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Two concrete structures, one with a vent and one a square pit, on a path amidst lush green foliage and trees, in an illustrated style.

Two concrete structures, one with a vent and one a square pit, on a path amidst lush green foliage and trees, in an illustrated style.

Where openings below grade provide required natural ventilation, the outdoor horizontal clear space measured perpendicular垂直 to the opening shall be one and one-half times the depth of the opening. The depth of the opening shall be measured from the average adjoining ground level to the bottom of the opening. See more