Should "occupant impact with the airbag" be written as:
"occupant airbag impact" or "airbag occupant impact"?
And should "interaction between occupant and airbag" be written as:
"occupant airbag interaction" or "airbag occupant interaction"
In each of the examples, I'd consider the first two words as a compound modifier of the third word. As such, I'd hyphenate them:
It's hard to find one web citation that covers this situation. But see http://www.grammar-monster.com/lessons/hyphens_in_compound_adjectives.htm for hyphenating compound adjectives, and http://grammarist.com/grammar/nouns-as-adjectives/ for using nouns as adjectives.
A common example that fits the same pattern of three nouns in a row (where the first two are a compound which modifies the third) would be the "wave-particle duality" of light: https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality https://www.sciencedaily.com/terms/wave-particle_duality.htm
I don't think the order of the first two words matters: "Whether the stone hits the pitcher, or whether the pitcher hits the stone, it's going to be bad for the pitcher." That's certainly true for the "interaction." If you want to emphasize the object-vs.-subject of the "impact," then I think your only choice is to re-word the sentence to make that explicitly clear.