1.Definition of compartment fire Fires happen in a room, a bus, a car, a ship or train compartment, etc. are all compartment fires. A compartment fire ( ) means a fire that takes place in a compartment. A compartment is an enclosure with walls, roof and openings (such as windows and doors). A compartment fire is a fire that takes place in a compartment, such as a room, a bus or a train compartement.
The big Garley building fire,1996, Hongkong Airport terminal fire, 1996, Duesseldorf, Germany
MTR train compartment arson fire, January 2004 (up) Ship fire: The fire broke out an hour after the ship left the port of Miami (Right)
Bus fires: Burnt to the top within 10 min Burnt completely within 10 min
2. Why compartment fires present added danger? Compartment fires are quite different from those fires burning in the open air because of the walls and ceiling. When a fire occurs in free space, heat and smoke generated would be lost to the ambient ( ) rapidly. But for a compartment fire, most of the heat and smoke generated would be confined in the upper part of the compartment.
Outdoors, fire grows steadily. Indoors, trapped heat and smoke cause temperature to suddenly go up.
3. Ignition ( ) of a Compartment Fire ignition temperature oxidizer For ignition of a fire to occur, a fuel must be heated above its ignition temperature ( ) in the presence of sufficient oxidizer for a fire to occur. An ignition source is anything which can heat even a small portion of a fuel to its ignition temperature.
Smouldering Fires After ignition three kinds of fires may follow: After ignition three kinds of fires may follow: A fire in solid fuel which is heat-limited (energy-limited) or ventilation limited will smoulder. 3. Development of a Compartment Fire 3. Ignition ( ) of a Compartment Fire Flaming Fires 3.1 Smouldering Fires Glowing Fires
A Heat-limited Smouldering Fire
A Ventilation-limited Smouldering Fire
Fate of a Smouldering Fire The smouldering fire may eventually gain enough heat (through reflected radiation or enhanced ventilation) to burst into flames; Alternatively, the fire may self-extinguish due to radiant heat loss or lack of fuel or oxygen.
After Ignition Three Kinds of Fires May Follow: 3.2 Glowing Fires Glowing combustion is associated with the surface oxidation of carbonaceous ( ) materials or char. Glowing combustion differs from smouldering only in that thermal degradation of the parent fuel does not occur.
A Glowing Fire
Fate of a Glowing Fire: Glowing fire is normally of short duration and is apt to self-extinguish.
After Ignition Three Kinds of Fires May Follow: 3.3 Flaming Fires A flaming fire may develop immediately after ignition, particularly in cases of arson ( ), or may develop from a smouldering fire after a delay which may be hours.
A Flaming Fire
Fate of a Flaming Fire: The fire burn itself out without involving other items of combustible material; If there is enough fuel but inadequate ventilation, the fire may self-extinguish or continue to burn at a very slow rate dictated by the availability of oxygen; If there is sufficient fuel and ventilation, the fire may progress to full room involvement in which all exposed combustible surfaces are burning.
Temperature Time 4. Development of a compartment fire Flashover Growth stage (pre-flashover) Fully developed stage (post-flashover) Decay
4.1 Growth stage (Pre-flashover) (1) Average temperature is low. (2) Fire localization is small. In the growth or pre-flashover stage, the average compartment temperature is relatively low and the fire is localized in the vicinity of its origin.
4.2 Fully developed stage (post-flashover) (1) Average temperature is high. (2) The whole compartment is in fire. In the fully developed or post-flashover fire, all combustible items are on fire. Flames appear to fill the whole compartment and emerge from the windows and other ventilation ( ) openings. This may continue until the available fuel is consumed.
4.2 Fully developed stage (post-flashover)
4.3 Decay Stage Average T 80%T max The decay period is often identified as the stage of fire after the average temperature has fallen to 80% of its peak value. At this stage, fire becomes smaller and temperature drops lower due to the consumption of fuel.
4.4 Flashover Growth stage Fully developed stage Transition Flashover The transition is very short. So flashover is considered as an event not a stage. The transition ( ) is very short. So flashover is considered as an event not a stage. Temperature will increase quickly. Temperature can reach as high as During flashover, flames will spread rapidly from the area of localized burning to all the combustible surfaces within the room.
Once flashover has occurred in one compartment, its hardly for the occupants of the rest of the building to evacuate ( ). The duration from onset of burning to flashover is directly relevant to life safety within a buiding.
