Is it impossible to make plaster casts of the newly found bodies of Herculaneum because their bodies were vaporized immediately by a pyroclastic surge?

Answer 1

It is not possible to make the same kind of casts at Herculaneum as Fiorelli made in Pompeii. In Pompeii, the ash fallout settled around bodies then hardened, creating a cavity in the shape of the body. Herculaneum experienced different conditions to Pompeii in the eruption; it was covered in a thick layer of hot volcanic material sometimes described as 'mud' which did not harden around the shape of the bodies in the same way as the ash did in Pompeii. So the remains that have been found in Herculaneum have been skeletons, (remembering that of course in Pompeii a skeleton is inside the plaster cast, and many skeletons were also found there that were not cast).
Interestingly, the casting technique is today being used to make a modern cast of the actual remains; these can be displayed without the issue of whether human remains should be viewed. Some of the skeletons of Herculaneum from the beachfront have been recently cast in this way for display purposes.
See 'Pompeii & Herculaneum: Interpreting the Evidence' by Dr Brian Brennan and Dr Estelle Lazer.