Investigators are treating a fire that closed the main railway line in Berkshire as an arson attack.
Clouds of black smoke were seen rising from the factory
Rail services between Reading and London Paddington were suspended by the blaze, which police believe started in a bin and spread to a plastics factory.
A 200m exclusion was put in place around the factory site while gas cylinders were cooled.
First Great Western have said train services are back to normal following Sunday's fire in Langley, near Slough.
Thames Valley Police said the fire started at about 1100 BST on Sunday on Deseronto Wharf, near St Mary's Road.
Four railway lines were closed for six hours, which affected services from Oxford and Bristol as well as London Paddington and Reading.
Det Con Stuart Ritchie said: "Thankfully nobody was injured during [the] incident which caused major chaos to local roads and affected train commuters."