It has been four years since BP’s biggest refinery exploded in Texas, killing 15 people and injuring hundreds in the worst US industrial accident in more than a decade. Yet US authorities have not yet succeeded in getting the UK oil major to bring the facility into compliance with safety standards required by its settlement agreement.

The lapses have caused even the unit in charge of enforcing compliance – the labour department’s Occupational Safety & Health Administration (Osha) – to be criticised for not increasing its supervision of the facility.