Both hands of the harpist use the same basic position. The thumb turns upwards and plucks the string away from the body of the harpist. The other fingers are held horizontally and are slightly curved. They pluck the strings towards the body of the harpist.
The harpist uses four fingers in each hand to pluck the strings: the thumb, second, third and fourth finger. The fifth finger is too short to reach the string comfortably.[Chaloupka1979]
Each hand can easily span an interval as large as a tenth. The span of the hand obviously differs according to the size of the harpists hands, nevertheless a 10th is a secure reference that is valid for two note intervals as well as four-note chords.
Arpeggiated chords and intervals, however, can span much larger intervals. If the chord spans large intervals the speed of the arpeggio will become slower.