how about add a new poi:"underground station"or "subway station"
Mission:
wastebin fire
fare dodger
same as train station
new mission:
station fire
need unit:3 engine,1 rescue unit,1 mobile air,1-3 ems unit,1 battalion chief unit
30% patient has to be transported
automatic fire alarm
need unit:2 engine
30% become"station fire"
passenger under train
need unit:2 engine,1 rescue unit,1 ems unit
100% patient has to be transported