[Legacy Report] Causes and Mitigation of Manhole Events

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Joint meeting with PES. Seminar format. Abstract: Manhole events are dominated by “smokers” and fires, with relatively few explosions. This suggests that the conditions which result in explosions are a small subset of those which result in “smokers” and fires. Our objective is to gain a quantitative understanding of the phenomena on which the evolution of manhole events depend in order to eliminate the conditions which result in explosions. We have found that manhole events can be divided into those driven by electrical fault energy, which are a small minority, and those driven by fire in which electrical energy starts the event which can evolve thereafter to a manhole explosion without any further input of electrical energy. This latter, dominant, class of manhole events is driven by fire, which requires air flow down the duct. We believe that by controlling air flow, fire-driven manhole explosions can be eliminated, and we are presently in the process of modeling the fire-drive process using computational gas dynamics. In addition to the above issues, the material properties which result in fire-drive manhole events will be discussed, along with quantitative measurements of gas evolution from decomposition of secondary cable insulation and jacket.

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