Dartmoor National Park mine shafts to be fenced off over safety fears
"Potentially dangerous" mine shafts are being fenced off in a national park following safety fears.
Landowner, the Duchy of Cornwall, said a "comprehensive survey" of mining activity on Dartmoor had resulted in 22 sites which needed to be fenced off to protect people and livestock.
Dartmoor National Park Authority said after heavy rain the mine shafts "had the potential to collapse".
Previously, sheep and ponies have had to be rescued from the shafts.
Derelict mine shafts are capped with timber and rubble, but many are unfenced and unmarked.
Head ranger Rob Steemson said heavy rainfall during winter 2013/2014 had caused some shafts to collapse.
He said to "mitigate any risk to grazing livestock and the public's safety" the Duchy planned to fence the sites using local materials.
Mr Steemson added there were hundreds of capped mine shafts across the moor.
Landscape historian Peter Herring said the shafts were "potentially dangerous" if they collapsed and could prove to be fatal.
He told BBC News tin from the area's many mines was exported around the world, with several of the original buildings still well preserved, including mills and engine houses.
Mining expert Tom Greeves added: "It was the best quality tin available to the Medieval world, with the largest mine employing about 200 people in the mid-19th Century.
"There's always a risk some shafts will collapse because they didn't have health and safety laws in place."
Mr Greeves said one mine was 500ft (152m) deep with most being between 100ft (30m) and 200ft (61m).
The Duchy of Cornwall said: "There is no new or increased risk, but by combining historical data with modern mapping and GPS, we have identified a small proportion of new sites which will be fenced off as a precautionary measure."