Learn Icelandic: Ekki standa við neyðarútganginn! - Do not stand by the emergency exit!

When the preposition við is used to describe physical proximity or attachment—meaning "by," "next to," or "attached to" a spatial location—it takes the accusative case. Since the person is standing right next to the exit, við forces the noun into the accusative.

Why is the infinitive standa used instead of an imperative command form?

In Icelandic, negative commands (telling someone not to do something) are usually formed by placing ekki directly in front of the infinitive form of the verb. So "Do not stand" is simply Ekki standa. If it were a positive command ("Stand!"), you would use the actual imperative form: Stattu!

How is the compound word neyðarútganginn broken down?

It is built from neyð (emergency/distress) and útgangur (exit). The first part, neyðar, is in the genitive (possessive) case, essentially making it "exit of emergency." The final part is -inn, which is the attached definite article meaning "the."

What is the dictionary form of neyðarútganginn, and how exactly did the ending change?

The dictionary form (nominative) is neyðarútgangur. Because it is masculine and in the accusative case, the -ur ending drops, leaving the stem neyðarútgang. We then attach the masculine accusative definite article -inn to the end, resulting in neyðarútganginn.