"Blinded by science" is an old expression that means "to deliberately confuse someone with highly complex knowledge". For too many firefighters, the same can be said when it comes to firefighting and the phenomenon of fire. For too many firefighters, the act of "putting the wet stuff on the red stuff" is all that is needed to know and the rest is just "blah-blah."
This article is about the science of fire and why we as firefighters must be able to recognize how it develops, most importantly within a structure, and then react to the signs of an impending hostile fire event. This article is also about how lessons from within a flashover simulator, affectionately called "The Box," can greatly assist in knowledge of fire and fire development recognition skills.
From a perspective of fire service culture, current fire education focus, and important fire incident data, ominous trends concerning firefighter deaths and injuries have developed:
- Fire service culture — It cannot be denied that our business has focused on speed toward extinguishing (or killing) a reported fire to the extent it is killing us! Aside from the numerous firefighter deaths involving vehicle accidents, we are in such a "fast attack" mode that we are missing the important information that a structure fire provides us upon our arrival. A slower, more deliberate response would allow a 360-degree look at the structure, a better analysis of the smoke and possibly a better idea of the location of the seat of the fire. We are in such a hurry while rushing into a structure that we are missing the "signs of life" that would allow us to keep our safety intact. One of the signs of life is what the fire is telling us. This article will address that important clue.
- Current fire education focus — In most firefighter basic education curriculums, there is a minimal amount of time dedicated to fire behavior. While knowledge of fire behavior is important, and is a cited competency in National Fire Protection Association (NFPA) 1001, Standard for Fire Fighter Professional Qualifications, 2008 edition, only approximately three hours is devoted to it in many firefighter educational programs. As far back as the 6th century B.C., the Chinese General Sun Tzu wrote that in warfare it is important to "know the enemy." In the 20th century, the great Francis Brannigan wrote that in firefighting it is important to know "the building is the enemy". But, with apologies to Brannigan, shouldn't the modern firefighter know and understand fire as the true enemy?
- Fire incident data — The NFPA reports that while structure fires have steadily declined since 1977, firefighter death and injury rates have stayed steady. In fact, 2007 data show that the rates of deaths and injuries have significantly increased. NFPA data also show that the firefighter injuries and deaths inside structure fires have been increasing. Possible reasons for this increase include the trend toward lightweight construction, the effects of fire on lightweight building components, and also the changes in the fire load and flame propagation curves over the years. In other words, times have changed and the modern firefighter must recognize the changes.
The Quest to Know Fire
Fire, first and foremost, is a chemical event. We know that it is rapid oxidation and evolves heat, light, smoke and fire gases. Being a product of chemistry, fire can also be easily reproduced and therefore observed and documented. Most of us have enjoyed campfires over the years and those experiences have led to a certain comfort level with fire.
What changes the dynamics of fire is when it is placed inside a structure. Now, the chemical phenomenon of fire affects the compartment and contents because of the physics of the event. Confined heat communicates into objects in the space and causes them to be heated and consequently off-gas. This process of pyrolysis breaks down solid compounds within the affected fuels to form more volatile gases, which in turn burn more readily because of the presence of fire.
The whole process of the fire within the room escalates as more and more fuel is broken down and combusts. It has been stated that fire doubles in intensity every 30 seconds, but it really depends on the fuel that is pyrolyzed. Flame propagation curves can be steep in the case of hydrocarbon-based fuels or show a gradual growth in the case of solid cellulose material. The quality and characteristics of a fire's smoke also depends on the fuel that is burning. Hydrocarbon-based fuels, such as the synthetic fabrics and foam products, produce toxic, thick, black smoke that is also flammable in nature. Wood products also produce somewhat toxic smoke and also more of a brown or even a gray smoke.
It is also important to note the difference between synthetic materials and wood materials in terms of Btu's (British thermal units). Hydrocarbon-based or synthetic materials generate between 20,000 and 24,000 Btu's per pound when they combust, compared to approximately 8,000 Btu's per pound for wood products. This information is compounded when heat release rates (HRRs) are also factored into the equation. That is, HRRs are the energy released per unit of time as a fuel burns. As an example, a polyurethane sofa has a 10 times greater HRR than a cotton mattress (Essentials of Fire Fighting and Fire Department Operations, fifth edition, Copyright 2008, International Fire Service Training Association/Fire Protection Publications).
In today's modern environment, with most room-and-contents fires having a substantial synthetic fuel load, the dynamics of an enclosed fire have changed significantly. It has been proven that the average time to flashover in a scientifically controlled setting has been continually decreased over the past 30 years because of the synthetic fuel load. Furthermore, recent National Institute of Standards and Technology (NIST) studies have indicated that in certain conditions, flashover can occur as soon as three minutes after ignition in an enclosed space.
The chemistry of the fire involves what is burning and to what degree the fire is allowed to breathe. In order for a well-balanced, clean-burning fire or reaction to occur, the fuel must be oxidized by oxygen in a proper ratio. Clean-burning (or fuel-controlled) fires produce little waste and mostly water vapor and carbon dioxide. Today's materials give off far more waste when they burn because a clean-burning fire with synthetic materials is nearly impossible in chemistry terms and coupled with lack of oxygen (or a ventilation-controlled fire), synthetics burn dirty with numerous toxic and flammable materials generated in the smoke. Materials such as carbon monoxide, hydrogen cyanide, hydrogen sulfide, acrolein, formaldehyde and many other compounds, depending on the fuel, are emitted from today's modern fire.
