Birgitt, et al, I have not done open space in prison, but I worked in the field of corrections for nearly 15 years, including a stint at the National Institute of Corrections. While that wa before I had ever heard of Open Space, I have no doubt about the potential of the process in a prison setting. I have participated in dialogues among inmates, between inmates and staff as well as between inmates and "citizens." Most often I felt more confident in the inmates than the others.
My caution is related to pre-work: People who have not worked in or around jails and prisons, especially in the United States, often carry a fair amount of misinformation, myths and personal baggage into encounters with the people and the institutions. This baggage may make it difficult the "straight" facilitator to be fully present to create and hold space. So, I suggest some personal work.