The prisons watchdog has criticised the authorities in Mountjoy for repeated failures by prison staff to notice that an inmate had died in his cell.
Inspector of Prisons Patricia Gilheaney called for the Irish Prison Service (IPS) to show "zero tolerance" over failures to do mandatory checks at regular intervals on prisoners, with disciplinary action to be taken against officers who fail to perform such duties.
It follows a report into the death of a 41-year-old inmate at Mountjoy on January 10, 2018, which found officers had missed at least four opportunities to notice he had died during the night.
The report noted that the prisoner had gone unchecked for two periods of two-and-a-half hours when he should have been checked hourly.
Ms Gilheaney said a night guard as well as prison officers who unlocked and locked the prisoner's cell for breakfast and who later unlocked his cell to allow him out to attend morning activities had all failed to identify a serious situation.
The unnamed prisoner, who was serving a life sentence, was found unresponsive in his cell by two other inmates at 9.57am.
One officer who rushed to the cell said his face appeared to be covered in vomit.
Ms Gilheaney said officers unlocking a cell for breakfast should ensure they sought and received a verbal response from each prisoner to ensure they were alive.
The report said CCTV had also found that the officer with responsibility for the landing had not remained at their post for the duration of their shift.
"Prisons are required to provide safe and secure custody and it is critically important that staff carry out their duties and in accordance with IPS policies and procedure," Ms Gilheaney said.
However, she welcomed a new operating procedure introduced by the IPS last April that relates to the monitoring of prisoners by officers on night duty.
The inspector said the director general of the IPS, Caron McCaffrey, had accepted all four recommendations contained in the report and an action plan was being implemented.
The IPS said failure to carry out mandatory monitoring of inmates would be regarded as serious misconduct, which could result in dismissal.