The physics of the fire involves the communication of the heat produced and where the smoke and flame is allowed to travel. The heat of the fire communicates to surrounding materials by direct flame contact, by convection of air currents, by conduction of hot materials touching cooler materials and by radiation of infrared waves. Heat is also communicated through radiation from smoke. Fire spread is often through smoke and the ignition of smoke in a room-and-contents fire. Because smoke rises, it travels through a structure easily. Also, because a fire is a chemical event, it produces a positive pressure as a result of its heat output and energy produced. This causes a contained fire to seek a lower pressure area; in other words, fire will travel to an area of low pressure within or even toward the outside of the structure.
In combination, the chemistry and physics of a fire, especially a modern fire in a structure, produce a dynamic and energetic event. Fires in the 21st century get hotter faster! It behooves firefighters to know of these dynamics in order to recognize the situation and then react accordingly. In essence, it is all about safety! The modern-day firefighter simply has to know these principles intrinsically in order to safely fight fires and return home after each alarm.
Lessons from "The Box"
The flashover simulator is the best method of observing the dynamics of fire because it is a fairly safe and controlled setting. Much like a chemistry laboratory is a place where the theory of chemistry can be observed and practiced, a flashover simulator is really a "fire" laboratory. It is a setting where fire can be observed and the lessons are abundant. In reality, though, the box is really a fire-behavior simulator because a real flashover does not really happen. What happens is that smoke ignites, small fingers of ignited gases that can be called "rollover" at first, and then gradual ignition of the whole smoke within the box for what can be called a "flashover."
Students are briefed before they enter "The Box" on what to expect. They are allowed entry only with full personal protective equipment (PPE) and a complete check by an outside safety person. Additionally, instructors brief all students on what behavior is expected and the hoseline demonstrations that will be shown. All students are made aware that the flashover simulator is merely a steel box laboratory with an enclosed fire and real structure fires may not be the same experience.
• Lesson 1 — Commonly, the first reaction to the flashover simulator experience is "Wow!" First-time students are simply amazed at what they see and feel and hear. The "wow" experience lasts for the first three experiences or so, then, around the fourth or fifth experience the lessons start to soak in. Students tend to be amazed about being around the smoke ignitions, but begin to see the patterns of how fire develops and grows in an enclosed space. They begin to observe the life cycle of fire and become more comfortable with the dynamics of fire.
The flashover experience helps to develop a strong respect for fire behavior. Indeed, a poorly developed sense of fear or understanding can and has killed firefighters. This lesson from "The Box" concentrates on the recognition of flashover conditions and how to react.
Much of the student's experience within "The Box" depends on the knowledge and skill of the instructor. Becoming an effective instructor is much more than merely experiencing several flashovers themselves. Effective instructors must be able to verbalize what students are seeing, but they also must be able to relate the experience to modern firefighting. Instructors also must have a firm understanding of the ventilation and nozzle techniques that can control the fire in the simulator. Critical is the ability of an instructor to tell students why the fire behaves as it does when control techniques are performed.
• Lesson 2 — After several visits to "The Box," a person tends to experience far less apprehension because they know what to expect. While the experience within the box does not necessarily represent real-life fires it comes as close to reality as is safely possible with training fires that are compliant with NFPA 1403, Standard on Live Fire Training Evolutions. Knowing where the simulator experience leads, students can start to pay more attention to what is going on and how to control the setting. Long after the "wow" factor has been digested, students tend to pick up the subtle nuances of the flashover experience and can better account for their awareness of the situation.
• Lesson 3 — A final noteworthy lesson from "The Box" is the importance of ventilation on the life or death of a fire. A dying fire is one that lacks breath, suffocates and eventually succumbs because of a lack of oxygen. More smoke is produced because the burning process is incomplete and the fire eventually becomes concealed or out of view. This process of breathing and dying can be seen in the simulator when the back door and roof vent are manipulated effectively. Essentially, when the roof vent is opened both heat and smoke are allowed to vent outside of the simulator. If the displaced air is replaced by fresh air from an opened back door, a natural air current develops. This condition provides more visibility and the fire grows. When both the roof vent and the back door are shut, the cycle begins again and flashover conditions can be developed and observed. As students observe the fire dynamics, they should have a better idea of how fire grows and reacts in a closed environment. They should also have a better idea how ventilation can affect the fire's dynamics. And, they should better understand how to recognize the signs of a flashover and how to react to those signs.
While the flashover simulator experience is called "Phase I," students sit on the floor as smoke cloud ignitions pass over their heads. While the student is passive in the simulator during the first phase, Phase II involves an active student who reacts properly to impending hostile fire events with a hoseline and effective nozzle techniques. Phase II is where fire theory meets fire tactics. Finally, Phase III has students observe from a safe distance the phenomenon of a "backdraft." In totality, all three phases have the ability to show the fire service the changes in our structural firefighting environment. It is up to us to respond to those changes.
It is all about science. If firefighters understand the chemistry and physics of fire, especially in a closed setting, they should be able to recognize impending hostile fire events and then react accordingly. The recognition and reaction skills, along with the knowledge of science, should enable them to be safer. That is the bottom line. Armed with knowledge of the dynamics of fire, firefighters should never again be "blinded by science."
DAVID F. PETERSON is a lieutenant in the Madison, WI, Fire Department, where he is the lead fire and hazmat training officer. He is in his 30th year as an emergency responder. Peterson is enrolled in the National Fire Academy's Executive Fire Officer program and is a master instructor for the International Association of Fire Fighters (IAFF). He is the managing member of the Wisconsin FLAME Group LLC, a leadership and management company, and operates www.hazmatpetie.com, a hazardous materials response training website. Please send your comments and questions to him at www.hazmatpetie.com or firstname.lastname@example.org.