Thermodynamic Analysis of Explosive Events in Manholes and Electrical Vaults

A computer code is used to simulate the conditions that exist during a manhole event consisting of an electrical fault and a gas explosion. When energy is generated within the structure, pressures can reach levels sufficient to propel the cover from its frame. The code quantifies the effects of the event and provides guidelines for the design of safety devices that can minimize the potential danger of the event. Differences between chemically-driven and electrically-driven events are shown to require different design criteria for cover restraint systems. Devices designed to restrain the cover must be able to withstand explosive forces and react in sufficient time to reduce internally generated pressures. By understanding the fundamental characteristics of arcing faults and gas explosions and their effect on the internally generated pressures, safety devices can be designed to mitigate the effects of the event in manholes and vaults and thereby reduce the potential danger to maintenance crews, first responders and the public.