Fire Dynamics Flashcards
1
Q
What are the four principles of FIre Science?
A
- Combustion
- Fire
- Heat
- Temperature
2
Q
True of False. All fires involve a heat-producing chemical reaction between some type of fuel, oxidizer and combustion.
A
False, all fires involve a heat-producing chemical reaction between a fuel and an oxidizer. The combustion IS the chemical reaction.
3
Q
What is the most common Oxidizer?
A
Oxygen
4
Q
Are Oxidizers Combustible?
A
Not by themselves, but they will support combustion.
5
Q
What common use do these Oxidizers have in everyday life? Calcium Hydrochlorite Chlorine gas Ammonium Nitrate Hydrogen Peroxide Methyl Ethyl Ketone Peroxide
A
-Cleaning pool water
-Drink water purification
-Fertilizer
-Industrial Bleaching
Catalyst in plastics manufacturing.
6
Q
What is Physical Science?
A
Study of matter and energy
7
Q
Why is it important for firefighters to understand fire dynamics?
A
-To be able to anticipate how the fire will behave in the future and how that affects fire operations
8
Q
What is a Physical vs a Chemical change?
A
A Physical change is when a sustance changes forms like in size, shape, appearance but remains the same chemically. Ex: Water going from ice to liquid to gas.
A Chemical change is when a substance changes from one type of matter to another.
9
Q
What is Oxidation?
A
A chemical reaction involving an oxidizer and another material. Rust is a slow oxidation and explosions are rapid oxidation.
10
Q
What is potential energy?
A
The amount of energy that a substance can release in the future.
The potential energy available for release is known as the Heat of Combustion
10
Q
What is potential energy?
A
The amount of energy that a substance can release in the future.
The potential energy available for release is known as the Heat of Combustion
11
Q
What factors limit the release of potential energy?
A
- Chemical composition
- Arrangement
- Density of the fuel
- Availability of the oxidizer
12
Q
What is Kinetic Energy?
A
The energy that moving objects have. In fire, the movement occurs in the movement of the molecules of the fuel.
13
Q
What unit of measurement measures Energy and how is it defined?
A
4.2 Joules is the amount of energy required to heat 1 gram of water by 1 degree celcius.
14
Q
What is the other imperial unit of energy measurement, and how does it compare to the joule?
A
The British Thermal Unit BTU. how much energy it takes 1 pound of water to heat up by 1 degree fahrenheit. 1,055 joules equals 1 BTU
15
Q
What is an endothermic reaction?
A
A reaction that absorbs heat. Turning water into steam or ice into water.
16
Q
What are the componants of the fire tetrahedron?
A
- Reducing agent (Fuel)
- Oxidizing agent
- Heat
- Chemical Chain Reaction.
17
Q
Can liquids and solids burn?
A
Only if they are first converted to a gaseous state.
In solids it is called Pyrolysis
In liquids it is vaporization
18
Q
What is the difference between Piloted ingnition and Autoignition?
A
Piloted ignition is when a mixture of fuel and oxygen encounter a hot enough external source to start a combustion.
Autoignition occurs one the surface of the substance is heated to a point where it ignites on its own without a spark or flame.
19
Q
What is the Autoignition Temperature?
A
The temperature at which a substance needs to be heated in order to start self sustained combustion.
20
Q
True or false. Auto ignition temperature is always lower than piloted ignition temperature.
A
False. It is always higher.
21
Q
Can combustion occur without visible flames?
A
Yes
21
Q
Can combustion occur without visible flames?
A
Yes
22
Q
What are the main differences between flaming and nonflaming combustion?
A
Nonflaming occures at a lower temperature and burns slower. Ex: coals.
Flaming combustion is what people know as fire. It requires the perfect combination of all elements of the fire tetrahedron. Solid and liquid fuels are tranformed into gas by heating. Oxygen comes into the reaction through the inlet flow and the exhaust leaves through the outlet flow.
23
Why does smoke rise from the fire?
The heat causes expansion of the exhaust particles, which creates boyancy in the air surrounding it, so the particles rise.
24
What are the two by-products of fire?
Heat and smoke.
25
True or false. more people die due to exposure to heat of the fire than the toxic gases in the smoke.
False, more people die due to the toxic fumes in smoke.
26
What is smoke?
Product of incomplete combustion
27
Can smoke burn?
Yes because it is an incomplete reaction.
28
True or false. Less oxygen creates more smoke in a structure fire.
True. Less oxygen means more incomplete reactions.
29
What are the two major types of fuels in structure fires?
- Carbon-based (wood)
| - Hydrocarbon (plastics)
30
True or false. All smoke is toxic to a certain degree
True. while some are far worse than others, it is never advised to consume smoke of any kind.
