Fire Science

what is fire, the fire triangle, principles of heat, methods of heat transfer, and gas laws

what is fire caused by?

rapid oxygenation of fuel source

what does fire release? energy wise

heat light and flames

what by-products does fire release?

smoke ash and gases

what is combustion?

oxidation reaction that produces heat and possibly light

how does combustion initially take place?

vapors produced by heating of combustible material combine with oxygen

what state does combustion occur at?

gaseous state

incipient phase of combustion

no visible signs,decomposition occurs on surface due to some sort of heat, invisible to eye

smoldering phase of combustion

decomposition starts increasing rapidly and smoke appears as unburnt gases, no flames

what are the products of combustion given off during the smoldering phase

water vapor, carbon monoxide and dioxide

flaming stage of combustion

ignition occurs and flames are visible thus seeing combustion

heat stage of combustion

heat is transfered to atmosphere and nearby fuel by processes of conduction, convection, radiation and direct burning

what components does fire require? the fire triangle

heat, oxygen and fuel

whats the fire tetrahedron

chain reaction, heat, oxygen, fuel

class of fire; fuel type A

wood paper

class of fire; fuel type B

flammable and combustable liquids

class of fire; fuel type C

flammable gases

class of fire; fuel type D

flammable metals

class of fire; fuel type E

electrically energised

class of fire; fuel type F

cooking oils and fats

what is flammability range?

a flammable gas will only burn in air if its composition lies between certain limits

IM

ideal mixture

whats the IM for LPG gas %

4%

whats the meaning for an IM

no visible products of unburnt combustion and flame is at its highest intensity

LEL

lowest exposure limit

UEL

upper exposure limit

what level of O2 would be visible with UEL

lower levels of O2

what is pyrolysis

heat of the fire is sufficient to cause chemical breakdown of fuels

what degree can pyrolysis be produced at

80

what temperature would pyrolysis occur in wood

150-200

what is the primary source of heat?

Fire

what two ways can ignition happen?

piloted and spontaneous

piloted ignition

requires a source,initiated by flammable vapour/ air mixture. electrical arc or independent flame

spontaneous ignition

sufficient heat is available, AIT

AIT

auto ignition temperature

flash point

lowest temperature in which a liquid produces a flammable vapour

flame or fire point

lowest temperature a liquid produces and sustains a flame from flammable vapour

whats absolute zero with heat c/k

-273c/0k

heat is?

total energy of molecules in motion in a substance

temperature is?

the average energy of molecules in motion in a substance

what are the three main principles of heat?

temp and energy, HRR, heat flux and transfer

HRR

heat release rate

what is HRR

the amount of heat produced by fire or heat source.

heat flux

the rate of heat is falling on or passing through surface

what is the three fundamental ways heat is transfered?

conduction, convection, and radiation

whats the temperature of a flashover, ceiling height vs floor level

600c vs 20 kw/m2

conduction

contact transfer of heat through materials

thermal conductivity

the rate that heat transfers from hotareas of solid to cold

convection

heat or mass transfer of fluids such as liquids, gases or plasmas

how does convection work

hot air expands becoming lighter and moves upwards. cool air is more dense and takes its place

radiation

heat transfer by the emission of electromagnetic waves

when using radiation how does an object catch fire when it hasent even been in contact with flame.

the surface temperature radiates the heat off the fire without connection obtained and when reaching that auto ignition temperature it will bust into flames.

what does charlies law state?

volume of fixed mass of gas at a constant pressure, is directly proportional to its absolute temperature

what happens when gas is heated

when heated, gas expands, becoming ess dense and rises, when temps increase volume of gas will too