According to the United States Department of Corrections, there exist 4 primary levels of prison security levels; these levels are the following:
1. Maximum Security: This prison security level is the highest and most stringent; only the most violent offenders are incarcerated within a maximum security prison. Within a maximum security unit, there exist sub-units such as solitary confinement, protective custody, and special housing units (SHU). In most cases, maximum security prisoners are confined to their cells for up to 23 hours a day and are under strict monitoring.
2. Close Security: This prison security level is akin to maximum security in its construct – consisting of single cells and close monitoring – yet close security prisoners are entitled extended outside of their cells.
3. Medium Security: This prison security level most resembles a large residence hall which houses as many as 70 inmates in large, bunked sleeping quarters, as well as group toilet facilities. Although there is consistent monitoring, medium security prisoners are afforded various work assignments, which permits them to be out of their cells for longer periods of time.
4. Minimum Security: Akin to the medium security prison, minimum security prisoners are housed in dormitories, but are considered to be the lowest risk to the public. As a result, these prisoners are afforded the opportunity to participate in groups, sessions, and rectification projects in order to reform themselves.