How long should automatic doors delay closing?

Automatic doors have a sensor that detect whether people are present, and when there are none, and after a delay, the doors close.

How long should that closing delay be?

• Does it depend on factors like type of traffic, and if so what?
• Are there any guidelines or safety regulations for it?
• Does it depend on the properties of the door, like closing speed and sensor range?

To be specific, I'm interested in automatic doors that serve public foot traffic, for building entrances, of the see-through kind that do not cause significant injury when closed.