By knowing the capacitance and inductance (i.e. stored energy) in the circuit that the switch could interrupt; you then assume this stored energy gets dissipated by the arc. If there is no appreciable inductance, then the possibility of an arc is greatly diminished (no flyback voltage spike to initiate an arc). You could measure the arc dissipation with a suitable o-scope tracing current and voltage across the switch during an opening transient, you then need to convince people that the next switch won't be 2x or 10x worse...or test every switch and circuit combination.
FWIW, you might try posting this in the Electronic Engineering forum, where more sparkies are likely to lurk. If you do that, just post a link back to this question, don't repost your question there, that is considered rude.