One householder said: “It sounded like a jumbo jet taking off – that’s as bad as I’ve heard it for a while.”
According to Ineos, the flaring was not due to a planned shutdown at the site and the matter is currently being investigated.
An Ineos spokesman said: “One of the Petroineos refinery units at the Grangemouth site was safely shut down on Monday night. During this process excess gases were flared. We apologise for the inconvenience caused during the flaring.
“We are investigating the circumstances surrounding the plant shutdown. The plant will remain shut down until we have completed our investigations and then we will take the necessary steps to safely restart the plant.
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“Fuels remain available to our customers.”