Gavins: essentials of firefighting 7th edition chapter 4
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300 Terms
Fire dynamics
The study of how fires start, grow, spread, and develop.
Combustion
A chemical reaction involving a fuel and an oxidizer that releases energy.
What is required for combustion?
Fuel, heat, and an oxidizing agent.
What is the most common oxidizer in a fire?
Oxygen in the atmosphere.
What percentage of normal air is oxygen?
About 21%.
Fuel
The material or substance being burned in a combustion reaction.
Oxidizer
A substance that supports combustion.
Is oxygen itself flammable?
No, but it supports combustion.
How does extra oxygen affect fire?
It generally increases burning intensity and heat release rate.
Matter
Anything that occupies space and has mass.
Physical change
A change in size, shape, or physical state without creating a new substance.
Chemical change
A change in which one or more substances become different substances.
Oxidation
A chemical reaction involving an oxidizer.
Can oxidation happen slowly?
Yes, such as rusting.
Can oxidation happen rapidly?
Yes, such as fire or an explosion.
Energy
The capacity to perform work
Potential energy
Stored energy.
Kinetic energy
Energy associated with motion.
Heat of combustion
The total amount of thermal energy that can be released by a fuel during combustion.
Fuel load
The total amount of combustible material in a building or area.
How does a larger fuel load affect a fire?
It can increase fire duration, heat release, and severity.
Joule
The SI unit used to measure energy.
How many joules are needed to raise 1 gram of water 1°C?
About 4.2 joules.
BTU
The amount of heat needed to raise 1 pound of water 1°F.
About how many joules equal 1 BTU?
About 1,055 joules.
Exothermic reaction
A reaction that releases energy.
Is fire exothermic?
Yes.
Endothermic reaction
A reaction that absorbs energy.
Example of an endothermic process
Turning liquid water into vapor.
Heat
Thermal energy transferred from a warmer object to a cooler one.
Temperature
A measurement of how hot or cold a material is.
Heat vs. temperature
Heat is energy transfer; temperature measures thermal condition.
Power
The rate at which energy is transferred.
Watt
A unit of power equal to 1 joule per second.
Kilowatt
1,000 watts.
Megawatt
1,000,000 watts.
Heat release rate (HRR)
The amount of heat energy released by a fire per unit of time.
What units are commonly used for HRR
Kilowatts and megawatts.
What factors affect HRR?
Fuel type, amount, arrangement, surface area, and oxygen supply.
What generally happens to HRR when more oxygen becomes available?
It increases.
Heat flux
The amount of heat energy transferred to a surface per unit area.
How is heat flux commonly measured?
kW/m².
Why is heat flux important to firefighters?
It represents the thermal energy striking PPE and skin.
Common sources of ignition heat
Chemical, electrical, and mechanical energy.
What is the most common heat source in combustion?
Chemical energy.
Self-heating
Heat produced internally by oxidation without an outside heat source
What can self-heating eventually cause?
Spontaneous ignition.
Spontaneous ignition
Ignition caused by self-heating without an external flame or spark.
Examples of electrical heat sources
Resistance heating, overloaded wiring, arcing, and sparking.
Examples of mechanical heat sources
Friction and compression.
How does friction create heat?
Movement between surfaces converts mechanical energy into heat.
What can happen when a gas is compressed?
Its temperature can increase.
Thermodynamics
The study of heat and energy transfer.
Thermal equilibrium
When objects reach the same temperature and no net heat transfer occurs.
Which direction does heat naturally move?
From hotter areas to cooler areas
What increases the rate of heat transfer?
A greater temperature difference.
What are the three methods of heat transfer?
Conduction, convection, and radiation.
Conduction
Heat transfer through direct contact or through a solid material.
What three major factors affect conduction?
Surface area, temperature difference, and thermal conductivity.
Thermal conductivity
A material's ability to conduct heat.
Which generally conducts heat better, metal or air?
Metal
Why is trapped air a good insulator?
Air is a poor conductor of heat.
Convection
Heat transfer through movement of a liquid or gas.
What commonly transfers heat by convection in a structure fire?
Smoke and hot fire gases.
What causes hot gases to rise?
Buoyancy
What generally causes gases to move sideways?
Pressure differences.
What factors affect convection?
Temperature difference, area exposed, and speed/turbulence of the gases.
Radiation
Heat transfer by electromagnetic waves.
Does radiation require direct contact?
No
Does radiation require air or another medium?
No
How fast does radiant heat travel?
At the speed of light
Why is radiation important in fire spread?
It can heat and ignite fuels away from the original fire.
How does distance affect radiant heat?
Increasing distance decreases radiant heat exposure.
How do dark surfaces react to radiant heat?
They generally absorb more radiant energy.
How do polished or light-colored surfaces react to radiation?
They generally reflect more radiant energy.
What happens to radiation as fire temperature increases?
Radiant heat increases
Do conduction, convection, and radiation usually occur at the same time?
Yes
How much does water expand when converted to steam?
About 1,700 times its liquid volume.
Pressure
Force applied per unit area.
Normal atmospheric pressure at sea level
About 14.7 psi.
How do gases move because of pressure?
From high pressure toward low pressure.
What happens to gas movement when the pressure difference becomes greater?
Gas movement becomes faster
Buoyancy
The tendency of heated gases to rise.
Why do heated gases rise?
They expand and become less dense
Entrainment
The drawing of surrounding air into a moving fire plume.
What happens during entrainment?
Cooler surrounding air mixes into the rising plume.
Smoke
A mixture of gases, vapors, and solid particles produced by combustion.
Smoke is mainly associated with what type of combustion?
Incomplete combustion.
How should firefighters treat all smoke?
As toxic
Incomplete combustion
Burning in which fuel is not completely oxidized.
Common products of combustion
Heat, smoke, water vapor, CO₂, CO, gases, vapors, and particulates.
Carbon monoxide (CO)
A colorless, odorless, toxic, and flammable gas produced by incomplete combustion.
Why is CO dangerous?
It prevents the blood from carrying oxygen effectively.
How strongly does CO bind to hemoglobin compared with oxygen?
About 200 times more readily.
Carbon dioxide (CO₂)
A combustion product that can displace oxygen
Hydrogen cyanide (HCN)
A highly toxic combustion product produced when nitrogen-containing materials burn.
How does HCN harm the body?
It prevents cells from properly using oxygen.
What materials can produce HCN?
Nylon, polyurethane foam, wool, silk, and other nitrogen-containing materials.
Hydrogen chloride (HCl)
A toxic irritant associated with burning chlorine-containing materials such as PVC
Formaldehyde
A toxic irritant that can be present in smoke.