the Fire Tetrahedron Identify the relationship of the concentration of

Transcription

1 Fire Behavior

2 Objectives Identifyy the components p of the Fire Triangle g and the Fire Tetrahedron Identify the relationship of the concentration of oxygen to combustibility and life safety Identify the products of combustion commonly found in structure fires that create or indicate a hazard Identify the potential consequences of exposure to products d off combustion b i Identify the following heat sources: chemical, electrical mechanical and nuclear electrical,

3 Objectives Identify the methods of heat transfer Identify the physical state of matter in which fuels are commonlyy found Identify common fire conditions Identifyy the p process of thermal layering y g as it relates to a structure fire Identify how to avoid disturbing thermal layering Identify the development and prevention of a backdraft

4 Fire Triangle Oxygen Must be available in sufficient quantities Fuel Combustible fuel must be present Heat Source of ignition must be present

5 Fire Tetrahedron Oxygen Must be available in sufficient quantities Fuel Combustible fuel must be present Heat Source of ignition must be present Chemical Chain Reaction Added to maintain a self sustaining self sustaining fire, keeps the reaction going

6 Oxygen Concentrations 21% Normal breathing air 17% to 19.5% Judgment and coordination impaired, lack of muscle control 14% and greater Can support combustion 14% and lower Can not support combustion 12% Headache, dizziness, nausea and fatigue 9% Unconsciousness U i 6% Respiratory arrest

7 Oxygen Concentrations Effecting Combustion b A diminished amount of oxygen will cause the combustion process to slow A higher amount will cause the chemical reaction to accelerate Some S materials t i l can ignite i it spontaneously t l Permits some materials to burn that would not burn under otherwise normal oxygen concentrations

8 Oxygen Concentrations Effecting Life f Safety f 23.5% 23 5% and above Considered oxygen enriched Presents an increased fire risk 21% Normal level in atmosphere 19.5% and below Considered oxygen deficient Presents a hazard to anyone not wearing SCBA

9 Products of Combustion Heat eat Byy product p oduct o of tthee co combustion bust o p process ocess tthat at helps e ps to spread the fire by preheating adjacent fuels and making them more susceptible ignition Smoke An aerosol composed of gases, vapor and solid particulates Vapor and particulates give smoke its varied colors Materials that make up smoke vary from fuel to fuel Oil, Tar and soot Fire gases Generally colorless Flame (light) The visible, luminous body of a burning gas

10 Consequences of Exposure to Products d off Combustion b Heat Dehydration Damages respiratory tracks Heat exhaustion Burns B Smoke Breathing discomfort Inflammation of the eyes, respiratory tract and skin

11 Consequences of Exposure to Products d off Combustion b Fire gases Carbon monoxide Hydrogen y g chloride Benzene Hydrogen y g cyanide y Carbon dioxide Flame (light) ( g ) When mixed with the proper amount of oxygen, the flame becomes hotter and less luminous

12 Heat Sources Chemical The energy created by a chemical reaction, most common source of heat Endothermic Absorbs heat Ice packs p Oily rags Exothermic Produce heat Rust Making ice cubes

13 Heat Sources Electrical The flow of electrons from a place where there are plenty to a place where they are lacking Lighting Arcing Electrical systems Static Stati electricity ele tri it Induction heating

14 Heat Sources Mechanical Converted to heat when two materials rub against each other and create friction Fan belt against a seized pulley Typical cause of machinery fires

15 Heat Sources Nuclear Generates heat from a radioactive material Very unstable Constantly breaking down Not much can be done to safely fight a nuclear fire

16 Methods of Heat Transfer Conduction Heat flows through and between solid objects by direct contact Convection Transfer of heat energy from a fluid (liquid or gas) to a solid surface Radiation Transmission of energy as an electromagnetic wave without an intervening medium

17 Physical State of Matter Which Fuels l are Commonly l Found d Solids Have a definite size and shape and react differently when exposed to heat Liquids Have mass and volume but no definite shape p except p for a flat surface Can assume the shape of their container Flow downhill Pool in low areas Density of liquids is compared to that of water Has a specific gravity of 1 Gas Have mass but no definite shape or volume When placed in a container, will diffuse and completely fill the available space Depending on their density relative to air Density of air is 1

18 Common Fire Conditions Ignition / Incipient The point when the three elements of the fire triangle come together and combustion occurs

19 Common Fire Conditions Growth / Freeburning Fire begins to grow, other combustibles heat up and ignite, ignite spreading to other flammables Speed and growth dependent on: Oxygen supply Fuel Container size Insulation

20 Common Fire Conditions Fully developed All combustible materials in the compartment are burning Releasing maximum amount of heat Large volumes of fire gases The fire is ventilation controlled

21 Common Fire Conditions Decay ecay / Hot Smoldering Point where fuel is consumed or when the oxygen concentration falls to the point where combustion can no longer l be b supported t d

22 Common Fire Conditions Rollover / Flameover Condition where unburned fire gases accumulated at the top of a compartment ignite and flames propagate through the hot gas layer or across the ceiling Usually occurs during the growth stage Indicator of impending flashover Different than a flashover due to only gases att the th upper llevels l igniting

23 Common Fire Conditions Flashover Rapid transition between the growth and the fully developed fire stages but is not a specific event such as ignition All the contents of a room reach their respective ignition temperatures, usually in seconds Death or serious j to anyone y injuries caught in one

24 Process of Thermal Layering Thermal Layering Tendency of gases to form into layers according to temperature Heat Stratification Hottest gases form top layers while cooler gases form bottom layers As A the h pressure increases i the h temperature increases also

25 Disturbing Thermal Layering Thermal imbalance Disruption of heat stratification (hot gases mix throughout room) Water sprayed into the upper part of the room Steam is produced Pushes the smoke layering down Prevention Venting superheated gases from the building as fire attack is underway Avoid A id directing di i water at the h ceiling ili

26 Backdraft Development Generates quantities of combustible gases These gases are heated above their ignition temperature Requires closed, confined spaces There s a limited supply of oxygen Oxygen yg concentration is reduced Decrease in combustion

27 Backdraft Signs Of Puffing Smoke Yellow-Gray Smoke Walls Too Hot to Touch Dull Orange Glow or Visible Fire Darkened Windows Rattling Windows Hot Unbroken Glass

28 Backdraft Prevention Ensure that superheated gases are vented from the top of the fire room Ventilation and water application must be done in the proper sequence

29 Q&A