Fire ants usually avoid places that are disturbed so a compost pile that is turned will be an unattractive home for those biting critters.  Also, ants do not like wet feet, so keep your pile moist.  Reaching higher temperatures in the early stages of composting may also discourage the fire ants.   Most fire any activities are the result of abandoning the composting process.

Once the ants become established, it may be difficult to remove them.  If they persist or are a hazard to you, try pouring boiling water on the nest.  As a last resort, you may use fire ant bait killer NEAR but not in the compost pile.  However, avoid direct application of pesticides directly on the compost and follow the pesticide label's instructions for use.  For further assistance, consult with you local Cooperative Extension Service Office.