In Tennessee William's The Glass Menagerie, it appears that the fire escape represents Tom more than his mother or sister. Tom is the one who feels more confined that the rest of his family. He is forever slipping out to "escape" the confines of his restrictive life—unable to pursue his dreams, and responsible for the family his father left behind. Even if he only goes out to smoke, it affords him a separation from the household that he finds so stifling.
Tom was not meant to spend his life in a warehouse: he is clear about this. In fact, he has the soul of a poet. (He often sneaks off when things are slow at work to write poetry. For this reason, Jim calls him "Shakespeare.") Jim warns Tom that his job is in jeopardy:
You're going to be out of a job if you don't wake up.
Tom is eventually fired from his job:
...I was fired for writing a poem on the lid of shoebox.
Tom definitely needs to escape. His mother nags him about everything. The play begins as she lectures him regarding the value of chewing one's food. She returns one of his books to the library because she believes it is inappropriate (though her son is an adult). She even takes to "conquering" his cowlick with a brush, and taking him to task for not dressing warmly enough when he goes out. Amanda treats him like a child, but makes demands of his as the adult male in the family. Besides this, he absolutely hates his job. But how can he leave when he financially supports his mother and sister?
You think I'm crazy about the warehouse? You think I'm in love with the Continental Shoemakers? You think I want to spend fifty-fiveyears down there in that—celotex interior! with—fluorescent—tubes? Look! I'd rather somebody picked up a crowbar and battered out my brains—than go back mornings!
Tom flees down the fire escape to go to the movies—or so he says. (In that he has come home acting crazy from time-to-time, we can assume he must go out drinking as well.) When Tom tries to please his mother and look out for his sister by bringing home a "gentleman caller," Jim turns out to be engaged, and Amanda (Tom's mother) verbally attacks Tom, accusing him of bringing home an ineligible friend on purpose. It is after this that Tom finally does what he has wanted to do for so long: he leaves.
Unfortunately, he does what his father did before him: he abandons his family.
I'm like my father. The bastard son of a bastard!
Unlike his father, however, Tom cares about his mom and Laura. The audience can feel some sympathy for Tom, for he cannot be free and stay at home...
...his greater desire is to relieve his frustration at his confining situation.
While Tom makes his physical escape from his life with Amanda and Laura, emotionally he is cannot get away. The play ends as he speaks to an imaginary Laura:
Oh, Laura, Laura, I tried to leave you behind me, but I am more faithful than I intended to be!
More than any other character, the symbolism of the fire escape applies to Tom.