31
True of false. Structure fires can create both CO and CO2
True. Carbon in the air combines with the consumed oxygen to form CO and CO2
32
What is asphyxiation?
Death due to low oxygen levels in the blood.
33
What is Carbon monoxide?
The product of an incomplete combustion of carbon based materials.
34
True of false. Carbon Monoxide is flammable?
True, since it is an incomplete reaction, it can still burn.
35
How can Carbon monoxide kill people?
Levels of 0.2 % can cause unconsciousness in under 30 minutes. CO attaches to hemogloben and prevents Oxygen from attaching. too much CO can result in not enough oxygen going to the body and can cause death.
36
True or false. Hydrogen Cyanide is caused by complete combustion?
False. it is caused by incomplete combustion of substances that contain nitrogen and carbon.
37
Is HCN more or less toxic than CO?
35x more. It prevents the body from being able to use the oxygen it gathers. High concentrations can lead to death in minutes.
38
Is CO2 the product of complete combustion?
Yes, of organic materials
39
What is the unit of measurement for Pressure?
Kilopascals. The atmosphere of the earth is 101 kPa
40
What is the defference between Heat and Temperature?
Heat is the thermal energy needed to release the gases inside solid or liquid fuels. Heat is transfered, convectively, conductively and through radiation.
Temperature is the measurement of heat. The average kinetic energy of the particles at combustion.
41
True or false. Temperature is a good predictor of heat transfer.
False. Because one candle burns at the same temperature as ten candles, but the heat released by ten candles in ten times greater than the one. This increases the heat transfer.
42
What is the measurement of heat transfer to a unit area (Heat flux)?
Kilowatts per square meter.
43
What is Chemical Energy?
The most common source of heat combustion. Almost always results in production of thermal energy.
44
What is self-heating?
Oxidation of a substance that results in a tempertature increase from contact to Oxygen. Can lead to Spontaneous ignition.
Rags soaked in Linseed oil can self-heat to the pont that it ignites spontaneously.
45
What are the types of Electrical Heating?
- Resistance Heating
- Overcurrent or Overload
- Arching
- Sparking
46
What is Electrical Resistance Heating?
When an electric current travels through a conductor and creates heat. Lightbulbs, heaters and other appliances are designed to make use of Resistance heating.
47
What is Electrical Overcurrent or Overload?
When a conductor is given more electricity than it was designed to handle, it creates an excess of heat.
47
What is Electrical Arching?
A luminous arch of electricity that can cause heat.
48
What is Electrical Sparking?
When an arch occurs, hot particle can form and splatter.
49
How is Mechanical Energy formed?
Friction and compression of mechanical equipment. Compressed gases, sparks from friction.
50
What is Thermal Equilibrium?
When two objects that are in contact have the same temperature. due to heat transfer.
51
What is Thermal Conductivity?
The speed at which a material is able to transfer heat to another object.
52
What two factors affect the rate of heat transfer between two objects?
Heat differential and Thermal Conductivity.
53
What are the three dependent factors of Conductive Heat Transfer?
- Area being heated
- Temperature differential of the two objects
- Thermal conductivity of the two objects.
54
What three factors influence convective heating?
- Area being heated
- Temp difference between the hot fluid or gas and the material being heated
- Turbulence and velocity of moving gases
55
True of False. White materials absorb more radiation heat that dark materials.
False
56
True or False. The distance between the source of radiation heat and the surface affects the heat transfer.
True, the greater the distance the lesser the heat transfer.
57
True or false. The hotter the radiating heat source, the more heat will be transfered to the absorbing material?
True. more heat equals more radiation, equals more asborbtion.
58
At what speed does radiation travel?
Speed of light.
59
True or false. Smoke cannot release radiation.
False, it releases small amonts of radiation.
60
At what temperature does skin receive a first, second and third degree burn?
48C, 55C, 72C
61
What is a synonym for Fuel in a combustion reaction?
Reducing Agent
61
What is a synonym for Fuel in a combustion reaction?
Reducing Agent
62
What is Power and how is it measured?
Power is the rate at which energy transfers. watt (1 joule per second).
63
What is vapor density?
The density of gases in relation to air.
64
What is Specific gravity?
Density of liquids in relation to water. If it is more dense than water, it will sink to the bottom, if it is less dense it will rise to the surface.
65
True or False. In order for liquids to become vapor, they need to be exposed to a pressure lesser than that of the atmosphere.
False, they need to be exposed to pressures greater than that of the atmosphere. Every liquid substance has a unique vapor pressure.
66
True or false. The flashpoint of a flamable liquid is higher than its fire point.
False. the flash point is the minimum temperature at which the liquid is able to vaporize and ignite, but not sustain combustion.
The fire point is the temperature at which a liquid is able to sustain combustion.
67
Is it always a good idea to put water on a flame caused by a flammable liquid?
