Areadamage on surface elements

[Duke92]

Hi,

I have three questions about areadamage:

1. Is it somehow possible to NOT damage surface elements with an attack that causes areadamage?
I try to build a mod turret, whose projectiles work like grenades (with a decent range between 1 or 2 km), BUT I don't want to destroy every single surfaceelement.

2. Is it possible to add more than one areadamage (per effects, influence or whatever)?
For another turret I want two different areadamages, first a normal one and a few second later shield damage.

3. And something I don't understand, the "bullet"-macro contains the "areadamage", "time" and "lifetime" and the "effects"-library contains the "range", "falloff" and "duration".
What are "time" and "lifetime" for? How do the two values influence the final areadamage/range?

Thanks in advance for any help