Fire Dynamics for the Nozzle Nerds

After we discussed the size-up and stretch, Deployment, and stretching long, we need to start to address the fire dynamics for the nozzleman. As mentioned in the first part, the nozzle will experience the most heat and products of combustion on the tip of the line. It is vital that they understand fire dynamics while operating in IDLH environments. This will ensure they are able to identify worsening conditions and make the necessary decisions due fire attack.

After we have successfully stretch our line, called for water and ready to make entry into the building, we must stay keen on our environment. We cannot get so fixated on the fire that we lose situational awareness around us. Even though there is no fire, smoke is significant hazard. Smoke is just unburned fuel and we must remind ourselves of that. We need to see what the smoke is doing, where it is going and what it looks like. A mentioned another post, I care most about volume and velocity of the smoke. These two key factors can tell a lot about what the fire is doing and its level of involvement. If presented with light hazy smoke, the fire is small and can be contained rather quickly. If the smoke is heavy and moving quickly, I have the potential for a well developed and hot fire. As a note, these may not always hold true as the size of the building and opening which the smoke is coming influences smoke conditions. Large warehouses my present with light lazy smoke, but this could be due to the size of the building and the smokes inability to fill the container.

Neutral Plane

One of the greatest indicators for firefighters and the nozzleman to recognize is the neutral plane. This is the point where there is no outflow and no inflow of air from the fire building. When an opening is created, we have air either going in or out. When air is moving in one direction, this is called uni-directional. When air is moving in and out of an opening, this is called bi-directional. When we think of air movement and ventilation, we can have three situations. We can have an opening which has all the air moving inward, which would be uni-directional inlet. We can also have all the air moving outward, this is a uni-directional outlet. We can then have the third, which is a bi-directional, where the opening is both an inlet and outlet. In this case we have the neutral plane.

The neutral plane can tell a lot in regards to the fire location and development. A neutral plane occur at both a door and windows. When making an opening, the smoke is going rush out, as the lid on the container has been opened. This will present as a uni-direction outlet, occupying the entire opening. After a few seconds, the pressure inside and outside the building will level out depending on the fire conditions and location.

When presented with a neutral plane at the front door, we can begin to make some predictions of the fire location and development. If the neutral plane is high in the doorway or in windows, we can assume we have a small fire located on the same floor or a small fire in the basement with smoke traveling to the first floor. As the neutral plane begins to drop in the doorway and windows, it begins to indicate worsening conditions on the inside. A neutral plane that is only a few feet from the floors can indicate a fire developed fire inside the structure either in the first floor or below. When the neutral plane drops to the floor, nozzlemen need to be highly suspicious of a basement fire. if we think about how smoke travels, its going to rise until it reaches a point of resistance to stop its travel upward. When smoke rises and hits the ceiling, its will be gin to bank down. This is when we start to see stratification and the neutral plane begin to develop. Fires located on the smoke plane as the opening will need to maintain a inlet to provide oxygen for the fire to continue to grow and burn. If that inlet of oxygen is stopped or the building can no longer provide enough oxygen, the flaming burn of the fire may dissipate. The fire can then begin to decay or, if the room is hot enough, the fire can continue with flaming burning. This creates a dangerous situation as the introduction of oxygen will create a rapid involvement of the heated smoke, creating a backdraft or flashover.

Stratification

When entering an environment with the building up of smoke inside the compartment, we call this stratification. Hot smoke will be collecting high in the environment as heat rises and cooler smoke will settle towards the bottom. Depending on the development of the fire, the smoke at the ceiling level can be upwards of 1000F or greater, while smoke at the 1-3 foot level from the floor can read 200-300F. This is why it is important to develop good nozzle mechanics and advancement techniques to remain low in the superheated environment. Remember, smoke is unburned fuel. Having a lot of hot gaseous smoke overhead can be a potential for significant fire development and rollover/ flashover. A good nozzle should never want to disrupt the stratification within the compartment until they are ready for fire extinguishment or to cool the superheated gases overhead.

Reflectivity

When fire starts and begins to burn, the fire will transmit heat in several different methods. As the fire burns, heat will be transmitted via convection, conduction, and radiation. This begins to heat up other materials inside of the compartment. As items in the compartment heats up, they too begin to produce heat. When this happens, the walls begins to absorb and reflect heat back into the compartment, perpetuating the continued heating of the compartment. As this heating continues, materials in the compartment begin to reach their smoking point and eventually the ignition point. We can see this with many of the NIST videos where the carpet begins to off-gas and eventually ignites without having been set on fire by flame. As the nozzleman, this is important as to nozzle mechanics and the operations of the nozzle and water stream. We need to understand where the heat is coming from and also the physics which is adding to the increasing fire and heat development. By understanding this, the nozzle can direct their fire stream to the entire compartment, coating all six sides for fire extinguishment.

Water Mapping

Water mapping and fire stream movement is critical for the success of any nozzleman. The nozzle cannot be effective if water is not getting to the seat of the fire. If the origin of the fire is not extinguished, the nozzle will experience rebound, where the fire will soon reappear because the fire was not extinguished. Proper water mapping is critical for the success of the nozzle. Ray McCormack has some great videos of water mapping, I would encourage you to go watch them. Water mapping allows the nozzle to apply water to the compartment to cover and coat the room surfaces to reduce the heat and potential fire in the room. When a fire stream is directed at the ceiling, the water does not simply hit the ceiling and drop to the ground but rather will spray out and even run the walls and ceiling. This is because of 2 things, first is the velocity of fire stream from the nozzle. The water will hit the ceiling disperse because of the high velocity the fire stream is producing. Secondly, the surface tension of the water to the ceiling will make the water “stick” to the ceiling surface. This can be shown when in a hallway and the water is directed at the ceiling, water will be running down the side walls and further down the ceiling.

Why is this important? As we just mentioned above, fire will heat the compartment and the surfaces in that compartment. As the material heats up, those material will also begin to heat other objects in the compartment. If we are able to stop that reflective heat back into the environment and begin to take some of the heat out of the compartment surfaces we are slowing the reflective heat and also slowing the progression of radiant heat because the water will run the ceiling and the walls, which the water will absorb the heat. In addition, with the sprinkler like effect of the fire stream, the water has the ability to have a path to the seat of the fire if the fire is located behind objects or hidden from view of the nozzle. It is also a good idea to sweep the floor with the nozzle prior to move because of the heating of the carpet. If we can direct the nozzle towards the carpet, we can cool the carpet material and displace any debris in the way prior to moving across the area. This will make your movement more effective and without the hazard of sticky carpet or running into debris.

The old days of only flowing water at fire is gone as our environment is different from several decades ago. We have all seen the NIST and UL videos showing the difference between legacy v. modern building. Our fires are burning faster with an increase in smoke production (incomplete burning) because of the synthetics we are using. Smoke is fuel and will ignite when we add heat and oxygen. If we are timid to cool this fuel down, we are at risk for getting caught in that situation. A good nozzle learns what hot is and when too and not to open the line to cool the environment. Never be afraid to open the line high in a solid/straight pattern high to cool the environment. As many have termed black fire, smoke is just as dangerous or more than the fire is.