A Practical Understanding of Fire Behavior And a thought outside the box.

By John Mark Piper

The Conceptual Evolution Jones and Bartlett Publishers begin their introduction to “The Fundamentals of Fire Fighter Skills” by suggesting that extinguishing fire is both a science and an art. This fact is clearly evident when looking at the conceptual evolution of firefighting. In the beginning, the first uncontrolled fire incidents involving early man were most likely a “save your own” response of “retreat to beat the heat!” But as the knowledge and understanding of fire science increased, so did the creative elements of preventing it and extinguishing it. Thus, a more proactive and aggressive approach to the containment, control and extinguishment of fire evolved - the art and science of fire fighting. At first glance of today’s firefighter responsibilities and daily duties might lead one to wonder why this vocation is referred to as “Fire Fighting”. The actual time a “firefighter” spends physically extinguishing fire is minuscule compared to the time he/she spends on other tasks such as maintaining tools, answering emergency medical calls, responding to vehicle accidents and miscellaneous calls for assistance or 911 calls reporting the smell of something burning that turns out to be baby’s pacifier melted over the heating element of the dish washer. A more in-depth look however, reveals that Firefighters actually wage the fire battle 24 hours per day, 7 days per week, 365 days per year. And, we do so, on every conceivable front. From educating the public and enforcing strict building codes to relentless training and learning new data, fire fighters are most successful if out-of-control fire is prevented by never reaching an ignition point. Benjamin Franklyn put it best when he coined the phrase, “an ounce of prevention is worth a pound of cure”. Though not as exciting as an interior fire attack, firefighters wage their battle on as many layers as possible with all means possible on a continuous basis. Why? Because out of control fire usually leads to disaster and devastation. The first Phase: The first phase toward training for the battle begins with a basic understanding of fire science which focuses on understanding the principals of the Fire Tetrahedron. In the scientific world, fire requires four components which together make up the fire tetrahedron:

1. Fuel 2. Heat 3. Oxygen 4. Chemical Chain Reaction

Before the Fire Tetrahedron, the Fire Triangle outlined the three components necessary to create fire: fuel, heat and Oxygen. As knowledge of fire grew, the Fire Triangle expanded

into the Fire Tetrahedron which added Chemical Chain Reaction. However, as firefighters, it might be beneficial for us to add our own ingredient to the recipe: TIME. Yes, to the firefighter, "time" is very important and therefore should be considered in all elements of fire perception.

THE FIREFIGHTER’S PENTAHEDRON

1. Fuel 2. Heat 3. Oxygen or Oxidizer 4. Chemical Chain Reaction 5. TIME:

• Rate of Oxidation • Rate of heat dissipation

If you examine each of the four elements of the tetrahedron and then consider “time”, you’ll realize that time is naturally included in all firefighter activity but not included in the Fire Tetrahedron. This is probably because scientists don't fight fires. Learning to slow down the chemical chain reaction or speed up the dissipation of heat may soon become even more valuable factors to consider as we learn new ways and create new materials. In addition to being a scientific component of fire science, the consideration of "time" is also present in our "quick to respond" and "ready to react" training that is universally accepted as an extremely important feature in safe firefighter activities. Why? Because if we get there before the fire has reached flash over or fully developed, we can save lives and property more safely.

• Consider the following definition: Combustion (or fire), is a process involving rapid oxidation at elevated temperatures accompanied by the evolution of heated gaseous products of combustion, and the emission of visible and invisible radiation. Oxidation occurs all around us in the form of rust on metal surfaces, and in our bodies by metabolizing the food we eat. However, the key word that sets "fire" apart from other forms of oxidation is the word “rapid”.

Isn't "Time" everywhere in this definition? One of the most basic factors influencing "time" as it relates to fire is the “surface to mass ratio” or STMR. Experience dictates that paper burns faster than wood and smaller particles burn faster than large dense ones. We know this through common experiences but we may not know the "scientific" reason. Most of us have seen steel wool ignite with relatively low heat and grow into a burning steel fire in seconds. If you can light steel wool with a match or simple 9 volt battery, why can’t you light a nail? Or a cast-iron pot made of the same material?

