Manhole cover
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A manhole cover is a removable plate forming the lid over the opening of a manhole, an opening large enough for a person to pass through. It is used as an access point for an underground vault or pipe
A round manhole and its cover
Ancient Roman sewer grate made out of lime sandstone, 1st century AD, excavated at Vindobona (present-day Vienna)
Pick holes in manhole cover, Palo Alto, California, USA
Manhole valve made in 2022
Operation Plumbbob
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Operation Plumbbob was a series of nuclear tests that were conducted between May 28 and October 7, 1957, at the Nevada Test Site, following Project 57, and preceding Project 58/58A.
Manhole cover
…manhole covers stolen in a single day. A manhole cover was accidentally launched from its shaft during an underground nuclear test in 1957. During the Operation Plumbbob nuclear tests, a 900-kilogram (1,984 lb) steel plate cap was blasted off the test shaft at an unknown speed and appeared as a blur on a single frame…
Plumbbob-Rainier device
Plumbbob-John launch, via F-89