first responder
noun /ˌfɜːst rɪˈspɒndə(r)/
  /ˌfɜːrst rɪˈspɑːndər/
 (especially North American English)- a person such as a member of the police or fire department in a position to arrive first at an emergency, who has been trained to give basic medical treatment
- first responder training
 - citizen/community first responders (= members of the public who have had special training for emergencies)