Part of William Bradley Bessire's job as project co-ordinator at BP's Texas City refinery was to put on a lavish "safety lunch" to reward the workers in his section for every week without an accident.

At such a lunch on March 23 2005, Mr Bessire finished a big plate of fajitas, rice and beans, congratulated the workers on another good week and headed back to the trailer that served as his office – just as the refinery's nearby isomerisation unit was being restarted.