Sparks are usually generated when the media has completely failed. The determining factor in whether a fluid fails is field strength, not voltage or current. The electric field distribution is different, the voltage shape is different, and the breakdown voltage is different (because only the voltage can be measured, the field intensity distribution is generally difficult to measure, so the voltage of breakdown is generally studied).
The current during breakdown is related to the breakdown voltage and the wave impedance of the air gap. As the spark discharge channel when removing a sweater, the current is very small (the specific amount is not sure, but it's probably in the mA range, I don't know), and the lightning current is almost of the order of kA.