A number of people living in Thornton reported being woken by an 'explosive bang' at the former ICI site this morning (July 12).
Families said they had been 'jolted awake' by the thunderous sound at around 7.30am.
According to one resident, the noise was swiftly followed by the wail of emergency alarms from the chemical site.
"Anyone else hear what sounded like an explosion on the old ICI site earlier this morning?
"Followed shortly by an alarm sounding?", asked one concerned resident on Facebook.
The mystery 'explosion' has prompted much speculation as to what happened at the site.
Lancashire Fire and Rescue Service said they had not responded to any incidents at the site this morning.
But the Gazette can now confirm that something did happen at the site this morning.
What caused the 'loud bang' at the former ICI site this morning?
Responding to our query regarding a potential incident at the site this morning, AGC Chemicals Europe have confirmed that an incident did occur.
A spokesman said: "AGC Chemicals Europe Ltd can confirm that at 7.30am on July 12, 2019, a premature operation of a rupture disk occurred.
"This would have produced a loud noise in the vicinity.
"The operation of this disk does not pose a risk to either employees or the public.
"A routine investigation into the operation of this disc is underway."
What is a rupture disk?
A rupture disk, also known as a pressure safety disc, is a safety device that, in most uses, protects a pressure vessel, equipment or system from overpressurization or potentially damaging vacuum conditions.
Rupture disks are commonly used in petrochemical, aerospace, aviation, defence, medical, railroad, nuclear, chemical, pharmaceutical, and oil field applications.
Has anyone been injured?
AGC Chemicals confirmed that no employees have been injured in the incident and there is no risk to the public.