HMP Dartmoor, located in Devon, UK, will temporarily close due to the detection of high radon levels.

The Ministry of Justice (MoJ) announced that the prison's 175 inmates will be relocated to other facilities.

The process begins on Thursday, moving 40 prisoners at a time.

The Prison Officers Association aims for all inmates to be transferred by the end of July.

Peak radon levels at Dartmoor were found to be 10 times the recommended workplace limit in both 2020 and 2023.

The dangerous gas, radon, is odorless and colorless, often resulting from decaying uranium in rocks and soils.

Dartmoor, an area rich in granite, had previously faced closure in 2023 before the decision was reversed in 2019 due to rising prisoner numbers.