Fire Behavior

Pushing Fire Revisited

In my opinion the topic of “Pushing fire with water” is the single greatest piece of fire attack research which has been communicated poorly or misunderstood. UL is elaborating greatly and providing much better context/more clearly stated material for us to understand the early studies. If you have heard the phrase “you can’t push fire with water” don’t stop at this result or statement. There is much more to the story.

 

Do not take a snippet of information and tailor your training programs to provide the “latest fire attack research and recommendations”. Firefighters have a habit of taking research results (from multiple disciplines) and applying them to training exercises without context. That being said UL is also to blame for this miscommunication. Firefighters typically do not separate their discussions of water application and air entrainment during training. For many firefighters these are one in the same. Even though different patterns yield different results, some create more air entrainment and others much mess, there is no on/off switch to turn the air off at the nozzle.


Firefighters need to understand context, they need to understand the background and significance of these research projects. Reading the first and last paragraph of a 100 page research paper doesn’t provide you with a good foundation. It gives you results without context. To communicate as an instructor you need context and to translate that information into training and drills you need to understand the background and significance of these processes. Without context your drill becomes a training exercise prepped to fail. Adult learning typically happens in phases. 1. Rite, 2. Understanding, 3. Application, and 4. Correlation. Students participating in a drill need to get to the application phase and instructors need to live in the correlation phase. At the beginning of basic training we learn through Rite or memorization. We don’t quite grasp where or why and we have a hard time applying the skills during the initial phases of training. Once a student understands the skills we can apply those skills which provides a much better outcome. Skipping steps will only lead to confusion in the training process. Aaron Fields and I had a discussion one time and he provided me with a great teaching tool. He said, “If you have a student that says [I don’t see where this fits] you have missed the application phase of learning.” The student doesn’t understand how to apply the skill.


Lastly, just because you read it, watch it, or listen to it doesn’t mean it isn’t flawed. Research projects are very difficult to construct without some flaws. Most applied research projects literally have a section in the paper which explains the problems or flaws that might’ve occurred during the process. Make your drills purposeful, give them context, and your crews will perform at a much higher level. Follow the link below to understand this topic in much more detail. 

 

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Heat Release Rate vs. Temperature

A topic I discuss very often in classes is the difference between Heat Release Rate and Temperature. This is a fundamental concept all firefighters need to understand in order to make sound decisions on the fireground. We all seem to grasp the reference of temperature very quickly because of how much we rely on temperatures in daily life. However, a candle on fire and a room on fire are two completely different things even if they are burning at the same temperature. The video above offers a very good introduction to the basics of heat release rate and temperature. This video is produced by the Firefighter Safety Research Institute (FSRI) and they have many more videos and resources available for you to learn about fire research and science. You can click here to visit the FSRI website or you can click here to visit their YouTube Channel.

Bernoulli's Principle Applied to Firefighting | Box Alarm Training

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Bernoulli's Principle is not the first thing that comes to our minds when discussing firefighting tactics. However, it directly affects many of our operations. In fire behavior courses we learn about how fire will travel from areas of high pressure to areas of lower pressure. This is the basis of understanding how ventilation and flow paths work. Before we discuss Bernoulli's Principle and how it applies to our tactics let's look at a couple of fireground operations that are affected by Bernoulli's Principle.

Traditional Ventilation

You were probably taught that ventilation was the systematic removal of hot gases, smoke, etc.  This definition led to a general misunderstanding of what ventilation actually does inside of a structure. Discussions in classes often communicated that ventilation cools things down and makes our operations easier. The discussion deserves a little more time in order to clarify. Modern fires are generally limited by ventilation and not fuel. This means that when we ventilate things actually heat up, they do not cool down. However, traditional ventilation still offers many advantages, like controlling the flow path or creating lift from low areas. These are often huge topics presented by firefighters because lifting gases can increase victim survivability.  In general when we ventilate a structure we are creating an area of low pressure for the fire to travel to and exit. When we break a window typically the fire will move toward the window you just broke. However, if the window is broken revealing a higher pressure area outside, such as a wind driven fire, you will be opening a new inlet for air to move into the structure. This can cause the fire to travel to another outlet and in many cases creates a very dangerous environment for crews working inside of the structure.

Positive Pressure Ventilation (PPA)

Positive Pressure Ventilation attempts to create a significantly higher pressure area inside the structure than outside of the structure. This will force fire and gases out of the structure as they seek areas of lower pressure. This can also create problems by forcefully pushing gases and fire into void spaces that are difficult to detect. Many departments all over the United States use positive pressure successfully but these departments also understand some of the concerns with using positive pressure. Once a fire leaves a confined area, such as a bedroom, positive pressure can create a chase for the fire attack team. The fire will rapidly seek low pressure and can outrun an interior fire attack crew very quickly.

Nozzle Operations

When we use our nozzle we are not only flowing water, we are flowing air. This air can create areas of higher pressure just like positive pressure fans and cause fire to travel towards areas of lower pressure. A nozzle can very quickly over pressurize a room causing the exhaust to push back on the fire attack team.

Bernoulli's Principle

Bernoulli's Principle states "an increase in the velocity of a stream of fluid results in a decrease in pressure". Water flowing from a nozzle will create an area of low pressure and draw even more air into the area you are directing the stream. This is significant when fighting fires in under ventilated spaces or flowing water into a structure from the exterior.

In the video below we will discuss Bernoulli's Principle and how it relates to fire attack concepts.

https://youtu.be/zk6CsoUqERU