DOW Corning has reassured residents that there was no risk to public health after a plume of black smoke was spotted emerging from a stack on the Barry site.

Residents were alarmed to see the smoke rising from the Cardiff Road site on Sunday, June 18.

The company said an event occurred at the combined heat and power plant (CHP) on Sunday afternoon, when a gas turbine and boiler tripped.

The CHP is operated & maintained by ENGIE on Dow’s behalf.

A Dow Corning spokeswoman said: “The ENGIE operators had difficulties in restarting the boiler.

"This resulted in some soot generation in the boiler until the operating conditions could be stabilised. This was the cause of the black smoke.

“This was an operational upset that had no risk to the public during the event.”