Access cover anatomy

This large and elaborate East Bay MUD access cover, on San Leandro Avenue in deep East Oakland, displays a lovely radial design. It also includes good examples of some typical features of access covers.

At the top and bottom edges, at 12 and 6 o’clock, are lifting notches, where a worker attaches the hooks to raise the lid safely. Halfway out from the center is a ring of aeration holes, arranged on the major compass points. They happen to filled with dirt, except for the one marking Northeast. Their function is to equalize the pressure between the hole and the atmosphere, guarding against the effects of unusual events, like a tornado in the air or a sudden flood or explosion down below, that might push the lid out of its rim.

The smaller lid on the right side has its own lifting hole. Presumably it allows access so someone can monitor conditions in the shaft without going through the chore of pulling off the large lid. Because a smooth finish could present a slipping hazard, the secondary lid was textured by a welder. Perhaps there’s an arcane pattern in it representing a message, but it’s more likely to be a random set of metal bits, a scribble arranged by eye and intuition.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: