It sounded like Armageddon.

We had a large power failure at the steelworks today. The blast furnace, which is like a huge pressure cooker, has devices called bleed valves which open in an emergency to release the pressure. The kind of emergency that happened today. The noise was absolutely biblical. I was out in the open at the time, 100 metres away, and it was impossible to tell which direction it was coming from (even though I knew). The sound was through and all around me. Some people thought there'd been a terrorist attack. It was a reminder of how dangerous the place can be.

Of course we spent the rest of the day resetting computers and repairing panels. It was an interesting day.