Despite visiting crime scenes that, not two hours prior, were home to some truly horrifying acts of human cruelty, you're typically not in much danger at all. The danger has passed (even if it has passed recently), and if a criminal were stupid enough to return to the scene of the crime, well, it's not like you'd be there alone. They'd face a welcoming committee of armed police.
In the lab, things are slightly more precarious. But not by much. When you're working with toxins, weapons, needles, and blood, common sense should tell you to not run around like it's the McDonald's Playplace. Still, there are procedures for handling these sorts of things, and the nature of your work incentivizes you to work with these items carefully anyway. With proper training, we wouldn't worry too much about it.