The Alexander L Kielland was a semi-submersible platform accommodating the workers of the bridge-linked Edda oil rig in the Ekofisk field, approximately 235 miles east of Dundee, Scotland, in the Norwegian Continental Shelf. The Phillips Petroleum-operated platform capsized in March 1980, killing 123 people.

Only 89 out of 212 workers survived the accident and most died by drowning as the platform turned upside-down in deep waters. The platform capsized after the failure of one of the bracings attached to one leg of the five-legged platform structure after strong winds created waves of up to 12 m high on the day of the accident.

Ref: https://en.wikipedia.org/wiki/Alexander_L._Kielland_(platform)

Image Credit: Norwegian Petroleum Museum