WHAT SMOKE CONDITIONS TELL YOU

WHAT SMOKE CONDITIONS TELL YOU

BY BOB PRESSLER

You are responding as the first-due company to an unknown type of fire. The fire is in a neighborhood of medium-size, one-family dwellings. The driver slows the apparatus to check addresses as you get closer to the area. A short distance down the block, a small group of people are waving frantically to get your attention. You proceed to their location and pull up in front of a 212-story frame house. Light smoke is showing from several different areas of the home.

What can you learn from the visible smoke? How can color, density, and volume tip you off to what is burning and possibly to the location of the fire in the building?

CASE 1

On arrival, your firefighters work to open up the sealed vacant building. The visible smoke is light in color. Although the smoke is showing at several points, there is not a great volume of smoke issuing from any one location. In addition, the visible smoke is not pushing from the building under pressure.

From your vantage point in the street, what appears to be burning and what is its probable location in the building? This type of visible smoke condition is very typical of a rubbish fire in a vacant building. With most of the windows already out of the building, the smoke does not bank down to floor level in any of the rooms. It escapes to the outside via the opened windows in the building. It spreads to the upper floors of the house via the open staircase. So the smoke, as it spreads throughout the house, collects at the ceiling level. This happens in most of the rooms of the house, not just in the fire area. Trying to determine which level the fire is on may be a little tough. Most times, the lowest level from which the smoke is showing will be the fire area. But because of many factors, such as atmospheric conditions, the temperature of the smoke itself, and void spaces in the structure, the smoke may show from an area lower than the actual fire area.

What if this same smoke condition is showing from the open windows of an occupied building? All indicators are for a minor fire–probably clothes, paper, or rubbish but also possibly food on the stove. The biggest difference is that with food on the stove, the volume of smoke may be much greater, depending on how long the pot has been burning. Even if the volume of smoke is greater, there should not be much of a “push” to the escaping smoke. There is really little heat to make the smoke move, so it will not be venting under great pressure. One other tip-off to food on the stove might be the smell. Even as you`re getting off the apparatus in front of the house, you may be able to smell the “burning” aluminum pot.

CASE 2

As the type of fire increases in severity, the smoke conditions will also start to change. This time your companies arrive on the scene to find a more serious fire. This fire in the rear apartment of a multifamily house has gained some headway as the first-due engine and truck start their attack. The door to the fire apartment has been forced as the engine flakes out the first handline. The color and volume of the smoke indicate a more serious fire than just rubbish. The darker color shows that the fire has developed from its original fuel source into a room-and-contents fire. The smoke also has a little “push” to it. In other words, as soon as the door is forced, the smoke starts to move from the structure rapidly.

After that initial roll of heavy smoke immediately after the door is forced, the smoke shows from the doorway mostly at the upper level. This indicates that the fire is somewhat removed from the door area, even if only to the opposite side of this room or an area immediately adjacent to this room. Although the fire is remote from the door now, by making this opening, you have given the fire a new source of oxygen. The fire will now start to draw in the direction of the new air supply. The members of the engine team must continually observe the conditions at the doorway. If the fire starts to show in the escaping smoke before they have water, they should partially close the door until they have received water and are ready to advance into the fire area.

CASE 3

At this daytime fire in an unoccupied storefront church, the arriving companies face a more difficult fire. The engine company stretches the line into place as the ladder company forces entry. As the door is forced, the smoke condition that escapes from the building is brown in color and is pushing under pressure. What should this brown smoke indicate to these companies? Even though this building has a brick exterior, it is of ordinary construction. This means that the floors, roof boards, and most other interior partitions are constructed of wood. The brown color of this smoke should send a warning to the companies. The fire has gone from its original fuel source, which in this case was a large candle that had been left burning, and has communicated to the wooden structural elements of the building. The candle, which had been left on the floor, had burned down and communicated to the floorboards. As the fire continued to burn, a hole formed in the floorboards. This let the fire extend down into the area between the basement floor beams. Now the fire is feeding on the wooden components of the building itself. This becomes a dangerous operation for the companies, as most of their operations will be conducted over the main body of fire located in the floor area. When smoke is pushing from a building with this color and density, the incident commander must suspect that the fire is attacking the structural components of the building. In older buildings, in which structural elements sometimes helped contain the fire or at least caused it to spread more slowly, this is not as serious a problem as it is with new construction. With new, modern construction, many components have shown that they fail rapidly once fire has attacked them. Where floor joists once acted to contain fire to the bay(s) of origin, modern truss lofts rely on the four outside walls to limit horizontal fire spread. Buildings with lightweight trusses or wooden I-beams have failed without warning at numer

