Two brave prison officers were assaulted after trying to break up fights between rival inmates at Mountjoy last weekend.
The incident happened in the A wing as tensions rose as a result of overcrowding and rows between various prisoners.
It is understood their injuries are not life-threatening but the warders were extremely traumatised by the acts of violence and are now off on sick leave as they recover from their ordeal.
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Prison insiders say they were assaulted as they intervened and tried to stop the fights. Staff are reviewing video footage to identify the culprits and severe action is expected to be taken against them.
The source said: "Our colleagues were extremely lucky their injuries were not more serious. They were attacked in the crossfire and they are very shaken.
"Tensions are very high in Mountjoy at the moment, the worst I've seen for years.
"There was talk of putting part of the jail into lockdown last Monday but then senior management changed their mind."
It is understood at least 50 to 100 prisoners on average have been sleeping on mattresses in the prison over the past several weeks,
Mountjoy can cater for over 700 prisoners in single cells but there are fears the amount of inmates sent there could rise to 1,000 in the coming weeks as the court services catch up with a backlog of cases nationwide caused by the Covid-19 pandemic.
The cells in Mountjoy are so small they can really only accommodate one prisoner.
But the move to double up and put two in a cell in some parts of Mountjoy is causing deep anger and resentment among existing prisoners and staff.
Prison officers believe putting two in a cell in Mountjoy is illegal and a breach of human rights because of the individual cell size.
The prison source added: "Management feel they have no other choice but to place two in a cell because of the rapidly rising prison population and shortage of prison accommodation.
"However, it is creating tension in Mountjoy and this has a knock-on effect on staff in terms of safety and morale. Our officers were lucky last weekend that they didn't end up in hospital.
"But Mountjoy is a ticking time bomb at the moment waiting to explode."
The Irish Prison Service condemned the assaults on staff and said warders are working in an extremely challenging environment on a daily basis and any act of violence against a person is unacceptable.
A free counselling service for prison officers is also being provided.
The IPS said in a statement: "The Irish Prison Service must accept all prisoners committed by the courts. As such the IPS has no control over the numbers committed to custody at any given time and the prison system is subject to peaks and troughs.
"As of March 9 there are 804 people in custody in Mountjoy and 54 of those are sleeping on mattresses.
"The Government has provided significant capital funding to the IPS in order to enhance the existing prison infrastructure.
"The commissioning of a new male and female prison accommodation in Limerick Prison will provide an additional 90 male spaces and 22 additional female cell spaces. This new male accommodation is now partially open with 30 cells currently in use and will be fully operational by the end of April."
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