I haven't tried this pefore, but thought of doing something like that for a flamethrower. Check this out, it might help:

http://unity3d.com/support/documentation/Components/class-WorldParticleCollider.html

there is a component called particle collider that you can use to make particles lose energy or bounce or ... when colliding with other particles. there is a check box (bool value) in this component called SendCollisionMessage that if you check it a OnParticleCollision event will be called in all scripts attached to the GameObject containing the particle collider and the GameObject that particles collided with. so you can use this function in your mesh object and do what you want when particles collide with you. as you can see in the sample of documentation you can see the object that you collide with in the passed argument.