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In my setting I have monsters that breathe elemental clouds/blasts of certain substances, assume them to basically be dragons. Among the largest (and I mean, Godzilla sized) are some that spit hot volcanic ash (as of a pyroclastic flow) which they siphon from active vents. Don't ask about the biology because the answer is, they aren't. Simple curiosity. Suppose this dragon breathed an essential mini-vesuvius/st. hellens every time it wanted to attack (one that might fit out of Godzilla's mouth, I'm not all too certain how much that would be). Comparing that with if they straight up spat fire, let's say analogous to a methane fueled inferno, which one do you think would have more destructive potential?

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  • $\begingroup$ What's the internal volume of your "dragozilla", or rather the volume of the material it can expel? Are these somehow related anyway, or is it just "large monster" and "as much ash as I need for story purposes", with no need to have any logical consistency? $\endgroup$
    – hyde
    Aug 22, 2022 at 10:26
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    $\begingroup$ It is much easier to defend against exposure to ash than to fire. Breathing through cloth, especially wet cloth, will make a huge difference against volcanic ash, but not much against fire. $\endgroup$ Aug 22, 2022 at 12:59
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    $\begingroup$ Is this "siphoning" of ash from vents like a magical portal (i.e. the creature doesn't need to "carry" the ash, a creature of any size can barf up limitless ejecta given enough time), or do they inhale/drink the volcanic effluent and then spit it back up? $\endgroup$
    – Nick T
    Aug 22, 2022 at 17:53
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    $\begingroup$ As evidenced by incoming answers, you've left ambiguous the question of how hot these ashes are. Without that constraint, it's difficult to gauge who is most correct. Depending on the arrival temperature of the ash flow, the secondary conflagrations caused by direct fire stand a very good chance of being most deadly - hot ash may be hot but it's also an insulator less prone to surrendering that heat to it's environment than an actual burning fire. $\endgroup$
    – user8827
    Aug 22, 2022 at 18:20
  • $\begingroup$ @NickT's question is important. Otherwise, you're limited to a mass of ash that's probably around the mass of one dragon, give or take. $\endgroup$ Aug 22, 2022 at 19:26

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I'm gonna go against the grain and suggest "less lethal"

If I take a shovel full of ash from my fireplace, even if the fire is burning, and throw it into the room, what happens? There's a small chance something might start burning and a good chance somebody might start coughing, but for the most part what's going to happen is my wife getting really hacked off because I made a nasty mess in the room. I'll be spending the day vacuuming and cleaning every atom of ash out of her house.

If I take a shovel full of embers from my fireplace, which requires the fire to be burning, and throw them into the room, what happens? There's a moderate chance something might start burning, but what's really going to happen is a bunch of holes burnt into the furniture and melted carpet fibers. The mess is less, but the damage is greater. My wife's initial reaction isn't as bad as with the ash, but the end result is much, much worse. I'll be sleeping on that couch with holes burnt into it and working two jobs to replace it.

Fire... I can't even imagine why everybody thinks ash is worse. Unless your dragon can expel absolutely magnificent amounts of ash (as in whole-country-covering amounts of ash, which volcanoes can do, but just Godzilla-spewing amounts of ash, what can Godzilla do? cover a couple of cars or a couple of city streets as he walks by?), ash will never be as devastating as fire. Why? Fire spreads — ash doesn't. Throw a shovel full of burning logs into the room and the house burns down. Now my wife has divorced me for being so stupid that she doesn't want to be responsible for the children I might spawn.

Fire is worse, because it keeps causing damage long after the dragon has gone home to pop a cool one and watch my debut on the Darwin Awards. All ash would do is improve the economy of dry cleaners and street sweepers.

According to Disney's "The Incredibles," volcanic soil, aka ash, is some of the most fertile on Earth. And who's gonna deny the sage wisdom of Disney? Fortunately, they're also right. An ash-spewing Godzilla would be doing the local farmers a favor.


Edit: A number of comments have pointed out that ash from a fireplace and ash from a volcano are different things. True! One comes from wood and the other from rock. But if you think they're significantly different in this context, you've missed my point.

Yes, there is ash that comes from the mouth of a volcano — but what's really coming from that volcano and what's really a threat is magma. Ash is what you have after something has finished combusting and cooled down. But let's examine the idea of ash just as hot as it can be coming from the throat of a Godzilla-sized monster.

  • Low volume.
  • Rushing through a high volume of air.
  • And unless Godzilla is magically channeling tons and tons of ash, the big guy runs out of it very, very, quickly.

