Who was killed by the flames of the furnace in Daniel 3?

Answer: The men who carried them up

The furnace was so hot that the flames killed the soldiers who carried Shadrach, Meshach and Abednego up to throw them in.

“The king’s command was so urgent and the furnace so hot that the fiery flames killed the men who carried up Shadrach, Meshach, and Abednego.”— Daniel 3:22 (BSB)