"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...
To access the remainder of this piece of premium content, you must be registered with Firehouse. Already have an account? Login
Register in seconds by connecting with your preferred Social Network.
Complete the registration form.
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."