A bridge to a black swan

I live in Orlando: the city's Central Park lake is home to many black swans -- we also have the white kind too -- thus, I'm ok with black swans. On the other hand, Orlando doesn't any big bridges -- you have to drive 90 minutes to Tampa on the Gulf coast to get to a big bridge.

But, we read about bridges, and some of the black swan events that go along with big bridge projects.
So, here's one of those "Who knew?!" project events that most would call a black swan:

Remember the earthquake in San Francisco in 1989? Some of us do; it came right in the middle of a major league baseball game on television. The upshot was that major damage was done to the bay bridge that connects SF with Oakland. (Not the Golden Gate, but the other bay bridge)



Now we learn:

... in the San  Francisco bay bridge project ... [it] seems there are these bolts.  No ordinary bolts mind you but rather critical mission failure bolts in the bridge's earthquake design ....

The new bridge, whose foundation will reach the bedrock underneath, will be the world’s largest self-anchored suspension bridge, ... That is why the failure of some high-strength steel bolts attaching shock-absorbing devices called shear keys to a concrete crossbeam under the roadway raised alarms. When workers tightened the 17- to 24-foot-long bolts in March, 32 in a batch of 96 snapped.

Engineers blamed hydrogen-assisted cracking, in which atoms of hydrogen infiltrate steel and make it brittle, but they have yet to determine its cause.

I really can't remember the last time I put hydrogen-assisted cracking on a project risk register... perhaps never! Indeed, I can't ever remember discussing it, so -- prima facia -- it must be a black swan: Something not envisioned; something with devasting effects; something evident in hindsight.