Daniel Timbers, 29, and Barry Joy, 56, were working at Harford Attachments in Spar Road when they were killed, shortly after 09:00 BST on Monday.
The men are believed to have been working in a paint-spraying area.
Their bodies were removed from the site on Tuesday afternoon.
A forensic search has been carried out at the company, which makes buckets for diggers.
Det Ch Insp Paul Durham said "significant progress" had been made with forensic inquiries and obtaining witness statements.
"Evidence gathered so far suggests there has been a flashover explosion, which occurs when you have a build-up of toxic fumes," he said.
"This, combined with some sort of ignition, has caused a fire-ball effect."
The Health and Safety Executive said its inspectors and electrical safety experts would be gathering evidence.
Two men killed in an explosion at a factory in Norwich died from the "effects of fire and inhalation of fumes of combustion", post-mortem examinations have found.