Prática de Shadowing: An Introduction to Flashover - Episode 9 - Aprenda a falar inglês com vídeo
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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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Vocabulário e dicas de fala para esta lição
Esta aula de conversação usa o vídeo “An Introduction to Flashover - Episode 9”. As palavras que mais se repetem: flashover, heat, fuel, gases, temperature. Este vídeo tem 182 frases e 2333 palavras para praticar shadowing. A fala dura 14:07. O falante fala em ritmo natural, cerca de 165 palavras por minuto, próximo de uma conversa do dia a dia. 85% das palavras estão entre as 3.000 mais comuns do inglês; vale a pena estudar o restante antes de começar.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| oxygen substantivo | /ˈɑksɪd͡ʒən/ | oxigênio, oxigénio |
| flame substantivo | /fleɪm/ | chama, flama |
| occur verbo | /əˈkɜː/ | ocorrer, acontecer |
| transition substantivo | /tɹænˈzɪʃ.ən/ | transição |
| automobile substantivo | /ˈɔː.tə.məˌbil/ | automóvel, carro |
| ignition substantivo | /ɪɡˈnɪʃən/ | ignição |
| layer substantivo | /ˈleɪ̯ɚ/ | camada |
| neutral adjetivo | /ˈnuː.tɹəl/ | neutro |
| ceiling substantivo | /ˈsilɪŋ/ | teto |
| indicator substantivo | /ˈɪn.dɪˌkeɪ.tə(ɹ)/ | indicador |
| combustion substantivo | /kəmˈbʌs.t͡ʃən/ | combustão, queima |
| extent substantivo | /ɪkˈstɛnt/ | extensão |
| flash verbo | /flæʃ/ | lampejar |
| refer verbo | /ɹɪˈfɜː/ | encaminhar |
| rapid adjetivo | /ˈɹæp.ɪd/ | rápido |
Phrasal verbs que você vai ouvir
| Palavra | Pronúncia | Significado |
|---|---|---|
| go ahead verbo | /ˌɡoʊ əˈhɛd/ | vai em frente |
| go back verbo | voltar | |
| spread out verbo | espalhar-se |
Gramática neste vídeo
As estruturas que o falante mais usa, com as palavras exatas do vídeo:
| Estrutura | No vídeo |
|---|---|
| Present perfect have/has + particípio passado — uma ação passada que ainda importa agora | we've covered · haven't seen · have shown |
| Voz passiva be + particípio passado — o foco está no que acontece, não em quem faz | being drawn · being radiated · is radiated |
| Orações relativas who / which + oração — informação extra sobre uma pessoa ou coisa | flashover which is · atmosphere, which is · monoxide, which is |
Pronúncia para ficar de olho
O falante usa 54 contrações e formas reduzidas, como we're, we've, they're. Diga-as na forma curta, do jeito que você ouve.
- Os sons de “sh” e “zh”: transition /tɹænˈzɪʃ.ən/, ignition /ɪɡˈnɪʃən/, flash /flæʃ/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, transcription /tɹænˈskɹɪpʃən/
- Palavras longas — acerte a sílaba tônica: automobile /ˈɔː.tə.məˌbil/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, accordingly /əˈkɔɹ.dɪŋ.li/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/
Sons difíceis para falantes de português:
- Consoante final — sem acrescentar um “i” depois: extent /ɪkˈstɛnt/, rapid /ˈɹæp.ɪd/, indicate /ˈɪndɪˌkeɪt/, pump /pʌmp/, generate /ˈd͡ʒɛn.ə.ɹeɪt/
- /l/ final — a língua toca o céu da boca, não vira “u”: automobile /ˈɔː.tə.məˌbil/, neutral /ˈnuː.tɹəl/, triangle /ˈtɹaɪˌæŋɡəl/, stable /ˈsteɪ.bəl/, artificial /ˌɑː.tɪˈfɪʃ.əl/
- s + consoante no início — sem um “i” antes: stable /ˈsteɪ.bəl/, spontaneous /spɑnˈteɪ.ni.əs/, spontaneously /spɑnˈteɪ.ni.əs.li/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Comece na velocidade 0,75×, faça shadowing frase por frase e volte à velocidade normal quando ficar fácil.
- Grave a sua voz e compare com o original, prestando atenção a palavras como oxygen, flame, occur.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.