A certain man exposes himself  to imminent danger in order to save the life of a fellow being, knowing beforehand that he himself will die; would this be considered a suicide?

From the moment in which there is no intent to seek death, there is no suicide, but devotion and self-denial despite the certainty of dying. But who can be so certain? Who can say that Providence has not reserved an unexpected means of salvation at the most critical moment? Could not Providence save someone who is right in front of the mouth of a cannon? On many occasions, Providence wishes to prolong the trial of resignation to the ultimate limit, when an unexpected circumstance diverts the fatal blow.

St. Louis (Paris, 1860)