5. The Necessary Condition for Safe Evacuation Where t p is the time elapsed from ignition to the perception ( ) that a fire exists; t a is the time between perception to the start of the escape action; t rs is the time taken to move to a place of relative safety; t u is the time (from ignition) for the fire to produce untenable ( ) conditions at the location. t p + t a + t rs t u
6. Factors Affecting Fire Growth The nature, amount and distribution of the combustible contents; The size and shape the compartment; The width and height of the ventilation openings.
Ventilation Factor kg/minkg/min kg/skg/s or Here AH 1/2 is called ventilation factor.
Theoretical Deduction of the Ventilation Factor
kg/minkg/min kg/skg/s or Ventilation Factor
Control Forms of a Compartment Fire Fuel-controlled fire Ventilation-controlled fire Fuel Air (oxygen) Supply
/A f Kg/m 2 s m/A f kg/m 2 s
Influence of Ventilation on the Control forms of fire Fuel-controlled fire Ventilation- controlled fire
Fuel-controlled fire Ventilation- controlled fire Opening factor: a measure of the rate of temperature rise of a fire, defined as the ratio of the ventilation factor and the total bounding area of an enclosure. Opening factor: a measure of the rate of temperature rise of a fire, defined as the ratio of the ventilation factor and the total bounding area of an enclosure.
Summary 4. Factors Affecting Fire Growth (ventilation) 1. Introduction of compartment fire. 2. Explanation of why compartment fires are more dangerous than outdoor fires. 3. Ignition & development of a compartment fire. GrowthFully-developedDecay Flashover
Questions Definition: Compartment fire; ventilation factor Why indoor fires are more dangerous than outdoor fires? How many stages are there in the development of a compartment fire? What are they and what are the characteristics of each stage? What are the two control forms of the compartment fire? What is the difference between them?
Chapter 8 Compartment Fire Lesson 2 Flashover
Key Words & Phrases Flashover Fire plume Heat flux Pyrolyze (pyrolysis) Radiation feedback heat Structural failure Collapse Hose-line
Temperature Time Development of a compartment fire Flashover Growth period (pre-flashover) Fully developed period (post-flashover) Decay period
The term 'flashover' was first introduced by UK scientist P.H. Thomas in the 1960s and was used to describe the theory of a fire's growth up to the point where it became fully developed. 1. Definition of Flashover
The transition from a localized fire to the general conflagration ( ) within the compartment when all fuel surfaces are burning; The transition from a fuel ( ) controlled fire to a ventilation ( ) controlled fire; The sudden propagation ( ) of flame through unburnt gases and vapors collected under the ceiling. Most commonly used Definitions of flashover are as follows:
Definition of Flashover The International Standards Organisation (ISO) use a similar wording: "The rapid transition to a state of total surface involvement in a fire of combustible materials within an enclosure". Other Popular Definitions The definition of flashover is given in a British Standard as a: The definition of flashover is given in a British Standard as a: "Sudden transition to a state of total surface involvement in a fire of combustible materials within a compartment". (BS 4422, 1987) "Sudden transition to a state of total surface involvement in a fire of combustible materials within a compartment". (BS 4422, 1987)
Initial development of a Fire Plume ( ) in a Compartment. 2. Formation of flashover
A hot layer of smoke forms under the ceiling of the room. And it will produce radiation feedback heat.
When all the combustible surfaces reach a certain high T, they will pyrolyze and release flammable gases. When the temperature reaches a certain value, other combustible objects will pyrolyze ( ) and release pyrolysis gases.
There is a certain auto-ignition temperature (AIT) ( ) for a certain mixture of flammable gases. When T reaches the auto-ignition temperature of the flammable gases inside the room, suddenly, all the flammable gases and all the combustible surfaces will be on fire. The T will suddenly go up and it can exceed The T will suddenly go up and it can exceed The flames will fill the whole compartment and get out of the openings. The flames will fill the whole compartment and get out of the openings.
Flashover Fire Cases
Video 1: Flashover experiment
Fire in Bradford City Soccer Stadium, England, P1: first visible flames P2: 90 seconds P3: 150 seconds
3. Consequences of Flashover Great damage Large number of deaths and injuries Large number of deaths and injuries Trapped building occupants ( ) Firefighters Building structure Properties
3.1 Death and injury caused by flashover Flashover happens very suddenly. During flashover, fire grows so rapidly that people do not see the need for evacuation( ) until evacuation is impossible. Flashover usually leads to tripled( ) death in fire. Firefighters : If wearing full protective clothes, any firefighters caught in a compartment which reaches flashover still have seconds to evacuate. Most firefighting tragedies happen because most of time firefighters are too focusing on searching and rescuing others without noting that flashover is going to happen.
