Wash. Rev. Code § 49.24.230
When firing by electricity from power or lighting wires, a proper switch shall be furnished with lever down when "off".
The switch shall be fixed in a locked box to which no person shall have access except the blaster. There shall be provided flexible leads or connecting wires not less than five feet in length with one end attached to the incoming lines and the other end provided with plugs that can be connected to an effective ground. After blasting, the switch lever shall be pulled out, the wires disconnected and the box locked before any person shall be allowed to return, and shall remain so locked until again ready to blast.
In the working chamber all electric light wires shall be provided with a disconnecting switch, which must be thrown to disconnect all current from the wires in the working chamber before electric light wires are removed or the charge exploded.
Before blasting, the blaster shall cause a sufficient warning to be sounded and shall compel all persons to retreat to a safe shelter, before he or she sets off the blast, and shall permit no one to return until conditions are safe.
RCW 49.24.230