If the "emergency is being observed by a lot of people".
The bystander effect happens when there are many other people present at the scene and it demoralizes a person from mediating in an emergency circumstance. Bibb Latané and John Darley who were psychologists advanced the idea following the notorious 1964 Kitty Genovese murder in New York City. Genovese was murdered outside her flat while onlookers who watched the incident did not venture in to help or call the police. Every spectator ended up thinking from their neighbors' inaction that their very own assistance was not required.