Lock out, tag out and Try out

At 8:30 a.m. on March 6, 2017, Employee #1 was using an eight foot A-frame fiberglass ladder to remove the steel top cover of the natural gas fuel filtration skid and replace the filters. The employee began to unbolt the steel top cover when it exploded and struck the employee. Employee #1 did not lock out/tag out, nor was the vessel de-energized/purged prior to removing the top cover. The employee sustained blunt force trauma to his body, causing complete amputation of both arms, killing him.
Source:Osha.gov