Six prison officers were taken to hospital after they intervened in a huge fight involving up to 20 inmates at the Midlands Prison.
One staff member is reported to have suffered a dislocated shoulder while a colleague needed stitches to his head.
Others suffered broken ribs and ligament damage.
The violence erupted on Sunday between two gangs, just as lunch was being served at the country’s largest jail.
A prisoner attacked a member of an opposing gang as they were collecting food, sparking off a row described by one senior source as “a large-scale fight”.
Separate sources said the fight appeared to be linked to a Limerick feud but not related to the organised crime gangs in the city. Senior members of the McCarthy crime gang are incarcerated in the prison.
The fight, in the prison’s A Division, was captured on internal CCTV systems.
“One prison attacked anther at the ‘servery’ and then up to another 15 got involved from two distinct, clear, groups,” said one source.
“They began fighting each other. It was a melee.”
Another source described it as a “major disturbance”.
The source said the fight, itself, lasted about a minute: “It was hot and heavy. It was fairly serious, a lot of digs were being thrown.
“The inmates were throwing crockery at each other and breaking them to make improvised weapons.”
He said staff intervened very quickly: “There were a couple of officers who battled really hard to bring under control individuals who were hell bent on assaulting others.”
Some estimated it took some 10 minutes for officers to bring the landing under control, though other sources said the process took longer.
One insider said staff injuries included a dislocated shoulder, stitches to the head and broken ribs.
Sources said up to 18 inmates were “directly involved” in the violence and 13 were immediately relocated internally.
Up to five ringleaders were transferred to Mountjoy.
A spokesman for the Prison Officers’ Association said: “This is another example of what we highlighted at our annual conference: That violence is continuing and that this is a difficult and dangerous job that we do.
“We have repeatedly highlighted this issue with the Irish Prison Service but these instances continue unabated.”
A spokesman for the Irish Prison Service said: “There was a serious incident in Midlands Prison in which a large number of inmates were involved.
“Prison staff responded very quickly and, as a result, staff were injured. The IPS commend their bravery and professionalism. They dealt with it very effectively and brought this under control very quickly.
“We are conducting an investigation and disciplinary action will be taken against any prisoners involved. Gardaí have been notified.”
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