Luyện nói tiếng Anh bằng Shadowing qua video: An Introduction to Flashover - Episode 9
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G'day everyone my name is Matt and welcome back to The Fire Show.
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So far in the series we've covered a range of different topics including the fact that smoke burns, pyrolysis, formability range, spontaneous combustion and heat transfer.
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In today's episode we're going to be talking about flashover which is a combination of all of these elements.
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So if you haven't seen those videos I suggest you go back
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and have a quick look at them first and then come back to this one.
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Now flashover is a term that gets thrown around a lot by firefighters
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and sometimes it gets used correctly and sometimes it gets used incorrectly.
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Now, without wanting to get too bogged down in the specifics of terminology,
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we're going to have a quick look at what the actual term flashover is referring to
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and then we're going to have a look at how it actually occurs
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and what we can do to start reading it
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and what we can do to actually stop it from occurring in the first place.
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Now, a textbook example of flashover is the transition from a localised fire to the general conflagration within the compartment
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when all fuel surfaces are burning.
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and if you're wondering what conflagration means it's basically just a fancy word for fire
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if we wanted a much simpler definition for flashover we could say
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it's the transition from a fire within a room to a room
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that is entirely on fire now for an example of
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that transition what we have is a fire burning in the corner of the room here
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and as that fire begins to grow it pumps more
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and more heat and flames and smoke into that overpressure above the fire
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and this is really important because as
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that smoke layer begins to build up
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it radiates a of heat back down on all the fuels in the room
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and as all of those fuels begin to heat up they get closer
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and closer to their auto ignition temperature until a point where everything in
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that room catches on fire at around about the same time and we see what's called a flashover
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so what we're going to do is go ahead
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and talk about how this actually happens
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and how we can begin to read the signs that are actually indicating that a flashover is imminent
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and in fact what we can actually do about it now
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flashover is no different to any other fire where it actually relies on a combination of heat,
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fuel, oxygen and a chemical reaction so it can actually occur.
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But if we think about it in these terms, it does make flashover easier to understand.
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Now if we have a look at this room, we can see that the fuel is coming from the couch
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and the TV and the carpet and the walls and those kinds of things.
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The oxygen is already present in the room when the fire starts, it's coming from the air that's already present in the room,
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and in fact it's coming from the air that's being drawn in through the door as the fire burns.
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now the heat actually comes from the fire itself
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and as it starts to burn it pushes more heat
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and smoke and flame up into that over pressure area
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and by the process of convection that heat spreads out across the room
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and can actually start to move into other rooms because
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that convection current takes hold
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and what we actually see is cold air being drawn in through the door
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while smoke will actually start to push out through the top of the door and
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while this process is actually happening what we're seeing is a
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lot of heat being radiated back down on everything in the room
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which is slowly starting to heat all of these things up
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and in fact for most fuels approximately 30 percent of the
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heat liberated in the flame is radiated to the environment
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and the rest is actually dispersed convectively in the buoyant flume now this actually means
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that around about 70 of the heat produced by the fire is actually being transported by the convection current
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which means that 70 % of the heat is actually being moved up
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and away from the fire and is therefore available to actually heat up other objects throughout
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that room and throughout the building
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so as the convection current moves through the building it radiates heat down on all of the fuels
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that are confined within that area
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and as those fuels begin to heat up they then start to pyrolysis
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and the fuels will start to pyrolysis at different temperatures depending on what they're made of for instance
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if it's a natural fiber, it's going to pyrolicize at a much higher temperature than if it's an artificial fuel,
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such as a plastic or a foam.
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Now, as they start to pyrolicize, they're releasing more and more fuel into that atmosphere, which is then available for the fire to burn.
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Now, some studies have shown that at a ceiling temperature of approximately 600 degrees centigrade, flashover can occur.
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And a reason for this can be found in the auto -ignition temperature for carbon monoxide, which is about 609 degrees so as we're seeing
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that ceiling temperature get up to around about
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that 600 degree level we're seeing the carbon monoxide in the smoke spontaneously combust
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which then increases the heat release rate greatly
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and then we see a rapid progress towards flashover as a result
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now this is actually an early warning sign for flashover flames in the overpressure region is actually showing
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that we're reaching that 600 degrees and
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that flashover isn't very far away now the next thing we start to see is all of our fuels
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which are pyrolysis are starting to reach their auto ignition temperature which means
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that we're getting very close to the point where all of
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those pyrolysis gases are simply going to burst into flames on their own accord even
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if there is no direct flame impinging from the fire itself
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now this is where the fire triangle comes back into it
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because if we don't have our mixture of heat fuel
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and oxygen we simply can't get the chemical reaction
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that starts our flashover now in the room we know
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that we have our heat because our ceiling temperature is reaching around about
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that 600 degrees level we're seeing the flames in
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that overpressure our fuel is everywhere it's been readily pyrolysis by the fire
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and we're seeing all of our couches and walls and floors
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and all these sorts of things releasing all of these pyrolysis gases
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so the the final variable is oxygen now oxygen is something
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that is very variable within a structure fire whether the fire is in a fuel controlled
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or a ventilation controlled state we're going to be talking about fuel controlled
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and ventilation controlled more in a later episode but it's important to note
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that oxygen is a really key component to a structure fire actually occurring
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and a lack of oxygen can actually stop a flashover happening
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altogether whereas the addition of more oxygen can actually cause flashover to happen faster
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and this is why it's really important that
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when we actually make entry to a building we do so
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when we're ready to actually get in and apply water to
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that fire without actually allowing it to get in excess of oxygen before we actually suppress that fire.
