The results of the first study to use computer modeling to simulate midair collisions between manned and unmanned aircraft in detail strongly suggest that the danger of such real-world collisions must be taken seriously. Researchers found that the notoriously volatile lithium polymer batteries used to power most drones pose less risk of a post-impact fire than expected, but the structural damage a drone collision can create was more severe than expected.
Source: aopaDrone collisions with aircraft modeled