This is simply a question of surface area versus mass. Why? Because the burning process, which is rapid oxidation of the metal, has to bring nearby iron to its ignition temperature fast enough to sustain a chain reaction. Thick pieces of iron conduct heat away far too quickly, therefore slowing the oxidation process and lowing the heat below the metal’s ignition temperature. This same principal holds true with heavy lumber vs. saw dust or paper. A dust fire explosion is simply millions of tine fires occurring very rapidly. Slow the process down and it is a bunch of simple small fires. Slow it even further and you have nothing more than warm dust or browning, aging paper. But in the case of the burning steel wool, you have very thin strands, of metal. There’s nowhere for the heat to go fast enough and a burning patch can race along the length of the wire, converting a whole steel-wool pad into iron oxide in less than a minute. Rapid oxidation. One generally accepted definition of combustion, is a process involving rapid oxidation at elevated temperatures accompanied by the evolution of heated gaseous products of combustion, and the emission of visible and invisible radiation. Oxidation occurs all around us in the form of rust on metal surfaces, and in our bodies by metabolizing the food we eat. However, the key word that sets combustion apart from other forms of oxidation is the word “rapid”. The faster a material oxidizes the hotter it gets. Therefore the future may introduce ways to slow the oxidation process. It may become a bigger part of the process of preventing, controlling and suppressing fire than that of cooling fire with water. Because heat travels by diffusion (from high heat to low heat) we can use water on flames to extinguish it. By doing so, we are actually dissipating the heat rapidly through steam particles. Heat from the fire transfers rapidly to the water, turning it to steam thus extracting heat from the burning mass. With water, we are able to use natural physics to pull enough heat from the fire to result in cooling it below it’s ignition temperature. Perhaps the future may bring other methods of lowering the temperature of a fire that would do so without destroying the contents of a home with water. We may learn new ways of slowing the oxidation process through other means that eliminates the destructive flame and reduces the need to cool it with destructive water. Imagine a synthetically manufactured ultra high molecular metal that would suck the heat and dissipate it from a burning structure. Or a synthetically manufactured gas that could be injected into a compartment fire that could slow the oxidation process to the point of "decombustion". Currently, we use several means to extinguish fire. Removing the fuel: This can be done by allowing the fire to burn all the available fuel and is sometimes done in a wilderness fire that is burning toward a natural boundary such as a road or large body of water.

Saponification is a method of extinguishing Class K fires. It is a wet chemical agent that turns cooking fat into foam or detergent (eliminating the fuel) and then creates a thick blanket of foam that smothers the fire. You must never move or agitate the foam after applied until the agent had cooled or the flames could reignite. Remove or displace oxygen: This method is most common in electrical fires with the use of carbon dioxide extinguishers or simply putting a lid over a pan of burning grease. Dry powder extinguishment is another way of smothering a fire and is used primarily on metal fire. It melts and forms a solid crust around the burning metal and suffocates it. Lowering the Temperature: Water and ventilating is the most common form of extinguishment that lowers the temperature below the ignition point of a fuel. Foams are also used to increase the Interrupting the Chain Reaction: Dry chemical fire extinguishers work in two ways. They interrupt the chemical chain reaction and also very effectively cool the temperature. Did I miss anything…. TIME: There are many variables to consider when adding the element of "TIME" to the Firefighter's Pentahedron. First off, the firefighter must always be prepared for the challenge at hand. This means training, studying, having his/her gear ready, knowing the elements and general phases of fire and the types of fuel it consumes and of course, the best way to extinguish it safely. By getting to a structure fire quickly, the firefighter can fight a smaller fire and put it out before it reaches its fully developed phase. The earlier the fire can be confronted, the less dangerous it is to rescue victims and save property. If the firefighter arrives during the growth phase of a fire, he/she can estimate how much time there is to safely search for victims, fight fire interiorly to save property or get out because it's too late. By understanding the different phases and rate of combustion of materials, firefighters can cool with water in to delay or eliminate flashover and the fully developed phase. Understanding the four phases of fire and recognizing evidence of those stages, an experienced firefighter can estimate how much time, water, heat and chance for saving victims in a structure fire have. The four phases of fire are: Ignition, Growth, Fully Developed and Decay. At the end of the growth and beginning of the fully developed stages there is a critical and deadly period called the "Flashover". Flashover occurs when the contents of a room have put off enough flammable gasses and the room has heated up to the ignition temperature of those fuels. At this point,

everything ignites at once. The temperature of the room is not survivable even for firefighters in full gear. Typically, flashover occurs when temperatures are between 900 and 1100 degrees but it must be noted that all situations are different. It is possible for flashover to occur at much lower temperatures - especially with the amount of today's plastics used in the modern home. Once the hot gasses have been ignited, the room temperature rise to its maximum and far above survivable. Flashover can usually be predicted by observing very high heat and door knob level smoke. Anytime you are forced to be down low to avoid heat and smoke, flashover should be considered possible. It can also be predicted by observing a factor known as "rollover". Rollover is the ignition of hot gasses toward the ceiling. This is a clear indicator that flashover is almost imminent and you should exit the area immediately or cool down the fire at the base without upsetting the thermal layer. Understanding the phases and how to read a fire is a key factor in using time as one of your methods of controlling and extinguishing fire. There is yet another way to use time. That is by "time travel". Sounds ridiculous but we've all done it. We've done it by stopping fires before they happen. We stop them with building inspections, building codes and training exercises. In a way, we foresee the future when we inspect a building and find code violations. We see a fire waiting to happen and we use time to prevent it. Perhaps the most important element of fire behavior pertinent to firefighting is "TIME".