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Now our fire has continued to burn and we're seeing more
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and more of these pyrolysis gases starting to come out of our fuels
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and we're also starting to see more and more of
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that flame activity above the overpressure which is indicating
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that it's at least 600 degrees
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now the next step is we're going to start to see these fuels reach their auto ignition temperature
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and they're going to spontaneously combust
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now they're not necessarily going to do it all at the same time we're going to see the objects
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that are more vulnerable or higher in the room
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spontaneously combust first then we're very quickly going to see the others spontaneously combust
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and we're going to see that transition from the fire within a room to a room
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that is entirely on fire and this is what we refer to as flashover it's
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that transition from a fire within a room which is feeding
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that convection current to a room that is entirely on fire
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and that's where we see our heat release rate increase rapidly to a very large extent
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and in fact after flashover has occurred temperatures of 900 to 1100 degrees celsius can be reached throughout the room
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now after flashover has occurred there is a lot more heat being generated from the fire
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because there's simply a lot more fire being created
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because we've got an entire room that's on fire rather than just a small section of that room.
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Now the result of which is all of these fire gases
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and all of this heat have to go somewhere and
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so they're going to be heading out of whatever openings they can find
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and generally that's going to be a door or a window
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and you can see here that once our room is flashed over all
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that heat that's being generated quickly starts to heat up the next room and then the room after that.
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So flashover isn't a single occurrence.
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What we actually see in a house fire is one room will flash over
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and then another and then another
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and all of this of course is based on how much air
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that is available to allow that combustion process to fully oxidize those fuels.
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Now this means that flashover really does rely on the three sides of the fire triangle,
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meaning we really need that heat to be radiating down on our fuels
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so that they can start to pyrolysis and reach their auto -ognition temperature.
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We also need the oxygen to allow that combustion process to occur
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and of course we need the fuel because without the fuel itself there's nothing for this process to affect.
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Now
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if we were to talk about some important signs of flashover
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we will be talking about a lowering of the neutral plane
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or that smoke layer as some people will call it we're going to be seeing
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that smoke layer become more and more unstable in the process as well
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because it's going to be needing to try
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and even itself out between the hot overpressure gases and the cold or under pressure gases as the air comes in
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we're going to be seeing objects
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and surfaces around the room start to emit pyrolysis gases as they heat up
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and break down and this is a really late sign as well
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if there's things pyrolysis around the room you know
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that they're being heated to a really extreme extent and that flashover isn't far away.
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We've also talked about flames in the overpressure and we know
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that that's a really late indicator that flashover isn't far away
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and it's really important that
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if we're seeing those flames in the overpressure
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we cool those gases down otherwise we're going to start to see a really rapid progression to flashover.
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Now of course with those really high temperatures above the neutral plane
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we're also going to be getting some really intense and painful radiant heat.
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So if we're in a fire and being force down by the heat, that's a really good indicator that flashover isn't far away
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and we really need to cool those gases down so
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that we can try to create a safer environment for ourselves to work in.
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And while cooling these gases down is really important to ensure
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that we can actually maintain our environment and actually have a safer working environment
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while we try and make our way to the fire, once we reach the fire we need to make sure
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that we attack it in an aggressive manner because the longer we leave it,
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the more it's going to be able to pump out these hot fire gases
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and the more that
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that convection current is going to be pushing hot fire gases throughout the building
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and radiating heat down on all of the fuels and allowing that fire to progress
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so now we've seen how flashover works and we know what some of the signs are
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I'm just going to play a video
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so we can actually follow a fire all the way through from a developing fire all the way through to flashover.
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And we'll actually see quite a lot of these indicators as we go through.
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Now bearing in mind outside the box is quite windy
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so we actually do struggle to get a nice stable neutral plane and a number of points of this fire.
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But that's just because the box is really quite small and it was a fairly windy day.
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Transcription by CastingWords Thank you.
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We'll be right back.
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Thank you.
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Transcription by CastingWords Thank you.
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All right, so now we've seen how flashover works, and we've also seen that it's not really a rare occurrence.
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In fact, it happens at pretty well every structure fire that continues on to being fully involved.
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We've also seen that it's not just one flashover.
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In fact, that each and every room in that house or the building can actually flashover, which is why it's really important that as firefighters,
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when we're entering into these buildings, we're actually looking for the signs of flashover so
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that we can predict the fire's growth and actually act accordingly and actually suppress that fire while keeping ourselves safe.
