The Old Testament doesn't have a Hell, that's a Christian concept that Jesus first introduced in the Gospels. Taken on it's own, the OT just has Sheol, or the grave. There's a realm of heaven, thought to be beyond the sky, but it's not a place the dead go as far as I'm aware. This is based on my understanding of Judaism and the OT, I might be mistaken.
In the old Testament, Satan is allowed in heaven and is a special councilor to God. In the book of Job, for example, God allows Satan to set the conditions to test the faith of Job. God gave Satan the power to challenge God. In the old testament, Satan is in charge of the earth. This is sanctioned by God, with Satan the CEO in charge of the earth operation. Satan has the ear of God and has control over day to day things. There is no hell, since Satan is allowed in heaven; heaven and hell merged together.
It is not until Revelations that Satan is thrown from heaven. At this point, Satan is fired as CEO, which means if you followed him, now, you are no longer compliant with company policies. A distinction appears between sanctioned and unsanctioned behavior. In my humble opinion, what is often attributed to God of the old Testament, is Satan acting on God's behalf as the CEO of earth.
An analogy, in modern times, of this distinction, is murder. If one kills someone, but they are not in their right mind, it is considered different from someone who premeditates and then kills. In the old testament, the people were not in their right mind, so to speak, but where acting on impulse that may have been induced by Satan, who was condoned by God as CEO. After Satan is thrown from heaven, the insanity defense is no longer appropriate, and each person has to accept responsibility for actions.
Just as the temporarily insane person will never see the electric chair; old testament, the old testament person does not go to hell. The willful person, of the new Testament, who does the same thing, will see the chair; hell. Although, many states have done way with the death penalty, which is loosely analogous to trying to put Satan back into heaven; old way where one is less accountability.