YearPlaceDeath 1981Dublin Los Angeles Petersburg Dusseldorf UK Paris 5 Death caused by flashover in some fire cases In the USA, NFPA statistics recorded between 1985 and 1994 demonstrated a total of 47 US firefighters lost their lives to 'flashover'. In the USA, NFPA ( ) statistics recorded between 1985 and 1994 demonstrated a total of 47 US firefighters lost their lives to 'flashover'.
Firefighters confronted a flashover. Firefighter caught inside a flashover.
Wooden beams ( ) will char ( ); Steel ( ) will be permanently weakened. Then it will expand and damage surrounding structural components ( ); Concrete ( ) and masonry ( ) will spall ( ) and may crack into pieces. 3.2 Great damage caused by flashover Great damage Building structure Properties Structural Failure
After those structural failures, the roof of a building will generally collapse ( ) first, due to the concentration of high temperature gases and flames at the top of the structure. The walls may follow. Firefighters must be aware that the building could collapse at any point after a compartment reaches flashover. Firefighters must be aware that the building could collapse at any point after a compartment reaches flashover.
Catastrophic Collapse of a Building
Video 2: Non-Flashover experiment Does flashover occur in all the compartment fires?
The Development of Fire With and Without Flashover
4. Fuel and Ventilation Conditions Necessary for Flashover
Fuel and Ventilation Conditions Necessary for Flashover 1. Mass burning rate: 2. Ventilation factor:
4. Criteria of flashover ( ) Based on the observations and measurements of compartment fires, different criteria of flashover were proposed: Radiation heat flux at floor level ( ) reaches 20kW/m 2 ; Gas Temperature at ceiling level ( ) reaches 600 ;
5. Three ways to delay flashover: Venting: By venting windows of a burning room you release the build up of heat in the room. This slows down flashover in addition to improving visibility in a smoke-filled room. Not venting: by not venting and instead closing the door to the burning room, you can also delay flashover. By not venting, you starve the fire of oxygen, which slows down the combustion rate and the build up of heat in the room. This may be done when there is a delay in stretching a hose-line and all persons are out of the burning room. Portable extinguisher: The use of a portable extinguisher can cool the heat down in a burning room temporarily and delay flashover.
The sudden lowering of the existing smoke layer (smoke interface). Sudden increases of heat forcing you to crouch low; 6. Warning signs of flashover Flames are running overhead on the ceiling; Flames are running overhead on the ceiling; Perception of rollover: Perception of rollover: Rollover is defined, as sporadic ( ) flashes of flame mixed with smoke at ceiling level. Rollover is defined, as sporadic ( ) flashes of flame mixed with smoke at ceiling level.
7. Point of no return The point of no return is a distance inside a burning room beyond which a searching firefighter will not escape and will not reach the door or window entered. How far inside a burning room can a firefighter be and still escape back out the door alive and not suffer serious bums after a flashover occurs? How far into the burning room that appears about to flashover should a firefighter go? Five feet is the point of no return after the room explodes into a flashover.
7. Point of no return 1. Fire temperatures of F cause intense pain and damage to exposed skin. ( ) 2. The average temperature in a room that flashes over is 1000' to 1500' F. ( ) 3. The average person moves 2.5-feet per second when walking 4. How long can a firefighter take 1000'-1500' F on the neck, ears, wrists and any other exposed portion of the body? Just two seconds. Five feet is the point of no return
8. Defensive Search Procedures: A firefighter should check behind the door for the victim, then enter the hallway or room not more than five feet, sweep the floor, look for unconscious persons, call out and listen for a response. If no response is forthcoming, close the door and wait for the hose-line. As the attack hose-line advances, conduct a search and rescue behind the line, searching room and space outward from the hose-line. A firefighter should check behind the door for the victim, then enter the hallway or room not more than five feet, sweep the floor, look for unconscious persons, call out and listen for a response. If no response is forthcoming, close the door and wait for the hose-line. As the attack hose-line advances, conduct a search and rescue behind the line, searching room and space outward from the hose-line. At a Doorway:
At a Window: If flames and signs of rollover are seen in the smoke, the firefighter should not enter the burning window. Instead the firefighter should crouch down below the heat and sweep the area below the windowsill ( ) with a tool. If flames and signs of rollover are seen in the smoke, the firefighter should not enter the burning window. Instead the firefighter should crouch down below the heat and sweep the area below the windowsill ( ) with a tool. In some instances a person may collapse at the window and fall right below the sill. If a victim is found, a firefighter on the ladder might be able to crouch below the heated smoke and flashes of flames mixed with smoke coming out the window and pull the victim to safety on the ladder. In some instances a person may collapse at the window and fall right below the sill. If a victim is found, a firefighter on the ladder might be able to crouch below the heated smoke and flashes of flames mixed with smoke coming out the window and pull the victim to safety on the ladder.
