The Mossmorran gas plant has been flaring throughout the night, creating an orange glow in the skies over Fife once again.
Locals are furious at the unannounced flaring which began on Tuesday afternoon and continued into Wednesday.
It follows a similar incident in February where the skies to the north of Edinburgh were left looking like Mordor.
Workers at the site also staged a walkout in protest over pay and working conditions.
The petrochemical plant's owners, ExxonMobil, said they had encountered an unexpected problem with a compressor at the site.
An unearthly orange glow was visible from as far as East Lothian on Tuesday night, with some comparing it to a northerly sunset.
One local posted that the plant was "belching black smoke" as well as the flames.
The Mossmorran Action Group, which has been campaigning on behalf of residents near the site, raised concerns about the plants safety.
Spokeswoman Linda Holt said: "Once again ExxonMobil is forced to resort to emergency flaring because something has gone badly wrong.
"As the ground shakes, and a huge bright flame amid clouds of black smoke looms over communities, they are expected to suffer in ignorance. SEPA expects the flaring to last all night but Exxon cannot say when it will stop.
"Since the 'catastrophic breakdown' of the plant last August which caused continual ground flaring, the problems restarting according to schedule, the 'apocalyptic flaring' a couple of weeks ago and a walk-out by workers over safety issues, neither ExxonMobil nor HSE nor Sepa have offered any explanation.
"Reassurances that the plant is 'safe' do not wash. A whistleblower told MAG two weeks ago that the plant restarted prematurely with only two out of three boilers and these were 'unfinished.'
"Is the Scottish Government waiting for a major accident before it steps in?"
Exxon Mobil said: "To keep the rest of the plant running and reduce total duration of flaring, we safely manage this process through the use of our elevated flare.
"We are taking actions to reduce the size of the flare during this work, including maximising the use of ground flares.
"We apologise for any inconvenience to our local communities."
