^^ Rear wing vortices, not on top of front tires...
The accident was unfortunate but these things happen everyday at constructions sites etc. It's a simple accident. Allthou i enjoy a lot of good from H&S (= health&safety, in showbusiness stricter H&S has saved lives and i approve them, even when it makes the job a bit harder..) But there's a limit of what you can think can happen. Too strict H&S on the other hand is counter productive, i doubt there very much you can do for this type of accident. There are millions of people working right now beside heavy machines that can shred you to pieces in seconds if you trip at the wrong moment.. If you read the H&S regulations here, you can't step on a ladder that's more than 1m from the ground without safety harness... that's just stupid, mostly impossible to do and no one follows that rule, and it starts to ripple and soon no one knows what rule is actually good and what is made by someone in an airconditioned office looking at statistics. Of course, in F1 there are more actual racers who make the rules so they do know what they are doing.
For this incident, a lot of things had to happen in the right/wrong time and order, guy drops his radio, trips while retrieving it, the tractor driver happened to look at the other side etc etc. These kinds of accidents are unavoidable, of course there are lot of important people thinking what they can do about this but no matter what they do, you can factor in the unknown..