California Fire and Life

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Book: California Fire and Life Read Online Free PDF
Author: Don Winslow
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 forpractical 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 which 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
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