As temperatures plunged across the West Midlands inmates at Birmingham Prison reached boiling point when they were told snow meant they could not exercise outdoors.
Up to 70 inmates in P Wing of the Winson Green lock-up staged a violent protest on Friday, at one point starting a fire in a bid to force an emergency evacuation.
It is the latest incident to cause concern at the trouble-hit HMP Birmingham, which has been run by private security firm G4S since October 2011.
Trouble at the prison began when inmates were told outdoor exercise had been cancelled because of the wintry weather conditions.
Snow was falling and there was the risk that lags might slip and hurt themselves.
During the trouble that followed, G4S staff faced a stand-off before managing to restore order.
An inside source said that during the fracas, one prisoner ended up on netting which runs across the gaps between landings.
One prisoner started a fire in a waste bin, in an attempt to set off fire alarms.
We were also told that told that one inmate had to be taken to hospital with a broken wrist - a claim denied by G4S, who say that staff defused the rising tensions rapidly, and returned all inmates to their cells.
A father of one of the inmates at the privately-run prison said: "That jail is terrible at the minute - it's not safe.
"There was about 60 or 70 of them who rioted. It was about 2pm on Friday and the riot bell went off.
"There was fighting and one of them started a fire. One bloke was thrown on to the netting. My son told me one lad was taken to hospital with a broken wrist and a broken rib."
A spokesman for G4S confirmed that there had been an incident, but played it down.
"Due to the weather conditions on Friday, there was no period of outside exercise at HMP Birmingham," he explained.
"Regime times at the prison were brought forward and on one wing, prisoners were reluctant to co-operate with instructions from staff to be put in their cells at the rescheduled time.
"Staff managed this situation very professionally, and ensured that the regime quickly returned to normal."
The spokesman added that no-one had been injured during the fracas, which he said involved around 20 inmates.
It is the latest in a series of disturbances at the jail since G4S took over.
In December last year three guards were injured after being attacked when 60 inmates went on the rampage on C Wing.
While in November four officers were hurt when a prisoner attacked them with glass from a broken TV set.
And last week it emerged that G4S had to fork out £415,000 to change the locks at the prison after a set of keys which opened every cell door got lost.
One prison source said problems had been caused because bosses have not replaced senior staff who have left.
One HMP Birmingham guard, said: "The situation is so serious, I fear someone will die in there.
"Senior staff have left and they have not been replaced. We cannot go on like this. We are short-staffed at weekends and there are no managers at night."