Firefighters tackled a “needless” blaze at the former Manganese Bronze plant in Ipswich on Sunday night.
The fire in the top floor of the two-storey derelict building, behind houses on Hadleigh Road, was caused by trespassers.
The fire was reported at around 5.30pm on April 30 and six crews, including an aerial appliance, were expected to battle the blaze for several hours last night.
Station Commander Jon Southgate, of Princes Street station, said the fire was caused by someone deliberately or accidentally setting the fire.
“There are numerous discarded needles around the site and from experience we know there will be needles inside as well,” he said. “We will not be entering the building because I want to ensure the safety of our firefighters.
“It is a shame that we are now going to have four crews fighting a completely needless and preventable fire.”