Professor Oliver Craig from the University of York's Department of Archaeology said: "The realisation that collagen was present in the Herculaneum bones was completely unexpected.
"We realised then that commonly held assumptions regarding the manor of their death could not be true.
"If the bones were exposed to extreme heat then we would expect the collagen to be lost very quickly from the bone. Finding collagen was our first indicator of lower temperature exposure."
Tests conducted on the ribs of 152 individuals from the fornici revealed they did not match the patterns expected if they had been exposed to extremely high temperatures of 300 - 500C.
Forensic expert Professor Tim Thompson, the lead author from Teesside University, said: "The people hid for protection, and got stuck. The general theory has been that these individuals were instantly vaporised.
"What was interesting was that we had good collagen preservation but also evidence of heat-induced change in the bone crystallinity. We could also see that the victims had not been burned at high temperatures."
The research team said it may have that the pyroclastic flow was relatively cool, with some estimates suggesting it was only 240C. The fornici may have also provided some insulation, further lowering the temperature people were exposed to.
The researchers said the collagen preservation in the bones of the Herculaneum victims has opened up a range of new avenues of research, including using stable isotope measurements to generate a snapshot of the Roman diet.
Mount Vesuvius victims who died at Herculaneum had much more painful deaths than previously thought, British scientists have discovered.
It is commonly thought that people living in the seaside town, who fled to stone boat houses along the beachfront when the volcano erupted, were vaporised by the extreme heat of the volcanic eruption.
But new analysis of skeletons from the scene shows that they may have lived long enough to suffocate from the toxic fumes of the pyroclastic flow - the devastating, ultra fast stream of hot gas and volcanic matter which flows from some eruptions.
Archaeologists found that the structure of the skeletons and remaining collagen was inconsistent with vaporisation, suggesting that the bodies were not exposed to temperatures as extreme as expected.
The eruption of Vesuvius in AD79 famously buried the Roman town of Pompeii and the pyroclastic flow destroyed nearby Herculaneum. More than 340 people who took refuge in the town's vaulted stone boathouses (fornici) perished.