You don't need to worry about a backstop if you are shooting pigeons in trees with an air rifle though. . Granted you need to consider potential ricochets, but the pellet is not going to harm anyone when it lands, even if some-one is looking up and it gets them in the eye.
If that last bit's your attitude towards safety then I'm glad you live a very long way from me.
To be honest I thought some one would make that remark which is half the reason I wrote it!
I have an extremely high regard for shooting safety thanks and I was trained by both a very fastidious relative and the military. However I have never heard of anyone being harmed by an air rifle pellet when landing after being fired upwards into trees, but I have heard of people being both hit and harmed by .22 lr bullets fired upwards into trees (and by upwards I do not mean vertically). However when I raised this point early in this thread it was subject to total ridicule by several members.
Now you are suggesting that I am wrong to suggest that we can safely shoot vermin out of trees with an air rifle if there is no backstop. I would argue that it is safe to do so, but still with commnon sense. So for example I would not shoot an air rifle upwards if the pellet is going to land in an area where there will definitely be people. My comment about someone looking up and being hit in the eye by a gently failing air rifle pellet was intended to be a little flippant, but it is still probably true. So far no-one other me is it seems is going to stick their neck out and say that an FAC air rifle is useful for vermin in trees whereas a .22lr would be risky and in some cases dangerous.
Some-one else made the point about plod reading these threads. However I really doubt the laws of the land will be modified on the basis of this thread!