Four firefighters died in the warehouse fire
Three fire service staff have been arrested over the deaths of four firefighters in Warwickshire in 2007.
Police said a man, 43, from Nuneaton, a 49-year-old man from Leamington Spa and another man, 48, of Warwick, presented themselves at a police station.
They will be questioned on suspicion of gross negligence manslaughter and offences under health and safety laws.
The fire took place at a vegetable packing plant in Atherstone-on-Stour in November.
All four firemen who were killed were from Warwickshire.
A director of Wealmoor Atherstone Ltd, owners of the plant and warehouse, has said no sprinkler system was installed.
The bodies of Ashley Stephens, 20, John Averis, 27, and Darren Yates-Badley, 24, were found inside the remains of the building, a vegetable packing plant, days after the fire.
Ian Reid, 44, died in hospital.
A Warwickshire Police spokesman said: "This morning a 43-year-old man from Nuneaton, a 49-year-old man from Leamington and a 48-year-old man from the Warwick area presented themselves at a Warwickshire police station, where they will be questioned on suspicion of gross negligence manslaughter and offences under the Health and Safety at Work Act."
A Fire Brigades Union (FBU) spokesman said he could confirm the arrested men were fire service staff and members of the union.
They will be getting legal representation from the FBU.
Last month, the union said it had been told three of its members would be questioned under caution over allegations of gross negligence manslaughter.
Police said in January that the investigation was still continuing and that many people had been interviewed, including fire personnel and Wealmoor employees working at the plant on the day of the fire.
Mr Yates-Badley and Mr Stephens were based at Alcester fire station.
Ian Reid was based at the Rugby and Stratford-upon-Avon fire stations, while John Averis was at Stratford.
A massive search operation, involving more than 100 fire officers from Warwickshire, Hereford and Worcester and the West Midlands, took place at the packing plant for the firefighters' bodies.