Transitioning Workplace Risk Assessments from Qualitative to Quantitative

Risk-assessment grew out of a need for a feasible means to compare risks of a system after application of risk-reduction tactics. In workplace risk assessments, common parameters considered are predicted severity of hazardous outcomes and estimated likelihood of such outcomes occurring. Two fundamentally different ways of characterizing risk are qualitative and quantitative. Both approaches use a rectangular area for locating a risk indicator. This article explains these two approaches and how they affect accuracy of the risks depicted in the area. The qualitative approach uses a table structure in which columns are labeled using ordered terms for severity, while the rows are labeled using ordered terms for likelihood. Where rows and columns meet are cells, like in a spreadsheet, where entries indicate level of risk. The quantitative approach also uses a rectangular area but without being filled with rectangular cells; instead, risk indicators (RI) may be located anywhere with the risk area based on RI = Severity x Likelihood.Qualitative approaches involve dividing the risk area into rectangular spaces, like a chess board, where words or colors indicate risk level. A common approach to creating numbers for the cells is to assign order numbers to both severity and likelihood axes, then inserting a numeric into each cell based on multiplying the row and column order numbers. Although multiplying order numbers make no sense mathematically, the risk indicators resulting from this approach provides an easy means for separating zones of similar risk indicators. Quantitative approaches have a means for computing a numerical RI value for any point on the rectangular space. The system safety community has been using this approach for high-risk hazards like aviation crashes, nuclear power generation, and highly-hazardous chemical processes. The occupational safety community has recognized the mathematical validity of this approach, but embraced it only for high-hazard systems.A novel, mathematically justifiable, feasible, and accurate approach to create a valid risk-assessment matrix is described in this paper. It involves establishing each axes using a 0–100 scale with points in the risk area being RI = Severity x Likelihood. By connecting points of equal RI on a risk space, lines of iso-risk can be drawn in the risk area and used to serve as an employer’s criteria for risk acceptance or tolerance. An essential property of the axis scales for this approach is making each axis use a continuous scale in the range 0–100 based on prior research. The process envisioned for implementation of the quantitative approach involves using a risk-assessment team to evaluate a recognized hazard by: (1) each team member becomes familiar with the hazard, (2) uses judgment to assign numerical values to both severity and likelihood, then (3) plotting the team’s mean ratings on a risk area for comparison with an employer’s risk criteria. The whole process is to complement the typical compliance-focused approach to achieve safety by recognizing possibilities for reducing risk through reducing severity, reducing likelihood, or both.