Collective Fall Protection for Informal Construction: A Low-Cost Perimeter Guardrail Sized from Site Materials

Design and first-principles sizing of a low-cost perimeter guardrail for informal construction, built from sawn timber, bamboo culms, scaffold tube offcuts, or reinforcing bar. SIMULATED, NOT MEASURED; nothing was built or field-tested. The governing load is a stumbling worker: 1.54 kN point load on the top rail. Timber (125x50 mm rails, 120x100 mm posts at 2.0 m) and scaffold tube (48.3 mm at 1.5 m, braced posts) pass; bamboo passes at 1.75 m with three-culm posts; rebar fails as a rail at every practical spacing. Installed cost is $6.49/m (bamboo) to $13.26/m (timber), or $273-$557 for a typical small building with 42 m of edge. A harness kit is cheaper per project ($102 for six workers) but needs 5.6 m of fall clearance against a 3.0 m storey height. In a stated task-share scenario the guardrail covers 65.6% of worker-hours at height; leading-edge work during erection itself is not covered.