"Impairs" is the right word to put in the first blank because in this context it is used to describe situations where it is not very easy to see what is ahead of you. In other words, a person's view is being influenced such that they can't see much.
For the second blank, "called off" is good because it describes the remedial action the authorities took because of the impaired visibility.
Wiglaf says that his comrades boasted of how brave they would be when Beowulf needed them and that they would give their life if he needed them . In lines it ...
