September-October 2009 Issue

	September-October 2009

Reading Smoke, Part 6

By John Mittendorf

READING EXTERIOR SMOKE

Reading smoke should begin as you stop in front of an incident as smoke is the fire talking to you. Before committing yourself and/or resources, take a few seconds and evaluate the five attributes of color, density, amount, pressure, and dynamics as follows:

Color

Smoke color is indicative of the type of material burning if only one material is burning. The majority of smoke being produced at a structure fire is not coming from what is burning but from materials that are being burning and/or heated. As materials dry out, they break down and the smoke color changes. Wood or cellulose materials change to tan, grey, then black as they heat up. Plastics start off smoking white, then emit grey then black as they heat up. Therefore, smoke color viewed from the outside of a building is really indicative of heat. Whiter smoke is early stage heating and blacker smoke is hotter regardless of the type of material. Also remember that as smoke flows through a building, soot and hydrocarbon particles deposit themselves on surfaces. Therefore, black smoke can actually change to a lighter color before it leaves the building if enough distance or resistance to smoke is present. Additionally, lighter smoke is an indicator of less particulates in the smoke and darker smoke is an indicator of more particulates. Remember that particulates will readily burn at the right temperature! The color of smoke can be easily divided into four categories:

Note: When reading the color of smoke, be aware that smoke from a fire involving oil based roofing materials such as tar paper and composition shingles will give off a thick black smoke that can easily darken lighter colored smoke and give a false reading.

White or lighter colored smoke with minimal pressure and heat. In this case, this is an indicator of residual smoke from the fire being extinguished. The potential of this smoke suddenly flashing and burning is extremely low. Visibility will likely be moderate inside the building.
Smoke with some color, heat, and pressure. The moderate color, pressure, and heat associated with this type of smoke is an indicator of a moderate hazard (or potential) of the smoke suddenly flashing and burning. Depending on the amount of smoke inside the building, visibility will be minimal to moderate.
Dark smoke with pressure and heat. This type of smoke is a candidate to flashover, and visibility will be non-existent and is normally an indicator that the fire is well advanced in the building and the black color of the smoke indicates that significant heat and/or petrochemical compounds are probably involved. This condition is often referred to as black fire. This term indicates that although fire is not visible, there is sufficient heat within the smoke to pyrolize wood (and enhance the removal of gang nail plates in lightweight trusses (if present). This smoke can quickly become a prime candidate to flash and burn with significant intensity. Visibility will definitely be non-existent!
Fire or the “red stuff.” In some cases, fire will be visible inside a building. although radiated heat from the fire can be greater than the previous examples, this type of fire will not readily flash and burn as it has completed its goal of burning the interior portion that is visible to suppression personnel. Until this type of fire is extinguished, interior visibility (although moderate) is not a primary issue until the fire has been extinguished.

Density

The density of smoke can often be a graphic indicator of the potential flammability of the smoke, and the visibility (or lack of visibility) within a building. As an example, assume smoke has a lighter color and density. In this case, this type of smoke is an indicator of three considerations: (1) the chance of a flashover is relatively low, (2) although limited, there will be some visibility inside the building, and (3) the smoke is an indicator that either the fire has been extinguished or is about to be finally extinguished.

Note: Remember that when you are reading smoke that is some distance from its origin, it can cool and become lighter, thus giving a false reading.

Amount

The amount of smoke is normally not associated with the color of smoke, but it can be a graphic indicator of the quantity of fire, its extension, and its potential flammability. To keep the previous sentence in its proper context, remember that it takes fire to make smoke, and smoke is capable of burning. Let’s apply that statement to quantity of fire, extension, and flammability:

The relationship of the perceived size of a fire in relation to the size of a building must be considered. As an example, a fire of a given size in a routine building can visibly produce a large quantity of smoke, whereas the same fire in a large commercial building may not exhibit the same quantity of smoke, as the size is able to contain more of the smoke without it being visible. A large quantity of smoke visible from a large building (i.e., concrete tilt-up, etc.) is a good indicator of a large fire.
The amount of smoke from a building can be an indicator of the extension of fire. As an example, assume a fire in a basement of a three-story dwelling, and there is heavy smoke showing from several basement openings only. This is a good indicator that the fire is contained to the basement area. Now assume that heavy smoke is showing from several basement openings and there is moderate smoke showing from windows on the top floor. Obviously, this is an indicator that the smoke (and fire) has extended from the basement to the top floor. Always compare the area of most smoke to any area of lighter smoke and the distance between these two considerations. Also, always look for areas where smoke has not extended to as this can be as important as where smoke is visible.
Lighter smoke or smoke that has some transparency indicates a cooler smoke with less combustible material, and heavy smoke is an indicator of more combustible products within the smoke. The amount of smoke can also be a graphic indicator of the amount of smoke from a fire. As an example, a hot free-burning fire will likely yield minimal smoke, whereas an oxygen deficient fire can yield a significant amount of smoke.

In our next article, we will look at pressure and dynamics.

Chief Mittendorf is the author of Truck Company Operations and Facing the Promotional Interview. To purchase, return to the Main Page and scroll down to Fire Nuggets Books and Videos.

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