No, some liquids do not mix with water, which means that the water will only increase the flames.
68
True or false. Miscible materials will easily mix with water.
True
69
If a flammable liquid is able to mix with water, will water application be able to extinguish it?
Yes
70
Is it easier to extinguish a fire from a liquid that is more or less dense than water and why?
More dense is easier because the water will settle on top of the liquid and prevent access to the oxygen. Whereas the opposite is true with less dense liquids. they will settle atop the water and continue to burn. Also, using water with less dense liquid will likely spread the flammable liquid around and exacerbate the issue.
71
What is the surface to mass ratio?
The more surface area to mass a solid has, the more easily it will be able to ignite. That is why newspaper is so easily ignited, because it has a massive surface area for its mass. On the other hand, a huge tree has a massive surface area, but in relation to its mass, its surface area is actually quite small. That is why you can't light an entire tree on fire with just a match, but you can light newspaper with a match. The smaller the surface to mass ratio, the more heat is required to ignite it.
72
Why is orientation of solid fuel important?
If you have a horizontal piece of cardboard and light it on one side it will burn accross relatively slowly, but if you tilt it vertically, it will burn much quicker. Heat transfer is quicker because there is more convective heat preheating the cardboard.
73
What percentage of the air in the atmosphere is Oxygen?
21%
74
How is availability of Oxygen important in compartment fires?
Often there is limited air supply in structures, which limits the intensity of the flames. If a window is opened the fire will increase in intensity.
75
What is the minimum % of oxygen in the atmosphere that a fire can still combust at?
15%, but smouldering can occur at very low oxygen percentage.
76
What is the lowest Oxygen % at which humans can breath easily?
19.5% this changes for people that live in very elevated areas.
77
True or false. Some petroleum based products will autoignite in oxygen enriched areas.
True
78
Is it possible to have too much vaporized material for a fire to burn?
Yes, too much is considered above the Upper Explosive Limit (UEL) and too little is considered below the Lower Explosive Limit (LEL)
79
What are Free Radicals?
They are electrically charged particles that are free floating in the atmsophere after a combustion reaction. They can attach themselves to molecules to form another molecule.
80
What is the difference between a fuel-limited fire and a Ventilation-limited fire?
Fuel limited fires have enough air to burn inside a compartment, but they lack the necessary fuels to grow quickly.
Ventilation-limited fires are those that have limited oxygen supply but lots of available fuel.
81
True or false, all compartement fires start as fuel-limited.
True.
82
List the four stages fo fire development.
- Incipient Stage
- Growth Stage
- Fully Developed Stage
- Decay Stage
83
What characterises the Incipient Stage of Fire Development?
Ignition occurs as all component of the fire triangle come together and combustion begins.
Fire is very small
84
What characterises the Growth Stage of FIre Development?
The Incipient fire gains heat and intensity as it spreads to other fuels with conduction, convection and radiation heating. If sufficient fuel and oxygen is present, the fire will become fully developed, otherwise it will decay.
85
What characterises the Fully Developed Stage of Fire Development?
All the available fuels are burning at their peak heat release and oxygen is not limited. If the fire is allowed more fuel it will spread and could get larger, otherwise it will begin to decay as the fuels are consumed.
86
What characterises the Decay Stage of Fire Development?
As the fire burns, all the available fuel and/or oxygen are consumed and the heat release decreases,. The fire will either extinguish or begin to smoulder. If more fuel or oxygen becomes available the fire may startup again.
87
What is a Ceiling Jet?
In the incipient development stage, the fumes and gases hit the ceiling of the compartment and spread horizontally.
88
What is Thermal layering?
In the Growth Stage, as hot gases and smoke form, they rise due to their heat. The cool outside air rushes into the room and the hot gases and air exit through the upper half of the entrance. Cool air comes in through the bottom half of the entrance. The hot gases accumulate on the ceiling and form a high pressure zone. Isolated flames can reach into the mass of hot gas and ignite it.
89
What is the Neutral Plane?
The interface between the hot gas layer and the cool oxygenated air entry.
90
True of False. Open doors and windows typically allow enough airflow for compartment fires to become fully developed.
False. Even with these openings, most compartment fire enter into decay before they can become fully developed.
91
Describe the stages of Ventilation-Limited decay
1. The hot gases accumulate on the ceiling and form a mass of hot gas. The gas mass grows and the neutral plane decends. As the mass of gas decends to the floor, it burns most of the available oxygen, effectively smothering itself.
92
True of false. once ventilation decay is complete and the fire is smoulderng there is no more danger of reignition.
False. The accumulated heat and gas mass can work together to create a larger fire if oxygen is quickly reintroduced to the compartment.
92
True or false, the pressure inside a burning compartment is lower than the pressure outside the compartment.
