The 7th time we find the word Sheol used in the Old Testament is in Deuteronomy 32:22 which is also the final time we see it in the Pentateuch (or the Five Books of Moses).
This time, it is in the context of a song that Moses gave the congregation of Israel shortly before his death. (cf. Deut 31:30)
This song begins from Deut 32:1 until Deut 32:43 and is typical of Hebrew poetry in that God is portrayed as a loving God, then it shows His anger at the betrayal of His people and their subsequent punishment and finally ends with redemption and hope. It is a recurring theme in the Old Testament.
However, our study is about Sheol and Hell. Deuteronomy 32:22 says (translated directly from Hebrew):
"For a fire is breaking out in My anger, and it shall burn to lowest Sheol, and it shall devour the earth and its produce, and it shall scorch the foundations of the mountains."
Clearly the "it" refers to the fire, except the obvious place of "its" produce, which refers to the earth.
This passage describes the totality of God's wrath at some future time period, since the earth has not been devoured by fire, nor have the mountains been scorched in human history.
Bear in mind that this is not only a poetic description of God's wrath to Israel for their idolotry, but also a glimpse of end-time prophecy where all nations will be punished.
But does this tell us that Sheol, the grave, is a place of burning? Clearly not in this context. God's wrath, manifested in fire, has not taken place yet. So, Sheol, at least in this passage is not burning, yet.
There is something else interesting about this passage, in that it uses an adjective "lowest" to describe Sheol. This has the implication that there are different "depths" of Sheol. Let's keep that in mind as we continue on with the remaining 57 instances of Sheol in the Old Testament.