You're probably thinking of "Good Samaritan" law, maybe?Don't know if it is still a law or not, maybe it's a state by state law!
I know if you have specific training, such as medical, and pass an accident (as an example), you could possibly be liable. The Good Samaritan law varies from state-to-state, as mentioned before. People have saved lives, and then afterwards been sued for one reason or another.