SUMMARY 1) Definition of flashover; 2) Formation of flashover; 3) Sequences of flashover; 4) Conditions Necessary for Flashover; 5) Criteria of flashover; 6) Three ways to delay flashover; 7) Warning signs of flashover; 8) Point of no return; 9) Defensive Search Procedures.
QUESTIONS 1. How does a flashover happen? 2. What are the necessary conditions for the occurrence of flashover? 3. What are the warning signs of flashover? 4. What are the two criteria of flashover? 5. What is the point of no return?
QUESTIONS 4. According to fire protection engineers flashover is caused by which one of the following? A. Radiation heat B. Radiation feedback heat A. Radiation heat B. Radiation feedback heat C. Conduction heat D. None of the above C. Conduction heat D. None of the above 5. Which one of the following is not a method used by firefighters to delay flashover? A. Venting to release heat A. Venting to release heat B. Not venting to starve the fire of oxygen and thus B. Not venting to starve the fire of oxygen and thus slow down heat generation slow down heat generation C. Use a portable extinguisher on the fire to cool it down C. Use a portable extinguisher on the fire to cool it down D. Remove combustible from the fire area D. Remove combustible from the fire area
REVIEW 1) Definition of flashover; 2) Formation of flashover; 3) Sequences of flashover; 4) Conditions Necessary for Flashover; 5) Criteria of flashover; 6) Three ways to delay flashover; 7) Warning signs of flashover; 8) Point of no return;
1. Definition of Backdraft The NFPA definition: The explosive or rapid burning of heated gases that occurs when oxygen is introduced into a building that has not been properly ventilated and has a depleted ( ) supply of oxygen due to fire." The IFE (Institution of Fire Engineers) definition: The IFE (Institution of Fire Engineers) definition: An explosion, of greater or lesser degree, caused by the inrush ( ) of fresh air from any source or cause, into a burning building, where combustion has been taking place in a shortage of air." An explosion, of greater or lesser degree, caused by the inrush ( ) of fresh air from any source or cause, into a burning building, where combustion has been taking place in a shortage of air."
Smoke Is Combustible
Limited ventilation can lead to a fire in a compartment producing fire gases containing significant proportions of partial combustion products and un- burnt pyrolysis products, which are all combustible. If these accumulate then the admission of air when an opening is made to the compartment can lead to a sudden deflagration. This deflagration moving through the compartment and out of the opening is a backdraft. A Basic Scenario
2. Formation of Backdraft 1) A fire burning in a room with poor ventilation 2) Accumulation of flammable gases 3) Air introduction at the breaking of openings 4) Formation of mixture within flammability limits 5) Ignition of the mixture 6) Explosion or deflagration and pressure rise
3. Conditions Nece s sary for Backdraft 1) The accumulation of smoke consisting of un- burnt pyrolyzates and incomplete combustion products in a poorly ventilated compartment. 2) Air introduction when windows or doors are opened or broken. 3) The newly formed mixture of air and flammable smoke is within its flammability limits ( ). 4) An ignition source of sufficient energy such as a flame, spark or glowing ember ( ). It is also possible for super-heated gases to ignite (auto- ignition), without a source of ignition being introduced.
Pressure rise due to backdraft will force the burning gases in the compartment out through the openings with a high velocity, possibly igniting some of the unburnt pyrolyzate ( ) that had already left the compartment. This can create a significant fire-ball outside the compartment. 4. Consequences of Backdraft
Backdraft Is a Kind of Explosion Explosions kill and injure firefighters in several ways. The blast ( ) can blow a firefighter across a street; flying glass and shrapnel ( ) can decapitate ( ) a firefighter; flame accompanying the explosion can cause serious burns and an explosion can collapse walls, partitions and iron shutters ( ), crushing firefighters beneath them.
