Multiple tasks at the same time in combination with quickness of response. Try to stay calm when a fire, a massive car accident, and a chemical cloud are ruining the game. But this is also what makes the game challenging ofcourse, so it's not that bad. A single car accident while there is nothing else happening gets very very boring after a while. The most difficult task on its own is the chemical fire. You need to close off the area to prevent people from getting contaminated, extinguish the fires, call HAZMAT, decontaminate and treat people. When you're not fast enough, you have a major problem dealing with the infected people.