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Risk & Liability in Engineering . Source: www.readin.com. On September 11, 2001, terrorists attacked the Twin Towers by flying two hijacked 727’s into them. Each jet impacted approximately 2/3 of the way up.
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Source: www.readin.com On September 11, 2001, terrorists attacked the Twin Towers by flying two hijacked 727’s into them. Each jet impacted approximately 2/3 of the way up. The resulting fire, fueled by high-octane aviation gas, isolated more than 2000 workers in the floors above the impact. Only 18 of these workers made it to safety, while in contrast almost all of the workers in the floors below escaped. In the hour following the crashes, the intense heat (above 1000F) caused the steel floor beams in each tower to sag. The floor structures broke away from the external vertical load-bearing beams. As the floors fell, they created loads the lower floors could not support. As a result, the towers collapsed.
What about acceptable risk and our approach to that risk as engineers?
Consider Definitions • Risk = compound measure of the probability and magnitude of adverse affect • Product of the likelihood and the magnitude of harm • Harm = limitation or impairment of a person’s freedom or well-being • Public Perception • Public rarely has all the facts • Many priorities set by a public more concerned with perceived risks than actual risks due to lack of knowledge • Acceptable Risk: probability and magnitude of harm probability and magnitude of benefit • This is where the engineer must apply capable judgment
How Does the Engineer Approach Risk and Safe Design? • As a minimum, design MUST comply with applicable laws • Design must meet standards of current engineering practice • Must explore potentially safer designs • ALWAYS compare • ALWAYS seek alternatives • Engineer must attempt to foresee potential misuses of design • Design for these misuses • Realize the ramifications of misuses
Public Perception of Risk • Perception of real risk frequently varies between those that know facts (engineers) and those that do not know facts (public) • Public frequently drastically underestimates risk • Sometimes leads to misunderstanding of need for safe and secure engineering design • We must respect individuals right to choose and decide: Acceptable risk = Risk assumed by free and informed consent Risk is justly distributed or properly compensated
How Do We Evaluate Risk? One Method – Fault Tree • Objective, systematic way to account for and evaluate types and probabilities of risk • Typically termed ‘Risk Assessment’ • Begin with the undesirable event (such as a car not starting) • Reason BACK to events that might have caused this undesirable occurrence • Anticipate hazards – especially those for which there is little or no direct experience • Systematically analyze failure modes
