The full facts of what went wrong at Hei Ling Chau prison to spark such a serious riot will not be known until the inquiry delivers its report. However, one conclusion can be drawn with confidence. It was not caused by any of the familiar undercurrents usually responsible for an outbreak of violence. This was not a story of bored inmates locked up for long hours in overcrowded cells inside a grim fortress with nothing but barbed wire and a grey exercise yard to look out on. Pictures of the minimum security institution show a variety of buildings scattered over a green island, where the only real barrier is the sea. It is a place where, according to many accounts, some prisoners can swim or do creative work making gardens and fish ponds. The tensions that erupted in Hei Ling Chau reportedly hinged around privileges rather than deprivation. But no matter how aesthetically pleasing the surroundings, the loss of liberty and the stress of living in close proximity with 500 other prisoners from different backgrounds will always be something of a psychological powder keg. Regrettably, animosity between local inmates, foreign prisoners and mainlanders is common in local jails and an obvious excuse for the aggrieved to vent their frustration. In that respect, Correctional Services Department officers are at a disadvantage. They have to be especially sensitive to minority groups under their charge. But in the hothouse atmosphere of a jail, any symptom of favouritism can foment trouble. On this occasion, it seems the outbreak was spontaneous and unforeseen - and soon got out of hand. Prison officers are not complaining about under-staffing. They insist that, bar minor hitches, co-operation between the disciplined services called in to help was smooth and problem free. But it was a nasty incident, in which facilities were destroyed, buildings set on fire, personal possessions stolen and 35 people injured. Since up to 70 particular troublemakers were in the prison population, one question that should be asked is whether it is appropriate to house them in such relaxed surroundings. When trouble breaks out in remote areas, reinforcements take time to arrive. Inmates recognised as potential agitators should be transferred to secure confinement before they have a chance to stir up trouble.