<p>Explicit risk analysis, a powerful structural safety decision-making tool, was applied to investigate the collapse of a movable scaffolding system (MSS) during construction of the River Verde Viaduct at Almuñécar, Spain in 2005, in which six workers lost their lives. Systematic qualitative risk analysis was conducted to identify the MSS structural safety hazards that may have theoretically caused the collapse. Based on exhaustive experimental and theoretical studies, these hazards were classified by their relevance to the accident. Logical combinations of the hazards were subsequently established to ascertain possible failure scenarios. This was followed by quantitative risk analysis, in which probabilistic methods were deployed to corroborate the likelihood of occurrence of the scenarios envisaged. Without such methods, no credible conclusions could have been drawn.</p>