Terumos 1:6

Five types of people may not separate terumah but if they did, it is valid terumah. These five are: a person who cannot speak, a drunk person, a naked person, a blind person, and a man who had a seminal emission.

Terumos 1:7

One does not separate terumah by measuring, weighing or counting, but he may take terumah from produce that was measured, weighed or counted. (The volume of terumah is only estimated.) Terumah may not be separated using a container of a specific volume (since that would be measuring it), but he may use such a vessel if he only fills them partially (so that the exact volume of terumah is only estimated). One may not half-fill a seah measure because a half-seah is also a measured volume in such a container.