Safe current limit for human contact?
Here is an article titled "A review of hazards associated with exposure to low voltages" which I used as a reference when answering a medical safety question (I design embedded hardware and firmware for medical devices which go through FDA approval).

Because the body has a minimum resistance of around 550 ohms, to get enough current to do damage a minimum theoretical voltage level of around 16.5 Vpeak is required (corresponding to a current of 30 mApeak, which can induce respiratory paralysis if conducted across the chest for several minutes of contact at this low voltage). Based on the cases studied by the author, the single lowest voltage reported to cause transdermal electrocution in an adult is 25 volts.

For less than one minute of contact, currents >40 mA are required to cause ventricular fibrillation, corresponding to a theoretical voltage of 27.5 Vpeak. For less than one second exposure, >100 mApeak and 55 Vpeak are required. The author states that in all the cases he studied, there was no accidental electrocution from short-term exposures to voltages below 50 Vpeak.