Fire Dynamics

By: Mark van der Feyst

Rapid fire developments (RFD) are when we have a sudden and immediate change in the fire environment. At one moment we have thick, dark, black smoke with intense heat and the next second, we have a ball of fire from floor to ceiling – this is an RFD.

Every fire department will face RFD’s no matter what type of structure they are dealing with – if it has four walls and a roof, then there is the space and environment for an RFD. The different types of RFD’s are going to be flashover, back draft, and smoke explosions. The three are different in how they develop and react but are the same with the outcomes – deadly outcomes. RFD’s produce RIP’s (Rest In Peace) for the fire service.

Of the three RFD’s, flashover is going to be the one that will occur the majority of time at any and every structure fire. So, what is a flashover? A flashover is the simultaneous ignition of unburned fire gases within a room. It occurs when hot gases rise to the ceiling and spread out across the walls. These hot gases are what we call black smoke – unburned particles of combustion. As it spreads out across the ceiling and the walls, it starts to heat up the items found within the room such as the paint on the walls, the furnishings, clothing, mattress, flooring material, etc. – until they all reach their ignition temperature. Once they are all at their ignition temperature, an RFD occurs.

Before a flashover occurs, there are warning signs that are presented or given off by the fire to indicate that flashover is impending. These warning signs are presented to us both visibly and tactically – our eyes can see and our bodies can feel them.

·       Heat buildup – based upon the temperature range of flashover, there will be a period of time when excessive heat buildup will occur. This heat buildup will descend down towards the lower levels of the room pushing the firefighter down to the floor. This will be the result of radiant heat being produced by the unburnt particles of combustion spreading out from ceiling to walls and then down to the floor area. When this quick increase in heat occurs, and it is an intensive heat; flashover is impending. 

·       Roll over – this is a visible indicator as it reveals itself in the smoke. A roll over or flame over is when small gaps open up in the smoke layer allowing air to mix with the unburned particles of combustion and ignite. Small flames can be seen in the midst of the smoke for momentary periods of time and then disappear. When this occurs, this is a warning sign that flashover is coming.  

·       Thick dark smoke – this is also a visible indicator as it will present itself outside the building as well as inside the building. On the inside, you will not see anything except total blackness: but on the outside, you will notice this. Whenever you have thick dark, acrid black smoke pushing out from a structure under high pressure and with high velocity, flashover is impending. This is an outside warning of what is waiting for us on the inside.

What has been described above are the common signs that we will see and feel at every fire – it is important for the firefighter to learn and understand the basic concept of what a flashover is before being able to learn the actions that can be used to aggressively cool the fire or escape the situation if warranted.

About the Author:

Mark van der Feyst is a 25 year veteran of the fire service and is currently the Senior Battalion Chief at the Six Nations Fire & Emergency Services in Canada and a part time firefighter with the Fort Gratiot Fire Department in Michigan. He has worked in both the USA and Canada for various fire departments and holds a Masters of Science degree in Safety, Security & Emergency Management from Eastern Kentucky University.

The Importance of Firematics

by Nicholas Higgins

It has been said time and time again, "You can never train too much for a job that can kill you." As we are aware, firefighting has many aspects to it. Many of these are common to every fire department, no matter their location, size, or status (career or volunteer). Other aspects are specialized areas that not all departments focus on or specialize in, such as medical, hazardous materials or technical rescue. In any case, having a sound basis in the area of “firematics” is a stepping stone to success for yourself and for your crew. We will briefly touch on key areas every firefighter should have a sound understanding and strong knowledge of. Many of these areas are touched on briefly in probationary/training school and then oftentimes, pushed aside once graduated. However, these areas are the core foundation for everything we do as firefighters and lay the groundwork for everything else we do on the fire ground. The skills of understanding these concepts, terminology and definitions is in fact, simple in theory. The difficulty is understanding the strategies and tactics behind them in order to implement them. All good leaders and firefighters must understand these core areas of which everything else is built from. 

The areas I would like to briefly touch upon are: building construction, fire behavior, reading smoke and size-up.

Building Construction

In the American Fire Service, there are oftentimes six different types of building construction however this may be different in various parts of the world based on the materials used to build structures. As firefighters, it is imperative that we know our enemy and know everything we can about it. Without having at least an understanding of our enemy, it becomes difficult to defeat it. In almost every one of our cases, the enemy is the building structure. In order to be a successful firefighter in any capacity, on any apparatus, in any area, understanding and having a solid foundation of building construction knowledge is vital. Just as a world-class fighter studies their opponent in the months leading up to a fight, us as firefighters MUST study our buildings in our areas, so we too are prepared to fight…and WIN. 

