Re: voluntary overtime
I agree with SCRN1. The word "voluntary" means that you can choose to do it or not do it. Make your choice and let them make their choices. If they give you a hard time about it, tell them that you have other important things in your life as well as work and choose not to work overtime. Remind them politely that they are free to make their own personal choices as well.
As I have said many times on this site, as long as nurses agree to work overtime, the administration has little incentive for solving the underlying staffing issues. While I think everyone should pitch in and help a little during a temporary crisis, if the understaffing is a long-term problem, then continuing to cover shifts more than you would like to is only enabling the administration to continue to avoid solving the underlying problem.