跟讀練習: An Introduction to Flashover - Episode 9 - 通過影片學習英語口語

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G'day everyone my name is Matt and welcome back to The Fire Show.

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.

In today's episode we're going to be talking about flashover which is a combination of all of these elements.

So if you haven't seen those videos I suggest you go back

and have a quick look at them first and then come back to this one.

Now flashover is a term that gets thrown around a lot by firefighters

and sometimes it gets used correctly and sometimes it gets used incorrectly.

Now, without wanting to get too bogged down in the specifics of terminology,

we're going to have a quick look at what the actual term flashover is referring to

and then we're going to have a look at how it actually occurs

and what we can do to start reading it

and what we can do to actually stop it from occurring in the first place.

Now, a textbook example of flashover is the transition from a localised fire to the general conflagration within the compartment

when all fuel surfaces are burning.

and if you're wondering what conflagration means it's basically just a fancy word for fire

if we wanted a much simpler definition for flashover we could say

it's the transition from a fire within a room to a room

that is entirely on fire now for an example of

that transition what we have is a fire burning in the corner of the room here

and as that fire begins to grow it pumps more

and more heat and flames and smoke into that overpressure above the fire

and this is really important because as

that smoke layer begins to build up

it radiates a of heat back down on all the fuels in the room

and as all of those fuels begin to heat up they get closer

and closer to their auto ignition temperature until a point where everything in

that room catches on fire at around about the same time and we see what's called a flashover

so what we're going to do is go ahead

and talk about how this actually happens

and how we can begin to read the signs that are actually indicating that a flashover is imminent

and in fact what we can actually do about it now

flashover is no different to any other fire where it actually relies on a combination of heat,

fuel, oxygen and a chemical reaction so it can actually occur.

But if we think about it in these terms, it does make flashover easier to understand.

Now if we have a look at this room, we can see that the fuel is coming from the couch

and the TV and the carpet and the walls and those kinds of things.

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,

and in fact it's coming from the air that's being drawn in through the door as the fire burns.

now the heat actually comes from the fire itself

and as it starts to burn it pushes more heat

and smoke and flame up into that over pressure area

and by the process of convection that heat spreads out across the room

and can actually start to move into other rooms because

that convection current takes hold

and what we actually see is cold air being drawn in through the door

while smoke will actually start to push out through the top of the door and

while this process is actually happening what we're seeing is a

lot of heat being radiated back down on everything in the room

which is slowly starting to heat all of these things up

and in fact for most fuels approximately 30 percent of the

heat liberated in the flame is radiated to the environment

and the rest is actually dispersed convectively in the buoyant flume now this actually means

that around about 70 of the heat produced by the fire is actually being transported by the convection current

which means that 70 % of the heat is actually being moved up

and away from the fire and is therefore available to actually heat up other objects throughout

that room and throughout the building

so as the convection current moves through the building it radiates heat down on all of the fuels

that are confined within that area

and as those fuels begin to heat up they then start to pyrolysis

and the fuels will start to pyrolysis at different temperatures depending on what they're made of for instance

if it's a natural fiber, it's going to pyrolicize at a much higher temperature than if it's an artificial fuel,

such as a plastic or a foam.

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.

Now, some studies have shown that at a ceiling temperature of approximately 600 degrees centigrade, flashover can occur.

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

that ceiling temperature get up to around about

that 600 degree level we're seeing the carbon monoxide in the smoke spontaneously combust

which then increases the heat release rate greatly

and then we see a rapid progress towards flashover as a result

now this is actually an early warning sign for flashover flames in the overpressure region is actually showing

that we're reaching that 600 degrees and

that flashover isn't very far away now the next thing we start to see is all of our fuels

which are pyrolysis are starting to reach their auto ignition temperature which means

that we're getting very close to the point where all of

those pyrolysis gases are simply going to burst into flames on their own accord even

if there is no direct flame impinging from the fire itself

now this is where the fire triangle comes back into it

because if we don't have our mixture of heat fuel

and oxygen we simply can't get the chemical reaction

that starts our flashover now in the room we know

that we have our heat because our ceiling temperature is reaching around about

that 600 degrees level we're seeing the flames in

that overpressure our fuel is everywhere it's been readily pyrolysis by the fire

and we're seeing all of our couches and walls and floors

and all these sorts of things releasing all of these pyrolysis gases

so the the final variable is oxygen now oxygen is something

that is very variable within a structure fire whether the fire is in a fuel controlled

or a ventilation controlled state we're going to be talking about fuel controlled

and ventilation controlled more in a later episode but it's important to note

that oxygen is a really key component to a structure fire actually occurring

and a lack of oxygen can actually stop a flashover happening

altogether whereas the addition of more oxygen can actually cause flashover to happen faster

and this is why it's really important that

when we actually make entry to a building we do so

when we're ready to actually get in and apply water to

that fire without actually allowing it to get in excess of oxygen before we actually suppress that fire.

