The fire at the British Engineerium in Hove last week was started deliberately, according to East Sussex Fire and Rescue Service.
Detectives are investigating the arson attack which happened late on Thursday afternoon (11 June).
East Sussex Fire and Rescue Service said that it was still investigating the cause of another fire which started at about the same time in Gloucester Road, Brighton.
The fire service said: “East Sussex Fire and Rescue Service can confirm a fire at Hove Engineerium was deliberate.
“Firefighters were called out at 5.40pm on 11 June. Four fire engines, an aerial ladder platform and an incident command unit were sent to the scene.
“Sussex Police are continuing to investigate.
“No further details will be released at this stage by East Sussex FRS.
“East Sussex Fire and Rescue Service continues to investigate a serious fire in Gloucester Road in Brighton.
“The fire at the building above the Bathstore was reported at 5.36pm on Thursday 11 June.
“The investigation is expected to take several days while investigators gather information and examine the scene.
“It is believed that the fire started in one corner of the roof area and wooden decking caught alight.
“At the height of the incident six fire engines from Brighton, Roedean, Seaford and Barcombe were sent to the scene along with the aerial ladder platform from Brighton and the incident command unit from Lewes.
“The fire was put out by crews using eight breathing apparatus, water jets and firefighting foam.”
Nancy Platts, who chairs the Brighton, Hove and District Labour Party, said: “It must have been very frightening for people living and working near to the fires breaking out across the city and our firefighters did a tremendous job protecting life and property.
“It was reassuring to see that additional resources could be pulled in from neighbouring areas to help but I am fearful of a similar outbreak of fire in 2016 after further cuts have been implemented.
“All the Labour councillors on East Sussex Fire Authority voted against the cuts that will take effect in 2016, when we will lose one of our five fire engines and 24 firefighters in the city.
“At roughly the same time, the remaining cuts will take effect in nearby fire authorities and statistics show that some are struggling to provide fire cover within their own borders, let alone supply back up to East Sussex.
“This combination will leave us desperately short of fire cover and put the lives of local residents and our firefighters at risk.
“I am asking the fire authority once again to reconsider its decision to cut one of our fire engines in Brighton and Hove.”
I am all for restoring the level of Fire provision in East Sussex – but will Nancy Platts be asking Labour-run Manchester to do the same?