US Patent 9004810 Explosion mitigating cover

A manhole cover assembly configured to behave as a relief valve in an explosion event, opening so that fluid, such as air or explosive gas, may vent from an underground area. The manhole cover assembly may include a manhole cover and a frame, and may be configured to limit movement of the manhole cover with respect to the frame in response to increased pressure on the manhole cover. In one embodiment, the manhole cover may include legs that are configured to enable a range of movement of a portion of the cover such that the cover can be unseated at an angle with respect to the frame to allow fluids to escape from the underground area.