That is because I agree with Ayn Rand's philosophy. I also acknowledge that most people, including philosophers, reject Ayn Rand. Even so, an argument from authority is not sufficient to refute her claims.
As far as the circumstances listed, yes, there are reasons to risk your life for other people. Firemen use their training and knowledge to safely get people out of burning buildings. It makes sense for them to do this as that is their job. Saving people's lives gives them self-eesteem and makes their life worth living. What is important to remember however is that is not a sacrifice.