A DANGEROUS cache of more than 20 World War Two grenades were discovered by workmen in Swanage town centre on Monday afternoon.
Two of the devices - known as number 76 special incendiary, or 'sip' grenades - ignited after their protective glass bottles were shattered by a mechanical digger, causing a fire.
Emergency services placed a 50-metre cordon around Shore Road, where the explosives were discovered during excavation work at 3pm.
They were thought to be releasing phosphine gas, which is highly flammable and toxic.
Dorset Fire and Rescue's district commander for Purbeck, Mike Cox, said workmen had been carrying out ground-levelling when they uncovered four of the devices.
However, officers from the Royal Logistics Corps' Explosive Ordnance Disposal Regiment discovered at least 16 more, which were then dealt with in a controlled explosion.
The grenades consisted of bottles containing phosphorus, which is exposed to the air when the bottles are smashed.
Staff Sergeant Andrew Blacker said: “We have a tried and tested method for dealing with these sip grenades.
“They were used by the Home Guard during World War Two in case of a German invasion. They come in batches of 12 and 24, and they ignite in contact with oxygen, so we're going to go carefully.”
Smoke from the controlled explosions seen drifting across the bay. Picture by Andy Lyons
The specially-trained officers worked for more than an hour to carefully excavate the grenades before transferring them to a skip.
Edward and Betty Dickson, who are holidaying in Swanage, said: “We didn't know what was going on.
“It's scary to think about what might have happened.”
Paul Dunesby, 47, who has lived in Swanage throughout his life, said: “I can't get along the seafront, there are police everywhere.
“You wouldn't normally get that in Swanage.”
Paramedics were called to the scene to check over workers at the site as a precaution after the two bottles broke.
A spokesperson from South Western Ambulance service said three people who were exposed to the gas were treated at the scene.
Grenades uncovered as part of ongoing work over landslip fears
THE grenades were uncovered as part of ongoing work to move Swanage War Memorial over landslip fears.
Ground surveys ahead of the £2.1 million stabilisation scheme initially found the war memorial area required no attention.
However, when work began following last winter's rainfall, engineers realised the area is at risk of slippage.
The Swanage Town Council funded project also includes the construction of two tiers of beach huts, new public toilets and a permanent kiosk on the corner of Shore Road and Victoria Avenue.