Drilling rigs are equipped with enclosed lifeboats that can be dropped into the ocean in an emergency and owners must meet a series of technical and operational requirements for how to plan and carry out evacuations.

"All the audits identified a nonconformity from the regulations. This was the same for Maersk, Transocean and Odfjell," PSA said, adding that the firms had been asked to explain how they would fix the shortcomings.

"The PSA has now received a response from (each) company, but this does not describe how the breach of the regulations is to be corrected," it said in a statement.

The three companies did not immediately respond to Reuters requests by phone and email for comment.

The companies were given a March 31 deadline to fix the shortcomings.