Physical Danger
You may have to supervise at construction sites, and those are dangerous places. A construction worker may fall on you from ten stories. And most of them are hefty, donut-totin' union fellows.
But for the most part, danger isn't a physical threat in this gig. You may be hunched over a drafting table, which could mean back pain, but it's more likely that you'll be doing your designing on a computer, in which case you'll instead be hunched over a computer monitor, meaning a lesser degree of back pain.
And then, of course, there are the usual eye strain and carpal tunnel hazards, but you're not going to need your eyes or hands in fifty or sixty years anyway.