Repellents that contain chemicals such as DEET do repel foraging fire ants. However, spraying these repellents will not deter "angry" ants from biting and stinging after they emerge out of disturbed mounds.
The best advice for working in fire ant-infested areas is to look for mounds so you can avoid stepping on them. Also wear protective clothing, such as boots with pant legs tucked inside, to help you see the fire ants and brush them off before they can sting.
Dust baby powder or talcum powder on hard objects such as tool handles to prevent fire ants from crawling up these surfaces. As long as the powder is kept dry, it will prevent fire ants from climbing up the hard objects to sting. Powder can also be dusted on rubber boots to prevent fire ants from climbing onto your body.
Find more information about fire ants in eXtension's Imported Fire Ant Resource Area.