250mA will kill you if it runs though your heart. Depending on circumstances takes normally around 20V to pass though your skin.
There is a reason for the old "one hand rule" because the most direct path between your right and left hand includes your heart.
Also remember that you nervous system runs on nA (1/100000000 of an Ampere) and pV (1/100000000000) of a Volt), which are almost un-measurable without specialized equipment.
Most of those images were of electrical burns, As to the machine shop stuff. Depends on what class you are going into and your background. Someone like me would most likely not have a problem around the tools where some other would. I'm real familiar with most tools just do not have the money to buy them.