Chapter 4 Study Set Review

flaming combustion occurs in what state?

occurs when a gaseous fuel mixes with oxygen in the correct ratio and heats to ignition temperature.

Gas always move from

areas of high pressure to areas of low pressure.

velocity and speed increase

as temperature increases causing increase in convective heating

what is convection?

convection is the transfer of thermal energy by the circulation or movement of a fluid (liquid or gas)

chemical energy is the

most common source of heat in combustion reactions

hydrocarbon fuels

plastics and synthetic fibers.

lateral movement is usually the result of

pressure differences (high to low pressure)

Inhaled HCN enters the blood stream and

prevents the blood cells from using oxygen properly which kills the cells.

in compartment fires...

radiant heat transfer plays a huge role in development and the spread of compartment fires.

what is a flashover?

rapid transition from growth stage to the fully developed stage is a flash over. materials and fuels ignite almost simultaneously. Conditions in room change from hot layer on cold layer to a single well mixed hot gas condition. can reach temp above 1100

what is conduction?

transfer of energy from one place to another by contact. The transfer of heat between solids. example, fire fighters hand on hot door.

radiation is the

transmission of energy as electromagnetic waves, such as light waves, radio waves, or x-rays without an intervening medium. Radiant heat can become the dominant mode of heat transfer as the fire grows and ignites objects nearby.

At normal ambient temperatures, materials can ignite and burn at oxygen concentrations as low as?

15%

Smoke is the product of

Incomplete combustion. Smoke and ash are both examples of left over fuel from incomplete combustion.

when hot gasses follow the flow path from areas of high to low pressure, they...

convect heat to a larger portion of the structure.

objects at same temperature

do not transfer heat

at openings, lower pressure gasses

entrain below the neutral plane

at openings, hot gases at higher than normal ambient temperature

exit through top of opening above the neutral plane

smoke is

fuel

Hot air means

high pressure

Temperature is the..

measurement of heat. The average kinetic energy in the particles of a sample of matter.

the increased use of engineered or lightweight construction and trussed support systems

pose a danger to ff's. Unprotected steel trusses can fail after 5-10minutes of exposrue to fire or heat alone. 1,000 degrees steel trusses begin to melt.

Complete combustion of methane in air

results in the production of heat, light water vapor and carbon dioxide.

the faster the smoke,

the hotter it is

What is pyrolysis and how is heat transferred from it?

A chemical change causes the off-gassing of solids. When heat is transferred to a liquid or solid the temperature rises and starts to off-gas. In liquids, off-gassing is called vaporization.

What is smoke?

fuel that has not ignited

Fresh cool air will

generally travel toward the fire which creates a connective flow.

What are the products of combustion?

heat and smoke.. Smoke is an aerosol comprised of gases, vapor and solid particulates.

when air supply is limited the rate of incomplete combustion is

higher which produces more smoke.

Carbon Monoxide is a toxic and flammable product of the

incomplete combustion of organic materials. It is a chemical asphyxiant.

increased heat-release-rate results in an

increased heat transfer rate to an object (heat flux)

low smoke means

low neutral plane. Smoke banks down on layering

heated gas will

rise, remain aloft (buoyant) and generally travel up and out.

A significant indicator of flashover is

roll over. Roll over describes a condition where the unburned fire gases that have accumulated at top of a compartment ignite and flames propagate through the hot gas layer or across the ceiling.

The flow path is defined as the

space between the air intake and the exhaust outlet.

vertical movement is due to

the bouyancy of smoke and fire gasses.

ignition is where..

the combustion process begins

If a structure is on fire and all doors close

the fire will decay

For flaming combustion to occur, fuels must be in what state?

the gaseous state. Thermal energy is required to change solids and liquids into the gaseous state.

what is the neutral plane

the interface between the hot gas layers and cooler layer of air.

as the pressure difference between high and low pressure areas increase,

the speed with which gases will move from high to low also increases.

heat is

the thermal kinetic energy needed to release the potential chemical energy in a fuel. As heat begins to vibrate the molecules in a fuel, the fuel begins a physical change from a solid or liquid to a gas. The fuel emits flammable vapors which can ignite and release thermal energy. It then starts to heat other uninvolved fuels converting their energy and spreading the fire.

Difference between combustion and fire.

Combustion is a chemical reaction while flaming combustion is only one possible form of combustion. Combustion can occur without visible flames.

is flaming combustion fast or slow?

Combustion that results in a flame is very fast and is called burning. Combustion can only occur between gases.

Carbon Dioxide (CO2) is a byproduct of....?

Complete combustion of organic materials. Displaces oxygen which creates an oxygen-deficient atmosphere. C02 is a respiratory stimulant.

What is flaming combustion?

Flaming combustion is commonly referred to as fire.

What is pressure?

Pressure is force per unit of area applied perpendicular to a surface. Differences in pressure above or below standard pressure creates movement in gasses.

Smoke Indicator of flashover

Rapidly increasing volume, turbulence, darkening color, optical density and lowering of the hot gas layer and or neutral plan

What happens if you remove one element from the fire triangle?

Remove any of these elements and the fire will be extinguished.

What is the difference between the fire triangle and fire tetrahedron?

The fire triangle illustrates the three components needed for a fire while the fire tetrahedron demonstrates the four components of a self-sustaining fire. The fire triangle, is the oldest and simplest model that shows three elements necessary for combustion to occur, OXYGEN, FUEL AND HEAT. The fire Tetrahedron includes an uninhibited chemical chain reaction to occur. The tetrahedron includes the chemical chain reaction to explain flaming or gas-phase combustion).

HCN is a significant byproduct of the combustion of what?

The polyurethane foam used in many household furnishings. Also released during the off-gassing as an object is heated.

What is hydrogen cyanide (HCN)

A toxic and flammable substance produced in the combustion of materials containing nitrogen, commonly in smoke, but at lower levels than Carbon Monoxide. The incomplete combustion of substances that contain nitrogen and carbon produces HCN. 35x's more toxic than CO. Prevents the body's use of oxygen at the cellular level. Can be inhaled, ingested, or absorbed into the body

Does heat from a fire increase or decrease pressure?

Heat increases the pressure of surrounding gasses in a fire. This heated gas will seek to expand and equalize with areas of lower pressure.

heat transfers from warmer objects to cooler objects because

Heated materials will naturally return to a state of thermal equilibrium in which all areas of an object are a uniform temperature.

backdraft

a ventilation-limited compartment fire can produce large volume of flammable smoke and other gases due to incomplete combustion. Heat release rate decreases elevated temp still remains. An increase in ventilation such as opening a door can result in an explosively rapid combustion of the flammable gasses called a back draft.

cold air means

low pressure

When does flaming combustion occur?

when a gaseous fuel mixes with oxygen in the correct ratio and heats to igniton temperature.

carbon-based fuels

wood cotton...etc