4. Consequences of Backdraft Great damage Deaths and injuries ( Firefighters ) Deaths and injuries ( Firefighters ) Building structure Properties
Before opening a door or window to the compartment, the firefighter should be aware of: 1) A fire in a compartment with few openings that has been burning for some time. 2) Oily deposits ( ) in windows. 3) Pulsating ( ) smoke from openings. 4) Hot doors and door handles (windows); 5. Warning Signs of Backdraft
1) Blue flames (ghosting or dancing flames) in the hot gas layer. 2) Smoke drawn back through opening: 3) Whistling and roaring sounds It may be an indication that a backdraft is in progress at which stage there is probably little action that can be taken by a firefighter to prevent it. 5. Warning Signs of Backdraft When inside, or looking into a compartment a potential backdraft may be indicated by:
Smoke Drawn Back through Opening
Lessons Learned 1. These warning signs are important to know. 2. Firefighters must know that explosions happen fast, sometimes too fast for firefighters to take cover and protect themselves. The only real protection from the blast of a backdraft or a flashover is full protective gear: helmets( ), hoods( ), gloves( ), boots( ), bunker pants( ), coat and face mask( ). Protective fire gear may be hot, cumbersome ( ) and slow you down, but if you are caught in an explosion, it will determine whether you survive the blast and how serious your burns will be.
The Peru ( ) firefighters force entry just prior to the backdraft Amazing Peru Backdraft The Aftermath ( ) !!! An exterior defensive operation is mounted following the backdraft.
6. Preventing Death and Injury There are three tactics that can reduce the chances of getting caught in a backdraft: Venting ( ) Quenching ( ) Flanking ( )
6.1 Venting ( ) Venting a roof skylight ( ) over a burning room is one of the most effective methods of protecting firefighters from the blast of a backdraft. 1) When roof conditions permit, the quick removal of a glass skylight by firefighters can vent a smoke filled room and break up an explosive mixture. 2) Even if the smoke explosion occurs, the blast will be diverted upward out of the roof vent opening away from the firefighters advancing the hose-line.
Quenching: Before a superheated confined room is entered, charged hose-line should be positioned near the entrance. Firefighters in full protective equipment should immediately discharge ( ) a hose stream into a fire area when it is opened up. 1 This water can cool a potentially explosive atmosphere. 2 Before the air and searching firefighters enter a potentially explosive fire area, the stream of a powerful water discharge might break up the explosive atmosphere. 6.2 Quenching ( )
Firefighters in Australia get to grips with an 'entry & attack-module' trainer.
Flanking: When there can be no venting and the quenching of a quick dash of a hose stream is not possible, the officer in command can order two hose-lines into position, one on each side of a door or window of a burning room. After the hose lines are charged with water and firefighters are in full protective equipment, the door or window is broken. Both flanking hose lines, safely out of the path of any potential explosive blast coming out of the opening, can be directed into the burning room. ( ) 6.3 Flanking ( )
Tactical Firefighting Training Staffordshire County firefighters (UK) training with a backdraft demonstrator ( )
7. Backdraft and flashover, what is the difference? Flashover and backdraft are distinctly different events which occur in different ways. A flashover can occur in a compartment when a small localized fire rapidly develops into a fire involving all the combustible surfaces. In contrast a backdraft occurs after air is admitted to a poorly ventilated compartment and mixes with un- burnt pyrolysis products from the oxygen starved fire. Any ignition source, such as a glowing ember, can ignite the resulting flammable mixture. Expansion due to heat created by combustion can then expel burning gases out through the opening.
Differences There are four main differences: 1. First of all, backdraft does not happen often at fires as flashover does. You may experience only one or two during your entire career. Flashover - sudden full room involvement in flame - happens often. You will probably see one at your next fire.
2. A second difference is that a backdraft is an explosion; a flashover is not. There will be shock waves ( ) during a backdraft that will break the confining structure around the explosion. Windows may break, blasts of smoke and flame may blow out a doorway or a part of the structure may collapse. Flashover is rapid fire development, but it stops short of an explosion's speed of chemical reaction. Differences
3. The triggering or cause of them. Differences Flashover: a heat induced development of the fire Backdraft: a ventilation induced ignition of the gases Air introduction sets off the backdraft explosion. As firefighters enter a confined smoke filled area and bring fresh air with them, sometimes a backdraft or smoke explosion happens; The trigger of a flashover is heat. The theory of flashover is that heat, which is re-radiated back into a burning room, raises the gases and furnishings in the room to the auto- ignition temperature and triggers a flashover.