The most vital piece of information I can provide here is simple. It makes a difference in knowing the different types of structures and how to identify the differences, however, what makes it even more important is the ability to identify the types and how they will react under fire conditions while in the moment! This leads us to fire behavior.

Fire Behavior

Fire behavior is the foundation on which all firefighter knowledge is built upon. Moreover it is our understanding of fire behavior from which we can gain an understanding of fire and how to suppress it properly. The lack of fire behavior knowledge creates an even greater risk for serious injury or death. Understanding fire behavior is truly being able to operate as a firefighter. The understanding of fire behavior is the basis for understanding fire suppression and the understanding how to properly perform other tactics such as ventilation, forcible entry on some occasions and overhaul.

As society changes or in many cases evolves, so does fire behavior. The reasoning behind this is simple - the introduction and presence of synthetic materials (also known as plastics). These materials in their solid form are petroleum- based products, therefore producing an increase in the output of thermal energy. This reasoning alone is a cause for a more rapidly spreading fire regardless of the type of structure it is in. More so than not, it is causing our enemy (the building) to have more fuel to hurt us. To understand fire behavior, it is important to understand the phases that come along with it and it’s attributes – ignition, growth, full development (flashover is present) and decay (back draft is likely). To understand these areas takes years of studying and training to become proficient but having the basic concepts down is a great start to proficiency in fire behavior for firefighters of all levels and experience.

With fire comes smoke.

Reading Smoke

An important aspect on the fireground for many reasons is understanding smoke and smoke behavior. Many clues from the smoke alone can help identify the location and status of the fire. Command and company officers, as well as firefighters, need to be able to read and interpret all of the clues while conducting their size-up upon arrival and throughout the incident. 

Here are some clues to take into consideration: potential fuel, density, color, velocity, and volume.

Smoke is fuel. In today's world and the modern-day fire service, the products of combustion are highly toxic, flammable and potentially explosive. The smoke’s chemical composition is different at each fire due to the different fuel sources yet, one thing remains the same; smoke contains high levels of carbon monoxide.

Density identifies the thickness of the smoke, it’s level of energy and if there is a potential for a flashover or for fire spread.

Color tells you how flammable the smoke is and what is burning.

Velocity tells us how fast or slow the smoke is moving and by doing so helps determine the location and its flow path.

Volume on the other hand doesn’t speak to firefighters about smoke or fire but it does give firefighters the amount of fuel that is burning. By knowing how much fuel is burning, provides insight to the size and intensity of the incident.

Understanding smoke provides the fundamentals for reading and identifying changes in fire and smoke conditions in the interior or exterior of a structure, along with identifying and possibly preventing flashover or fire spread.

Size-Up

The size-up is for all intents and purposes, our game plan or battle plan, if you will, against the structure we are working at. The size-up is where firefighters and fire officers gather information in order to make safe, efficient, and effective fireground decisions. Fireground decision making, as we know, is meant to be quick, but with an emphasis on safety and ensuring the tactics are done efficiently and effectively. This is done in three phases; the pre-incident size-up, the on-scene size-up and the after action review. All three of these have their purposes.

Pre-incident size-up allows firefighters to gather as much information as we can about the structure and contents inside and helps guide our on-scene strategies and tactics.

On-scene size-up is where firefighters utilize our pre-incident size-up and put it to work. This size-up is where more information is provided specific to the incident and can now confirm our findings from the pre-incident size-up. Further, this is where company operations are assigned and take place.

After-action-review is the final stage in the pre-planning process. This is the time for firefighters and officers to discuss and share the information obtained and to discuss the success and failures experienced at the incident. It is also a time to ask a few key questions. 

What did we expect to happen?

• What actually occurred?

• What went well and why?

• What can we improve upon and how?

The benefit of asking these questions allows for strengths to be easily identifiable and make it easier to uncover areas of weakness. By uncovering areas of weakness, you can develop ways to improve them!

In closing, I’d like to leave you with this piece of advice. If we think of firematics as an orchestra and each piece getting broken down into sections, we can identify each area as its own unique piece yet, an integral piece to the orchestra as a whole. With practice, each section sounds in harmony and sync with one another, but without practice or even a section missing, the harmony and synchronization doesn’t happen. This is the same for firematics, you cannot have one without the others.

For further information on these topics, you can refer to my book, “The 5-Tool Firefighter” where these concepts are laid out in greater detail along with other areas of interest to guide all firefighters on their journey to success.

About the author
Nicholas J. Higgins is a firefighter and district training officer for Piscataway Fire District #2 in Piscataway, NJ. He is a New Jersey State Level 2 Fire Instructor, a National Fallen Firefighters Foundation state advocate and a member of the Board of Directors for the 5-Alarm Task Force Corp. a 501 (c) (3), non-profit organization. Nick is the founder and contributor of The Firehouse Tribune website.