Where it is possible for the public to pass under, or next to a scaffold, the space between the top rail and toeboard shall be enclosed with a wire screen composed of not less than no. 18 steel wire gage with a maximum 1/2 inch (13 mm) mesh or equivalent synthetic safety netting. For the purpose of this provision the term "where it is possible for the public to pass under, or next to a scaffold" shall mean when the setback from the scaffold to the area used by the public is a distance equal to or less than half the height of the scaffold.