This fire is probably a literal fire. It would be Jesus’ premeditated answer to the cry of the murdered saints in Rev 6:10. If so, “the fire” will not happen until the last of the chosen few has been killed and the full number (144000/288000?) has been filled; according to Rev 6:11.
Many righteous people has already been martyred since the first martyr Abel:
And so upon you will come all the righteous blood that has been shed on earth, from the blood of righteous Abel to the blood of Zechariah son of Berekiah, whom you murdered between the temple and the altar. (Mat 23:35).
However most of the chosen few will probably be martyred during the coming Great Tribulation (Rev 7:14). With this event the salt that prevented the world from decay is removed, and it starts to disintegrate rapidly:
“You are the salt of the earth”. (Mat 5:13; NIV)**
9 When he opened the fifth seal, I saw under the altar the souls of those who had been slain because of the word of God and the testimony they had maintained. 10 They called out in a loud voice, “How long, Sovereign Lord, holy and true, until you judge the inhabitants of the earth and avenge our blood?” 11 Then each of them was given a white robe, and they were told to wait a little longer, until the full number of their fellow servants, their brothers and sisters, were killed just as they had been. (Rev 6:9-11: NIV)
13 Then one of the elders asked me, “These in white robes—who are they, and where did they come from?” I answered, “Sir, you know.” And he said, “These are they who have come out of the great tribulation; they have washed their robes and made them white in the blood of the Lamb. 15 Therefore,“they are before the throne of God and serve him day and night in his temple; and he who sits on the throne will shelter them with his presence. 16 ‘Never again will they hunger; never again will they thirst. The sun will not beat down on them,’ nor any scorching heat. 17 For the Lamb at the center of the throne will be their shepherd; ‘he will lead them to springs of living water.’ ‘And God will wipe away every tear from their eyes.” (Rev 7:13-17; NIV)