12VDC 18Amps dangerous?
All voltages below 50V are considered safe to touch.

although I would not advise putting -48V on your tongue to check if a phone line is working as the ring voltage is much higher. ( although I have )

You can try a 9V battery on your fingers then your knee , and you might be able to feel it. Your tongue will feel a strong burning sensation with a quick 9V battery test. 

However you can create high voltage spikes with any inductive coil break in current from a low voltage.

Also beware that >4% Hydrogen concentration (LEL) is considered explosive to static discharges in that container.