Forensic Engineering Metallurgical Analysis of PTO Air Compressor Rupture and Fire

Abstract

The coalescer of an air compressor mounted on a utility truck ruptured, resulting in the expulsion of burning oil onto a nearby employee. An investigation ensued to determine the root cause of the injuries. Many potentialcontributing factors were examined, including system and component manufacture, design, installation, maintenance, and use. Metallurgical and failure analysis procedures were used to determine root cause of the system failure and related injuries. A power take-off (PTO)-driven compressor operates at high temperature (200°F) and pressure (110 psig), creating opportunities for dangerous conditions. The system has a safety shutdown control to prevent the system from going over temperature and pressure limits. The exploded coalescer and fire in this case indicated the temperature and/or pressure systems were compromised as well as the control system. Compressor failures are not uncommon; however, violent failures that cause fire and injury are much less common. PTO compressors are relatively simple machines with only about 25 components. However, the proper function of most components is essential to the safe operation of the unit. In this investigation, it was necessary to look at each component relative to its fitness for service and potential contribution to the system failure.