Question: why did the pyroclastic flow of Pompeii of 79AD fossilize the people?

Kate Dobson answered on 12 Nov 2014:

Some of the people who died in Pompeii and Herculaneum and other parts of the Bay of Naples in the Vesuvius eruption of 79AD were trapped in the ash and probably suffocated. Others were caught in the pyroclastic flow which was probably at temperatures of about 300C by the time it reached Pompeii. These people would have died from thermal shock. The pyroclastic and ash deposits solidified around these people forming the “casts” that the archeologists have discovered.