It depends on the incident. There is no one size fits all response to a pipeline accident, or any other kind of accident or emergency. In some cases, emergency responders will want people to stay in place because they already are safe. In others, they will want people within a certain vicinity of the incident to evacuate. The extent and direction of an evacuation would depend on the nature of the accident, weather conditions at that time and any other factors affecting conditions on the ground.
If there were a major pipeline emergency, many fire, ambulance and police departments would respond. There would be numerous first responders on the scene working to get people to safety. As a result, people near the emergency would find out quickly what they should do.