Elevated flaring has stopped at the Mossmorran petrochemical plant in Fife.
It follows the unplanned shutdown of a major compressor at ExxonMobil's site just before 15:00 on Tuesday. Unplanned flaring followed while the compressor was restarted.
Residents said flames were visible from Edinburgh and as far away as Dundee. Production at the plant only resumed on 21 February after a temporary shutdown.
The site was closed for five months in August after two boiler explosions.
Chris Dailly, Sepa's head of environmental performance, said: "Having been in regular contact with ExxonMobil Chemical Limited over the last day, Sepa has been notified that normal operations have now resumed, and elevated flaring has ceased.
"Our officers have continued to deploy air and noise monitoring during this period of unplanned flaring, and initial data suggests no breach of UK air quality standards.
"As we've stated, we're disappointed that flaring occurred again so soon after the restart.
"Whilst recognising that flaring is an important safety mechanism, this is a further reminder of why the short and medium term steps being taken by Sepa to require the operator to mitigate flaring is so critical, including noise-reducing flare tips in 2020/21 and bringing forward plans for fully enclosed ground flares."
He added: "We remain focused on the rapid conclusion of our current criminal investigation into unplanned flaring to an evidential standard."