RCW 49.24.300: Buckets in vertical shafts.

In all vertical shafts in which hoisting is done by means of a bucket, suitable guides shall be provided when the depth exceeds ten times the diameter or width of the shaft, but in no case shall the maximum depth without guides exceed one hundred and fifty feet. In connection with the bucket, there shall be a crosshead traveling between these guides. The height of the crosshead shall be at least two-thirds of its width, but the height in no case shall be less than thirty inches.