During the San Francisco summer, fog is a way of life. Limiting ship operations under the Bay Bridge during foggy conditions could have threatened to shut the port down, so the structure was exempted from a list of fog-limited operating areas during the most recent update to operating regulations.

That decision may have played a role in the recent collision between the a 752-foot oil tanker and the Bay Bridge, where more than $500,000 in damage was done. The bridge avoided damage to its superstructure as a result of bumper system that were in place.

Certain operations are limited when visibility is under a half of a mile. At the time of the accident, visibility was reported to be about a quarter of a mile, according to the Coast Guard.

The pilot who was aboard the ship at the time of the accident had radioed before going underway that visibility was about a half mile, but apparently denser fog set-in before the ship reached the bridge. Strong currents under the bridge, driving the ship dangerously close to its structure, could have exacerbated the conditions.

It was not the first accident in the pilot’s record, who had previously been involved with three incidents ranging from inadvertent contact while docking to running aground.

Read the full story at the Mercury News.