He draws an equation: 2H2 + 02 = 2H20 + heat.
"A basic oxidation reaction," Fuller says. "When you combine hydrogen and oxygen, you get two molecules of water, and heat. Heat is measured in BTUs – British thermal units. One BTU is the amount of heat that it takes to raise the temperature of one pound of water by 1 degree Fahrenheit. So the more heat you have, the greater the temperature you're going to get. Put simply, the more BTUs, the hotter the fire."
Fuller continues, "Look, gentlemen, to sustain a fire you need to have three things working together: oxygen, fuel, and heat. If you have no oxygen, oxidation obviously can't take place – no fire. If you have no fuel, there is nothing to oxidize – no fire. If the fuel doesn't contain enough mass of heat, then the fire dies out."
He strikes a match.
"Observe," he says. "We have oxygen, we have fuel, we have heat."
The match burns for a few seconds, then goes out.
"What happened?" Fuller asks. "We had plenty of oxygen, but not a lot of fuel and not a lot of heat."
He strikes another match.
"I will now attempt to burn down the classroom."
He holds the match to the metal desk.
The flame makes a slight scorch on the metal, then burns out.
"What happened?" Fuller asks. "We have oxygen, we have heat, it's a big desk – plenty of fuel – where is our sustained fire?"
"Most metals don't burn easily," Jack says.
"Most metals don't burn easily," Fuller repeats. "Which is the lay person's way of talking about flammability. Some substances burn more easily than others. Witness…"
He rips a page from a legal pad, strikes another match and holds the match to the paper.
"It ignites immediately," he says. He drops the burning paper into a metal trash can and puts a lid on it.
"Thereby depriving it of oxygen," he notes. "Look, paper has a lower flash point than the metal of the desk. Flash point is the temperature at which a fuel ignites. A simple match will ignite paper but doesn't have nearly the BTUs to create enough temperature to reach the flash point of the metal in this desk. It simply can't sustain the oxidation reaction needed to set the desk on fire and keep it on fire.
"Now, were we to add more fuel to the fire, and developed enough BTUs to raise the temperature, there is a point at which we could indeed melt the desk.
"It's a chain reaction, gentlemen – a chemical chain reaction. Difficult to break down into a description because it is a never-ending cycle of chain reactions, which are really quite fascinating in detail. But for practical purposes it's all about fuel. The amount of fuel, the flash points of that fuel, and the conductivity of that fuel.
"So, the amount of fuel – in proper terminology the fuel load, or the fuel mass. Why is it important to establish a fuel load for a structure that has suffered a fire? If, for instance, you find a melted metal desk in a burned structure where the pre-fire fuel load could not have produced sufficient BTUs to melt that metal, you have an anomaly that you need to resolve.
"You'll want to be taking notes on this because you'll need this terminology to pass the bloody test."
Jack takes notes.
He doesn't want to pass the bloody test.
He wants to ace it.
12
So he has to learn certain definitions.
Like fuel load.
Fuel load is the total potential BTUs per square foot of the structure in question. You calculate it by determining the total pounds of matter in the structure and multiplying the total weight by the total BTUs of the various materials in the structure – 8,000 BTUs per pound of wood, 16,000 BTUs per pound of plastic, et cetera, et cetera, et cetera.
Certain materials give off more heat than others. Wood, about 8,000 BTUs. Coal, about 12,000. Flammable liquids, somewhere between 16,000 to 21,000 BTUs.
Another term: heat release rate. This is the speed at which a fire grows, depending on the fuel upon which it is feeding. Some materials burn fast and hot, others are slow. HRR is measured in BTUs per second, otherwise known as kilowatts. A plastic trash bag, filled with the usual garbage, is going to have somewhere between 140 and 350 kilowatts. A television set about 250. A two-square-foot pool of kerosene, 400. Kerosene gives you a hot, fast fire.
Jack learns that fuel load isn't just fuel load, but is divided into two parts: dead load and live load. Dead load is the total weight of the materials in the structure plus the total weight of any permanent built-ins. Live load is the total weight of the materials of items added to the structure – furniture, appliances, artwork, toys, people, and pets. The irony of the phrase "live load" is that if they are found in the fire, they are most likely dead.
Conductivity – that is to say, the amount of heat a substance on fire transfers. Some materials retain most of their heat; some transfer it to other materials in the structure. Jack learns for a fire to spread it has to encounter material that is conductive, that transfers and adds to the BTUs. Paper, for example, is highly conductive. Water isn't – it absorbs more heat than it transfers. Air is highly conductive, being made up of about 21 percent oxygen. So most structural fires spread by convection, meaning the transfer of heat by a circulating medium, usually air. Fire burns up, because that's where the air is.
"It's all about fuel," Fuller lectures. "You are what you eat, and fire is no different. You can determine its severity, its origin, its direction and rate of spread, and how long it burned, by the fuel in the structure."
Jack aces the chemistry test.
Fuller passes out the results, which apparently launch him to new rhetorical heights.
"So," he asks, "what happens in a fire?
"It has all the dramatic structure of your classic three-act play, gentlemen. It has the rhythm of a love affair.
"Oxidation occurs. Act One: The Smoldering Phase. The seduction, if you will, the chemical reaction between oxygen and solid molecules in which the oxygen tries to induce heat in the solid matter. The seduction might take a fraction of a second – in the case of a hot number like gasoline or kerosene or some other liquid accelerant, the roundheels of the flammable street corner, I might tell you. Switching metaphors, liquid accelerants are the aphrodisiacs of the fire seduction. They are the storied Spanish fly, the fine wine, the manly cologne, the American Express Platinum Card left casually by the side of the couch. They can get the passion ignited in a big hurry.
"Or the smoldering phase might last hours or even days. The material, the fuel, wants to be wined and dined, courted, taken to dinner and the movies. Come to Sunday dinner and meet my parents. But fire is a patient seducer, comrades. If it can just hang in there long enough to generate a little heat, if the affair is given a little air to breathe, it lingers. A kiss on the neck, a hand under the blouse, the steamy heat of the backseat at a drive-in movie, fellows. Working, working, trying to melt the fuel to liquid and then into burning gas. A questing hand under the skirt, trying to generate enough heat to reach the ignition point, smoldering, smoldering and then…
"Ignition. Act Two: The Free-Burning Phase. The flash point is reached. Open flames, my boys. Passion. Heated gas is lighter than air so it rises – witness your Goodyear blimp. It starts eating up the air and then it hits the ceiling. If the fire is hot enough to ignite the ceiling materials you have more ignition. The fire might even blast a hole in the roof to get to that easy, tasty air. The heated gases themselves become a source of radiation, now spreading the heat downward to ignite material below. This is why the ceiling might burn, by the way, before the furniture does.