CASE 4

As the fires in-crease in severity, the color and volume of smoke will continue to change. One of the problems associated with using smoke to do your size-up is that some building features might act to mask what the smoke is trying to tell you. At this fire, a close look at the windows reveals that this building has had aluminum, triple-track storm windows installed. These storm windows help hold the products of combustion inside the building. Just like their modern counterpart, the energy efficient window, these window assemblies make the fire area difficult to read from the exterior. A closer look at photo 4a shows heavy smoke showing at the three front bay-style windows, but most of the smoke is being forced out of the partially open middle window. A quick look at the adjacent window shows very little smoke passing by the storm-type window. The little smoke that is showing is very dark in color. Looking at the floor above the fire floor, you see that these windows are also showing smoke. Even though the amount of smoke is nowhere near the volume that can be observed on the fire floor, the color is also dark. This dark gray, almost black smoke that is boiling out this small opening and pushing out around the closed windows is a true indicator of a very heavy body of fire that is being held back only by the windows. All that is missing is oxygen. Once the windows are taken, the rapid influx of air will cause the rooms to light up in fire.

CASE 5

In commercial buildings, the volume and degree with which the smoke is issuing from a building are as useful as the color. At this fire, not only is the smoke very dark in color, indicating heavy involvement of the contents and the building components, but the fact that the smoke is exiting the building forcefully through the entire door opening indicates that this is a deep-seated fire that has control of most of the interior of the building. The two handlines that are trying to push into the building do not have the reach or the volume of water needed to reach the seat of the fire. Just the heat radiating from the smoke shows how deep-seated this fire is.

Smoke showing from a burning building can help the IC make an initial size-up. Although not completely foolproof, the color, vol-ume, and pressure of the escaping smoke are clues to what is happening in the fire building.

CASE 6

One of the problems with relying on smoke color alone to determine exactly what is burning is that great amounts of plastics are used to make furnishings today. In this fire, the normal household furnishings have produced a smoke condition that rivals a fire in an oil depot. Instead of a fire that involves cotton, wool, wood, and paper, fires in today`s housing units frequently involve products made entirely of plastic. Compared with the materials that we were previously familiar with in our house fires, these new plastic furnishings can produce almost three times the Btus when they burn. This makes for hotter and smokier fires. When the fire is 10 or 15 floors above conventional operations and at the end off a long narrow hallway, the fire problem becomes more complicated. Any time any smoke is seen issuing from a fire-resistive building, whether a high-rise or not, consider that energy-efficient windows may not be letting the full story out. An HVAC unit may control the interior environment in these buildings, and the windows contribute to a tightly sealed building. Little or no smoke may be showing, but a serious fire may be deep in the building. Operating units must be cautious when forcing doors or ventilating windows so that the rapid influx of fresh air does not result in a rapid fire buildup. Many times the smoke produced by these plastic-fueled fires is superheated and contains a tremendous amount of unburned fuel. All that is missing is oxygen. Once air is introduced, all the unburned fuel ignites at once, producing a rapidly expanding fire front. Sometimes the fire produces so much unburned fuel that the fire cannot burn within the room itself because there is not enough oxygen. When this happens, the escaping smoke will ignite away from the building when the mixture of heat, fuel, and air reaches the correct levels.

Although smoke issuing from a burning building will give you many clues about what is burning and its possible location in the structure, several factors may distort this message. Beware of fires in buildings that contain many plastics or synthetics. These fires may produce an inordinate amount of black smoke compared with what is really burning. Fires that are producing little heat may pro-duce a lazier smoke that may not rise to the higher levels of a home. This smoke may actually be showing at a level in the burning building below the one where the fire is actually located.

Other styles of construction will also affect smoke conditions. Lightweight trusses may be used as both floor and roof supports. When the floor trusses are of the open-web gang-nailed style, there is nothing to restrict the spread of fire or smoke throughout the truss void. A fire that originates in the truss loft, such as from a short from a light fixture, can spread undetected through the loft to the outside walls and upward throughout the entire structure. Until the entire void area is filled with smoke and heat, the fire may grow undetected. With this fire, the void space itself is small, but because of interconnected voids, the smoke may not show on the outside of the building. Larger voids, such as the attic area in a bowstring truss building, may also contain smoke conditions for a long period of time. Light smoke showing on arrival from buildings with numerous voids may not present a true picture of what is actually burning inside the building.

Keep in mind that the fireground is an ever-changing environment. Be sure to use any clues that can assist you in your operations. n


Photos by author unless otherwise noted.







Photo 6a by Mike Lindy.


n BOB PRESSLER, a 23-year veteran of the fire service, recently retired as a lieutenant with Rescue Company No. 3 of the Fire Department of New York. He created and produced the videos Peaked-Roof Ventilation and SCBA Safety and Emergency Procedures for the Fire Engineering video series OBread and ButterO Operations. Pressler has an associate?s degree in fire protection engineering from Oklahoma State University, is a frequent instructor on a wide range of fire service topics, and is a member of a volunteer department.

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