The safe to touch voltage limit is 60VDC. This is the max DC voltage that meets the definitions of a SELV circuit. That is why you see so many industrial 48V systems. These are able to stay beneath 60V even when charging batteries or using switching controllers. It is permitted to exceed 60V in a SELV circuit, if the voltage is higher frequency.
UL 60950-1 defines what a SELV circuit is for US markets if you want to read up on it. Note: IEC 62368-1 ES1 is going to replace UL 60950-1 SELV in December 2020. Basically these standards define circuits that are safe to touch (as in you won't get hurt if you touch the circuit when you are grounded).
F.Y.I. Low Voltage is legally defined differently in different countries. A "low voltage" AC power circuit can definitely kill you depending on where you are. It can be confusing. That is why pretty much everyone that matters from an industrial standpoint is switching to IEC-62368.