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Fire Everything > Chapter 5 Fire Behaviour > Flashcards

Chapter 5 Fire Behaviour Flashcards

1
Q

Combustion

A

Chemical process of oxidation that occurs fast enough to produce heat and usually light

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2
Q

Fire definition

A

Rapid oxidation, which is a chemical process resulting in heat and light

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3
Q

Heat

A

Form of energy characterized by vibration of molecules and capable of initiating and supporting chemical change

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4
Q

Temperature

A

Measure of a materials ability to transfer heat energy to other objects.
Measure of average kinetic energy of particles in a sample of matter

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5
Q

Fuel

A

A material that will maintain combustion

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6
Q

Oxidizer

A

Any material that readily yields oxygen or other oxidizing gas or that readily reacts to promote or initiate combustion

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7
Q

Matter

A

Anything that takes up space and has mass

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8
Q

All fire

A

Involves a heat producing chemical reaction between some type of fuel and oxidizer

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9
Q

Oxidation

A

Can be rapid like methane combusting or slow like rust.

Chem process when a substance combines with oxygen in air

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10
Q

Energy

A

Capacity to perform work

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11
Q

Joules

A

A force of one newton through a distance of one meter.
For ffers, the energy required to increase temp. 4.2joules to raise one gram of water one degree.
1055 J = 1 btu

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12
Q

Pyrolysis

A

Chemical decomposition of a solid material by heating. Pyrolysis often precedes combustion

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13
Q

Vaporization

A

Liquid into a gaseous state. Rate depends on heat, substances, pressure and surface area

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14
Q

Ignition

A

The process of initiating self sustained combustion

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15
Q

Piloted ignition

A

Moment when mix of fuel and oxygen encounter external heat sufficient to start combustion reaction

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16
Q

Auto ignition

A

Initiation of combustion by heat without spark or flame. NFPA 921
Always a higher temp for a given substance than its piloted temp

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17
Q

Fire triangle

A

Heat oxygen fuel

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18
Q

Fire tetrahedron

A

Fuel heat oxygen and self sustaining chemical reaction

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19
Q

Passive agent

A

Material that absorbs heat but does not participate actively in combustion process. E g drywall.

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20
Q

Nonflaming combustion

A

Burning is localized on or near the fuels surface where it is in contact with oxygent
Eg burning charcoal or smouldering wood or fabric
Flaming is when substance is vaporized and the vapours are ignited forming the flame

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21
Q

CO

A

Colourless odourless

0.2 percent unconscious in 30 minute. High concentration immediate collapse and unconscious

22
Q

Formaldehyde

A

Colourless gas. Pungent odor. 50-100ppm can cause severe irritation to respiratory track and serious injury. Can injure skin in high concentrations. Suspected carcinogen

23
Q

Nitrogen dioxide

A

Reddish brown gas or yellowish brown liquid which is highly toxic and corrosive

24
Q

Sulfur dioxide

A

Colourless gas with a choking or suffocating odor. Toxic and corrosive. Irritates mucus membranes

25
Hydrogen cyanide
Colourless toxic and flammable liquid below 26C. Produced by combustion of nitrogen containing products. Lower smoke concentrations than CO. Common from polyurethane furniture and bedding
26
Carbon dioxide
Colourless odourless heavier than air. Neither burns nor supports combustion. Used to extinguish class B or C fires by displacing oxygen
27
Irritants in smoke
Hydrogen chloride Formaldehyde Acrolein
28
Flame brightness
Luminosity will decrease with more complete combustion
29
Thermal energy
Heat. Kinetic energy transferred from high to low temp substance Heat is the thermal kinetic energy needed to release the potential chemical energy in a fuel Molecules vibrate. Release vapours which can ignite and release thermal energy
30
Temperature
Measurement of heat, more specifically measure of average kinetic energy in particles in a sample of matter
31
Sources of thermal energy
Chemical mechanical electrical (most common the result in ignition of fuel) but also light nuclear and sound
32
Chemical energy
Most common source of heat Self heating is a form of oxidation, normally lost to surroundings nearly as fast as generated. More heat means faster reaction means more heat
33
Common self heating materials
Charcoal linseed oil soaked rags straw and manure
34
4 types of electrical heating
Resistance heating Overcurrent (a type of resistance heating; too much electricity for design) Arcing Sparking
35
Mechanical heating
Friction or compression
36
Heat flux
Measure of rate of heat transfer to a surface expressed in kilowatts/m2, kJ/m2 x sec or btu/ft2 x sec * squared not doubled
37
Heat transfer is based on
Temp differential and thermal conductivity
38
Conduction
``` More dense molecules will more readily it will conduct heat Based on 3 factors: Area being heated Temp difference Thermal conductivity ```
39
Thermal conductivity of common objects in W/mK
Copper 386 Steel 36-54 Concrete 0.8-1.2 Wood 0.13
40
Radiation transfer factors
Nature of exposed surface - dark emits and absorbs heat better. Smooth or polished reflect more than rough surfaces Distance Temp difference - as temp increases radiant energy increases by a factor to the fourth power. Radiant heat travels in straight line at speed of light
41
Reducing agent
Fuel that is being oxidized or burned during combustion
42
Heat of combustion
Total amount of thermal energy by combustion reaction if a fuel were completely burned. Measured in btu per lb or mJ per kg
43
Heat release rate
Total amount of heat released per unit time
44
Power
Measured in watts. 1 watt = one J per second Defined as energy transferred over time or rate at which energy is converted from one form to another. In terms of fire power is described as hrr
45
Common flammable gases
Methane - vapour density 0.55, ignition temp 540C Propane 1.52 450C CO 0.96, 609C
46
Vapour density
1.0 is air. Under one rises
47
Specific gravity
Density compared to water. Less than one floats
48
Flammable liquid
Flash point below 37.8C (100F) and vapour pressure less than 40 psi absolute
49
Vapour pressure
Measure of the tendency of a substance to evaporate. The pressure at which a vapour is in equilibrium with its liquid phase for a given temp. High VP is more likely to evaporate
50
Flash and fire point
Flash is minimum temp for a liquid to ignite but not sustain Fire point is enough for a liquid to support combustion (for 5 seconds). Usually a few degrees higher for fire point Flash point is used to indicate flammability
51
Solubility
Degree to which a substance dissolves in a solvent (usually water) May be qualitative like slightly, completely or a percentage
52
Miscible
Will mix with water in any proportion

Fire Everything (14 decks)

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