A 22-year-old man suffered serious head and spinal injuries after falling through a warehouse roof in Portslade.
The man, who worked at the premises, was taken to the Royal Sussex County Hospital in Brighton.
Sussex Police and the Health and Safety Executive are working together to try to establish how he came to fall through the roof.
The incident happened at the Shepherd’s Plastic Building Products warehouse in Church Road, Portslade.
Shepherd’s is a building trade supplier.
The incident happened at 3pm yesterday and left the man with chest, back and head injuries.
Sussex Police said that he was in a stable condition.