Abstract: An air ventilation conduit and related process are provided for ventilating an enclosure accessed by a manhole. In one embodiment, the conduit has a pair of outer cylindrical sections and a central section having a cross-sectional shape of a crescent or a segment of a circle where it passes through the manhole to provide a minimum of obstruction for men and equipment passing through the manhole. Intermediate sections of varying cross-section connect the central section to the cylindrical outer sections so that the outer sections are offset from the axis of the manhole. The central section is configured to obstruct no more than about 10 percent of the manhole opening, while causing either no air flow rate reduction, or a reduction of no more than about 10 percent as compared to the flow rate through a cylindrical conduit similar to said outer sections.

Abstract: Air ventilation conduit for passing through manhole the conduit having a central section with a cross section having the shape of a crescent or a segment of a circle where it passes through the manhole to provide a minimum of obstruction for men and equipment passing through the manhole, cylindrical outer sections of the conduit for connection to flexible hose, and intermediate sections of varying cross section to connect the central section to the cylindrical outer sections offset away from the manhole.