An emergency plan in this case deals with the general sorts of emergencies we could face. That includes how to get first aid or even summon an ambulance when there is an accident. Obviously, the best time to prepare for that sort of thing is long before it becomes necessary.
Other emergencies are things that are possible but may never occur. This is where you find earthquakes, floods and fires. That list could also include hazards present in your workplace or even near your workplace. An example would be having a chemical plant as a next-door neighbour. If they had a problem, it could easily become your problem too.
As you can see an emergency plan covers all sorts of things and is really just a way of ensuring that you have a pre-planned response to a bad situation so that it does not get worse or is handled in the best way possible.