Safety standards and overcrowding are causing problems at a Nottinghamshire prison, a monitoring report said.
Police were not required
Inspectors said overcrowding at Ranby prison is likely to become a critical problem over the next 12 months.
The jail is due to expand later in the year to accommodate more than 1,000 prisoners. The prison governor rejected that the prison would run out of room.
The Independent Monitoring Board said prisoners were also using toilet facilities without staff supervision.
It considered this an "unacceptable" practice.
The report said some of the prisoners are vulnerable and the staff does not have "ready access" to check on their well-being - especially at night.
The prison was praised for its work in education, physical education and chaplaincy.
Prison governor Phil Wragg rejected some points in the report.
He said: "For a capacity of 858 to have only four prisoners on a self-harm form clearly indicates how pro-active my staff are in dealing with the needs of prisoners and ensuring they are living in safe, just and tolerant conditions to deal with their needs.
"It is something that we as members of staff at Ranby are very conscious of and something clearly that part of my senior management team who deal purely with self-harm and suicidal tendencies pay a lot of time and attention to."
A former World War II army camp, the prison houses around male 750 prisoners, including inmates sentenced to life.
The report also said there was "an accident waiting to happen" outside the prison on the Retford to Worksop road where many visitors cross a busy road to get to the training centre and car park.