Everyone who thinks that gasoline is potentially dangerous, put down your torch, carefully, and raise your hand. If you ask people if it is a good idea to pour a gallon of gasoline on the ground, they usually say no. Gas will sterilize the soil. In rain, gas runs off into surface water, and also get in to the groundwater. That's water, the stuff we drink.
Gasoline is a mixture of lots of chemicals, including known carcinogens, cancer-causing agents.
If you pour gas into a fire ant mound, some unburned gasoline will evaporate into the atmosphere, that mixture of gases we breathe to stay alive. Gasoline in the atmosphere is very bad. These covers keep gasoline vapors from escaping into the atmosphere as people fill their tanks. If you ask these same people if they would let their kids pump gas in their car at the gas station, they say no, it is too dangerous. Kids could inhale the vapors and get sick.