In other words, we're not talking about a volcano. We're not even talking about the mouth of a volcano. We're talking about what happens when a shovel full of hot grains of rock that are cooling very rapidly get lobbed through the air for a distance equal to at least the height of Godzilla.

And that's where my discussion, above, comes in. If Godzilla bent over and hurled up a few pounds (and that's all we're talking about on a per-moment basis) of super-hot ash, what would really happen? Unless he dumped the pile in a pile, he'd melt the carpet and burn some holes in the upholstery.

We are not talking about a volcano, and that's where, IMO, most of the other answers missed the boat. We're talking about a Godzilla-sized creature that would be lucky to haul around a half-ton of ash before having to haul off somewhere to get more. The biological chemistry of spewing either a flaming gas or a flaming liquid is a whole lot easier to justify — and if you're going to handwave how Godzilla gets tons of magma (ash... pyroclastic cloud... call it what you will) then you can trivially handwave how much damage it will do because at that point whether or not it's flame or ash is just an aesthetic to the story and not a rule of the world.

This is why I'm voting for "less lethal." In my humble opinion, it doesn't matter how hot it is coming from his mouth, the volume is so low and the tendency to spread so high through so much air that without the ability to continue combusting it's not as lethal or damaging as fire. That's my two cents.

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    $\begingroup$ I do admire that you believe your marriage could survive such acts. That aside, ash from a volcano is like crushed glass, ashe from a wood is quite different actually looks "blobby".. The heat from a true pyroclastic flow can reach 1500F. Estimated the one that engulfed Vesuvius was around 750f. A hot oak wood blacksmith fire is lucky to reach 1200 at peak with forced air. 300f - 500f for an average fire. the ashe is quite a bit cooler. I do agree however. A fire on the scale the OP describes the ash, a fire (depending on fuel) would be much worse. $\endgroup$
    – Gillgamesh
    Aug 22, 2022 at 15:28
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    $\begingroup$ I feel the danger of ash starting fires is downplayed way too much. $\endgroup$
    – Trioxidane
    Aug 22, 2022 at 16:49
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    $\begingroup$ @JBH the question states that one is spewing vulcanic ash similar to an active vulcano, though lesser in quantity. The other is "straight up spewing fire", though in all revisions it is burning methane. Also biology is to be ignored according to the question. The only biological constraint is the mouth size. Please read the question thoroughly before answering. And ince more, firemen keep dousing fire long after the fire has stopped. Embers are hot for hours or days, possibly starting new fires. $\endgroup$
    – Trioxidane
    Aug 23, 2022 at 5:41
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    $\begingroup$ @Trioxidane Suppose dragon throws out 10 kg of matter per blast of whatever. 10 kg of pure ethanol burning produces a VERY nasty fire effect killing the farmer, his house and the field. 10 kg of ash kills the farmer, annoys everyone that now need to clean the house and might even help the crops by fertilizing the field. The only viable dragon strategy with ash would be generation of large clouds of smoke which aren't harmful but hide the dragon which still has claws and teeth and tail to kill - NOT the hot lava-like thingy. Unless we are putting absolutely enormous amount of mass behind this. $\endgroup$ Aug 23, 2022 at 8:28
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    $\begingroup$ Volcanic ash is more or less foamy glass. tiny microscopic glass shards. its a poor isolator of heat therefore it radiates heat effectively. Even if it didn't they tiney particles would rely on the local cloud to retain its heat over any amount of time. 25,000 CM is poultry compared to a real volcanic eruption. ALSO... I missed the massive and wide spread fires caused by the Mt St Helens eruption, because there were none, except a few caused by down power lines and volcanic lightning. $\endgroup$
    – Gillgamesh
    Aug 23, 2022 at 12:00
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Volcanic ashes can be dangerous via various paths:

  • they might overload structures where they deposit, resulting in their structural collapse
  • they might obstruct/reroute waterways, resulting in flooding
  • they might result in mud avalanches when they mix with rain water while still not stabilized
  • they might interfere with aviation, as they might damage engines which happen to ingest them
  • they might interfere with living beings, obstructing their breathing and viewing

However on average all of the above effects are less instantaneous than a flame. I think that in the short term it won't be as lethal, but in the long term it might give heavier damages, in particular in terms of economic damage