Now our fire has continued to burn and we're seeing more

and more of these pyrolysis gases starting to come out of our fuels

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.

173

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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本課的詞彙與口語要點

這節口語課以影片“An Introduction to Flashover - Episode 9”為素材。影片中反覆出現的詞有：flashover, heat, fuel, gases, temperature。這段影片共有 182 個句子、2333 個單詞可供跟讀。講話部分時長為 14:07。說話人語速自然，每分鐘約 165 個詞，接近日常對話。 85% 的單詞屬於英語最常用的 3,000 詞，其餘的詞建議在練習前先學一下。

影片中的重點詞彙

影片中 15 個值得學習的單詞，附發音和釋義：

單詞	發音	釋義
oxygen 名詞	/ˈɑksɪd͡ʒən/	氧
flame 名詞	/fleɪm/	火焰, 火舌
occur 動詞	/əˈkɜː/	發生 /發生
transition 名詞	/tɹænˈzɪʃ.ən/	過渡 /過渡, 轉變 /轉變
automobile 名詞	/ˈɔː.tə.məˌbil/	汽車 /汽車, 車 /車
layer 名詞	/ˈleɪ̯ɚ/	層 /層
neutral 形容詞	/ˈnuː.tɹəl/	中立
ceiling 名詞	/ˈsilɪŋ/	天花板, 天棚
indicator 名詞	/ˈɪn.dɪˌkeɪ.tə(ɹ)/	指示符
combustion 名詞	/kəmˈbʌs.t͡ʃən/	燃燒 /燃燒
extent 名詞	/ɪkˈstɛnt/	範圍 /範圍
flash 動詞	/flæʃ/	閃光 /閃光
refer 動詞	/ɹɪˈfɜː/	談到 /談到
rapid 形容詞	/ˈɹæp.ɪd/	快, 迅速
indicate 動詞	/ˈɪndɪˌkeɪt/	表明, 表示

影片中出現的短語動詞

單詞	發音	釋義
heat up 動詞		加熱 /加熱
break down 動詞		壞了 /壞了, 出故障
get up to 動詞		幹 /幹, 做
go ahead 動詞	/ˌɡoʊ əˈhɛd/	請便 /請便
go back 動詞		回去, 返回
go through 動詞		通過 /通過

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	we've covered · haven't seen · have shown
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	being drawn · being radiated · is radiated
定語從句 who / which + 從句 — 補充說明人或事物	flashover which is · atmosphere, which is · monoxide, which is

需要注意的發音

說話人用了 54 次縮略和弱讀形式，例如 we're, we've, they're。請按聽到的簡短形式來說。

“sh” 和 “zh” 音: transition /tɹænˈzɪʃ.ən/, ignition /ɪɡˈnɪʃən/, flash /flæʃ/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, transcription /tɹænˈskɹɪpʃən/
長單詞——注意重音位置: automobile /ˈɔː.tə.məˌbil/, indicator /ˈɪn.dɪˌkeɪ.tə(ɹ)/, accordingly /əˈkɔɹ.dɪŋ.li/, ventilation /ˌvɛntɪˈleɪʃ(ə)n/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/

中文母語者容易讀錯的音：

/v/ — 不要讀成 /w/，上齒輕觸下唇: variable [ˈvæɹ.i.ə.bl̩], ventilation /ˌvɛntɪˈleɪʃ(ə)n/, aggressive /əˈɡɹɛs.ɪv/, vulnerable /ˈvʌln(ə)ɹəbl̩/, overpressure /ˌoʊ.vɚˈpɹɛʃ.ɚ/
詞尾子音 — 要讀清楚，後面不要加母音: extent /ɪkˈstɛnt/, flash /flæʃ/, rapid /ˈɹæp.ɪd/, indicate /ˈɪndɪˌkeɪt/, pump /pʌmp/
/r/ 和 /l/ 的區別: neutral /ˈnuː.tɹəl/, rely /ɹɪˈlaɪ/, variable [ˈvæɹ.i.ə.bl̩], accordingly /əˈkɔɹ.dɪŋ.li/, triangle /ˈtɹaɪˌæŋɡəl/

如何用這段影片練習

先完整聽一遍影片，不要開口，記下不認識的單詞。
先用 0.75 倍速逐句跟讀，熟練之後再回到正常速度。
錄下自己的聲音並與原聲對比，特別注意 oxygen, flame, occur 這類單詞。

什麼是跟讀法？

跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

影子跟讀法: 閱讀完整分步指南 →

跟讀練習: An Introduction to Flashover - Episode 9 - 通過影片學習英語口語

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