WE won't be reduced to ash at the second death. You and I have placed our faith in Jesus Christ, so after we are resurrected from death, we will not be destroyed by the second death. We will inherit eternal life from Christ, we will not die a second time.
But when the day of the Lord comes, the arrogant and evildoers will be resurrected for judgment and they will die the second death. They will be reduced to ash. Here is one scripture passage describing the day of the Lord (and there are many others)
The Great Day of the LORD
1 “For behold, the day is coming, burning like an oven, when all the arrogant and all evildoers will be stubble. The day that is coming shall set them ablaze, says the LORD of hosts, so that it will leave them neither root nor branch.
2 But for you who fear my name, the sun of righteousness shall rise with healing in its wings. You shall go out leaping like calves from the stall.
3 And you shall tread down the wicked, for they will be ashes under the soles of your feet, on the day when I act, says the LORD of hosts.
Malachi 4:1-3