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    $\begingroup$ I think that it will be much more lethal for any given temperature. What is a flame but a hot gas with glowing aerosol particles in it? By adding ash you are adding thermal capacity, the chance of prolonged contact, and possible impact damage. For any given amount of total energy, though, it's likely less destructive. $\endgroup$
    – user86462
    Aug 22, 2022 at 8:02
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    $\begingroup$ @SeanOConnor, OP has specified ashes, not ashes and fire. $\endgroup$
    – L.Dutch
    Aug 22, 2022 at 11:13
  • $\begingroup$ True, but: "essential mini-vesuvius/st. hellens every time"; Mt St Helens is famous for its hot gases. OP needs to clarify temperature. $\endgroup$
    – user86462
    Aug 22, 2022 at 19:01
  • $\begingroup$ @SeanOConnor I specified volcanic ash, ash that is molten. As different from a gas fire. $\endgroup$
    – Quinn
    Aug 22, 2022 at 20:40
  • $\begingroup$ Right, well if its molten, it's extremely hot. $\endgroup$
    – user86462
    Aug 22, 2022 at 20:51
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Ash>fire

Vs people: Ash sticks, and is about as hot as molten lava, while flame does not stick, even if hotter, so in case of a warrior hit by ash dragon blast, that warrior has less chances to survive if not incinerated in an instant. Also if a warrior can hold breath while dodging a blast of flame, and not inhale superhot air, as it will drift upwards by convection, ash can fall off the main blast and reach that dodger's lungs even if he breathes in cold air that just supplanted hot air from volcano blast, increasing blast lethality.

Vs buildings: Ash can build up and break a building if amassed, and being hot, will heat the inside after a single blast of the ash dragon, while in order to heat the inside of a building with fire, it will take longer and will require the fire dragon to constantly breathe fire at the building. So an ash dragon can plain FOO at a fort and move on, while its defenders will be slowly cooked in shell inside the ash-covered building, while a fire dragon will have to spend time roasting the fort and not leave, or else the building will cool down or soldiers might escape. Ash helps here too, as travelling through fresh hot volcano ash is more troublesome than running through flame.

Vs armored vehicles: Building principle applies, especially if the armor is made of metal, which has high thermal conductivity, but a fire dragon will take less time to cook a tank than a fort, also if an armor is hit by any dragon's blast, its engine will fail due to lack of oxygen in the air intake, eother because it's consumed by a fire dragon's inferno, or ash dragon's ash blast blocked the intake completely. Anyway, a tank is better be squished instead of breathed upon, so assuming equal deadliness here.

Vs airforce: I say both dragons would fail here if they don't fly, yet in case an ash dragon can form an ash clot and blow it upwards like a volcano bomb, it has nonzero chance to down an airplane with it, while a fire dragon is unable to hit a plane at high altitude with its breath at all.

Not as catastrophic though

Essentially a Godzilla-sized beast is deadly enough in itself, breathing ability is more of icing on the cake than a major factor of deadliness. Assuming that two dragons go against a single set of enemies to compete who would defeat them faster, the ash dragon is expected to win, because his breath weapon has a lingering effect vs fireproof objects that is not present for the fire dragon's, yet the overall speed of destruction would likely be limited to their ability to move fast enough, swing their limbs and reload their breathing weapon, not in the exact difference of breath. Except that if enemies are fortified, fortifications resist fire better than ash, depending on tech, by a factor of 2 to dozens. So an ash dragon would be about as deadly vs most targets as a fire dragon, and have an advantage vs fortifications and airforce in case it can throw volcano bombs.

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As mentioned in other answers the danger in ash comes from, either of three vectors. A wide spread ash fall, where it may make breathing difficult. Or create mud flows collapse structures. Breathing in the ash grains, the granes under a microscope look akin to crushed razor blades, thus can be deadly. Heat from a pyroclastic flow, will consume an area a cook anything caught in its's path. The truly disastrous nature of an ash flow is in it's scale sometimes covering hundreds of square miles, Thousands even. The heat from a small, tiny is comparison, flow from a breath weapon would dissipate quickly. While it would be no party within a godzilla sized ashe flow, far more deadly scenarios are easily imaginable.

Instead of a methane type fire use the ash to "thicken" the flames fuel. Effectually turning it into napalm where the flame would saturate the area and burn for far longer upto 1800F, OR with a bit more evil scientist imagination, thermite which burns at over 4000F hot enough to liquify steel, and can't be extinguished by water, indeed will continue to burn submerged in water.

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Ash is much more dangerous than fire

It is hands down ash. Yes it has a lower temperature than fire (a quick search shows 400-800°C vs 600-1500°C). Yet it has much more troubling effects.

During courses for fire safety you learn quickly that it isn't fire that is the most dangerous. It is the smoke and other debris. This poisons and/or suffocates anyone in it's path. In addition, this debris helps to transfer heat more efficiently. Sure the fire is hotter, but it's reach is limited by air. The debris moves around more easily, transporting much more heat energy despite lower temperatures.

Now you have vulcanic ash. It can suffocate and poison any lungs. It sticks to people, allowing for long heat transfer.

