Yes, it’s recommended that you put sand in the bottom of your fire pit. Putting sand in the bottom of your fire pit will help to absorb some of the heat and protect the bottom of the pit from coming in direct contact with the fire and hot ashes. This can prolong the life of your fire pit.
However, there are some fire pits that may not allow you to place a layer of sand at the bottom. Some fire pits have holes in the bottom of the base to encourage oxygen flow (to keep the flames going).