Two firefighters killed in a blast at a fireworks factory could not have known an explosion was imminent, an expert has said.
Independent consultant Mick Massey said any risk of a blast would have led to East Sussex crews moving to safety.
Investigations are pending but police and fire officers are still unable to enter the scene of the fire near Lewes.
The cause of the fire at Festival fireworks UK Ltd on Sunday is still unknown. Twelve people were injured.
Mr Massey said front-line crews would have assessed risks and the blast would have been caused by "something they didn't know about".
The expert, who served with London Fire Brigade for 30 years, said: "If there was a danger of an explosion of that magnitude then they would not have allowed crews in there."
He said crews would have made a "dynamic risk assessment" - a system followed by every brigade in the country.
He said the county's crews would have had prior knowledge of the depot, but added: "Any knowledge about the risks would obviously be based on the last time that officers looked at the building.
"What you can't legislate for is the unforeseen."
Fire service photographer and cameraman Brian Wembridge, 63, died in the blaze. He had been re-employed to give support at fires.
The other man who died was 49-year-old control room staff member Geoff Wicker, who was also a retained fire officer.
One body still has to be recovered.
Four people were taken to hospital - two firefighters, a police officer who needed surgery to his leg, and a passer-by.
Police said only the passer-by remained in hospital on Monday evening. The 39-year-old from Uckfield suffered chest injuries and needed facial surgery.
A 200m exclusion zone is in place because of fears up to 20 gas cylinders on the site could explode without warning.
An Army bomb disposal unit is at the scene and its remote-controlled vehicle is being used to assess the state of the cylinders, which have to cool for 24 hours before officers can enter the site.
Emergency services said they did not expect to be able to enter the site until Tuesday.
The firefighters were the first to die on duty in England and Wales this year, and Chief Fire Officer Des Pritchard said he believed they were the first in East Sussex since 1974.
A total of nine firefighters, a police sergeant and two members of the public were injured in the fire, which broke out at 1350 GMT on Sunday.
The investigation into the cause, which is expected to take "many weeks", will involve the police, fire and rescue service and the Health and Safety Executive.
It will also focus on whether licensing conditions were followed by the factory and, if so, whether they need to be tightened.
John McGhee, of 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.
Festival fireworks UK Ltd is one of the UK's biggest firework importers and was behind the millennium display along London's River Thames. The firm employed up to 50 staff.
John Winter, the owner's brother, said the fire could have been caused by an electrical fault.
It is understood the fireworks store was a concrete complex with steel doors.