If you get hit by a breath attack of fire it is lethal. I'm assuming the fire breath is incredibly hot, killing near instantly. But if we look at range it pretty much only destroys what it hits and only little surrounding area. A volcanic ash breath can suffocate a larger area, set fires that are more difficult to stop, spread into many electronics and other things.

Imagine a fire and an ash breath pointed at the city. The fire destroys a few buildings and sets a fire. The ash on the other hand will destroy a neighbourhood, set fires, suffocate, poison, incapacitate and generally be difficult to avoid.

Conclusion

Fire is dangerous, but it is only a reaction that quickly diminishes in power with distance. You need to rely on direct hits and setting things on fire after. Vulcanic ash is much more efficient in heat transfer, spreads to larger areas more easily, is deadly or incapacitating more easily thanks to suffocation or poisoning and can create a lot of hard to quell fires.

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    $\begingroup$ unless the ash and fire have the same volume, then the fire is say more dangerous. sure the there is more small long term health effects from ash but on such a small scale they are basically non-existent. actual volcanic eruptions are dangerous because of the huge volume. $\endgroup$
    – John
    Aug 23, 2022 at 13:40
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    $\begingroup$ @John why wouldn't they have the same volume? Do you mean mass? The fire Godzilla is able to spew "analogous to a methane fueled inferno". That sounds like a ridiculous amount. It seems to me vulcanic ash in such ridiculous volumes would be much more dangerous. $\endgroup$
    – Trioxidane
    Aug 23, 2022 at 16:38
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It depends on what you mean by "fire"

If they are expelled with the same material volume with the same force a napalm-like fire would be way more dangerous, simply because for the same force a liquid based fire will cover a much larger area and continue to burn. Volcanic ash cools very quickly in small volumes (not cubic kilometers) while there are many liquids that will continue to burn. More coverage and more likelihood to start fires makes liquid based fires far more dangerous.

If on the other hand it is a gas fire then the dangers are basically the same. Superheated air mostly kills through destroying lung tissue or displacement, just like ash, it can just do it faster, but ash can linger in the air for minutes so its kind of a wash, faster acting and thus harder to defend against on one side lasting longer on the other.

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It seems to me that what you really have in mind is a dragon that vomits a pyroclastic flow. In a worst-case scenario, that would mean spraying a 1000-degrees-C mix of gas and volcanic matter at a speed of 700 km/h. Such a flow would be more than just ash because it would include larger pebbles, and thus it would have serious impact force in addition to heat and toxicity. But, even without pebbles, if we still assume high velocity, the ash would add enough density to the stream to make a difference. (Added as an edit - a flow of ash this hot would be glowing bright red and might be described by witnesses as "fire" anyway. Only the hottest real flows are like this.)

On the other hand, if the dragon's mouth were a Space Shuttle Main Engine, it would emit flames at up to 3300 degrees C. The very high heat might be lethal over a larger area - you wouldn't have to be touched by the flames to be killed.

It may not be possible to rank the amount of damage on a scale - it may depend on the conditions.

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It is up to your Imagination.

We cannot use science to compare the damage of breathing fire and breathing molten ash because there is no such thing as "breathing fire".

Okay there is no such thing as "breathing molten ash" either but we can pretend it works like a pyroclastic flow.

Google says those guys go up to 800C. For comparison a methane torch might be 2000C but the torch does not spray material in all directions. It is the difference between putting your hand in the 100 degree kettle and putting your hand in the 200 degree oven.

Of course "fire breath" does not work like a methane torch because it needs to blast out and go KABOOM and not just melt Godzilla's teeth off. So you need to spit some hot burning stuff up with the fire.

Once you do that the fire and ash breath are essentially the same thing. They both chuck hot material at the target.

Then it is just a matter of how dense the burning stuff from the fire breath is. If it is denser than ash then it does more damage. If it is much less dense it does less damage.

The big difference is if your hot stuff provides its own oxygen like how napalm does. The ash will make it harder for stuff to catch fire by smothering the fire. But the fire breath might not have this problem if the reaction is self-sustaining.

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  • $\begingroup$ We can directly compare a jet of flame with a jet of ash, leaving aside the sources of those jets. $\endgroup$
    – SRM
    Aug 22, 2022 at 15:52
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    $\begingroup$ @SRM Different flames burn at different temperatures. If you leave aside the source then you must use your imagination to decide how hot is the jet. Same with jets of ash of course. They can be any hotness. $\endgroup$
    – Daron
    Aug 22, 2022 at 15:55
  • $\begingroup$ @SRM A "jet of flame" is actually a jet of fuel that happens to be burning. This answer suggests there could be much more suitable fuels than the methane specified in the question. So you're right, sources can be ignored; but substance can't be. $\endgroup$
    – David K
    Aug 25, 2022 at 0:22
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Catastrophically so

Structural damage.

