Atmospheric Fuzzy Risk Assessment of Confined Space Entry at Mine Reclamation Sites

A confined space accident that occurred in 2006 at the Sullivan Mine in Kimberley, British Columbia has brought to light that certain reclamation activities can lead to an atmospheric hazard that is difficult to recognize. In this paper, application of a fuzzy logic-based expert system to assess the risk of an atmospheric hazard at a waste dump site is described. AFRA is a rule-based system that estimates fuzzy values of four major elements (gas generation, gas emission, gas confinement, and human exposure) that affect the risk of creating a confined space hazard within an enclosed structure such as a sampling shed located at the toe of a sulfide waste dump. The system is able to generate realistic advice about a site even when data are imprecise estimates. Should discrete measurements be available, these are transformed into linguistic expressions with respective Degrees of Belief (DoBs) that combine with other inputs to generate a Degree of Belief in each element value through the use of heuristic weighted-average equations. The assessment depends on different conditions at a site. The system has been validated for a total of nine dump sites around the world (6 reference and 3 test sites). It is recommended that atmospheric risk assessments should be carried out for sulfide waste dumps and tailings dams on a regular basis especially when a change in climatic conditions, site design, or site operation takes place.