This paper describes the investigation and failure analysis of a welding regulator fire that resulted in explosive energy release and injury to an operator. The failure analysis revealed that an organic contaminant in the form of an insect had entered the cylinder valve prior to attachment of the regulator. Ignition of the insect and nest materials led to an explosion-like overpressure that blew the high-pressure poppet through the nozzle and forcibly separated the regulator bonnet from the main body. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) on the residue from the fire-damaged components confirmed that insect nest material was present at the time of the fire. Autogenous Ignition Testing (AIT) on similar insect debris revealed a very low ignition temperature and probable high heat of combustion. The explosion-like energy release was felt to be related to a momentary containment of the fire in the early stages of the combustion event which led to greater involvement of the cylinder valve's nylon seat and resulted in increased reaction kinetics.