Prison bosses face a formal public censure after inmates and staff were exposed to dangerous levels of radon gas at Dartmoor Prison.
Radon, a naturally occurring radioactive gas, causes about 1,100 lung cancer deaths in the UK every year, according to the UK Health Security Agency.
The Health and Safety Executive (HSE) said safety failures by HM Prison and Probation Service meant people were left breathing in radiation above legal limits for a prolonged period after the risk was not properly managed inside the Devon jail.
The prison service said the wellbeing and safety of staff and prisoners is “our priority” and radon monitoring had been strengthened.
The watchdog was first alerted in February 2023 after concerns about possible overexposure. The prison service has been approached for comment.
After the 2023 alert, follow-up checks confirmed radon levels in parts of the prison, including prisoner accommodation, were above the legal limit, putting both staff and inmates at risk, the HSE said.
Radon is measured in becquerels per cubic metre of air (bq/m3).
The average level in UK homes is 20 bq/m3, according to the UK Health Security Agency.
Monitoring carried out at HMP Dartmoor in March 2020 showed levels of radon in a number of areas exceeded that, including the kitchen which returned a reading of 2,988 bq/m3, nearly 10 times the limit.
Inspectors took action twice in 2023, warning that regulations had been breached.
As concerns grew, HMP Dartmoor, a crumbling Victorian prison on moorland in Princetown, was eventually mothballed in 2024.
A number of staff, prisoners and former inmates at the jail have launched legal action over radon levels.
Following the investigation, the HSE passed a file to its legal team, which has now authorised a Crown Censure against the prison service.
A Crown Censure is the strongest step the regulator can take against a government body.
It is not a criminal conviction and does not carry a fine, but, if confirmed at a hearing, it becomes a formal public telling-off and a lasting record of serious safety failures.
No further action is being taken against individuals or other organisations.
A prison service spokesperson said: “The wellbeing and safety of staff and prisoners is our priority. Since 2022 we have strengthened radon monitoring and mitigation across the estate.
“We have noted the Health and Safety Executive’s decision to begin Crown Censure proceedings, and it would be inappropriate to comment further while these are ongoing.”
BBC News – Jonathan Morris (May 13 2026)
Dartmoor Prison radiation failings bring censure of jail bosses – BBC News