Understand Fire Behavior to Improve Your Situational Awareness

BY BRYAN ALTMAN

I was looking back on my days in high school and laughed because I failed Spanish and hadn’t effectively learned a second language. At some incidents, we may have to deal with patients or victims with whom we can’t communicate because of a language barrier. I should’ve paid attention more in Spanish class.

Similarly, when we don’t know the language of fire behavior, firefighter injuries and fatalities result. That’s right; fire behavior is a language in itself and should be thoroughly understood so we can do our jobs safely and effectively. If we understand fire behavior, then we can improve our situational awareness to make correct decisions on the fireground. Many firefighters have been seriously injured and killed because they lacked situational awareness and made incorrect decisions on the fireground. According to the National Fire Fighter Near-Miss Reporting System, lack of situational awareness and poor decision making are the leading causes of near-misses.

In probie school, we learn about fire behavior and its importance and how you have to know what you are doing and why. But for most of us, the training stops after graduation. Fire behavior is the foundation of all firefighter knowledge; without it, we cannot understand fire and fight it properly. If we cannot fight it properly, then there is a greater chance for injury or death. Think about it: If you don’t understand fire behavior, how can you truly operate as a firefighter? If you don’t know how it behaves, then how can you control it or properly perform ventilation or overhaul?

As a firefighter, strive each day to ensure you understand fire behavior. Not that you shouldn’t concentrate on anything else–just that it needs to be covered more often. Fire behavior is changing, and fires progress more rapidly than ever because of the presence of synthetic materials, which are basically petroleum products in solid form. We must be aware of the resulting increased potential thermal energy output, or we could have a bad day on the fireground.

You must be able to understand what the fire is telling you. Effective communication consists of a sender (the fire), the message (behavioral aspects), the receiver (the firefighter), the decoding (reading the smoke and fire), and the feedback (your reaction–i.e., the firefight). All of these components must be present; if not, communication does not take place and misunderstanding is possible. Inside a burning structure is not a time for miscommunication. The fire will not repeat the message! You must have situational awareness and pay attention to detail. If not, the next decision you make could cost you your life!

Fire communicates with us throughout its development, from ignition to decay. Each stage is progressive and deals out its own dangerous hostile fire events–e.g., rollover, flashover, smoke explosion, backdraft, and rapid fire spread. The fire gives us clues to its progression, travel, and dangers; we just need to pay attention and listen.

Let’s review the four stages of fire–ignition, growth, full development, and decay–and discuss their associated hazards. The above order of progression for the stages of fire is common in fuel-controlled fires but not necessarily in ventilation-controlled fires, which are most common today because of well-sealed buildings. The old fire development curve looks like one big mountain where it starts with ignition and rises to full development, peaks, and falls to decay. In today’s buildings, it reaches a point in the growth stage where ventilation becomes the driving force of development and now that curve has peaks and valleys. Heat is present, but the available oxygen dictates the rate of burning and growth.

Ignition. In ignition, the first stage of fire, heat, fuel, oxygen, and a chemical chain reaction (the fire tetrahedron) combine and produce flaming combustion (fire). The fire does not greatly influence the fire compartment’s environment. There is very little heat at the ceiling and very little smoke and no major hostile event associated with this stage.

Growth. The fire is now influencing the environment. In the early growth stages, most heat is transferred by convection. Thermal layering is beginning to form as a result of gases and smoke forming layers because of their respective temperatures and densities. The hotter, lighter gases are at the ceiling and the cooler, heavier gases are toward the floor. As the fire burns, fast-moving hot gases move away from the fire and toward the ceiling, and fresh cooler air is drawn or entrained into the fire, which helps keep the fire burning and growing. As the fire continues to grow, the radiant heat bombards combustible surfaces until they can no longer absorb it. Unburned gases are collecting at the ceiling; with just a little more heat, they ignite, and fire spreads across the ceiling. We can see rapid fire spread because of the amount of hot unburned fuel given off during this time. Signs include trapped gases that mix with air and continue to be heated. All they need is a spark or flame to ignite. The heat continues to build, and the overpressure region (the ceiling) and underpressure region (floor) begin to equalize in temperature. Isolated flames (or “ghosting” as an earlier generation of firefighters called it) are seen at the bottom of the smoke line. Then suddenly, flashover! Everything that is exposed in the compartment is burning. You must understand that flashover isn’t just a stage but a transition to the next stage.

Full development. At the most intense stage of a fire, the heat release rate is at its maximum and the fire compartment has become totally involved. Conditions are untenable!

