Police are investigating what caused a toxic fire at a factory which led to hundreds of people spending the night in hotels or with family.
The fire caused substantial damage to the building
Up to 600 houses in the Coleraine area had to be evacuated due to smoke from the fire at a medical equipment plant.
John Armstrong, managing director of Armstrong Medical, said much of the plant in Wattstown Business Park would have to be demolished.
He said the fire may have been caused by an electrical fault in a trailer.
"The main warehouse and the main administration block have been totally destroyed," he said.
"I can't say categorically that there will not be job losses, but it is certainly our intention to minimise them."
John Armstrong said much of the plant would have to be demolished
About 80 firefighters tackled the blaze at the warehouse.
Peter Reilly of the Fire and Rescue Service said smoke from the fire had drifted for up to 15 miles.
"This fire, which was quite substantial, gave off large volumes of thick acrid smoke because it specifically involved plastics," he said.
"The smoke could be seen as far away as Lough Neagh and unfortunately for us it was descending into local housing estates and could possibly affect the health of the residents."
Brought under control
About 175 homes in the Windy Hall estate and another 400 homes in Knocklynn and Newbridge were evacuated until residents were allowed to return at about 0700 BST on Friday.
Residents had spent the night at an arts centre in Portstewart and Coleraine Leisure Centre.
The blaze broke out at about 1730 BST on Thursday and when fire crews arrived they found a well developed fire in a large two-storey warehouse building.
The fire was brought under control but a large store at the back of the plant has been destroyed.
Fire crews worked to bring the blaze under control
Armstrong Medical was established in 1984 to manufacture and sell respiratory disposable products for critical care applications.
Ulster Unionist Norman Hillis expressed fears for the jobs of almost 70 staff at the plant.
He added: "The fire could leave the immediate future uncertain for staff at Armstrong Medical Services.
"The company is one of Coleraine's most successful businesses and it has only recently expanded premises at Wattstown Business Park.
"The extent of the damage is not yet clear but certainly it is a major blow to this progressive company."