Figure 1.6: Interrelation between the total hazard potential for an activity and the distribution of
accepted risks, safety and risks due to human errors. Adapted from Schneider (1994).
Example 1.2 – Human error in bridge design
As a classical example of human errors, consider the Tjörn bridge shown in Figure 1.7 just
after completion. The bridge was intended for ship traffic to pass under the bridge midstream
as indicated with buoys positioned in the river.
Figure 1.7: Tjörn bridge just after erection, Göteborg, Sweden.
The fact that the river is equally deep close to the banks of the river and that the captains
normally sailing on the river were accustomed to sailing close to the banks rather than
midstream - in order not to worry about the ship traffic coming in the opposite direction – was
either not known to the designers of the bridge or not realized as a potential hazard. The result
was that the bridge after only a few months in operation was rammed by a passing ship and
collapsed completely into the river as seen in Figure 1.8. Subsequently, a new bridge was
built on the same location, but this time the designers had learned their lesson and decided on