He was killed by the mutated Fifield during his attack in the ship's hangar bay.
The mechanic was part of the team on board the Prometheus who gave maintenance to the all-terrain vehicles used to explore the surface of the LV-223 planetoid during the mission.
During Fifield's attack of the hangar bay, he was the first crew member killed by him.
After Janek noticed Fifield's spacesuit camera online and getting images just outside the hangar bay he orders the crew to check outside the ship. Mechanic 3 ordered Barnes to open the main hangar bay doors. After this he found Fifield in the ground in a strange pose. He kicked Fifield's boot trying to make him react and called Wallace, another mechanic, to take a look. While doing so the horribly mutated Fifield raised up and all the frightened mechanic could do was calling his name. Suddenly, the mutant monster brutally hit the mechanic's space helmet, shattering it and killing him instantly.