A lightning strike ignited methane gas at a food waste plant sending a huge fireball into the sky.
The Agrivert site at Benson, near Wallingford, Oxfordshire, was struck at about 17:20 BST on Thursday.
Commercial manager Harry Waters said lightning ignited gas stored in a waste digester, causing a fire which burned for 20 minutes and destroyed the roof.
He said staff who were on site at the time escaped injury and the plant was "fully functional".
'Act of God'
Mr Waters said staff ensured that the plant's engines kept running to consume the gas during the fire and also checked that automatic safety systems were working.
"It was a very unlucky event, an act of God, and we're pleased that our procedures have worked so well," he said.
Mr Waters said the storm overwhelmed the lightning protection systems at the site, which processes local food waste into energy from methane gas.
Emma Shepperd captured a video of the fireball from her home, while trying to film the storm.
She said: "I looked out of the window and it struck the top end and that's when it caught fire."
Agrivert said a fire crew from neighbouring RAF Benson was the first on the scene.
Oxfordshire Fire and Rescue Service said four fire crews were sent to the scene.
A spokesman said: "Firefighters wearing breathing apparatus tackled the blaze, which involved methane gas naturally produced at the site.
"Crews worked with site specialists to ensure the plant was left in a safe condition, leaving the scene shortly after 11pm."