4. The stage of fire growth in which they occur. Backdraft explosions occur when there is smoke in a confined space that is during the first and third stage of a fire. During the growth and decay stages, smoldering can take place and generate explosive CO gas; Flashover, on the other hand, only occurs in the growth stage of a fire and signals the end of the growth stage. Differences
Flashover or Backdraft?
The backdraft that blew apart an Illinois church on February 9th, 2004 has been named the largest backdraft ever documented in the U.S. The firefighters determined it was too hot and smokey to enter the church basement, so they opened the ground level windows. The door to the basement felt cold but suddenly blew out when the backdraft occurred. A Backdraft Case
Riddle had been in his command vehicle when the backdraft occurred. "I heard the noise and I looked up... this piece of roof was just being removed - it went up about 10 feet and then came back down," he said. There was no warning except that immediately before he blast, The guys on the scene said they heard a sucking ( ) sound," Riddle said. The backdraft blew the roof off the Church and knocked flat the eight firefighters on scene and two firefighters were injured. A firefighter who had felt the door suffered burns to his hand because he had taken his glove off. Another firefighter was blown out of the cab of the engine, and another was blown across an alley.
1. Definition of backdraft 2. Formation of backdraft 3. Conditions Necessary for Backdraft 4. Consequences of Backdraft 5. Warning Signs of Backdraft 6. Preventing Death and Injury 7. The differences between Backdraft and flashover. SUMMARY
QUESTIONS 3. What are the differences between a backdraft and flashover? 2. What are the three firefighting tactics that can reduce destructive effects of a backdraft explosion? 1. What are the warning signs of a backdraft?
Chapter 8 Compartment Fire Lesson 4 The Production and Movement of Smoke
1. Definition of Smoke Gross et al define smoke as the gaseous products of burning organic materials in which small solid and liquid particles are also dispersed. The visible volatile ( ) products from burning materials. (Shorter Oxford English Dictionary) The airborne ( ) solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion. Together with the quantity of air that is entrained ( ) or otherwise mixed into the mass. NFPF,1993c
2. Important Features of Smoke Two important features of smoke are that: Smoke contains toxic products of combustion. Smoke reduces visibility.
2.1 Reduced Visibility With very few exception, particulate ( ) smoke is produced in all fires. The effect of reduced visibility will delay escape and increase the duration of exposure of the occupants of a building to the products of combustion.
1) Toxic gases, such as HCN (Hydrogen cyanide) and CO. 2) Soot in the form of smoke aerosol ( ). The carbon particles of the soot are persistently deposited on the alveolar ( ) and bronchiolar ( ) surface. 3) Sensory irritants ( ) in the smoke. The irritants include notably acrolein ( ) and hydrogen chloride (HCl) that lead rapidly to functional impairment ( ). Acrolein has a synergistic ( ) role in the toxicity of carbon particles in addition to its directly toxic lung effects. 2.2 Toxicity of Smoke
What is important is the dose inhaled---in simple terms, the concentration-time product (Ct). If Ct exceeds a certain value (the effective dose which causes incapacitation or death), then the person is unlikely to escape unaided. Short exposure to high concentration of narcotic ( ) gases such as CO, or too long duration exposure to low concentrations are of the same hazard.
The two factors are generally related. Dense smoke is usually highly toxic and reduces visibility substantially. The length of exposure will increase if the visibility is poor, or if the combination products contain eye and/or respiratory irritants ( e.g. HCl hydrogen chloride) Indeed, statistics collected in the UK and the US suggested that more than 50% of all fatalities ( ) can be attributed to the inhalation ( ) of particulate ( ) smoke and toxic gas (Home Office 1995; NFPA 1997)
Smoke Influences Safe Evacuation t p + t a + t rs t u Smoke conditions have great influence on t rs The effect of reduced visibility will delay escape and increase the duration of exposure of the occupants of a building to the toxic products of combustion. Smoke conditions have great influence on t rs The effect of reduced visibility will delay escape and increase the duration of exposure of the occupants of a building to the toxic products of combustion. The Necessary Condition for Safe Evacuation:
Huge plumes of thick smoke and flames engulf the upper half of the 56-floor East Tower in Caracas, Venezuela, October (Reuters Photo). 25 people were injured due to the inhalation of smoke.
