In "The Story of an Hour," what was Mrs. Mallard's husband involved in?

In Kate Chopin's short story "The Story of an Hour," a wife is apparently left widowed when informed sources reveal her husband Mr. Brently Mallard was killed in a "railroad disaster." Although the character of Mr. Mallard pervades the telling of the story, very little is really known about him. The reader might presume that he was a successful and common sense man who, like most men of the patriarchal Victorian era, made the majority of the decisions when it came to his wife and home.
The story goes on to employ both situational and dramatic irony. Instead of spending her days in grief over her loss, it doesn't take long for Mrs. Mallard to realize she is now "free" from the kindly "repression" she has endured as a Victorian woman. She looks forward to a long life that now holds many different possibilities. In the end, however, her husband reappears no worse for wear and seemingly unaware of any accident. When he comes through the door, Mrs. Mallard drops dead of an apparent heart attack. In a case of dramatic irony (the reader knows more than the characters), the doctors conclude she died because her heart could not take the joy of having her husband back.