Welding sparks seen flying near a paint-spraying booth may have caused an explosion which killed two men, an inquest has heard.
Daniel Timbers, 28, and Barry Joy, 56, died in a "fierce fire" following an explosion at digger bucket maker Harford Attachments in Norwich in 2015.
An inquest was told there were a number of ways the fumes could have ignited.
Brian Mills, of the Health and Safety Executive (HSE), said the firm could have identified the ignition risks.
The explosions specialist said sources of electricity such as a walkie-talkie and a mobile phone had been found in the booth after the explosion and one of the deceased men had a lighter in his pocket.
"These type of items should not have been inside a spray booth... These sources of potential ignition were well within the control of the company," he added.
He told Tuesday's hearing that ventilation in the paint-spraying booth was switched off before the explosion, potentially leading to a build-up of flammable fumes.
CCTV footage shown to the jury shows welding work going on near to the booth before the booth erupts into flames and black smoke billows out of it.
Mr Mills said: "It's quite compelling when you see welding sparks flying over the wall of a welding booth and it's almost coincident with the explosion event occurring."
He said there are "such things as coincidences" and added: "It's impossible to say with 100% certainty which event caused ignition."
Mr Mills said a 205-litre drum inside the booth had exploded and showered it with its flammable contents.
"When the drum exploded it would have taken off like a rocket, hit the ceiling and come down to rest on its side," he added.
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 inquest continues.
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