A hard short is when circuit resistance goes to just about zero ohms. It's like when you take a piece of wire and put one end on the positive side of a battery and the other end on the negative side.
How can that happen in a
mod? Say the plastic insulator in the 510 connector deteriorates and the positive pin touches the outer, negative 510 surface. Hit the switch button and all the battery current flows from the positive battery end, through the 510 positive pin, through the 510 negative sleeve, through the
mod tube, down through the switch and right back into the negative side of the battery.
Resistance will not be quite zero ohms, but 0.0001 ohms is close enough to consider it zero.
Hope this makes
sense 