I believe there are warnings about hell in the Old Testament. Sheol is not a neutral place, but the place where the wicked are sent. The warnings about Sheol would not be warnings if Sheol was simply a neutral place where all dead souls go.
I’ve probably argued before that Sheol is merely the place of the dead, but having looked through the Old Testament texts again, I think that Alex may have half a point. Here I have roughly sorted much of the Old Testament data under what seem to me to be the most useful headings and then added a summary definition. My suggestion, briefly, is that while Sheol is in principle the place of the dead, the imagery of going down to Sheol carries the particular connotation of an unfortunate, wretched or god-forsaken death.