I also have never heard of anyone being harmed on 12 volts. But, the safety department in the electronic company I worked for, claimed there were very rare cases of people who were harmed at such voltages, usually with rings on their fingers, and then you have to get it somehow across your heart AND be a rare person who is especially sensitive.
Though the wedding ring as someone mentioned can burn your finger badly if it gets across the 12 volt connections. I stopped wearing wedding rings in the late 60’s and still do not. I don’t need a wedding ring to keep me straight.
I say again, I never personally knew anyone who was harmed below 28 volts.