• Maintenance supervisor assumed Permit to Work assured Pump A would not be started so didn''t tighten flange plate. • Maintenance supervisor assumed leaving the signed Permit to Work on the shift supervisor''s desk was enough to ensure he''d know Pump A couldn''t be used. • Shift supervisor assumed a Permit to Work showing a maintenance task had not begun meant that no other work had begun. • Engineers adapting the rig from oil to gas extraction assumed that changes in inter-modular containment were unnecessary. • Engineers designing the rig assumed that the safety systems and the equipment they were protecting were independent by physical separation. • Managers on other rigs assumed that the absence of request from Piper Alpha for them to stop pumping made it unnecessary. • Rig designers assumed that men would be able to reach lifeboats situated low on the rig.
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