At my hospital, we have a bunch of psych units. On my unit we have 20 beds, there are 3 RNs 4CNAs on days, 3RNs 3CNAs on eves and 1RN 2CNAs on overnights. If we have a patient in restraints(which is an automatic 1:1) or on 1:1s for safety we staff up and add another CNA. If someone goes on 1:1s for whatever reason during a shift, we are usually stuck and cover that from the compliment. We have a security team, and an on call psych doc, to help with restraints, but on my unit they are pretty rare (except when they aren't). We more often do 1:1s, and mostly to stop self injury rather than violence. Other units have different staffing ratios and different acuity, but for the most part it is pretty safe, even with high ratios.