A fire service photographer and cameraman was one of two fire crew who died at a blaze at a fireworks depot.
Retired officer Brian Wembridge, 63, one of the first on the scene near Lewes, East Sussex, had been re-employed to give support at fires.
An investigation is under way into the blaze, which also left two other fire crew members seriously ill in hospital.
A member of the public was also kept in hospital overnight. A 200-metre cordon is still in place around the site.
Chief Fire Officer Des Pritchard said it remained a "very difficult and dangerous scene" on Monday morning.
Small fires are still burning and gas cylinders have to be left to cool.
A total of nine firefighters, a police sergeant and two members of the public were injured in the fire at Festival Fireworks which broke out at 1350 GMT on Sunday.
One of the injured had critical head injuries.
Mr Pritchard said a number of buildings on the site were destroyed in an explosion and others severely damaged by the fire.
The investigation into the cause of the fire and explosion, which was expected to take "many weeks", would involve the police, fire and rescue service and Health and Safety Executive.
Sussex Police said the other man who died was a 49-year-old control room staff member who was also a retained fire officer.
"This was a tragic incident where two of our firefighters lost their lives," added Mr Pritchard.
He said having to tell the families their loved ones had died was the "most difficult task" of his 30-year career.
Lewes MP Norman Baker said: "We need to establish whether the licensing conditions were adhered to and, if they were, whether there needs to be some tightening of the way fireworks are held."
John McGhee from the Fire Brigades Union said it would be asking East Sussex Fire Authority whether proper plans were in place to deal with an incident at the factory.
The firefighters were the first to die on duty in England and Wales this year, and Mr Pritchard said he believed they were the first in East Sussex for three decades.
In 2004 an off-duty firefighter died while rescuing his brother, he said.
The fire service flag is flying at half-mast at East Sussex HQ in Eastbourne.
The explosion was so big it was heard by people in Uckfield, 12 miles away.
Eye-witnesses reported seeing a huge mushroom cloud of smoke and explosions of fireworks which sent debris through the air.
Twelve ambulances, 10 fire engines, and an air ambulance attended the premises at the Broyle, near Halland.
John Winter, whose brother owns the depot at Marley Farm, in Shortgate, told BBC News 24 there had been "an almighty bang, and the place shook".
He said his brother and family had managed to get out of the building safely, but their house had burnt down.
Meanwhile, Jason Winter, nephew of the depot's owner, said the family's pets had died.
"They have lost everything, even down to their dog, their dog's in the house, the dog has died," he said.
"They have lost the house, they have lost garages, offices, all the buildings, they've lost their vehicles, their lorries, they have even lost their guinea pigs."
Residents in the area spent the night at Ringmer Community College.
Festival Fireworks is one of the UK's biggest firework importers and was behind the millennium display along London's River Thames.
It is understood the fireworks store is a concrete complex with steel doors.
Jo Hyne, who lives about 500m from the depot, said she heard a loud bang which she had thought at first was thunder.
She said there was "a colossal amount of smoke, and rockets going off", before a much larger explosion that shook her house.
Another eye-witness, Richard Mitchell, watched the drama unfold from outside a pub in Lewes Road, Ringmer.
"It was like a fireworks display with a fire in the middle of it," he said.
Claire Freeman, from Ringmer, had been eating in the Wok Inn next door to the depot when the fire broke out.
She said diners were evacuated to the car park at the time of the largest explosion.
She told the BBC news website: "Pieces of wood [were] falling, hissing into puddles around us, at which point we left pretty sharpish."