Viton is a synthetic rubber material (a fluorelastomer) used, for example, in some engine gaskets. Stories have been circulating around the world about horrendous injuries that have occurred to unsuspecting people coming into contact with the breakdown products of fluoelastomers when a vehicle has been involved in a fire. Every few years these get resurrected and a new panic breaks out so, hopefully, this will set the record straight.
As with many urban or industry myths, there may be a tiny element of truth that makes the story more believable. In this case it goes back to 1981 at the National Nuclear Corporation in Risley (UK). An experiment was been carried out to see what happens when a Viton O ring was heated to about 400 Celsius in sealed test rig. When the worker dismantled the apparatus a clear liquid was ejected under pressure very close to his fingers. This led to discomfort and an untreated deep-seated burn developed over a period of days – eventually leading to amputation of part of his finger. The incident was investigated by HSE and, on repeating the experiment it was shown that hydrofluoric acid (HF) was produced (from hydrogen fluoride gas in presence of water). It can cause corrosive burns due to free hydrogen ions, and chemical burns from tissue penetration by fluoride ions. However, it is readily treated by the use of calcium gluoconate gel (See INDG 307 Hydrofluoric acid poisoning).
There is no verifiable incident related to HF from burnt out vehicles anywhere in the world. And for fairly good scientific reasons. Hydrogen fluoride is a gas and, in the event of it being produced from a fluoroelastomer in a fire, it would disperse very quickly with the flames. It also needs water to produce hydrofluoric acid but if you put out the flames with an extinguisher you also dilute and wash away any acid. It seems it is rather difficult to reproduce the 600 psi, sealed-vessel conditions of the laboratory experiment in a real vehicle fire situation.
It makes sense to wear suitable gloves to stop getting you hands dirty when dealing with burnt-out vehicles, so even if there was the tiniest chance of HF being present, you would be protected.