chapter 02-fire chemistry

© 2009 Delmar, Cengage Learning

Fire Chemistry

Chapter 2


Objectives

• Understand and explain the basic structure of atoms

• Explain how atomic structure determines the behavior of elements and compounds

• Understand basic chemical and physical properties and concepts and how they influence the behavior of materials involved in fires and hazardous materials incidents


Objectives (cont’d.)

• Correlate chemical structure with chemical names to allow for a general prediction of some hazardous chemical behaviors

• Understand key physical properties of chemicals and how these properties are related to fire protection


Introduction

• Gives basic information related to fires and chemicals that may be encountered by first responders

• Understanding of these chemicals and their reactions during the fire combustion process is essential for the safety of firefighters


Matter

• Matter:– Anything that occupies space and has mass – Something that occupies space and can be perceived

by one or more of the senses

• Physical appearance or physical properties of matter: – Mass, size, or volume

• Three states of matter:– Solid, liquid, or gas


States of Matter

• Solids– Consist of a portion of matter having definite volume

and definite shape

• Liquids– Have definite volume but not definite shape– Will take on the shape of the vessel in which it is

contained– Generally turn to gas when exposed to the

atmosphere or when placed under pressure and heat


States of Matter (cont’d.)

• Gases– Have neither definite shape nor volume– Shape determined by amount of pressure placed

upon it and shape of the container– Flammable gas: one that is flammable at atmospheric

temperature and pressure within a mixture with air of 13% or less or it has a flammable range with air of more than 12%


Chemical Properties of Matter

• All materials either inorganic or organic– Inorganic

• Chiefly composed of earth minerals like rocks, soil, air, water, and minerals in or below earth’s surface

• Majority not involved in the combustion process

– Organic• Generally found in once living organisms

• Consist of carbon, hydrogen, and oxygen


Cells

• Tiny mass of protoplasm usually containing a nucleus

• Smallest structural unit of living matter• Capable of functioning independently• Make up organs of human body• Organic chemistry important to firefighters for

understanding fire behavior and understanding the functioning of human body


Compounds

• Substance formed from two or more elements joined with a fixed ratio

• Consists of chemically combined molecules– Homogeneous– Have a definite composition regardless of origin,

location, size, or shape– Elements cannot be separated by physical means

• Approximately five million identified


Structure of Molecules

Figure 2-1 Woodsubdivided into the cell, molecules, and compounds.


Atoms

• Basic building blocks of matter• Smallest unit of an element taking part in

chemical reaction• Atoms of most elements can combine with

others to form molecules by chemical interaction– Example: water (H2O) is made up of two atoms of

hydrogen and one atom of oxygen


Structure of the Atom

• Consist of three types of subatomic particles– Nucleus is in center of atom and contains two kinds of

particles• Neutrons: heavy with no electrical charge

• Protons: equal in weight to the neutron and contains a positive electrical charge

– Orbiting around the nucleus are the third particles• Electrons: light and carry a negative charge


Combination of Atoms

• 109 elements• Atoms combine with other atoms to fill outer

electron shells, or rid themselves of extra electrons

• Atoms can have as many as one hundred or more electrons

• Atom’s behavior can be determined by the number of electrons in the outer shell


Elements

• Basic construction materials of matter• Simplest form of matter• Can be grouped into families

– Halogenated: any chemical reaction in which one or more halogen atoms are incorporated into a compound


Element Symbols

• Each chemical given a symbol, either a one or two letter abbreviation made up of a letter or letter in their name

• Firefighters’ knowledge of these symbols and chemical formulas may be helpful dealing with situations


Molecules

• Smallest part of a pure chemical substance that has all properties of the material.

• In constant motion, speed depending on its state • Physical change: molecules remain intact• Chemical change: molecules are altered


Mixtures

• A combination of substances held together by physical rather than chemical means

• Ingredients of a mixture retain their own properties

• Substance does not change in the formation of the mixture


Prefixes and Suffixes

• Pre-fixes are syllables added to the beginning of a word

• Suffixes are syllables added to the end of a word– Describe atoms that are added to a basic molecule– Denote groups of atoms added and behave as groups

called functional groups

• In firefighting, used as identifiers to provide a warning


Organic Chemicals

• Contain some form of hydrocarbons or combination of carbon and hydrogen molecules

• Number of carbon atoms that combine with number of hydrogen atoms determine the properties and reaction of the substance

• Organic peroxides can react explosively in the combustion process


Properties of Chemicals

• Atoms of a certain element have the same properties

• Properties make their behavior predictable, a valuable tool for firefighters when working with hazardous chemicals

• Atoms combine to create a chemical compound• Defining characteristic of compounds are

chemical formulas


Boiling Point

• Several definitions of BP– Temperature that the vapor pressure of liquid equals

pressure of the atmosphere around it – Temperature at which molecules in liquid are heated

until it begins to bubble and changes to vapor

• Once started, as long as heat is applied, boiling continues and changes to vapor