If it is spewed out with a huge amount of force. At this point, we would see structural collapse from either direct impact, or overloading. This is a lot more sadistic than a flame in fact, because after the battle, if people try to come back to the area, depending on what time period this is, it will either be highly costly (to buy equipment that can remove ash and protect the workers), or highly costly in lives (If this is pre industrial, and they don't have access to protection to the ash)

Deadly tsunami

Vesuvius spewed out ash at a speed of roughly 600,000 cubic meters a second, and lets say a mini one would do 10 times less (erring on the side of caution), so 60,000 cubic meters of ash coming out per second. Lets also assume that the thermal energy is 10 times less as well, so around 10,000 times the thermal energy of hiroshima-nagasaki bombings, and further decrease this another ten times because I think wikipedia counts lava, but I dont, as this dragon doesnt breathe it, so 1,000 times. Speaking of breathing, do you think you could if you are buried under 60,000 meters of ash countaining 20 times the energy of a nuke? Not to mention that this guy can keep going for who knows how long. Anyway, if you can breathe, you probably shouldn't, as those micro particles will bury themselves into your lungs, but don't worry, you'll get revenge. You'll bury yourself in them permanantly if you're not in a good position.

Volcanic winter

The most deadly attack this guy would have could be this - depending on how long he can do this for, he can simply tilt his head up, and shoot the ash into the sky, causing a volcanic winter. If he can't do this for long, then this might not be an option, but if he is able to do this permanently, I'm going to say this would be civilization level threatening. This wouldn't be something to do in a battle, but put him in a secluded area and let this bad boy run in the background and you got yourself a catastrophe. In fact, you only need about 2.4 cubic miles of ash before you have a noticable drop in sunlight, and with 60,000 cubic meters per second, he could release that in 40 seconds, though keep going longer, and you'll see more than a drop in sunlight, you might not see it at all!

Conclusion

Fire might look cool, but volcanic ash is the real herald of death. From structural collapse and making swathes of land contaminated with deadly particles, to causing a volcanic winter, this "dragon" is more of a destruction god.

TL:DR

Ash > Fire astronomical diff

Edit:

Doing some more calculations, due to the mouth size limitation, He may only be able to spray less than half my previous stated amout of 60000m^3/s (now calculated to be around 24, 740m^3/s)

Godzilla's current height is around 400 Ft (393), and lets say his mout can open to about an 8/th of that, so 50 meters, With a rough calculation using the hazen williams equation (v = k * C * R^0.63 * S^0.54), assuming the force used to expel the ash is the same roughly as a 10m drop over a 20 meter long pipe, and a roughness coefficent of 100, you get a flow discharge of aprox 25,000 cubic meters per second, (24, 740). Disclaimer: HW equation is used for water, so it isn't the most accurate, but it will be around the same due to liquid charicteristics of particles, and when assuming breath force, I was quite conservative saying it was the same a a 10 meter drop of a 20 meter long pipe.

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    $\begingroup$ all those require absolutely massive volumes of ash, the same volume of something like napalm would be far more dangerous, for one thing oxygen consumption would create multiple explosions as you get open air backdraft effects. you essentially have a fuel air bomb bigger than any in history. $\endgroup$
    – John
    Aug 23, 2022 at 13:59
  • $\begingroup$ @John Yes, I agree, spewing napalm would be more deadly. It was not specified in the question that napalm was the medium through which fire was breathed. You could also used greek fire or whichever suits your fancy and get different outcomes., I assume here the method of fire breathing is expulsion and ignition of gas such as methane. $\endgroup$
    – JNC4
    Aug 24, 2022 at 15:27
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Fire Works Better, but they're both dangerous

Sure, if a dragon could attack with ash instead of fire, it would still be very dangerous, but fire is faster acting. When it does its ash attack, anyone caught in the attack would be blinded, and probably suffocate, either by being buried or just having too much ash in the air to breathe causing them to choke. But that is going to take a bit of time to suffocate on and would be a painful death for whoever got caught in the attack, but if you just set them on fire completely, they will probably be dead much sooner. not only that, but fire breath would catch things on fire, causing the damage to spread. If you're looking for maximum damage potential in the shortest amount of time, fire breath is the way to go.

Of course, if the ash is superheated, then it would be comparable to fire. It would likely catch some things on fire and would probably kill people faster than they would suffocate. But that seems like a few steps extra. Why spit ash that can set things on fire, when you can just spit fire?

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