Good Samaritan laws cover the rescuer, and medically-trained people recognize each other by the handoff they give. I’ve begun an EMS work up on a train with no tools, praying I wouldn’t have to start CPR before we reached the next station, and gave a quick EMS/ALS history on a patient with an allergic reaction affecting his tongue. Sweeping airways are a bitch when you have no tools. An OD, you can breathe for them until someone arrives with an ambu-bag.