In general, the number of needed exits is calculated by the building official depending on the kind of use and occupant load of the structure or area. 10 of the California Building Code or by contacting the Community Planning and Building Department. The number of exits should be adequate for the type of business carried on at any given time. The required number of exits are divided into two categories: access and service. Access exits are those that provide egress from the premises for all employees and customers. These must be provided for each floor served by a single elevator. Service exits are those that provide egress for specific groups within the building. For example, a hospital might have service exits for doctors, nurses, patients, and other staff members. These should be provided for each floor served by a separate elevator. The required number of exits are also divided into public and private areas. Public areas are those where the general public is allowed. These include entrances, lobbies, corridors, and parking lots. Private areas are those where only authorized persons are allowed including offices, treatment rooms, and storage facilities. These require a different level of security than public areas but can usually be accessed by anyone with authorization. Public areas need to be cross-matched against possible threats. This means checking to see which doors lead outside and which don't. Some possibilities include ground-level doors, windows, and fire escapes.