The biggest risk with this exercise is having the barbell fall on you, while you can't push it back up. The heavy weight might fall on your neck and strangle you, or fall on your chest and crash your rib cage, or even drop on your face if you're really unlucky.
The best way to be safe is to bench press in the power rack, where the safety pins will catch the bar no matter what happens.
If you don't have a power rack you should get a spotter that knows how to spot, since most people aren't good spotters. Or do it in the smith machine, which won't help you if you suddenly drop the weight, but can help if you're close to failure and still can manage it.
if you don't have any, make sure to only use light weight you sure you can manage and avoid reaching failure.