Safety inspectors forget to replace a valve at the Piper Alpha Oil Rig
Money lost in 1994: $3.4 billion in repairs
Inflation adjusted price: $5.1 billion
In May of 1994, oil workers were evacuated from the Piper Alpha Oil Rig after an explosion. The explosion killed 167 of the 226 men working.
During a routine check, inspectors removed and replaced all safety valves, except for one, which was never put back. Unaware that the safety valve was missing, a worker pushed the start button, and gas began to leak out.