HARDING MEMORIAL LECTURE | BTS
Lack of communication 8%
Insufficient ground investigation 12%
Design errors 41%
Force Majeure 18%
Left, figure 2: Insurance industry interpretation of tunnel failure causes
Defective construction 21%
As a check on this result, information from the
insurance industry was evaluated. Reference 14 provided additional information which is summarized in figure 2. This places the blame on design error at 41% of the incidents, but with the exception of force majeure all of the other noted causes may also have had a contribution from human decision making. It was therefore considered that a much high percentage could be attributed to human error, and probably to far greater than 60% of failures. This coincided more with experience, but was it realistic?
ARE HUMANS THE CAUSE OF INCIDENTS? The logic of the way we undertake our work could be considered as follows: ● The laws of physics will apply. ● Materials follow the laws of physics and are predictable.
● Loads and forces are largely predictable, with a few exceptions.
● Designs are undertaken to tried and tested codes and standards and include safety factors applied to the loads and to the conservatively assessed material properties.
● The design and the construction methodologies we use are generally tried and tested.
● The ground we deal with as tunnelers has been in place for millions of years and, unless previously disturbed, will not behave differently today to how it would have behaved many years ago, or sometime in the future.
As a result of these considerations all we really appear to be left with in the majority of cases when an incident occurs is human error, within which we might include incompetence, carelessness, negligence, misunderstanding, poor communication, poor training and others. Why does this happen?
WHY HUMANS MAKE MISTAKES Our minds analyze and interpret huge amounts of data
from the outside world apparently instantaneously, monitoring and controlling our bodies without conscious thought. We learn new skills that are eventually undertaken with the minimum of conscious effort. Our minds are inventive, creative, empathetic, imaginative and flexible. But they are also messy, disorganized, illogical, confusing, sometimes contradictory, and lazy. The mind is the most complex and least understood part of our whole bodies. And every single one of them works differently. Our minds are also littered with operational bias’s (a
predisposition to favor a line of thought) and heuristics (short-cuts in thought processes) that affect the way we think and make decisions. There is a subtle difference between a bias and a heuristic, but they both refer to processes in thought such as confirmation bias, optimizm bias, substitution, availability, representativeness and hindsight bias rather than the larger issues of gender, religious, ethnicity or age bias. For those who believe these apply to others but not themselves, there is even a psychological mechanizm for that as well – the third person effect. As a result of these survival related thinking processes,
our normal decision making is highly efficient and usually very effective, but mistakes still happen, and they can be characterized as deliberate or inadvertent actions (see figure 3). Within the ‘deliberate’ mistakes category, ignoring greed or sabotage - which have a much larger potential to contribute to major incidents - the reasons people give, when caught in error and questioned, include: ● Low potential for detection. ● Peer pressure, competition, or conflicting requirements.
● Being unaware of the consequences. ● Precedent.
Although sometimes present, our industry does not encounter these too often. Of more relevance, are the reasons for ‘inadvertent’ mistakes, which may be considered as either accidental, or systemic.
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