The Mark 48 torpedo (the largest torpedo in the modern US arsenal) is 21 inches in diameter. Although most people could fit into a torpedo tube, it wouldn’t be comfortable, especially with a full diving rig or exposure suit. The torpedo itself is pushed out by a “water ram” (here is a diagram of the system) which uses water under a few tens of psi of pressure; it may not be enough to kill someone, but it would certainly be very uncomfortable and likely incapacitate the diver. The torpedo tube itself has a series of interlocks that prevent the loading hatch from being unlocked while the muzzle door is open for reasons that should be obvious to all, so it cannot be used as an escape hatch.
The escape hatch on a submarine (other than the normal opening in the sail to the bridge) are the forward and/or aft torpedo loading hatches on the upper side of the pressure hull. These are fairly large hatches designed to allow onload of munitions and supplies, and submariners typically refer to them as the “Mom hatch,” as in, “See, Mom, if we get in trouble, that is how we get out.” The reality is that in any real emergency that occurs at any significant distance below the surface, the likelihood of sailors escaping and surviving is pretty low. Many submarines also have one or more airlocks to support diving operations and/or external shelters; however, again the openings are as small as feasible and are not part of the general escape plan. In the case of serious damage (like onboard fire) from which the submarine can reach the surface, the crew musters to their FIRECON or DAMCON stations, and everyone else goes to the loading hatches, egresses to the topdeck of the hull, and piles into the inflatable life rafts that are tethered to either the hull or each other.