Disturbances in institutions are often thought to be due to special local circumstances. This paper outlines a general mathematical model for sudden outbreaks of disorder in an institution. The model is illustrated by applying it to the escalating sequence of events at Gartree Prison during 1972. Although the approach is largely theoretical some suggestions are made about the prediction and handling of disorder. In particular, the model suggests why the policy of ‘playing it cool’ is generally likely to be success