PRISON officers have blamed chronic overcrowding for the weekend riot by over 70 inmates at Mountjoy Jail.
There are current 609 inmates in the facility, which was only designed to hold 420 prisoners.
The Prison Officers Association (POA) last night demanded an urgent meeting with prison management after one of its members, who was reportedly smashed in the face with a fire extinguisher during the riot, suffered serious facial and dental injuries.
Four other prison officers and two inmates also received less serious injuries during the riot and have all been discharged from hospital.
Inmates seized hammers, chisels and planks of wood after breaking into a carpentry workshop on Saturday afternoon and were only disarmed when over 100 prison officers, wearing full riot gear, moved in.
The bravery of the prison staff was praised by the POA last night.
Although no official comment was forthcoming from the Prison Service yesterday, the Irish Independent has learned officials believe the riot was sparked by a successful clampdown on contraband -- including drugs and mobile phones -- rather than overcrowding, as claimed by the POA.
The disturbance began around 4pm in a basement recreation centre in the D Wing of the Prison.
Only two prison officers were on duty in the recreation room when a large number of inmates began throwing pool balls and pool cues at them and turned over tables.
The prisoners barricaded themselves in and managed to break into a number of adjacent workshops. A computer room, with thousands of euro worth of equipment, was thrashed by inmates who also ransacked a woodwork shop for weapons.
Senior management and the prison's governor, John Lonergan, were called in to attempt negotiations and the garda air support and emergency response units were also put on standby amid fears that prison officers could be taken hostage.
After a stand-off that lasted about two hours, some 100 prison guards in riot gear stormed the area and restored control. The operation had to be conducted in darkness after prisoners smashed all the lights in the barricaded area.
Two investigations -- one by the gardai and another by prison management -- were under way yesterday.
Gardai declared the D Wing a crime scene and it remained locked down last night as officers conducted examinations.
Prison sources said the wing was well monitored by CCTV cameras and footage will be used to prosecute those involved. Sources said a number of prisoners had already been identified as being among the ringleaders.
These included Dublin heroin dealer John Paul Kelly, another Dublin-born offender, Mark Byrne, and Cork criminal Colm Carroll. In a statement last night, POA general secretary John Clinton said the association was "deeply concerned" about Saturday's events.
"Over a considerable period the POA has repeatedly warned management that there are serious issues and a potential for violence inside Mountjoy and other prisons," said Mr Clinton.
"The POA solemnly believes that overcrowding is a main contributory factor to the ongoing tension and to yesterday's incident." Mr Clinton said the riot was only brought under control thanks to the "professionalism and courage" of prison officers.
Prison Service sources said that while the root cause of the riots hadn't been identified, they believed it had more to do with the lack of availability of drugs in the prison than overcrowding issues.
Visitors are now subject to airport style screening and drug dogs are also being used to detect visitors bringing in contraband.
"It is acknowledged that Mountjoy is running above capacity, but we believe that the riot was purely down to the lack of contraband getting in to the prison these days," a Prison Service source said.