Holding cells and ordinary rooms are being used at Mountjoy Prison to deal with overcrowding, the Prison Officers' Association has said.
Some holding cells have twice the number of prisoners they were designed for and the atmosphere at the prison was tense, said the POA, who held an emergency meeting yesterday.
The POA spokesman, Mr Tom Hoare, said the level of overcrowding was "intolerable" and staff wanted measures to deal with it. A meeting between the POA and the Department of Justice, Equality and Law Reform is to take place next week.
A Prisons Service spokesman said there were 776 prisoners in the jail built to take 450, putting great pressure on facilities and staff. "It has gone beyond that figure before and it tends to fluctuate quite a lot," he said.
He said Clover Hill remand prison in west Dublin would relieve the strain on Mountjoy when it opened. Clover Hill was built to take more than 400 inmates eventually. Work on fire and security systems by the contractor John Sisk and Sons should be finished next week and the prison should then be ready.
Mr Hoare said the association was looking for greater dispersals of prisoners to other prisons to alleviate the strain on Mountjoy.
He said management also promised to roster extra prison officers for parts of the day when the prison came under most pressure. "We need this to provide even the minimum service required," he said.
One of the main problems was that the prison did not know how many inmates it would have until late in the evening. "This makes it almost impossible to plan and it is something we want looked at," he stated.
If there was a maximum number of prisoners, then any extra would have to be dispersed elsewhere. "We would favour that, but Mountjoy is a committal prison so there are legal problems to be dealt with before that could happen," he said.
The prison governor, Mr John Lonergan, was not available for comment yesterday. The national steering group on deaths in prisons is to meet next week on whether new measures are needed to prevent suicides.