Principles of Fire Behavior

James G. Quintiere

• Editore: CRC Press
• Anno: 2016
• ISBN:
  9781498735704
• Edizione: 2
• Argomento: Derecho
• Categoria: Ciencias forenses

This text covers the four forms of fire: diffusion flames, smoldering, spontaneous combustion, and premixed flames. Using a quantitative approach, the text introduces the scientific principles of fire behavior, with coverage of heat transfer, ignition, flame spread, fire plumes, and heat flux as a damage variable. Cases, examples, problems, selected color illustrations and review of mathematics help students in fire safety and investigation understand fire from a scientific point of view.

1

Evolution of Fire Science

Learning Objectives

Upon completion of this chapter, you should be able to

• Describe what is fire

• Identify fire in history

• Describe the U.S. fire safety infrastructure and statistics

• Describe the history of fire research

• Describe the role of science to predict fire

1.1 Introduction

Before there was life there was fire. It has left its imprint on history in many ways. We need to understand the role fire has played in history, including prehistoric events as well. After all, fire has been around from the beginning. Creation may have begun with nuclear reactions, but fire was an essential consequence to the development of life. Even the ancients revered fire, as they imagined Prometheus stole it from Zeus and gave it to us mortals. Perhaps Zeus knew we would use it and abuse it, and so he punished Prometheus severely.

Today, fire in the form of controlled combustion is an essential ingredient of our technology. We could not easily survive without the burning of coal, gas, and oil. For these reasons, the study of combustion for useful power is driven by market forces that drive developed world economies. In contrast, the study of uncontrolled fire is motivated by clear risks to society and by societies having the means and desire to invest in such study. Consequently, we know a lot less about fire than controlled combustion. Fire events are chronicled and recorded in proportion to the damage rendered to people and property. But the study of fire to understand and to improve humankind is limited. It is a complex area involving many disciplines, and it is a relatively primitive field compared to other technological areas. Yet, over the past 50 years, steady progress has been made in its subjects. This book is a by-product of those studies.

It is important to understand the history of fire science research to appreciate its contribution to the science. Equally important, it is essential to appreciate the forces that drive such studies. The impact on people and property due to fire from recent history and from past history is a driver for learning. This chapter will try to present some of this information. Of significance today is an increasing recognition in formal academic study that fire, as a subject discipline, is important. Today, fire is being studied at numerous universities around the world. The United States has two postgraduate university programs, while there are several in the United Kingdom, two in Sweden, several in Japan, and more than a dozen in China. In fact, the Chinese People’s Armed Police Academy (university) outside of Beijing has about 7000 students with most studying fire regulations, firefighting, or fire investigation. Some of their faculty translated my advanced book on fire into Chinese:

詹姆士 G.昆棣瑞著 = Fundamentals of fire phenomena/James G. Quintiere; 杜建科, 王平,.; James G. Quintiere; Jianke Du; Ping Wang; Yaping Gao Publisher: 化学工, Beijing: Hua xue gong ye chu ban she, 2010.

Indeed, the first edition of the current book has been translated into Korean and Japanese. Its interest has been primarily from the nonengineering communities related to firefighter and fire investigator education. Its purpose was to attempt to translate the research developments into digestible knowledge for these fields. It is couched in terms of descriptions of dissected aspects of fire growth. In addition, it includes formulas that allow predictive estimates for these phenomena. In short, it is designed to bring tools from research to the practitioner.

As a firefighter you need to react to fire with reason and knowledge, not just training and instinct. As a fire investigator you need to support your opinion with knowledge and analyses to within a scientific degree of certainty.

In this chapter, the reader is introduced to the subject of fire with its many features. What is it? Where does it come from? How does it impact us? How did its research evolve? How can we use that knowledge? In subsequent chapters, specific aspects of fire are addressed. What is the temperature of a flame? Why does flashover occur in a room fire? How does ventilation affect the fire? We will answer these questions and more by knowledge from research and formulas that allow quantitative estimates. When this information is pieced together, you might explain what you saw in a fire or why it occurred, or you might defend what you think happened.

Now let us start at the beginning.

1.2 What Is Fire?

To understand fire, we must have a scientific definition of fire consistent with our perceptions. In scientific terms, fire or combustion is a chemical reaction involving fuel and an oxidizer—typically, the oxygen (O₂) in the air. But this definition is insufficient, as rusting and the yellowing of old newsprint fit this definition and they are not fire. The distinction to be fire or combustion is that significant energy has to be released. Can we distinguish combustion from fire? Of course we cannot. In scientific terms, combustion and fire are synonymous. In conventional terms, we generally treat fire as distinct from combustion, in that fire is combustion that is not controlled. Firefighters attempt to control it by adding water or other agents, but the process of fire is not “designed” combustion, as in a furnace or an engine. Combustion experts who study such systems may know very little about fire, and those who deal with fire may know very little about all aspects of combustion. The uncontrolled nature of fire makes it distinct.

Fire is a chemical reaction that involves the evolution of light and energy in sufficient amounts to be perceptible. Generally, that energy will emit light. The color associated with fire might be blue from formative chemical emitters in a flame or yellow to red from light emitted by soot in a flame or smoldering char. Will there always be light in a flame (fire)? No. For instance, the burning of hydrogen (H₂) with air or oxygen produces only water vapor from its chemical reaction. Although significant energy is produced, we would not visibly see flame. But in most other chemical reactions, we would see the combustion process in terms of light emission from gases or particulates. A fire or a flame would be energetic enough to be sensed, particularly with sufficient energy to damage our skin. It may not be very big, but its chemical energy release rate (per unit volume) would be sufficient to give us a local burn injury. This is an operational definition of fire. Fire is a chemical reaction of significant energy release with damaging ability. It need not be only a flame, as a surface reaction on solid can fit this definition. It is the result of striking a match, the glow of the charcoal briquette in your grill, the conflagration of the forest, and the spontaneity to ignition of a large haystack. Fire is combustion, and combustion is a chemical reaction of significant energy release to cause damage. Operationally, sufficient damage can be assessed as harm to human tissue or irreversible damage to materials.

One last word on this chemical reaction called fire. On Earth, it typically and naturally involves hydrocarbon-based fuels: those composed of atoms of carbon (C), hydrogen (H), and perhaps some oxygen (O) and nitrogen (N). Man-made materials have been added to this array of fuels (molecules), with the addition of chlorine (Cl), bromine (Br), fluorine (F), and other atoms. For example, wood molecules consist of the atoms involving H, C, and O; polyvinyl chloride (a plastic) contains H, C, and O plus Cl atoms; and polyurethane (another plastic) contains H, C, and O plus N atoms. These additions to the H—C—O base complicate the nature of combustion products and their potential threat to the environment. It is likely that other elements, even without the addition of oxygen, could meet our combustion. In short, fire or combustion is simply a chemical reaction that can suddenly occur to release significant energy with a relativel...