Cinnamon oil is also effective. At home, try pouing several gallons of boiling water on a mound or use products containing D-limone or spinosad, a bacterium derivative that disrupsts the ants' nervous system.
I've used a spray containing d-Limonene ([url=https://www.orangeguard.com/story.html]Orange Guard[/url]) that's made from orange peel extract and it's very effective against ants. I used them against Argentine, not fire ants but the effect is said to be the same. In fact, [url=https://www.orangeguard.com/orn&fire.html]Orange Guard has a Fire Ant version[/url]. Basically it dissolves the wax coating in their respiratory tract causing them to suffocate. I bought it at the local Ace Hardware Garden Center and used it all around my area and in the house. Haven't seen ants in the house for the past two years.
OrganicGardening.com has these recommendations:
Pouring hot water on the mounds is effective and environmentally friendly, but may require 3 or 4 applications to kill the colony. Water should be at least scalding hot, but does not need to be boiling. This works best when you use 3 to 4 gallons of water in each application. WARNING: Hot water kills grass and shrubbery and may cause severe burns if spilled.