False. The pressure of the hot gasses causes a higher pressure in the compartment
93
What is Flashover?
A very rapid development of the fire during the Growth or Fully Developed stage. During a flashover, the two layers of hot gas and incoming air are turned into one continuous layer of hot gas condition from floor to ceiling.
94
What is Rollover and how does it relate to flashover?
When the hot gases on the ceiling ignites and propagates through the room. Usually occurs in the Growth stage. It usually precedes flashover, and can generate the radiant heat necessary to start flashover.
95
What are the four commmon elements of flashover?
- Transition from Growth stage to Fully Developed stage.
- Rapidity
- Compartment is required
- Pyrolysis of all exposed fuel surfaces.
96
What two factors influence the occurence of flashover?
1. the size of the fuel. Small fuels might not have enough heat release to be able to activate flash over, but a large sofa likely will.
2. Sufficient ventilation.
97
What temperature is typically required for the hot gas mass to ignite?
The gas mass is mostly CO2 which has an auto ignition temperature of 595C
98
What building charcteristics are indicative of flashover?
Interior configuration, fuel load, ventilation, thermal properties
99
What indicators can smoke give that flash over may occur?
- Rapid increase of smoke
- Turbulence
- Dark dense smoke
- Lowering neutral plane.
100
What heat indicators suggest that flashover is imminent?
- Rapidly increasing temp
| - Distance fuel packages begin pyrolysis
100
What heat indicators suggest that flashover is imminent?
- Rapidly increasing temp
| - Distance fuel packages begin pyrolysis
101
What flame indicators suggest that flashover in possible?
-Isolated flames or Rollover near the ceiling
102
What does a high neutral plane indicate?
Fire is in incipient stage.
103
What does a mid-level neutral plane suggest?
Comapartment is not yet ventilated or that flash over is approaching.
104
What does a low-level neutral plane suggest?
Fire has reached backdraft conditions or that the fire is on the floor below.
105
True of false. Firefighter should always assume that flashover is approaching if they are uncertain that it is not.
True
106
What is Backdraft?
A room full of hot, fuel rich smoke is suddenly well ventilated and the room becomes explosive.
107
What are some of the indicators of backdraft?
- Pulsing smoke movements.
- Smoke stained windows.
- High velocity air intake.
- High Heat
- No visible flames.
108
Should firefighters always assume that there will be a backdraft behind every door they open?
No, they should look for the indicators and assess the dangers.
109
Where are Fully developed fires most commonly found?
Forest fires, vehicle fires and fires in colapsed buildings. Anywhere the ventilation is not limited to a few windows and doors.
110
Is it possible to control a compartment fire by increasing the ventilation to make it a fuel-limited fire?
No, only extinguishing the fuels with water will limit the fire growth.
111
In a ventilation-limited decay, what strategy do firefighters employ to avoid a flashover?
They open the door andquickly aim a stream of water at the hot gases to prevent rollover.
112
What are the two regions of the Flow Path?
- Ambient flow in
| - Hot exhaust flow out
113
What factors influence the flow of ambient air to the seat of the fire?
- Size of ventilation opening
- Distance from opening to seat of fire
- Obstructions
- differences in elevation
114
How much time should firefighters stay in the Flow Path?
As little as possible due to the potential of a fatal heatwave.
115
What is a smoke Explosion?
When a hot smokey air mass is ignited and the result is a large rapid combustion.
116
In what four ways can Firefighters influence the fire dynamics?
- Temperature Reduction- using water or foam to cool hot surfaces
- Fuel removal- moving potential fuel for the fire to avoid a Growing stage.
- Oxygen exclusion- using doors and ventilation to control oxygen supply
- Chemical flame inhibition - using chemical extinguishers
117
What are the two factors of building construction that pose a danger to firefighters?
- Conditions that contribute to the spread of the fire.
| - Conditions that make the building likely to collapse.
118
What factors determine the likelyhood of a building collapsing?
- Duration of the fire before arrival
- Building contents
- How contents affect the heat release rate
- Heat release rate and intensity of fire
- Renovations that may have compromised fire resistance
119
What are the dangers associated with Combustible roof material?
Possible embers flying, causing spread of the fire.
120
What are the five factors that are important to compartmentation and fire behaviour?
- Number of stories above and below ground
- Floor plan
- Openings between floors
- Continuous voids or concealed spaces
- Barriers to fire spread
121
Which is more fire safe? An open floor plan, or a compartmentalized floor plan?
Compartmentalized as it can contain the fire to one room.
122
Are modern homes more or less fire safe than legacy homes?
They are less fire safe due to sealed windows, open floor plans, synthetic materials adding to fuel loading.
123
What are the three thermal properties of buildings?
- Insulation
- Heat reflectivity
- Retention
