Safety First - 30G
Play an entire campaign with no Survivors taking friendly fire damage

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This can easily be done on easy in single-player. Because the 3 other survivors are computer controlled, they will rarely shoot another survivor by accident. You still need to be careful around them though. Just as long as you can control your own fire, you should be able to get this achievement with no trouble. This must be done in one sitting. You can't quit out and then continue from where you left off.