Decay. When the fire becomes either fuel-controlled (i.e., there is no more fuel to burn) or ventilation-controlled (i.e., there is not enough oxygen to sustain combustion), the fire decays to a smoldering state. However, heat can continue to build in this stage and, if the compartment is well sealed, it can create conditions for a backdraft. Backdraft can occur only during the smoldering stage in a highly sealed fire compartment with a low oxygen concentration. Any sudden introduction of oxygen will violently ignite the gases that are built up in the compartment. This can happen in isolated compartments, not whole structure events as shown in old texts.

Note that fire can be in different stages of development throughout the structure. This is where situational awareness comes into play so that you can correctly read the fire and smoke to make decisions for your next course of action.

For example, the fire’s message is that it’s rolling across the ceiling and thick black pulsing smoke is pushing to the floor, the combustibles around you are off-gassing, and the heat is pushing you to the floor. What is the fire telling you? Flashover! What is your feedback? Your response should be to cool the atmosphere and retreat to pose another attack. Remember that vertical ventilation and cooling will prevent flashover, but horizontal ventilation can accelerate it, resulting in a ventilation-induced flashover.

Here’s another example. You are in a high-pressure zone and the smoke is moving faster than you can crawl. What’s going on? This situation presents the potential for rapid fire spread, which is usually container influenced. This area features small, narrow stairs and hallways that allow for rapid heat buildup. What is your feedback? Cool the atmosphere! Vertical ventilation could put you in the path of the air track–a bad position. Remember that horizontal ventilation may accelerate the event. Many firefighters have been injured or killed because they failed to respond appropriately to the fire’s message because of a lack of situational awareness.

Most firefighters concentrate on the fire and do not take into account what the fire is actually doing–i.e., giving off heat, smoke (which consists of incomplete combustion products), and toxic gases [e.g., carbon monoxide (CO), carbon dioxide, hydrogen cyanide, hydrogen sulfide, and many others]. The smoke is just as dangerous and destructive as the fire; it contributes to the fire spread. The hotter and thicker it is, the more dangerous it is because it reaches flash point and ignition temperatures much more quickly. CO has an ignition temperature of 1,128°F, which is important to understand because these pockets of CO will ignite toward the bottom of the smoke layer, which indicates flashover is imminent. The old days of “don’t fight smoke” are long gone. When you make entry into the structure and are making your way to the seat of the fire, remember you are crawling through and past the fuel; pay attention to what the fire is telling you. The fire you see has already been produced, and the smoke you are crawling through is fuel for a major hostile fire event to take place. Cool it with your stream. If it hasn’t reached either its ignition or its flashpoint temperature, then it can’t cause an event. You have to manage your atmosphere and be prepared to deal with the signs of flashover (rollover; high heat; thick, black, turbulent smoke), backdraft (pulsating smoke leaving the structure, yellowish-grey smoke, underventilated), smoke explosion (growing fire, smoke collecting away from the main body of fire), or rapid fire spread (smoke moving faster than you can crawl, rapid buildup of heat and gases).

I responded to a working residential structure fire with heavy fire and smoke issuing from the rear of the structure. On entry, my crew was met with a heavy smoke condition in the living room. I gathered from the clues–high heat and dense black smoke–that flashover was imminent. While attempting to cool the atmosphere, I called over the radio for ventilation to take place at the fire room. Instead of ventilation occurring where I asked for it, which was at the fire room, it was done behind us, which pulled the fire toward us (situational awareness is very important). All the room needed was more air, which is what it got. I noticed what had happened and I ordered my crew to back out under the protection of the hose stream and suddenly, FLASHOVER! Luckily, we were just inside the room and able to escape without injury. If I would not have been able to recognize these signs, the outcome would have been much different. We would have become statistics!

Do not change the path of ventilation while crews are inside. Ventilation paths should pull or push everything back toward the area of origin. Anything that we do as fire crews that allows ventilation to push or pull the fire or smoke toward oncoming crews can cause a drastic turn that can lead to injury or death.

These are all very dangerous conditions. So my question to you is, Can you communicate effectively with fire and understand what it is telling you? If not, what will you do to change that? Fire behavior is the subject of numerous books, training videos on YouTube, the Fire Department Instructors Conference and other firefighter training events, and basic fire manuals. All of them will help you build your situational awareness so that you can make the right decisions. Fire has no conscience, so take it seriously, or it will take you!

ong> is a lieutenant with Worth County (GA) Fire Rescue. He served as a full-time instructor at the Georgia Fire Academy, teaching basic firefighting and assisting with live fire classes in 2011. An eight-year veteran of the fire service, he has served with the Tifton-Tift County (GA) Fire Department and Ashburn (GA) Fire and Emergency Services. He has a diploma in fire science, and his certifications include firefighter II, acting officer, live fire instructor, basic firefighter instructor, and fire instructor II.

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