March-April 2009

IN THIS ISSUE: (CLICK TITLE TO READ ARTICLE)
Reading Smoke, Part 4 . . . John Mittendorf Wildland/Urban Interface Response . . . Ted Corporandy	Estimating the Stretch . . . Andrew Fredericks Get Hold of Yourself . . . George Burk Can't We All Just Get Along, Part 3 . . . Paul Stein & Ettore Berardinelli
Other Members-only Features:

Reading Smoke

Part 4

By John Mittendorf

The ability to analyze fire, smoke, and interior conditions can provide valuable information that is necessary to assess the following conditions:

• Operations (exterior and interior)

• Location and extension of fire

• Fireground time that is available

• Your involvement

These four conditions can also assist in evaluating the level of inherent risk to fireground personnel.

Obviously, a key to safe risk assessment is the ability to read smoke (and the environment) from outside and inside a structure and is based on the practical application of “smoke is the fire talking to you!” To put this statement into practice, consider reading smoke from an exterior and interior perspective. Taking the time to analyze exterior smoke should provide information necessary to determine what operations are necessary and in which order. Additionally, evaluating the interior environment should assist in being able to determine how long you should be involved in interior operations.

Before we look at the basic elements of reading smoke, let’s consider a fundamental starting point that consists of two considerations as follows:

VENTED FIRES

If a fire is vented either by the progress of a fire or manually by fireground personnel, it should have a lower potential of flashover and a higher probability of safe access (visibility) to the seat of a fire. Although this perspective may not hold true for every fire, let’s consider the basic concept. Consider a building with fire, heat, and smoke venting through the roof of the building. As this process continues, several simultaneous events will take place. As the fire draws heat and smoke up and out of the building, the interior spread of fire will be reduced as the fire is being directed vertically, not horizontally.

Along with this event, fresh cooler air from the exterior of the building will be drawn into the building as the fire will create a negative pressure inside the building (as compared to the exterior of the building) and draw oxygen from the exterior to fuel the interior combustion process. The introduction of fresh air and oxygen will alter the interior conditions of this illustration by reducing the interior temperature of the environment, thereby decreasing the chance of a flashover. Additionally, it will also increase visibility (as the introduction of fresh air will thin the smoke to some degree) and allow a safer and timelier access to the seat of the fire. 

Of all of the factors to be considered when evaluating the interior conditions of a structure fire, visibility (or lack of it) should be at least near the top of the list of important considerations as visibility can allow timely access and egress into and out of a structure, and the ability to find and complete an intended task

UNVENTED FIRES

Conversely, unvented fires should have a higher probability of flashover and increased access/visibility challenges. Again, assume a fire in a building, but in this case it is unvented. This fire will not be able to draw fresh cool air and oxygen from the exterior of the building, and a lack of ventilation will result in an increase of heat and smoke within the building, creating two significant hazards that were not present in the previous vented consideration. 

First, as the amount of smoke increases, visibility will decrease. Secondly and potentially most importantly, as the interior temperature increases, so does the probability of a flashover. Remember, as the interior temperature increases to the point that the interior smoke and fire gases are heated to their ignition temperature, the potential of a flashover has been maximized, as has the danger to interior personnel.

With the preceding thoughts on the ability of vented and unvented fires to impact fireground operations, let’s continue by evaluating the basic elements of reading smoke from three perspectives which are:

1. Reading the extension of smoke

2. Reading smoke from the exterior

3. Reading smoke from the interior

READING THE EXTENSION OF SMOKE

The ability to read the extension of smoke can be based on numerous factors of which the primary considerations are where is it, where is it going, and what is it going to 

impact. If the location or the origin can be determined, then the best route of access to the source of the smoke and the most effective ventilation operations necessary to minimize it can be determined. Secondly, if the direction of smoke can be determined, then the pathway the smoke is taking can potentially disclose its spread and ultimate destination. Thirdly, if the impact of smoke on an environment can be evaluated, then priorities can be established. To overview extension, let’s look at three considerations:

• Six-side concept

• The four primary extension routes and inherent hazards

• Status of the cockloft/attic

Six-Side Concept

When analyzing any incident to determine the possible extension route of smoke, fire and other inherent hazards, consider the incident from the perspective of having six sides. As an example, consider a three story structure with fire visible on the second floor. Applying the six side concept to determine priorities:

 First, determine the need for an attack and backup line to the second floor, search, and ventilation (four sides)

 Second, check for extension, search, and ventilation on the third floor (fifth side)

Third, is salvage necessary on the first floor. Remember, fire goes up and water goes down (sixth side). Remember to check for any downward extension of fire

Status of the Cockloft-Attic

Determining the location of fire in relation to interior and roof personnel is critically important from the perspective of the basic fireground rule “falling debris always has the right of way!” When this rule is applied to fireground personnel, it can determine life or injury-death from the perspective of another basic fireground rule “if you can’t stand on it, you can’t stand underneath it!” To summarize these two rules into one simple viewpoint, the location of a fire in relation to fireground personnel should be a key consideration when determining either interior or roof operations. 

As a simple example, consider a single story SFD with a visible attic vent (which can be found on most habitational and commercial structures as they provide ventilation to an attic area). As a result, attic vents can be an excellent indicator that fireground personnel can utilize to determine the location and/or extension of fire in a structure. 

Now, let’s apply this concept to our example and assume a fire is located within this structure, and is confined between the exterior walls, floor and ceiling. In this scenario, there is no extension of fire and the potential of structural collapse (i.e., the building) is minimal. Now, let’s assume the fire has extended into the attic area and is visible as either smoke and/or fire from the attic vent. This scenario is a graphic example that unlike the previous example, there are now three major hazards that fireground personnel can encounter:

• The fire has extended to the structural members that support the roof and ceiling, which in the typical modern dwelling and moderate commercial buildings is 2x4-inch lightweight trusses.

• Interior personnel now can be subjected to an interior collapse of the overhead trusses.

• Roof ventilation personnel (if used) can also be subjected to a collapse of the attic trusses.

Another simple example of reading attic vents can be applied to multiple story structures. Assume a fire is visible on the third floor of a four-story building with visible attic vents. If the attic vents are clean, there is a good possibility the fire has not extended to the fourth floor, and the fire has definitely not extended to the attic area. However, if smoke was visible from the attic vents, then it can be assumed that fire has extended to the fourth floor and attic area. Therefore, when reading the smoke at a structural incident, look for the presence of attic vents, and if present, has the fire extended to the attic area. This simple consideration can assist in determining the extent of fire and the possibility of a potential collapse of overhead structural members.

In the next article, we will consider the four primary extension routes of fire and smoke.

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.