You must be able to not only stay calm in worst case situations but do the job properly. example: someone had sadly drown, You need to be calm despite the terror of whoever made the call. you must talk them on how to preform C.P.R and call a ambulance. You can't sound panicked at all and must be kind. You must act as though even if seeingly the person is dead, make it sound like they will live without exactly saying it. This could cause panic and have a possibly life threatening issue.
