Pressurized environments are becoming increasingly prevalent in today’s society, and are also increasingly at risk from unsavory elements. This applies not only to airliners, but to submersible vehicles, biological laboratories, upper stories on ever-higher skyscrapers, spacecraft, and space stations.
First of all, to clear up a popular misconception about pressurized environment perpetuated by many sensationalist disaster and science fiction movies, such as Total Recall, Outland, and many of the Airport movies: most pressurized environments will NOT explosively decompress within seconds if one or even several small holes are blown in them. They are all designed with possible blow-outs in mind, and are built with multiple redundancies to reduce the damage punctures can produce.
The one exception to this would be deep-diving submersibles; the pressure in the deep abysses of the ocean is measured in tons per square inch, and a single puncture can indeed lead to near-instantaneous disaster there.
But this is not to say that punctures are nothing to worry about in the other environments mentioned. Indeed, if left unattended too long, even a single small hole can eventually lead to significant drops in pressure and breathable air. In a firefight, a bullethole may end up in an unusual place, such as under a bolted-down seat or behind several tons of cargo or such, that would be hard to get to and repair. Also in vehicles such as an airliner or a spacecraft, the holes blowing out pressurized gas can add unexpected thrust vectors to the craft, making it that much harder to control.
PRESSURE ENVIRONMENT FIREARMS
Tech Level: 11
In an enclosed environment like an airline passenger cabin or a space station, weapons like standard handguns with high-velocity projectiles risk penetrating the hull or viewports, compromising pressure integrity and endangering the people inside. A Pressure Environment Handgun (PEH) gives security forces culprit-stopping power without endangering the pressurized environment.
PEH muzzle velocities would be deliberately subsonic and their ammunition would be designed to deform radically (basically break up or spread out to self-destruction, like the "crumple zones" in cars) upon impact, maximizing blunt trauma and soft tissue damage but minimizing penetration. The bullets will penetrate normal clothing and skin but little else, leaving, at best, shallow dents or cracks in metal or plastic bulkheads. Since most windows in pressurized environments are double or triple layered and made of impact-resisitant plastic, even a direct random hit on one by a PEH round will mean minimal risk of depressurization.
The ablative ammunition would probably be a variations on hollow point, dum-dum, or frangible bullets. Because of the cramped nature of most pressurized environments (at least in the forseeable furture), PEHs would probably be mostly small pistol configurations, though carbine or sub-machine gun PEHs are certainly possible.
The major downside to PEHs is that even minimal ballistic armor can greatly diminish their effectiveness.
Laser and maser weapons, if ever developed, would probably supplant PEHs, as they can deliver greater damage to organic tissue but barely scar metal and plastic unless deliberately "drilled" into one spot. This would be especially true in microgravity environments, as lasers would have no recoil.
Traveller RPG(various editions); "snub pistols"On The Web:
An article on the use of firearms on airliners: