Safety switch "breaking capacity" vs. voltage
If the switch is originally closed and a current of  \$I_b\$ flows, when suddenly the switch is opened, is the voltage \$U_a\$ now enough to generate an arc between \$A\$ and \$B\$?


Switches can be designed to open very quickly, but the opening time can never be zero. As a consequence, it must be assumed that an arc is formed. The current drawn influences the breaking of the arc as the gap rapidly increases. If the arc has not been extinguished by the time the switch is completely open, it may be sustained.

The current level influences the breaking of the arc in two ways. One is the temperature of the arc. The other is the voltage developed by the inductance to the circuit tending to maintain the flow of current.