RISK-INFORMED DESIGN IN MINING GEOTECHNICS

PIN

Most of the time, engineers calculate “factors of safety” for their designs. A factor of safety tells you how many times safer a design is than is really needed to serve its purpose. For example, an elevator may indicate a maximum load of 1000 pounds. That doesn’t include the factor of safety. If the factor of safety is 2, then the actual design load is 2000 pounds that can be carried safely.

That design doesn’t necessarily incorporate considerations of risk. What if all those people in the elevator are jumping? In a risk-informed design, the designers would quantify hazards and consequences, the product of which is risk. You develop a list of things that may go wrong. Then quantify the risks. Then once you know the risks, you can alter the design, where possible, to reduce those risks. According to NASA (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140005863.pdf), risk is operationally defined as a set of triplets: 1. The scenario(s) leading to degraded performance with respect to one or more performance measures (e.g., scenarios leading to injury, fatality, destruction of key assets; scenarios leading to exceedance of mass limits; scenarios leading to cost overruns; scenarios leading to schedule slippage). 2. The likelihood(s) (qualitative or quantitative) of those scenarios. 3. The consequence(s) (qualitative or quantitative severity of the performance degradation) that would result if those scenarios were to occur. The risk-based or rather “risk-informed design” approach is a kind of structured process that enables professionals from a variety of disciplines to examine and rank potential hazards and their consequences, which can often be characterized by a monetary value. Returning to the previously-stated NASA reference, a risk-informed design is an approach that allows for a designer to understand and account for the probability of some undesired outcome and the scenarios that would cause that outcome, given a specific design. It allows risk to be “traded” with other design components (such as schedule, cost, etc.) and is ideal for design comparison studies. According to a second NASA reference (https://tettra.co/wp-content/decks/nasa.pdf), in a risk-informed context, safety is an overall condition that provides sufficient assurance that “mishaps” will not occur, or, if they occur, their consequences will be mitigated. That says a lot, but it doesn’t explain it very well, so let’s break it down. If safety is “an overall condition”, then safety is the “guiding light” for the design process. And while developing the design, there should be enough understanding of what could go wrong, that those negative occurrences can be avoid, to the extent possible, or their damaging effects minimized. So: know what could go wrong; design to avoid things going wrong; and limit the impact for the things that can still go wrong. That’s a very lofty goal, but remember that is from NASA.

According to Ersdal and Aven (http://www.civil.ist.utl.pt/~joana/DFA-riscos-net/2007-08/risk%20informed%20decision-making.pdf), the idea of using a risk-informed design is to follow a process where the right decisions are made by addressing the overall performance of the system based on risk. Ersdal and Aven continue, stating that a risk-based approach does not provide answers on what are good or “right” decisions, and that risk only describes the possible consequences and associated uncertainties. Thus, there are dimensions of the decision-making that goes beyond risk, for example ethical and political issues.

Yikes! How did we get to the topic of ethics? Let’s leave that, but we may come back to it at some point.

So a risk-informed design, would be one that goes beyond the traditional engineering calculation for factor of safety, and looks at a laundry list of what-ifs. Risk analyses are often carried out by engineers as a normal part of their project assignment. A risk-informed design process is simply using the risk assessment during the design stage so that the design may be modified (improved) during the actual design process.

It is my belief that a coupled risk/engineering design process will be much more common in the future design work for tailings facilities.

You May also Like

Leave Your Comments