The worst accident in terms of life lost and involving floating Rigs or Drillships were the Alexander Kielland capsize at the Ekofisk field in 1980. 123 persons lost their life: https://officerofthewatch.com/2013/04/29/alexander-l-kielland-platform-capsize-accident/
The case is still being iin the news in Norway, as the relatives of those who lost their life is still not satisfied with the explanations that was given in the many investigations conducted: https://sysla.no/offshore/ny-horing-om-kielland-ulykken/
This accident resulted in major changes to the design criteria for offshore units, safety equipment, operating procedures and training and certification of personnel working offshore in Norwegian waters, or on Norwegian owned and operated offshore units working anywhere in the world.
These requirements applies regardless of the unit’s registration or ownership, or nationality of the crew, as long as they are engaged in activities on the Norwegian OCS, or in Norwegian waters.