The interior fire attack has operated for years based upon a calculated risk and an assumption of fire dynamics by “ducking and diving” under a veil of uncertainty. With today’s advanced technology in thermal imaging, we have the ability to see the unseen behavior of fire gases and predict potential flashovers before they occur. Recent research has demonstrated we can interrupt the process of fire growth and flashover development through pre-wetting, cooling or controlling the air flow.
From recent research, today’s modern fuels produce a higher heat release rate resulting in faster developing fires and reach flashover 700 times faster than legacy fuels. The majority of fires we encounter are considered vent-limited fires. These are fires that are in the decay phase and are recognized by the heavy smoke conditions that create an environment too rich to support combustion. Following the arrival of the fire department and creating openings or failures in windows allows smoke to leave and an influx of air to enter the structure either through one or more openings. When smoke — is considered mass — leaves a compartment it is replaced with air —also mass. So, when we look at the fire compartment as a whole, when mass leaves a compartment it is replaced with mass as physics attempts to maintain a neutral balance between high pressures and low pressures.
Why is this so critical to understand? When openings are created within a structure fire, they will create either an air inlet or a fire gas outlet that allows for the exchange of air and fire gases. As fire gases (smoke) leave the compartment they become cooler and mixed with entrained air from the inlet create an ignitable “ideal mixture.” When these gases become trapped in adjacent rooms they become potential remote fuel storage areas. They are ignitable but the fuel to air mixture is not ideal for ignition — similar to a carburetor — it is too rich to burn. When an inlet and outlet is created the venting gases and influx of air are brought back into their flammable range and since the heated gases are present all that is needed is an ignition source to result in flashovers. We see this event take place in many videos and case studies where the coordination between fire attack and ventilation doesn’t occur.
To prevent extreme events like this, the nozzle team must recognize the conditions for potential for flashovers and mitigate the threat through thermal observations and cooling of the gases and surfaces of fuels prior to entering the fire corridor as a means to provide a safer interior fire attack.
As with all thermal imaging cameras, we can determine temperatures by several methods. One way is by placing a small cross-hair or “dot” seen in the viewfinder onto any surface to determine its specific temperature — i.e. surface temperatures of a wall. This temperature is displayed as a numerical value in the corner in the viewfinder. A word of caution, this numeric value is not a reliable representation of the overall temperature of the environment. Instead, view the temperature scale and compare the colors seen in the viewfinder to the temperature scale. In a high temperature environment — greater than 500 F and 1000 F — some TIC units will indicate a red or orange color. This usually indicates an extreme temperature has been encountered.
Tactical Thermal Imaging
As previously mentioned, we are familiar using our TICs for search or overhaul operations but let’s focus using the TIC during the fire attack as a life-saving, better yet, a “firefighter-saving” technique. The question must be asked, “why are we not using this device to gain a perspective of the hazards of environment we are about to enter?”
Today’s synthetic fuels produce significantly more smoke than legacy fuels as seen in our training fires where using pallets does not serve as a true representation of the environment we are expected to perform. We should expect to encounter heavy smoke conditions that not only black-out our mask but also black out the TIC when the lens of the camera becomes covered in soot. This renders the TIC unreliable so keep your TIC lens covered or clean it often to ensure accurate temperature readings are seen.
The use of a thermal imager provides the nozzle team with the ability to see heat energy and gas movement for determining flow paths, extreme temperatures, and potential victims during the hose advancement. It provides us with the ability to communicate to the incident commander (IC) the temperatures encountered that enables the IC to create a more effective incident action plan.
To Go or Not to Go
When using the TIC during the fire attack, consider using a “traffic light” mentality. If you see red, stop! Scan, evaluate, cool and re-evaluate before proceeding. We can refer to this techniques as the “GO or NO GO test.”
It should be used by any fire attack, search, or vent team entering a working fire environment to determine if it is safe to proceed down the corridor. I would recommend using a temperature of 450 F as a basis for the “No-Go” command. Why 450 F you may ask? This is the temperatures that our PPE (SCBA mask) becomes susceptible to degradation. Why intentionally expose your gear to extreme temperatures? After all, it is designed to protect you during an unexpected flashover for seconds. Intentionally degrading your gear reduces its ability to protect you should the extreme event occur.
The Go No Go test first begins as the officer of the search or hose team directs the crew to prepare for the attack by gathering needed equipment.
- Officer/leader conducts a 360 degree assessment of the exterior of the structure using the TIC to observe visual cues to locate hotspots in the fire room, as well as, exits, inlets/outlets and other hazards.
- The officer should close any doors that may be contributing towards fire development or creating a flow path. (Closing the controlling of air slows fire growth and progression.) Prior to closing any openings, a quick search of the immediate area for escaping victims should be conducted, as well.
The Go-No Go Test
- As the officer meets up with the crew at the entry point, he/she performs a 3-5 second scan of the of the “closed” exterior door or entry point.
- The officer verbally calls out the temperature or hotspot findings to the crew or IC.
— This provides a quick look at temperatures of the door being used for entry prior to opening.
— If temperatures above 450 F are identified on a closed exterior door, chances are an eminent flashover or backdraft may be waiting for you on the other side once the opening in the door is created.
— Issue the “NO-GO” command and prohibit the interior advance should be delayed until the entry point can be cooled below the threshold temperature.
‘Wet To Protect’–
Surface and Gas Cooling
For decades, firefighters have been taught never to put water on smoke. We are taught not to open up the nozzle until fire is discovered. So meanwhile, we continue to crawl past room furnishings producing unburned fuel gases while also being preheated. Surface and Gas Cooling is intended to “pre-wet” the surface of fuels and reduce the heat energy from potential fuels “off-gassing” (pyrolizing) locally around us and remotely ahead of the nozzle team. In using two to three second short bursts from the nozzle into the gas layers we are reducing temperatures of potential fuel gases needed to support combustion while keeping the neutral plane intact. Cooling drastically reduces heat energy in all areas of the structure and reduces the potential for flashovers. By surface cooling, we also create an area of refuge for escape should the fire corridor rapidly deteriorate.
Through surface and gas cooling — in order for the area around us to ignite, the moisture must be evaporated and re-heated to begin off-gassing again. When water is converted to steam — isn’t steam an inert gas? If inert gases do not support combustion isn’t that a good thing for us? So, if we are to choose between gases within a fire corridor, instead of having synthetic fuels producing ignitable combustibles gases around us, wouldn’t we prefer to have inert (non-combustible) gases around us instead?
Surface and Gas Attack
- After conducting the Go No Go test and we discover the temperatures at the “closed” doorway are above 450 F threshold the nozzle team surface cools the immediate area surrounding the hose team prior to opening the door. (Header area, overhead porch, siding adjacent to doorway)
- After cooling the exterior of the door and immediate area, control the door and open it to perform another Go No Go test.
- If temperatures are above 450 F, continue to cool until temperatures drop below the threshold temperature then proceed down the corridor towards the source of the fire. The Go No Go also continues prior to ascending or descending stairwells, turning corners, entering adjacent rooms until reaching the fire area. The Go No Go should be mandated for VEIS operations since the entry point will become the outlet once the window is taken.
As with any technology it is subject to failure. This technique does not constitute abandoning traditional methods of using our senses and traditional tactics to determine temperature levels.
As with any new idea there must be training to get master this technique. Try it in your next live fire training event and I think you’ll be surprised at what you will see prior to entering.