From my understanding pain is a response to certain stimuli, those stimuli being composed of certain organic molecules, of which are able to "react" to external stimuli, ie external reactions etc, causing that which is alive, etc, to instinctly (key word being instinct) react to the so called "pain" or that which is "sensation causing external or internal chemical reactions" etc.
The problem is with inanimate objects, science currently does not possess enough information to explain that force which makes us all sentient as humans, let alone the semi sentientism or non sentientism (merely being considered "living").
We've yet to discover what it is actuslly that gives us all the spark of life, awareness etc, aside from electricity and neural synapses.
So that taken into consideration, from what knowledge we have, inanimate of objects appear to us to not be living, but how can we actually prove this? Just because they do not possess respiratory systems or functioning brains or organs, does not necessarily mean they don't have these systems ordered in such a way that our science would not recognize them.
Food for thought. I've always thought very deeply about life etc. And I'm my experience from a scientific viewpoint, science cell is true regardless of one's religion or predisposition etc. That aside science has not discovered everything, all though what we do know alludes to the fact that there are things out there beyond our wildest dreams that exist, our science is just not advanced enough to understand these things.
So can objects, inanimate, feel pain, who are we to say yes or no? Our limited sciences can only attempt to guess at what they can or can't do or feel, these objects.
See what I'm getting at?