Vapor Pressure

• Pressure placed on inside of closed container by vapor or molecules driven off the flammable liquid in space above the liquid– Open cup test measures release of the vapors in

terms of the pressure exerted at specific temperature– Closed cup test done by placing a lid on the cup

containing liquid and taking pressure reading when vapors are released from it


Vapor Density

• Mass of the vapor divided by the volume it fills• Carbon dioxide is 1.5 times as heavy as air

– Room filled with carbon dioxide will eventually blanket room with vapors at the floor level

– Oxygen in the room will be replaced or forced upward

• Butane gas is twice as heavy as air and has flammability range of 1.9% to 8.5%– Flammable vapors heavier than air may pool at lowest

point awaiting a source of ignition


Solubility

• Solubility in water indicates amount of a material that will dissolve and mix in water– Materials that are soluble in water are polar solvents

• Insoluble or slightly soluble materials will form a separate layer and will either float or sink depending on specific gravity


Specific Gravity (Water and Air)

• Density of the product divided by the density of water or air

• Water and air, the standards, are given the value of 1.0 at a certain temperature

• Specific gravity provides insight for firefighters to determine:– Best method of fire extinguishment– Best means of moving gas to the open environment


Flash Point and Fire Point

• Flash point is minimum liquid temperature at which enough vapors are present above liquid to ignite or flash but does not continue to burn

• Fire point is lowest temperature at which liquid produces vapor that can sustain continuous flame


Explosive Limits and Range

• Explosive range is range of concentrations of the materials in the air, which permit the material to burn

• Lower explosive limit is lowest ignitable concentration of a substance in air

• Upper explosive limit is highest percentage of a substance in air that will ignite

• See Table 2-5 for list of gases and their limits


Hydrogen Ion Concentration (pH)

Figure 2-2 pHvalues of commonsubstances


Appearance and Odor

• Important in the description of material, including its color, smell, and physical state at normal temperature and pressure.

• If all properties are carefully considered, it is impossible to find two chemicals with identical properties


Physical State• Physical states of hazardous materials

– Liquids, solids, gases, sludge

• Boyle’s law: the more gas is compressed, the more it becomes difficult to compress further

• Charles’s law: gas will expand or contract in proportion to an increase or decrease in temperature

• Special conditions– Sublimation, compressed gases, cryogenic liquids


Changes in Physical State

• Chemical reactions occurring during leak or fire cause change in physical state

• Leaking liquid may change to the gas form with increase in volume

• In vapor form, it may pool in lower areas or ascend depending upon its specific gravity


Combustible Dusts

• Materials in solid form can be made to combust or explode by converting them into dust

• Any organic dust can explode• Many dust explosions occur in pairs• Many metals in a dust or shavings form will also

explode


Boiling Liquid Expanding Vapor Explosion

• Occurs when a pressure tank has its container metal softened or weakened by heat or corrosion

Figure 2-3 BLEVE.


Chemical Reactions

• Endothermic: type of reaction in which energy is absorbed when the reaction takes place

• Exothermic: type of reaction that will release or give off energy

• Polymerize: the process in which molecules of a monomer are made to combine with other monomers


Water-reactive Materials• Water-reactive materials

react with water, often violently, to release heat, a flammable or toxic gas, or a combination of the two

Figure 2-6Magnesium reacting to firefighters’ hose line


Air-reactive Materials

• Reactive simply in presence of air when they escape their containers

• Some will ignite in air– Potassium metal is an example– Air-reactive white phosphorous must be stored

underwater to prevent its ignition


Oxidizers

• Oxidizers (oxidizing agents)– Present special hazards because they react

chemically with a large number of combustible organic materials

• Oils, greases, solvents, paper cloth, and wood

– Some inorganic peroxides are very reactive and sensitive to shock

– Other commonly encountered oxidizers:• Ammonium nitrate (see Figure 2-7), potassium

permanganate, ammonium persulfate, sodium nitrate


Figure 2-7 Federal building, Oklahoma City, Oklahoma


Unstable Materials

• When exposed to water, air shock or pressure materials designated as unstable can decompose, polymerize, or become self-reactive– Monomers: building blocks that form many types of

polymers• Spray foam insulation, which is sold in an aerosol

container at most hardware stores

– Once started, the reaction cannot be stopped


Incompatible Materials

• When some materials are mixed with others, they can adversely affect human health and the environment:– Generation of heat– Violent reaction– Formation of toxic fumes or gases– Formation of flammable gas– Fire or explosion– Release of toxic substances if they burn or explode


Catalyst

• A catalyst is a substance that is not created or destroyed in chemical reaction, but greatly affects the rate of reaction – Example: platinum, used in the catalytic converter of a

car exhaust system, causes the fuel to burn faster and cleaner without consuming the platinum


Toxic Combustion Products

• Formation depends upon the nature of the burning material and the amount of oxygen present– Many home furnishings and decorations made with

plastics that when exposed to fire release toxic chemicals into the atmosphere

• Self-contained breathing apparatus (SCBAs) are used to avoid inhaling this toxic material


Summary

• Basic chemistry and physical processes are important to firefighters for emergency response actions and their safety

• Firefighters must be equipped with knowledge and tools to investigate and determine the extent of the hazard

• Once the hazard is identified, firefighters can actively take action required to control and mitigate the situation