Leave school for an EMS call? They would have laughed at me if I asked to leave for that... Couldn't carry the pagers for anything, at all.
Now, if there was a large fire, they'd release 18 year old student volunteers. It only applied to those that had no tests and had driven to school, or were picked up, no carpooling. There was no manpower shortage to it, some fires just need a lot of hands, and the school released employees and students upon phoned request. I never left.