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.

Emergency services found a Mini had crashed head-on with a Volvo in Buxton Road, Hazel Grove, at about 16:00 BST on Sunday, police said.
Philip Clayton, 43, died at the scene. A 23-year-old man is in a serious condition in hospital.
Buxton Road was closed while investigations took place. Police are appealing for witnesses to contact them.
A man and a woman were also taken to hospital with serious but not life-threatening injuries.
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.
[NEXT_CONCEPT]
A man has died in a head-on crash in Greater Manchester.