1. Risk & Liability in Engineering

2. 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 1000F) 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.

3. Question 1 How could this structural failure happened? Question 2 Why did building codes not better protect the public? Question 3 How can we prevent such a disaster in the future? What about acceptable risk and our approach to that risk as engineers?

4. The Engineer’s Approach to Risk To assess a risk – an engineer must first identify it To identify a risk – an engineer must first understand the risk What constitutes a risk to an engineer?

5. 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

6. Consider a Disaster What about connections between specific harms and losses, such as personal property or reduction in quality of life? Immediately apparent consequences Opportunities for learning after a disaster Need for accurate, uniform, consistent metrics to evaluate hazards Broader, more indirect harms to society

7. 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

8. 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 = 1.Risk assumed by free and informed consent 2.Risk is justly distributed or properly compensated

9. Communicating Risk – an Engineer’s Responsibility Be clear – risk  probability of harm Be careful saying there is no such thing as zero risk – not easily understood Be aware public does not always trust experts – acknowledge limitations Government has obligation to protect public. It is not always about cost-benefit approach Be objective and listen to all sides

10. 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

11. Source: sixsigma.knowledgehills.com

12. Source: embedded-systems.com