Good point. I've only seen it once so far, so I will keep an eye out for it the next time. My interpretation was that the initial shockwave had hit the buildi

Good point. I've only seen it once so far, so I will keep an eye out for it the next time. My interpretation was that the initial shockwave had hit the building, and was causing all the structural damage that we saw as they were leaving the building. The shockwave passed, at which point they were trying to get to the ship and leave before the larger danger of "the horizon is missing" reached them.