Grenades from the Second World War sparked a huge chemical alert at a printing press in Lancashire.
The phosphorous grenades, issued as weapons to the Home Guard during the conflict, were discovered in a sealed cellar at Sprint Print on Station Road, Bamber Bridge on Thursday lunchtime.
A pair of engineers working on damp masonry at the building raised the alarm after noticing wisps of smoke rising from the former fire station building, and the bottle of acid was found in the cellar.
In total, five people were injured with two suffering chemical burns and three experiencing respiratory problems.
Two paramedics and six staff from Royal Preston Hospital, where the casulties were taken, subsequently complained of breathing difficulties.
A Lancashire Fire and Rescue spokesman said all 13 casualties were “responding well” to treatment and had been allowed home.
He added: “The source of the fumes and the cause of the injuries has been identified as an incendiary device, a phosphorous grenade, issued as a weapon to members of the Home Guard during the Second World War.
“The device is a glass bottle about eight inches high which on being thrown and hitting the target was intended to break and release the contents, a highly flammable mixture of phosphorus and benzene, self-igniting on exposure to air.
“It has now been made safe and removed from the building for disposal by an army disposal team.”
He added the icendiary device appeared to have been left there shortly after the conflict and forgotten about.
The cellar of the former fire station is linked to the neighbouring former Town Hall, now an estate agents, with six such devices found in a shared cellar space under the buildings.
The spokesman added: “Both cellars have been sealed off for some years.
“These too will be removed and disposed of safely in a controlled explosion.
“It is thought that in investigating the cause of damp, the contractor inadvertently dislodged one of the bottles in the stockpile, causing it to leak and release fumes.”