| 摘要 |
<p>A method of controllably venting gases generated by explosions in a manhole space having a manhole cover extending over said manhole space received within an opening in a frame structure, comprising the steps of arranging locking features on a perimeter of said manhole cover spaced apart from each other and extending radially outwardly to be aligned beneath portions of a said frame structure extending around said opening and with a vertical clearance between said locking features and said portions of said structure so as to allow said manhole cover to rise up in the event of an explosion to clear said structure and thereby create an annular gap between the underside of the cover and the top of said structure allowing venting of gases from said manhole space; and preventing further vertical movement of said manhole cover by interengagement of said locking features and said structure portions upon continued upward vertical movement of said manhole cover to thereby prevent said manhole cover from being blown completely free of said structure and able thereafter to drop down over said opening in said frame structure.</p> |
