A jury has been told they cannot conclude factory workers Daniel Timbers and Barry Joy were killed unlawfully as they retire at the conclusion of the two week inquest into their deaths.
Mr Timbers, 28, was working alongside Mr Joy, 56, in the paint spray booth of the Harford Attachments factory on Spar Road when there was an explosion and a fireball, Norfolk Coroner's Court in Norwich heard.
The inquest has heard details of working practices at the factory, including health and safety systems and the construction of the spray booth which had been bought from RAF Lyneham after it closed.
Summing up the case, area coroner Yvonne Blake described colleagues who made attempts to rescue the two men as 'very brave'.
She also ruled out a conclusion of unlawful killing, as the exact cause of the fire could not be determined.
'As a matter of law and based upon the evidence this is not a case of unlawful killing, suicide, natural causes or industrial disease,' she told the jury.
She added: 'You have heard evidence about the, I must say very brave, attempts to go in and save Mr Joy and Mr Timbers.'
She also quoted the Health and Safety Executive report from specialist inspector Brian Mills.
'He said the very many potential sources of ignition made it a probability something may occur that led to an explosion,' she said. 'It may never be known with absolute certainty but what can be said is the lack of control shown by the company made it almost inevitable a coincidence of ignition and flammable vapours would occur.'
In his report Mr Mills said the two most likely causes of the explosion were sparks from the nearby welding booths or poor installation of the equipment.
The jury were warned not to take adverse inference from the fact managing director of Harford Attchments Steve Kidd refused to answer repeated questions under legal advice.
Post-mortem examinations recorded that Mr Joy, of Spencer Street, Norwich and Mr Timbers, of Dereham Road, Norwich, both died as a result of the effects of fire and inhalation of fumes of combustion.
The jury took two hours deliberating to reach a narrative conclusion.
The foreman identified in the conclusion that there was no record of relevant training or risk assessments relating to the spray booth.
A HSE spokesperson said: 'Our thoughts remain with the families of Barry Joy and Daniel Timbers. We have fully supported the inquest process; three operational inspectors and a scientist from HSE's Science Division have given evidence to the jury.
'Our own investigation into this incident is on-going. It would therefore be inappropriate to comment further.'
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