3. Production of Smoke Smoke can be produced by Flaming fire Smouldering fire 1) Smoke from smouldering fire: The high molecular weight fractions condense as they mix with cool air to give an aerosol consisting of minute droplets of tar ( ) and high-boiling liquids. If they deposit on surfaces, they will give an oily look.
2) Smoke from flaming combustion: Smoke from flaming combustion is different in nature and consists almost entirely solid particles. Most of them are formed in the gas phase as a result of incomplete combustion and high temperature pyrolysis reactions at low oxygen concentrations. Particulate matter can be generated even if the original fuel is a gas or a liquid.
Common Combustion Product Concentrations in Residential Fires *Particulates are given as mg/m 3. IDLH stands for a concentration defined as immediately dangerous for life and health.
4. Smoke Movement The substantial majority of fire fatalities can be attributed to the inhalation of smoke and toxic gases. While a large number of them are found at points remote from the fire due to quick movement of smoke.
4.1 Forces Responsible For Smoke Movement For the movement of smoke within a building, the driving forces are as follows: Buoyancy generated directly by the fire; Buoyancy arising from differences between internal and external ambient temperature; Effect of external wind and air movement; The air handling system within the building.
4.2.1 Pressure Generated Directly by the Fire Burning in a compartment generates high temperatures which produce buoyancy forces responsible for hot fire gases being expelled through the upper portion of any ventilation opening. Smoke also moves due to the expansion of the hot gases.
Pressure Generated Directly by the Fire
Density of Air as a Function of Temperature Temperature (K)Density (kg/m 3 )
4.2.2 Pressure Differences due to Natural Buoyancy Forces
Chimney/Stack Effect The stack effect in tall buildings: (a) external temperature (T 0 ) T i, showing accompanying flows.
Chimney Effect The tendency of heated air or gas to rise in a duct or other vertical passage, such as in a chimney, stairwell, or building, due to its lower density compared to the surrounding air or gas.
Stack Effect The effect of stack on the movement of smoke in a high-rise building (T i > T 0 )
Smoke movement caused by fire in shaft. Smoke movement caused by stack action in heated building (a) low-level fire (b) upper-level fire
The Height of the Neutral Plane neutral plane
4.2.3 Pressure Differences Generated by Wind Wind blowing against a building will produce higher pressure at the windward side and will tend to create air movement within the building towards the leeward side where pressure is lower. The magnitude of the pressure difference is proportional to the square of the wind velocity. The pressure at surface of a building is given by:
4.2.4 Pressure Differences Caused by Air Handling System Many modern buildings contain air handling systems for the purpose of heating, ventilation and air-conditioning (HVSC). While the fans are idle, the ductwork can act as a network of channels through which smoke will move under the influence of the forces discussed above, including particularly the stack effect in multi-story buildings.
This will promote the fire spread throughout the building, an effect which can be even greater if the system is running when fire breaks out. Should fire occur anywhere in that part of the building served by HVAC system, this situation can be avoided by automatic shutdown, activated by smoke detector Pressure Differences Caused by Air Handling System
5. Smoke Control System Smoke extraction There are two basic approaches that may be adopted at the design stage to prevent lethal ( ) concentration of smoke accumulating in certain areas of a building to protect its occupants: Smoke containment Smoke containment Physical barriers such as walls, windows and doors, as well as smoke curtain. Natural venting Manual venting Smoke reservoirs Pressurization
5.1 Smoke Control in Large Spaces 1) To vent the smoke by creating an opening in the roof. Improvement of visibility Prevention of flashover and backdraft For undivided single-story building The number, size and location of vents necessary for efficient venting can be calculated considering: The size of the fire; the height of the building; the type of roof; and the pressure distribution over the roof.
2) Use of smoke curtain or screen ( ) under the ceiling. Smoke curtain will not only limit the spread but also allow the smoke to build up a buoyancy head below the ceiling which will enhance the flow through the vent.
If there is a positive pressure on the roof, created by the wind, then the effectiveness of the venting will be largely reduced: if this pressure is too great, the vent may operate in reverse.
5.2 Smoke Control in Shopping Centers Should a fire develop in a shopping center, the mall would become smoke-logged very quickly. Then there are two methods of controlling this situation: 1) Vent the smoke directly from the shop to the outside; 2) Provide smoke reservoirs fitted with automatic ventilators in the ceiling of the shopping mall.
