Mark 9:43 refers to "unquenchable fire" (Greek ἄσβεστον (asbeston) from which we get the word "asbestos").
The KJV calls it "the fire that shall never be quenched".
This verse also refers to this fire as "hell" (Greek γέενναν (geennan), from which we get the word "Gehenna").
The Outline of Biblical Usage describes "Gehenna":
This was originally the valley of Hinnom, south of Jerusalem, where the filth and dead animals of the city were cast out and burned; a fit symbol of the wicked and their future destruction.
In the next verse, Mark continues to describe this garbage dump:
Where their worm does not die, and the fire is not quenched
The fire will not be quenched and the worms will not die, at least not as long as there is fuel to feed the fire and flesh to feed the worms.
But there is nothing here that suggests that any of this lasts forever (have the worms been graced with immortality?).
Matthew 18:8 refers to "eternal fire" (Greek αἰώνιον (aiōnion) from which we get the word "eons").
This is fire that no one will ever extinguish, fire that will continue burning for as long as it needs to.
Except for minor variations, no one disputes that this is fire that will not be extinguished, and will burn for as long as it needs to, to the end of the age (eon) if necessary.
But such a fire, even if were to burn for all eternity, is not a problem for annihilationists, as the verse in question simply talks about being thrown into the fire.
There is no implication in the scripture that anyone would survive such an event.
If you were vacationing in Hawaiʻi and someone told you to be careful so you don't fall into the volcano, would you have any reason to think that doing so would somehow make you immortal?
Would you have any doubts that the actual result would be your permanent death and the physical destruction of your body?
Isaiah 66:23–24 is the scripture that Mark quoted:
And it shall come to pass that from one New Moon to another, and from one Sabbath to another, all flesh shall come to worship before Me,” says the LORD.
And they shall go forth and look upon the corpses of the men who have transgressed against Me.
For their worm does not die, and their fire is not quenched.
They shall be an abhorrence to all flesh.
Notice that this is talking about "corpses of the men" being viewed by living physical humans.
These are dead bodies and they will soon be eaten or burned, becoming nothing but ashes and soil.
There isn't the slightest implication that these corpses are aware of what is happening to them, much less that they are immortal and will continue to be burned and eaten over and over forever.
They are simply lifeless bodies, incapable of sensation or awareness.
Matthew 25:41 again refers to "eternal fire", and again there is no implication that anyone will survive being thrown into it.
Revelation 14:9–11 says:
Then a third angel followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives his mark on his forehead or on his hand,
he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb.
And the smoke of their torment ascends forever and ever; and they have no rest day or night, who worship the beast and his image, and whoever receives the mark of his name.”
This describes events around the time of Christ's return, at the end of the Beast's rule here on Earth.
These people have not been resurrected, they are normal humans, our descendants or ourselves, still living here at the end of the current age.
The "torment" is the knowledge these people have of what their fate will be.
They know they will end up burned to ashes and completely destroyed, gone forever.
And again, the "forever and ever" could mean until the end of the age, until it has served its purpose, that there's nothing they can do to extinguish it.
But even if it really did mean literally forever, it is still only the smoke and fire itself that lasts, not the torment.
Revelation 19:3 says "… Her smoke rises up forever …" (NKJV), using the Greek words
"kapnos autos" (καπνός αὐτός) for "her smoke",
and "eis ho aiōn" (εἰς ὁ αἰών) for "for ever".
Those same two Greek expressions are used in the Septuagint for Isaiah 34:10 "the smoke thereof shall go up for ever",
referring to the destruction of Edom.
Yet today, less than 3000 years later, there is no trace of that smoke.
The idea, both in the Hebrew and Greek scriptures, is that of something that burns without being extinguished before it runs out of fuel.
How do annihilationists respond to verses that indicate eternal hell fire?
Annihilationists don't deny that there will be a "hell fire", nor that people will be condemned to burn in it.
What they don't understand is why so many other people believe that anyone could survive the experience.
