Physical Danger
You could be involved in a terrible industrial accident while visiting a site as part of your research process. You could get exposed to a deadly virus while gathering the information you need for a write-up about a series of medical trials. You could fry yourself with a cell phone prototype while composing the end-user documentation.
Okay, not really. The only physical dangers you're likely to encounter as a technical writer are carpal tunnel syndrome and too many donuts.