A FULLY INTEGRATED SMOKE CONTROL SYSTEM Natural Smoke Control Products Casement ventilators Louvred ventilators Single Panel ventilators Double Panel ventilators Moveable louvres Attenuated ventilators Powered Smoke Control Products Powered extract fans In-line powered extract fans Smoke Curtain Systems Fixed and retractable
Operation of a vent in the absence of a substantial buoyant head (thin smoke layer). The same effect will occur with a deep layer if the area of vent is too large.
5.3 Smoke Control on Protected Escape Routes 1) Smoke doors between the fire and protected escape route will help smoke back but this relies on: A. the door being closed at the time of fire B. persons using the door to reach the escape route not keeping the doors open for a prolonged period.
2) Pressurization. One is to pressurize the escape route sufficiently so that even under most unfavorable conditions smoke will not enter as there is a net flow of air from the escape route into the adjacent spaces. Early studies show that the differentials of N/m 2 would be sufficient to overcome the worst conditions that might naturally (stack effect and wind), although with a very tall building the stack effect might override even this. In British Standard Code of Practice, a pressure differential of 50 Pa is called under emergency conditions.
5.3 Smoke Control on Protected Escape Routes
Pressurized Escape Route
1. Definition of smoke 2. Important Features of Smoke 3. Production of Smoke 4. Forces Responsible For Smoke Movement 5. Smoke Control System SUMMARY
QUESTIONS 1. chimney effect 2.What are driving forces responsible for the smoke movement? 3. What are the basic approaches to control the movement of smoke? 4. For a 30 m high building, if the ambient temperature T 0 is 290K and the temperature inside the building T i is 700K, then how much the pressure difference would be between the inside and the outside of the building?
Chapter 8 Lesson 5 Study on the compartment fire
Key Words & Phrases Simulator Modeling Thermocouple Electronic balance Pressure regulator Pressure gauge Hatch Data/image acquisition system / Water mist Rotameter
Key Words & Phrases Slot Contour Diesel oil Exhaust system / Digital thermometer Voltage regulator Valve Transformer
Bench Scale Fire Test Compartment Fire Research Lab
Intermediate Scale Fire Test Pacific Fire Laboratory, Inc.
Intermediate Scale Fire Test
Full Scale Fire Test Department of Fire Protection Engineering, University of Maryland
Real Scale Fire Test The University of Tokyo & Building Research Institute, Japan
2. Study on flashover
1. A box with opening 3. An electronic Balance ( ) 4. A printer ( ) 2. A tray ( ) 5. Signal detector ( ) ~ Thermal couples ( )
Use of Each Device Tray ( ): combustible materials will be put on the tray. (PMMA, polymethyl methacrylate, ) Electronic balance ( ): Detect the mass change ( ) during the fire process. Printer Print out the detected mass change. Signal detector ( ): Detect the temperature and radiation heat flux ( ) both inside and outside the compartment.
1. This box can be disassembled. That means we can change the material of its walls and ceiling. The building materials of the walls and ceiling 2. Both the width and height of the door can be adjusted. The height, width and localization of the opening
3. Different materials of different mass ( ) can be put on the tray and used as combustible material. The kinds of combustible materials The amount of combustible materials 4. Besides the above influencing factors, using this equipment, we can also study the mass burning rate during process of each compartment fire.
3. Study on backdraft
Study is concentrated on the following issues: 1. The opening geometries: six end opening geometries and two ceiling opening geometries. 2. The experimental variables included the fuel flow rate, the time during which the fuel was burned. 3. The quantities recorded before backdraft included temperature and the concentrations of oxygen, carbon dioxide, and carbon monoxide. 4. The gas velocities in the opening and also the pressures in the compartment were measured. 3. Study on backdraft
Study results: 1. The mass fraction of unburned fuel, whose critical value varies with the opening geometry, is a key parameter determining the occurrence of backdraft. 2. In addition, the experimental results using water mist, generated by a downward-directed pressure nozzle that was operated at pressure of 0.2 MPa, to mitigate backdraft are presented. The experimental results show that water mist is an effective mitigating tactic able to suppress backdraft in a compartment primarily by means of diluting the gas in the compartment and reducing the mass fraction of unburned fuel, rather than by a thermal mechanism of cooling. 3. Study on backdraft
4. Study on smoke movement
Evaluation of CFD to predict smoke movement in complex enclosed spaces
Figure F.6 - Temperature distribution and velocity vectors 2 metres above the ground, 120 seconds after ignition.
6. Modeling Smoke Visibility in CFD
Distribution of smoke mass fraction in the center plane of the room.