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And it's only through regular training
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that we're actually going to get used to actually looking for these signs and then acting accordingly.
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Alright well that's it for this one thanks very much for watching and I'll catch you in the next one.
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Bye!
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Từ vựng và ghi chú luyện nói cho bài học này
Bài luyện nói này dựa trên video “An Introduction to Flashover - Episode 9”. Những từ được nhắc lại nhiều nhất trong bài: flashover, heat, fuel, gases, temperature. Video này có 182 câu và 2333 từ để luyện shadowing. Phần lời nói dài 14:07. Người nói nói với tốc độ tự nhiên, khoảng 165 từ mỗi phút, gần với hội thoại hằng ngày. 85% số từ nằm trong 3.000 từ tiếng Anh thông dụng nhất; phần còn lại nên xem trước khi luyện.
Từ vựng quan trọng trong video
15 từ đáng học trong video, kèm phiên âm và nghĩa:
| Từ | Phiên âm | Nghĩa |
|---|---|---|
| oxygen danh từ | /ˈɑksɪd͡ʒən/ | ôxy, dưỡng khí |
| flame danh từ | /fleɪm/ | ngọn lửa |
| occur động từ | /əˈkɜː/ | xảy ra |
| automobile danh từ | /ˈɔː.tə.məˌbil/ | xe hơi, ô tô |
| layer danh từ | /ˈleɪ̯ɚ/ | lớp |
| neutral tính từ | /ˈnuː.tɹəl/ | trung lập |
| ceiling danh từ | /ˈsilɪŋ/ | trần, trần nhà |
| rely động từ | /ɹɪˈlaɪ/ | tin cậy, dựa vào |
| pump danh từ | /pʌmp/ | bơm |
| generate động từ | /ˈd͡ʒɛn.ə.ɹeɪt/ | sinh ra, gây ra |
| couch danh từ | /ˈkaʊ̯t͡ʃ/ | đi văng, đi-văng |
| triangle danh từ | /ˈtɹaɪˌæŋɡəl/ | tam giác, hình tam giác |
| windy tính từ | /ˈwɪn.di/ | có gió |
| topic danh từ | /ˈtɑpɪk/ | chủ đề |
| stable danh từ | /ˈsteɪ.bəl/ | chuồng, chuồng ngựa |
Cụm động từ bạn sẽ nghe
| Từ | Nghĩa |
|---|---|
| break down động từ | hỏng, hỏng hóc |
| go back động từ | trở lại |
Ngữ pháp trong video
Những cấu trúc người nói dùng nhiều nhất, kèm đúng cụm từ trong video:
| Cấu trúc | Trong video |
|---|---|
| Thì hiện tại hoàn thành have/has + quá khứ phân từ — việc đã xảy ra nhưng còn liên quan đến hiện tại | we've covered · haven't seen · have shown |
| Câu bị động be + quá khứ phân từ — nhấn vào việc xảy ra, không phải người làm | being drawn · being radiated · is radiated |
| Mệnh đề quan hệ who / which + mệnh đề — thêm thông tin về người hoặc vật | flashover which is · atmosphere, which is · monoxide, which is |
Phát âm cần chú ý
Người nói dùng 54 dạng rút gọn, ví dụ we're, we've, they're. Hãy nói theo dạng ngắn đúng như bạn nghe.
- Âm “sh” và “zh”: transition /tɹænˈzɪʃ.ən/, ignition /ɪɡˈnɪʃən/, flash /flæʃ/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, transcription /tɹænˈskɹɪpʃən/
- Từ dài — đặt trọng âm cho đúng: automobile /ˈɔː.tə.məˌbil/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, accordingly /əˈkɔɹ.dɪŋ.li/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/
Những âm người Việt thường gặp khó:
- Cụm phụ âm cuối — đọc đủ từng âm, đừng nuốt âm cuối: extent /ɪkˈstɛnt/, pump /pʌmp/, occurrence /əˈkɜɹ.əns/, intense /ɪnˈtɛns/, component /kəmˈpoʊ.nənt/
- Âm /tʃ/, /dʒ/ và /ʒ/ — tiếng Việt không có, đừng đọc thành “ch” hay “gi”: oxygen /ˈɑksɪd͡ʒən/, combustion /kəmˈbʌs.t͡ʃən/, generate /ˈd͡ʒɛn.ə.ɹeɪt/, couch /ˈkaʊ̯t͡ʃ/, mixture /ˈmɪkst͡ʃɚ/
- Âm /æ/ — mở miệng rộng hơn âm “e”: transition /tɹænˈzɪʃ.ən/, flash /flæʃ/, rapid /ˈɹæp.ɪd/, variable [ˈvæɹ.i.ə.bl̩], triangle /ˈtɹaɪˌæŋɡəl/
Cách luyện với video này
- Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
- Bắt đầu ở tốc độ 0,75×, nói đuổi từng câu, rồi quay lại tốc độ bình thường khi đã quen.
- Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như oxygen, flame, occur.
Phương Pháp Shadowing Là Gì?
Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.