Bright flares have been seen coming from the stacks at the Valero oil refinery near Pembroke recently.
People have been sharing images online and discussing why the flames are so much bigger and brighter than they normally are.
Darren Tucker, from Milford Haven , was one of the people who noticed that the stacks at the refinery were churning out large flames and thick black smoke: “It doesn't happen all the time. At the moment, they are burning off a lot of excess gas due to the plant being offline since the national power cut.
“I don’t think it’s too much to worry about, people just panic because they are not used to seeing the flares so big.”
One onlooker in Broad Haven captured an image of the glow from the Valero refinery on the horizon in the early morning.
The Valero plant suffered an outage during the UK-wide power cuts that affected nearly a million homes and businesses on August 9 and the increase in flaring is linked to bringing the plant fully back online.
Bad weather and lightning were partly blamed when two power stations at Hornsea and Little Barford lost power at the same time at the beginning of August.
A spokeswoman for Natural Resources Wales said: "NRW are aware through our regulation of the Pembroke Oil Refinery of flaring at the site.
"The large flares are taking place as units start back up after the refinery lost power from the National Grid on Friday 9 August 2019 which was a rare occurrence.
"Since the power cut, Valero had to undertake unplanned work to bring the refinery back on line.
"We have been in discussions with Valero and reduced flare size is expected over the next couple of days. The power loss at the refinery is subject to a full investigation which is currently on-going."
