SAN FRANCISCO (CBS SF) — It has been more than two years since an empty oil tanker collided with a tower of the Bay Bridge in heavy fog. Coast Guard investigators blamed the accident in part on a broken broken radar beacon on the bridge.

That piece of safety equipment was found to be broken again during a monthly inspection.

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One of the bridge’s three beacons — which alerts sailors to the midpoint between bridge towers — has not been working properly since December 17.

Caltrans is in charge of maintaining the beacons and has replaced the broken one twice, but the backups have failed.

Deb Self, executive director of San Francisco Baykeeper, tells KPIX 5 that these broken beacons are a disaster waiting to happen and she used the 2007 Cosco Busan oil spill as a reference for what might occur if the beacons aren’t fixed properly.

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“We have a very sensitive environment here and once you get oil into it, it’s very hard to get it out,” she said.

Container Ship

A container ship negotiates San Francisco Bay. (CBS)

The shipping rules have changed since the Cosco Busan incident. Now ships can’t leave the bay — or port — when there’s heavy fog, but they can still enter the bay.

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“You can’t ask them to just idle in the Bay until the fog goes away, so if they’re coming into Port, they’re gonna come in and they’re gonna come in under the Bay Bridge. So we have had ships coming in under heavy fog when the radar was down,” Self said.