105. Where the stability of surface pillars may not be insured on a long term basis, a fence built according to the standards prescribed in the second paragraph of section 103 shall be installed around the zone in question at a sufficient distance from the latter, established according to geotechnical considerations of rocky walls and overlying soils.
Signs warning of the danger of the zone in question shall be provided at the locations referred to in the first paragraph of section 104, at an interval allowing their visibility, at a distance that may not exceed 30 m.
The second paragraph of section 104 applies, with the necessary modifications, to the signs referred to in this section.