumes of smoke with very little fire.
Smoke Velocity is the speed of the smoke leaving the structure. The velocity is an indicator of pressure that has built up within the compartment. If the velocity of smoke leaving an opening is agitated or turbulent, then rapid-fire progress is likely to occur. In these cases, unless the structure is ventilated and cooled a backdraft, explosive burning of heated gases, will occur due to the improper ventilation.
Smoke Density refers to the thickness of the emission and how much fuel is laden in the smoke. Optical density refers to how difficult it is to see through the smoke. Thick or optically dense smoke contains a high concentration of particulates and is difficult to see through. The greater the smoke density the more likely a hostile fire event, such as flashover or rapid fire spread. The thicker the smoke, the more spectacular the flashover or fire spread. Worse yet due to the concentration, thick black smoke can be an ignitable fuel.
Smoke Color is the visible shade of the spectrum and tells the stage of the fire as well as helps determine the location of the fire. Petroleum products, rubber, and many plastics will produce black smoke. Wood and other ordinary combustibles will commonly produce smoke ranging from light gray to yellowish. It’s important to make a distinction that lighter-colored smoke frequently contains a substantial concentration of unburned, highly flammable, and deoxygenated materials. Under these conditions, the smoke can ignite and create a hazardous and possibly deadly situation for firefighters. When a fire produces dark brown or even black it is an indication that the fire is underventilated and/or it contains an abundance of petroleum products. Additionally, brownish smoke will tell you that fire has ignited wood, which usually means that the fire has infiltrated the structural integrity of the building and could provide a collapse hazard. The color of smoke is generally thought of as the most comprehensive indicator of fire behavior. However, it is essential to remember that smoke color is only one indicator that is a part of a number of indicators used to predict fire behavior and it must be considered in context. The above signs of reading smoke are excellent tools to have, but they are not all-inclusive. In The Art of Reading Smoke, David W. Dodson stresses that firefighters and incident commanders need to use their best judgment when reading smoke and committing firefighters to assignments. Here are a few tips Dodson shared in the first part of his book:
- Stop watching the fire. The first big barrier to learning to read smoke is that our eyes are naturally drawn to light and movement, both of which are exhibited by fire. “The fire is the endgame,” Dodson says. “An experienced fire officer looks away from the light.”
- Know the four characteristics of smoke: volume, color, velocity and density. More importantly, know how to look at smoke and quickly identify it in terms of these characteristics.
- Thin, black, fast smoke indicates a well-ventilated fire is nearby.
- Slow, white, dissipating smoke (first thick but thinning quickly) is a sign of steam, and indicates early stage heating.
- Brown smoke indicates unfinished wood burning. In lightweight construction, this can be a warning sign for building collapse.