I had no idea diazinon was taken off the market. I use it around the outside of my house for roach and general bug control. It worked extremely well. Fortunately I have a big bottle of concentrate in the rusty metal cabinet, in the dark dusty closet in the back corner of my garage....probably with a lot of other now illegal toxins, poisons and chemicals.
But I'm not sure how well diazinon will work on fire ants. I never used it for that.
I'm no toxicologist but I still remember a friend of mine, a very laid back, happy go lucky guy that nothing bad ever happens too, getting diazinon or some other acetylcholinesterase inhibitor all over him when he was trying to get the fleas and roachs out of his heavily infested dog pen. His wife and I (both medical students) kept suggesting he be careful. I'm not the most cautious guy in the world with pesticides but he was geting this stuff all over himself. Well, he finsished up and came inside and didn't go shower. About 30 minutes later he starts up with all the typical cholinergic side effects we'd read about in the text books. Excess salivation, blurred vision, some stomach cramps headache, a little slurred speech. Good old Ron just laughs it off, but we at least made him take a shower. A few hours and a few beers later and he was just fine.