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11 2. Human Fallibility and Limitations 3. Cognitive Effects of Having to Deal with Complexity Conversely, human factors which contribute to safety include (a) organizational ‘safety culture’, with a corresponding humble and vigilant attitude with regard to preventing failure, and (b) numerous best practices related to general design features of dams, and organizational and professional practices. Failures generally result when the human factors contributing to safety are not sufficient to outweigh those contributing to failure. Human errors can be categorized as “slips” (actions committed inadvertently), “lapses” (inadvertent inactions), and “mistakes” (intended actions with unintended outcomes due to errors in thinking) [1]. With regards to dam safety, mistakes have typically been labeled as the most common type of human error [1]. This article will attempt to highlight some of the more common human factors that have contributed or will contribute to past and future incidents and failures related to the life cycle of a dam. These are discussed in context of the dam design, construction, monitoring and maintenance, and emergency response. Design “All men make mistakes, but only wise men learn from their mistakes” – Winston Churchill The state of the practice in dam safety has evolved significantly over time through knowledge gained from studying dam safety incidents and failures. As we have gained more knowledge about how dams behave under various loading conditions, and how to predict those loading conditions, the industry has responded with changes to typical design criteria and standard design details. For example, filter design for earthen embankments is now common practice and rigid seepage collars have been replaced with engineered filter collars, rendering homogenous dams a practice of the past and a cause for increased scrutiny of existing homogenous dams. Hydraulic fill dams have also proven to be particularly susceptible to poor performance under certain loads and are no longer used in modern practice. Concrete spillways have seen changes in joint details, reinforcement and anchoring design, and the addition of more robust underdrain systems. Other changes have resulted from the advancement of technology in fields like hydrology and seismicity to predict design loads. All of these changes can be attributed to the advancement of technical understanding in the industry. This evolution of design practices in dam engineering can also lead to practitioners becoming outdated in their knowledge of current standard of practice, requiring diligence and dedication to stay on top of continuing education. It is also difficult for many individuals to recognize their own technical knowledge limitations, and to avoid practicing engineering outside their areas of experience and technical understanding. The acknowledgement that “I know enough to be dangerous” should be sufficient warning to stop someone from providing engineering advice beyond their area of expertise. The breadth of technical disciplines in the field of dam engineering is vast, and the depth of understanding one must have to apply engineering methods, criteria and parameters correctly, requires engineers to specialize in specific fields of practice. With all the guidance documents and analytical methods available, engineers must still apply judgement in most all that they do and poor judgement is a human fallibility. This challenge requires a multi-disciplinary approach to most engineering studies, analyses, and design. Construction ”The greatest mistake is to imagine that we never err.” – Thomas Carlyle The construction phase is similar to design in that it has seen significant changes in generally-accepted best practices and available tools. However, regardless of  Resource, budget and schedule constraints  Insufficient data or technical expertise to understand the data  Insufficient technical expertise of designers and lack of use of design best practices  Lack of multi-disciplinary diversity on the design team  Insufficient design conservatism HUMAN FACTORS IN DESIGN