Skill based behaviours are those that rely on stored routines or motor programmes that
have been learnt with practice and which may be done without conscious thought. Certain
skills (such as taking a ship out of the port) may be exercised at the same time as another
activity that requires conscious thought (such as conversation with a crew member).
Humans are able to do two things together as long as they do not compete for same
resources. Skill-based behaviour is dangerous because of the fact that an operator may
make the correct initial decision, but could be disturbed during exercise. In this case he
could fail to monitor his own activity and remain completely unaware of the mistake he has
made. A typical example is for instance if somebody wants to take a pump into operation,
gets disturbed, forgets to open a particular valve, comes back after the disturbances has
passed by, does not remember which steps he has already done, thinks the preparati on
was completed already, switches on the pump and is causing damage because the
particular supply valve was not open.